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tc2575 tc2575-1 3/13/00 ?2001 microchip technology inc. ds21398a 1.0a step-down switching regulator general description the tc2575 series of regulators are monolithic inte- grated circuits ideally suited for easy and convenient design of a step?own switching regulator (buck converter). all circuits of this series are capable of driving a 1.0a load with excellent line and load regulation. these devices are avail- able in fixed output voltages of 3.3v, 5.0v, 12v, and an adjustable output version. these regulators were designed to minimize the num- ber of external components to simplify the power supply design. standard series of inductors optimized for use with the tc2575 are offered by several different inductor manu- facturers. since the tc2575 converter is a switch-mode power supply, its efficiency is significantly higher in comparison with popular three-terminal linear regulators, especially with higher input voltages. in many cases, the power dissipated is so low, that no heatsinking is required or its size can be reduced dramatically. the tc2575 features include a guaranteed 4% toler- ance on output voltage within specified input voltages and output load conditions, and 10% on the oscillator frequency ( 2% over 0 c to +125 c). external shutdown is included, featuring 80 a (typical) standby current. the output switch includes cycle-by-cycle current limiting, as well as thermal shutdown for full protection under fault conditions. features 3.3v, 5.0v, 12v, and adjustable output versions adjustable version output voltage range of 1.23v to 37v 4% max. over line and load conditions guaranteed 1.0 a output current wide input voltage range; 4.75v to 40v requires only 4 external components 52khz fixed frequency internal oscillator ttl shutdown capability, low power standby mode high efficiency uses readily available standard inductors thermal shutdown and current limit protection applications simple and high-efficiency step-down (buck) regulator efficient pre?egulator for linear regulators on?ard switching regulators positive to negative converters (buck?oost) negative step-up converters power supply for battery chargers ordering information part temperature number package range tc2575-3.3vat 5-pin to-220 ?0 to +125 c tc2575-5.0vat 5-pin to-220 ?0 to +125 c tc2575-12.0vat* 5-pin to-220 ?0 to +125 c tc2575vat** 5-pin to-220 ?0 to +125 c pin configurations 5-pin to-220 note: * contact factory for availability ** adj = 1.23 to 37v. gnd v in output feedback on/off 1 2 345 tc2575
tc2575 1.0a step-down switching regulator 2 tc2575-1 3/13/00 ?2001 microchip technology inc. ds21398a absolute maximum ratings* maximum supply voltage ................................ v in = 45v on/off pin input voltage ..................... ?.3v v +v in output voltage to ground (steady state) ............... ?.0 v max power dissipation(to-220) ......... (internally limited) thermal resistance, junction-to-ambient ..... 65 c/w thermal resistance, junction-to-case ........ 5.0 c/w storage temperature range ................. ?5 c to +150 c minimum esd rating ............................................. 3.0 kv (human body model: c = 100pf, r = 1.5k ? ) lead temperature (soldering, 10 seconds) .......... 260 c maximum junction temperature............................. 150 c operating junction temperature range .... ?0 to +125*c supply voltage ............................................................40v *this is a stress rating only, and functional operation of the device at these or any other conditions beyond those indicated in the operation section of the specifications is not implied. exposure to absolute maximum ratings conditions for extended periods of time may affect device reliability. electrical characteristics: (unless otherwise specified, v in = 12v for the 3.3v, 5.0v, and adjustable version,v in = 25v for the 12v version. i load = 200ma. for typical values t j = 25 c, for min/max values t j is the operating junction temperature range that applies (note 2), unless otherwise noted. symbol parameter test conditions min typ max units tc2575-3.3 [(note 1) test circuit figure 2] v out output voltage v in = 12v, i load = 0.2a, t j = 25 c 3.234 3.3 3.366 v 4.75v v in 40v, 0.2a i load 1.0a t j = 25 c 3.168 3.3 3.432 t j = ?0 c to +125 3.135 3.465 efficiency v in = 12v, i load = 1.0a 75 % tc2575-5 [(note 1)test circuit figure 2] v out output voltage v in = 12v, i load = 0.2a, t j = 25 c 4.9 5.0 5.1 v 8.0v v in 40v, 0.2a i load 1.0a t j = 25 c 4.8 5.0 5.2 t j = ?0 c to +125 c 4.75 5.25 efficiency v in = 12v, i load = 1.0 a 77 % tc2575-12 [(note 1) test circuit figure 2] v out output voltage v in = 25v, i load = 0.2a, t j = 25 c 11.76 12 12.24 v 15v v in 40v, 0.2a i load 1.0a t j = 25 c 11.52 12 12.48 t j = ?0 c to +125 c 11.4 12.6 efficiency v in = 15v, i load = 1.0 a 88 % tc2575-adjustable version [(note 1) test circuit figure 2] v fb feedback voltage v in = 12v, i load = 0.2a, v out = 5.0v, 1.217 1.23 1.243 v t j = 25 c v fb feedback voltage 8.0v v in 40v, 0.2a i load 1.0a v out = 5.0v t j = 25 c 1.193 1.23 1.267 t j = ?0 c to +125 c 1.18 1.28 efficiency v in = 12v, i load = 1.0a, v out = 5.0v 77 % notes: 1. external components such as the catch diode, inductor, input and output capacitors can affect the switching regulator system performance. when the tc2575 is used as shown in the figure 2 test circuit, the system performance will be as shown in the system parameters section of the electrical characteristics. 2. tested junction temperature range for the tc2575: t low = ?0 c t high = +125 c
3 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ?2001 microchip technology inc. ds21398a electrical characteristics: (unless otherwise specified, v in = 12v for the 3.3v, 5.0v, and adjustable version,v in = 25v for the 12v version. i load = 200ma. for typical values t j = 25 c, for min/max values t j is the operat- ing junction temperature range that applies (note 2), unless otherwise noted. symbol parameter test conditions min typ max units tc2575-all output voltage versions i b feedback bias current v out = 5.0v (adjustable version only) na t j = 25 c 25 100 t j = ?0 c to +125 c 200 f osc oscillator frequency (note 3) t j = 25 c 52 khz t j = 0 to +125 c47 58 t j = ?0 to +125 c42 63 v sat saturation voltage i out = 1.0a, (note 4) v t j = 25 c 1.0 1.2 t j = ?0 to +125 c 1.3 dc max duty cycle (?n? [note 5] 94 98 % i cl current limit peak current a (notes 3 and 4) t j = 25 c 1.7 2.3 3.0 t j = ?0 to +125 c 1.4 3.2 i l output leakage current ma (notes 6 and 7), t j = 25 c output = 0 v 0.8 2.0 output = ?1.0 v 6.0 20 i q quiescent current (note 6) ma t j = 25 c 5.0 9.0 t j = ?0 to +125 c 11 i stby standby quiescent current, a on/off pin = 5.0 v (?ff? t j = 25 c 80 200 t j = ?0 to +125 c 400 v ih on/off pin logic input level v (test figure 2) v out = 0v t j = 25 c 2.2 1.4 t j = ?0 to +125 c 2.4 v il nominal output voltage v out = nominal output voltage v t j = 25 c 1.2 1.0 t j = ?0 to +125 c 0.8 i ih on/off pin input current a (test figure 2) on/off pin = 5.0v (?ff?, 15 30 t j = 25 c i il on/off pin input current on/off pin = 0v (?n?, 0 5.0 a t j = 25 c notes: 3. the oscillator frequency reduces to approximately 18khz in the event of an output short or an overload which causes the regul ated output voltage to drop approximately 40% from the nominal output voltage. this self protection feature lowers the average power dissipation of the ic by lowering the minimum duty cycle from 5% down to approximately 2%. 4. output (pin 2) sourcing current. no diode, inductor or capacitor connected to the output pin. 5. feedback (pin 4) removed from output and connected to 0v. 6. feedback (pin 4) removed from output and connected to +12v for the adjustable, 3.3v, and 5.0v versions, and 25v for the 12v, to force the output transistor "off". 7. v in = 40 v.
tc2575 1.0a step-down switching regulator 4 tc2575-1 3/13/00 ?2001 microchip technology inc. ds21398a representative block diagram and typical application tc2575 + + 3.1v internal regulator on/off on/off latch freq. shift 18khz reset thermal shutdown 5 2 1.0 amp switch d1 l1 c out +v in c in v out driver output gnd 4 1 for adjustable version r1 = open, r2 = 0 ? load regulated output feedback unregulated dc input r2 r1 1.0k current limit comparator fixed gain error amplifier + + + 52khz oscillator 1.235v band-gap reference 3 output voltage versions 3.3v 5.0v 12v 15v r2 ( ? ) 1.7k 3.1k 8.84k 11.3k pin description pin no. 5-pin to-220 symbol description 1v in this pin is the positive input supply for the tc2575 step-down switching regulator. in order to minimize voltage transients and to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be present (c in in figure 1). 2 output this is the emitter of the internal switch. the saturation voltage v sat of this output switch is typically 1.0v. it should be kept in mind that the pcb area connected to this pin should be kept to a minimum in order to minimize coupling to sensitive circuitry. 3 gnd circuit ground pin. see the information about the printed circuit boad layout. 4 feedback this pin senses regulated output voltage to complete the feedback loop. the signal is divided by the internal resistor divider network r2, r1 and applied to the non-inverting input of the internal error amplifier. in the adjustable version of the tc2575 switching regulator this pin is the direct input of the error amplifier and the resistor network r2, r1 is connected externally to allow programming of the output voltage. 5 on/off it allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total input supply current to approximately 80 a. the threshold voltage is typically 1.4v. applying a voltage above this value (up to +v in ) shuts the regulator off. if the voltage applied to this pin is lower than 1.4v or if this pin is left open, the regulator will be in the "on" condition.
5 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ?2001 microchip technology inc. ds21398a c in 100 f c out 330 f +v in 1 3 gnd 5 2 4l1 330 h output d1 1n5819 feedback on/off 7.0 40v unregulated dc input 5.0v regulated output 1.0a load tc2575 + figure 1. block diagram and typical application: fixed output voltages figure 2. typical test circuit c in 100 f/50v c out 330 f/16v v out regulated output v out regulated output v in 1 3 gnd 5 2 4 d1 in5819 d1 in5819 l1 330 h output feedback 5.0 output voltage versions v out = v ref ( 1 + r2 ) r1 on/off v in unregulated dc input 8.0 40v tc2575 (5v) + + load c in 100 f/50v r2 r1 v in 1 3 gnd 5 2 4 l1 330 h output feedback where v ref = 1.23v, r1 between 1.0k ? and 5.0k ? adjustable output voltage versions on/off unregulated dc input 8.0 40v tc2575 + c in 330 f/ 16v + load adjustable r1= r2 ( v out - 1 ) v ref
tc2575 1.0a step-down switching regulator 6 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a pcb layout guidelines as in any switching regulator, the layout of the printed circuit board is very important. rapidly switching currents associated with wiring inductance, stray capacitance and parasitic inductance of the printed circuit board traces can generate voltage transients which can generate electro- magnetic interferences (emi) and affect the desired opera- tion. as indicated in the figure 2, to minimize inductance and ground loops, the length of the leads indicated by heavy lines should be kept as short as possible. for best results, single point grounding (as indicated) or ground plane construction should be used. on the other hand, the pcb area connected to the pin 2 (emitter of the internal switch) of the tc2575 should be kept to a minimum in order to minimize coupling to sensitive circuitry. another sensitive part of the circuit is the feedback. it is important to keep the sensitive feedback wiring short. to assure this, physically locate the programming resistors near to the regulator, when using the adjustable version of the tc2575 regulator. design procedure buck converter basics the tc2575 is a buck or step down converter which is the most elementary forward mode converter. its basic schematic can be seen in figure 3. the operation of this regulator topology has two distinct time periods. the first one occurs when the series switch is on, the input voltage is connected to the input of the inductor. the output of the inductor is the output voltage, and the rectifier (or catch diode) is reverse biased. during this period, since there is a constant voltage source connected across the inductor, the inductor current begins to linearly ramp upwards, as described by the following equation: i l (on) = (v in v out ) t on l during this on period, energy is stored within the core material in the form of magnetic flux. if the inductor is properly designed, there is sufficient energy stored to carry the requirements of the load during the off period. the next period is the off period of the power switch. when the power switch turns off, the voltage across the inductor reverses its polarity and is clamped at one diode voltage drop below ground by the catch diode. current now flows through the catch diode thus maintaining the load current loop. this removes the stored energy from the inductor. the inductor current during this time is: i l (off) = (v out v d ) t off l this period ends when the power switch is once again turned on. regulation of the converter is accomplished by varying the duty cycle of the power switch. it is possible to describe the duty cycle as follows: d = t on , where t is the period of switching. t for the buck converter with ideal components, the duty cycle can also be described as: d = v out v in figure 4 shows the buck converter idealized waveforms of the catch diode voltage and the inductor current. figure 3. basic buck converter c out + v out r load + v in d1 power switch l figure 4. buck converter idealized waveforms time v d /(fwd) power switch off power switch diode power switch power switch off v on (sw) power switch on power switch on diode voltage time i min diode i load (av) i pk inductor current
7 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ? 2001 microchip technology inc. ds21398a procedure (fixed output voltage version) in order to simplify the switching regulator design, a step-by-step design procedure and some examples are provided. procedure example given parameters: given parameters: v out = regulated output voltage (3.3v, 5.0v or 12v) v out = 5.0v v in (max) = maximum dc input voltage v in (max) = 20v i load (max) = maximum load current i load (max) = 0.8a 1. controller ic selection 1. controller ic selection according to the required input voltage, output voltage and according to the required input voltage, output voltage, current select the appropriate type of the controller ic output current polarity and current value, use the tc2575 (5v) voltage version. controller ic. 2. input capacitor selection (c in ) 2. input capacitor selection (c in ) to prevent large voltage transients from appearing at the input a 47 f, 25v aluminium electrolytic capacitor and for stable operation of the converter, an aluminum or tantalum located near to the input and ground pins provides electrolytic bypass capacitor is needed between the input pin +v in sufficient bypassing. and ground pin gnd. this capacitor should be located close to the ic using short leads. this capacitor should have a low esr (equivalent series resistance) value. 3. catch diode selection (d1) 3. catch diode selection (d1) a. since the diode maximum peak current exceeds the a. for this example the current rating of the diode is 1.0a regulator maximum load current, the catch diode current rating must be at least 1.2 times greater than the maximum load current. for a robust design the diode should have a current rating equal to the maximum current limit of the tc2575 to be able to withstand a continuous output short. b. the reverse voltage rating of the diode should be at least b. use a 30v 1n5818 schottky diode, or any of the 1.25 times the maximum input voltage. suggested fast recovery diodes shown in table 4. 4. inductor selection (l1) 4. inductor selection (l1) a. according to the required working conditions, select the a. use the inductor selection guide shown in figure 32 correct inductor value using the selection guide from to 36. figures 32 to 36. b. from the appropriate inductor selection guide, identify the b. from the selection guide, the inductance area inductance region intersected by the maximum input voltage intersected by the 20v line and 0.8a line is l300. line and the maximum load current line. each region is identified by an inductance value and an inductor code. c. select an appropriate inductor from the several different c. inductor value required is 300 h. from table 1, or manufacturers part numbers listed in table 1 or table 2 table 2, choose an inductor from any of the listed when using table 2 for selecting the right inductor, the manufacturers. designer must realize that the inductor current rating must be higher than the maximum peak current flowing through the inductor. this maximum peak current can be calculated as follows: i p(max) = i load (max) + (v in v out ) t on 2l where t on is the "on" time of the power switch and t on = v out x 1.0 v in f osc for additional information about the inductor, see the inductor section in the external components section of this data sheet.
tc2575 1.0a step-down switching regulator 8 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a procedure (fixed output voltage version) (continued) in order to simplify the switching regulator design, a step-by-step design procedure and examples are provided. procedure example 5. output capacitor selection (c out ) a. since the tc2575 is a forward mode switching regulator with voltage mode control, its open loop 2-pole-2-zero frequency characteristic has the dominant pole pair dete- rmined by the output capacitor and inductor values. for stable operation and an acceptable ripple voltage, (approximately 1% of the output voltage) a value between 100 f and 470 f is recommended. b. due to the fact that the higher voltage electrolytic capacitors generally have lower esr (equivalent series resistance) numbers, the output capacitor s voltage rating should be at least 1.5 times greater than the output voltage. for a 5.0v regulator, a rating at least 8.0v is appropriate, and a 10vor 16v rating is recommended. 5. output capacitor selection (c out ) a. c out = 100 f to 470 f standard aluminium electrolytic. b. capacitor voltage rating = 16v. procedure (adjustable output version: tc2575-adj) procedure example given parameters: v out = regulated output voltage v in (max) = maximum dc input voltage i load (max) = maximum load current 1. programming output voltage to select the right programming resistor r1 and r2 value (see figure 2) use the following formula: v out = v ref ( 1.0 + r2 ) where v ref = 1.23v r1 resistor r1 can be between 1.0k ? and 5.0k ? . (for best temperature coefficient and stability with time, use 1% metal film resitors). r2 = r1 ( v out 1 ) v ref 2. input capacitor selection (c in ) to prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminium or tantalum electrolytic bypass capacitor is needed between the input pin +v in and ground pin gnd. this capacitor should be located close to the ic using short leads. this capacitor should have a low esr (equivalent series resistance) value. for additional information see input capacitor section in the external components section of this data sheet. given parameters: v out = 8.0v v in (max) = 12v i load (max) = 1.0v 2. input capacitor selection (c in ) a 100 f, aluminium electrolytic capacitor located near the input and ground pin provides sufficient bypassing. 1. programming output voltage (selecting r1 and r2) select r1 and r2 v out = 1.23 ( 1.0 + r2 ) select r1 = 1.8k ? r1 r2 = r1 ( v out 1.0 ) = 1.08k ( 8.0v 1 ) v ref 1.23v r1 = 9.91k ? , choose a 9.88k ? metal film resistor.
9 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ? 2001 microchip technology inc. ds21398a procedure (adjustable output version: tc2575-adj) (continued) procedure example 3. catch diode selection (d1) a. since the diode maximum peak current exceeds the regulator maximum load current the catch diode current rating must be at least 1.2 times greater than the maximum load current. for a robust design, the diode should have a current rating equal to the maximum current limit of the tc2575 to be able to with stand a continuous output short. b. the reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. 4. inductor selection (l1) a. use the following formula to calculate the inductor volt x microsecond [v x s] constant: e x t = ( v in v out ) v out x 10 6 [v x sec] v in f[hz] b. match the calculated e x t value with the corresponding number on the vertical axis of the inductor value selection guide shown in figure 37. this e x t constant is a measure of the energy handling capability of an inductor and is dependent upon the type of core, the core area, the number of turns, and the duty cycle. c. next step is to identify the inductance region intersected by the e x t value and the maximum load current value on the horizontal axis shown in figure 35. d. from the inductor code, identify the inductor value. then select an appropriate inductor from table 1 or table 2. the inductor chosen must be rated for a switching frequency of 52khz and for a current rating of 1.15 x i load . the inductor current rating can also be deter- mined by calculating the inductor peak current: i p (max) = i load(max) + (v in v out ) t on 2l where t on is the "on" time of the power switch and t on = (v out x 1.0 ) v in f osc for additional information about the inductor, see the inductor section in the external components section of this data sheet. 3. catch diode selection (d1) a. for this example, a 3.0a current rating is adequate. b. use a 20v in5820 or mbr320 schottky diode or any suggested fast recovery diodes in table 4. 4. inductor selection (l1) a. calculate e x t [v x sec] constant: e x t = ( 12 8.0) x 8.0 x 1000 = 51[v x sec] 12 52 b. e x t = 51 [v x sec] c. i load(max) = 1.0a inductance region = l220 d . proper inductor value = 220 h choose the inductor from table 1 or table 2
tc2575 1.0a step-down switching regulator 10 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a procedure (adjustable output version: tc2575-adj) (continued) procedure example 5. output capacitor selection (c out ) a. since the tc2575 is a forward mode switching regulator with voltage mode control, its open loop 2 pole 1 zero frequency characteristic has the dominant pole pair determined by the output capacitor and inductor values. for stable operation, the capacitor must satisfy the following requirement: c out 7.785 v in(max) [ f] v out x l [ f] b. capacitor values between 10 f and 2000 f will satisfy the loop requirements for stable operation. to achieve an acceptable output ripple voltage and transient response, the output capacitor may need to be several times larger than the above formula yields. c. due to the fact that the higher voltage electrolytic capaci- tors generally have lower esr (equivalent series resistance) numbers, the output capacitor s voltage rating should be at least 1.5 times greater than the output voltage. for a 5.0v regulator, a rating of at least 8.0v is appropriate, and a 10v or 16v rating is recommended. 5. output capacitor selection (c out ) a. c out 7.785 12 = 53 f 8 x 220 to achieve an acceptable ripple voltage, select c out 100 f electrolytic capacitor. table 1. inductor selection guide inductor code inductor value pulse eng renco aie tech 39 l100 100 hpe 92108 rl2444 415 0930 77 308 bv l150 150 hpe 53113 rl1954 415 0953 77 358 bv l220 220 hpe 52626 rl1953 415 0922 77 408 bv l330 330 hpe 52627 rl1952 415 0926 77 458 bv l470 470 hpe 53114 rl1951 415 0927 l680 680 hpe 52629 rl1950 415 0928 77 508 bv h150 150 h pe 53115 rl2445 415 0936 77 368 bv h220 220 hpe 53116 rl2446 430 0636 77 410 bv h330 330 hpe 53117 rl2447 430 0635 77 460 bv h470 470 hpe 53118 rl1961 430 0634 h680 680 hpe 53119 rl1960 415 0935 77 510 bv h1000 1000 hpe 53120 rl1959 415 0934 77 558 bv h1500 1500 hpe 53121 rl1958 415 0933 h2200 2200 hpe 53122 rl2448 415 0945 77 610 bv note: *contact manufacturer
11 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ? 2001 microchip technology inc. ds21398a table 2. inductor selection guide inductance current schott renco pulse engineering coilcraft ( h) (a) tht smt tht smt tht smt smt 68 0.32 67143940 67144310 rl 1284 68 43 rl1500 68 pe 53804 pe 53804 s do1608 68 0.58 67143990 67144360 rl 5470 6 rl1500 68 pe 53812 pe 53812 s do3308 683 0.99 67144070 67144450 rl 5471 5 rl1500 68 pe 53821 pe 53821 s do3316 683 1.78 67144140 67144520 rl 5471 5 pe 53830 pe 53830 s do5022p 683 100 0.48 67143980 67144350 rl 5470 5 rl1500 100 pe 53811 pe 53811 s do3308 104 0.82 67144060 67144440 rl 5471 4 rl1500 100 pe 53820 pe 53820 s do3316 104 1.47 67144130 67144510 rl 5471 4 pe 53829 pe 53829 s do5022p 104 150 0.39 67144340 rl 5470 4 rl1500 150 pe 53810 pe 53810 s do3308 154 0.66 67144050 67144430 rl 5471 3 rl1500 150 pe 53819 pe 53819 s do3316 154 1.20 67144120 67144500 rl 5471 3 pe 53828 pe 53828 s do5022p 154 220 0.32 67143960 67144330 rl 5470 3 rl1500 220 pe 53809 pe 53809 s do3308 224 0.55 67144040 67144420 rl 5471 2 rl1500 220 pe 53818 pe 53818 s do3316 224 1.00 67144110 67144490 rl 5471 2 pe 53827 pe 53827 s do5022p 224 330 0.42 67144030 67144410 rl 5471 1 rl1500 330 pe 53817 pe 53817 s do3316 334 0.80 67144100 67144480 rl 5471 1 pe 53826 pe 53826 s do5022p 334 note: table 1 and table 2 of this indicator selection guide shows some examples of different manufacturer products suitable for desi gn with the tc2575. table 3. example of several inductor manufacturers phone/fax numbers pulse engineering inc. phone + 1 619 674 8100 fax + 1 619 674 8262 pulse engineering inc. europe phone + 353 93 24 107 fax + 353 93 24 459 renco electronics inc. phone + 1 516 645 5828 fax + 1 516 586 5562 aie magnetics phone + 1 813 347 2181 fax coilcraft inc. phone + 1 708 322 2645 fax + 1 708 639 1469 coilcraft inc., europe phone + 44 1236 730 595 fax + 44 1236 730 627 tech 39 phone + 33 8425 2626 fax + 33 8425 2610 schott corp. phone + 1 612 475 1173 fax + 1 612 475 1786
tc2575 1.0a step-down switching regulator 12 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a table 2. diode selection guide schottky ultra-fast recovery 1.0a 3.0a 1.0a 3.0a v r smt tht smt tht snt tht smt tht 20v sk12 1n5817 sk32 1n5820 sr102 mbrd320 mbr320 sr302 30v mbrs130lt3 1n5818 sk33 1n5821 murs120t3 sk13 sr103 mbrd330 mbr330 murs120t3 mur120 11dq03 sr30 11df1 31dq03 her102 40v mbrs140t3 1n5819 mbrs340t3 1n5822 10bf10 murd320 mur320 sk14 sr104 mbrd340 mbr340 30wf10 10bq040 11dq04 30wq04 sr304 mur420 10mq040 sk34 31dq04 50v mbrs150 mbr150 mbrd350 mbr350 31df1 10bq050 sr105 sk35 sr305 her302 11dq05 30wq05 11dq05
13 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ? 2001 microchip technology inc. ds21398a external components input capacitor (c in ) the input capacitor should have a low esr for stable operation of the switch mode converter a low esr (equivalent series resistance) aluminium or solid tantalum bypass capacitor is needed between the input pin and the ground pin, to prevent large voltage transients from appearing at the input. it must be located near the regulator and use short leads. with most electrolytic capacitors, the capacitance value decreases and the esr increases with lower temperatures. for reliable operation in temperatures below 25 c larger values of the input capacitor may be needed. also paralleling a ceramic or solid tantalum capaci- tor will increase the regulator stability at cold temperatures. rms current rating of c in the important parameter of the input capacitor is the rms current rating. capacitors that are physically large and have large surface area will typically have higher rms current ratings. for a given capacitor value, a higher voltage electrolytic capacitor will be physically larger than a lower voltage capacitor, and thus be able to dissipate more heat to the surrounding air, and therefore will have a higher rms current rating. the consequences of operating an electro- lytic capacitor beyond the rms current rating is a shortened operating life. in order to assure maximum capacitor oper- ating lifetime, the capacitor s rms ripple current rating should be: i rms > 1.2 x d x i load where d is the duty cycle, for a buck regulator d = t on = v out t v in and d = t on = i v out i for a buck-boost regulator. t i v out i + v in output capacitor (c out ) for low output ripple voltage and good stability, low esr output capacitors are recommended. an output capacitor has two main functions: it filters the output and provides regulator loop stability. the esr of the output capacitor and the peak to peak value of the inductor ripple current are the main factors contributing to the output ripple voltage value. standard aluminium electrolytics could be adequate for some applications but for quality design, low esr types are recommended. an aluminium electrolytic capacitor s esr value is re- lated to many factors, such as the capacitance value, the voltage rating, the physical size and the type of construction. in most cases, the higher voltage electrolytic capacitors have lower esr value. often capacitors with much higher voltage ratings may be needed to provide low esr values, that are required for low output ripple voltage. the output capacitor requires an esr value that has an upper and lower limit as mentioned above, a low esr value is needed for low output ripple voltage, typically 1% to 2% of the output voltage. but if the selected capacitor s esr is extremely low (below 0.05 ? ), there is a possibility of an unstable feedback loop, resulting in oscillation at the output. this situation can occur when a tantalum capacitor, that can have a very low esr, is used as the only output capacitor. at low temperatures, put in parallel aluminium electrolytic capacitors with tantalum capacitors electrolytic capacitors are not recommended for tem- peratures below 25 c. the esr rises dramatically at cold temperatures and typically rises 3 times at 25 c and as much as 10 times at 40 c. solid tantalum capacitors have much better esr spec at cold temperatures and are recom- mended for temperatures below 25 c. they can be also used in parallel with aluminium electrolytics. the value of the tantalum capacitor should be about 10% or 20% of the total capacitance. the output capacitor should have at least 50% higher rms ripple current rating at 52khz than the peak to peak inductor ripple current. catch diode locate the catch diode close to the tc2575 the tc2575 is a step down buck converter, it requires a fast diode to provide a return path for the inductor current when the switch turns off. this diode must be located close to the tc2575 using short leads and short printed circuit traces to avoid emi problems. use a schottky or a soft switching ultra fast recovery diode since the rectifier diodes are very significant source of losses within switching power supplies, choosing the recti- fier that best fits into the converter design is an important process. schottky diodes provide the best performance because of their fast switching speed and low forward voltage drop. they provide the best efficiency especially in low output voltage applications (5.0 v and lower). another choice could be fast recovery, or ultra fast recovery diodes. it has to be noted, that some types of these diodes with an abrupt turnoff characteristic may cause instability or emi troubles. a fast-recovery diode with soft recovery characteristics can better fulfill a quality, low noise design requirements.
tc2575 1.0a step-down switching regulator 14 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a table 4 provides a list of suitable diodes for the tc2575 regulator. standard 50/60hz rectifier diodes, such as the 1n4001 series or 1n5400 series are not suitable. inductor the magnetic components are the cornerstone of all switching power supply designs. the style of the core and the winding technique used in the magnetic component s design have a great influence on the reliability of the overall power supply. using an improper or poorly designed inductor can cause high voltage spikes generated by the rate of transi- tions in current within the switching power supply, and the possibility of core saturation can arise during an abnormal operational mode. voltage spikes can cause the semicon- ductors to enter avalanche breakdown and the part can instantly fail if enough energy is applied. it can also cause significant rfi (radio frequency interference) and emi (electro magnetic interference) problems. continuous and discontinuous mode of operation. the tc2575 step down converter can operate in both the continuous and the discontinuous modes of operation. the regulator works in the continuous mode when loads are relatively heavy, the current flows through the inductor continuously and never falls to zero. under light load condi- tions, the circuit will be forced to the discontinuous mode when inductor current falls to zero for certain period of time (see figure 5 and figure 6). each mode has distinctively different operating characteristics, which can affect the regulator performance and requirements. in many cases the preferred mode of operation is the continuous mode. it offers greater output power, lower peak currents in the switch, inductor and diode, and can have a lower output ripple voltage. on the other hand it does require larger inductor values to keep the inductor current flowing continuously, especially at low output load currents and/orhigh input voltages. to simplify the inductor selection process, an inductor selection guide for the tc2575 regulator was added to this data sheet (figures 32 through 36). this guide assumes that the regulator is operating in the continuous mode, and selects an inductor that will allow a peak to peak inductor ripple current to be a certain percentage of the maximum design load current. this percentage is allowed to change as different design load currents are selected. for light loads (less than approximately 200ma) it may be desirable to operate the regulator in the discontinuous mode, because the inductor value and size can be kept relatively low. consequently, the percentage of inductor peak-to-peak current increases. this discontinuous mode of operation is perfectly acceptable for this type of switching converter. any buck regulator will be forced to enter discontinuous mode if the load current is light enough. selecting the right inductor style some important considerations when selecting a coretype are core material, cost, the output power of the powersupply, the physical volume the inductor must fit within, and the amount of emi (electro-magnetic interfer- ence) shielding that the core must provide. the inductor selection guide covers different styles of inductors such as pot core, e-core, toroid and bobbin core, as well as different core materials such as ferrites and powdered iron from different manufacturers. for high quality design regulators the toroid core seems to be the best choice. since the magnetic flux is contained within the core, it generates less emi, reducing noise prob- lems in sensitive circuits. the least expensive is the bobbin core type, which consists of wire wound on a ferrite rod core. figure 5. continuous mode switching current waveforms power switch 1.0 0 0 current horizontal time base: 5.0 sec/div (a) 1.0 inductor current (a) figure 6. discontinuous mode switching current waveforms 0.1 0.1 0 0 power switch current (a) inductor current (a) horizontal time base: 5.0 sec/div
15 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ? 2001 microchip technology inc. ds21398a this type of inductor generates more emi due to the fact that its core is open, and the magnetic flux is not contained within the core. when multiple switching regulators are located on the same printed circuit board, open core magnetics can cause interference between two or more of the regulator circuits, especially at high currents due to mutual coupling. a toroid, pot core or e core (closed magnetic structure) should be used in such applications. do not operate an inductor beyond its maximum rated current exceeding an inductor s maximum current rating may cause the inductor to overheat because of the copper wire losses, or the core may saturate. core saturation occurs when the flux density is too high and consequently the cross sectional area of the core can no longer support additional lines of magnetic flux. this causes the permeability of the core to drop, the inductance value decreases rapidly and the inductor begins to look mainly resistive. it has only the dc resistance of the winding. this can cause the switch current to rise very rapidly and force the tc2575 internal switch into cycle-by- cycle current limit, thus reducing the dc output load current. this can also result in overheating of the inductor and/or the tc2575. different inductor types have different saturation characteristics, and this should be kept in mind when select- ing an inductor. general recommendations output voltage ripple and transients source of the output ripple since the tc2575 is a switch mode power supply regulator, its output voltage, if left unfiltered, will contain a sawtooth ripple voltage at the switching frequency. the output ripple voltage value ranges from 0.5% to 3% of the output voltage. it is caused mainly by the inductor sawtooth ripple current multiplied by the esr of the output capacitor. short voltage spikes and how to reduce them the regulator output voltage may also contain short voltage spikes at the peaks of the sawtooth waveform (see figure 7). these voltage spikes are present because of the fast switching action of the output switch, and the parasitic inductance of the output filter capacitor. there are some other important factors such as wiring inductance, stray capacitance, as well as the scope probe used to evaluate these transients, all these contribute to the amplitude of these spikes. to minimize these voltage spikes, low induc- tance capacitors should be used, and their lead lengths must be kept short. the importance of quality printed circuit board layout design should also be highlighted. minimizing the output ripple in order to minimize the output ripple voltage it is possible to enlarge the inductance value of the inductor l1 and/or to use a larger value output capacitor. there is also another way to smooth the output by means of an additional lc filter (20 h, 100 f), that can be added to the output (see figure 16) to further reduce the amount of output ripple and transients. with such a filter it is possible to reduce the output ripple voltage transients 10 times or more. figure 7 shows the difference between filtered and unfiltered output waveforms of the regulator shown in figure 16. the upper waveform is from the normal unfiltered output of the converter, while the lower waveform shows the output ripple voltage filtered by an additional lc filter. heatsinking and thermal considerations the through-hole-package to-220 the tc2575 is available in a 5-pin to-220 package. there are many applications that require no heatsink to keep the tc2575 junction temperature within the allowed operating range. the to-220 package can be used without a heatsink for ambient temperatures up to approximately 50 c (depending on the output voltage and load current). higher ambient temperatures require some heat sinking, either to the printed circuit (pc) board or an external heatsink. figure 7. output ripple voltage waveforms unfilitered output voltage vertical resolution: 20 mv/div filitered output voltage voltage spikes caused by switching action of the output switch and the parasitic inductance of the output capacitor horizontal time base: 10 sec/div
tc2575 1.0a step-down switching regulator 16 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a thermal analysis and design the following procedure must be performed to deter- mine whether or not a heatsink will be required. first determine: 1. p d (max) maximum regulator power dissipation in the application. 2. t a (max) maximum ambient temperature in the application. 3. t j (max) maximum allowed junction temperature (125 c for the tc2575). for a conservative design, the maximum junction temperature should not exceed 110 c to assure safe operation. for every additional 10 c tem- perature rise that the junction must withstand, the estimated operating lifetime of the component is halved. 4. jc package thermal resistance junction case. 5. ja package thermal resistance junction ambient. (refer to absolute maximum ratings on this data sheet or jc and ja values). the following formula is to calculate the approximate total power dissipated by the tc2575: p d = (v in x i q ) + d x i load x v sat where d is the duty cycle and for buck converter d = t on = v out t v in i q (quiescent current) and v sat can be found in the tc2575 data sheet, v in is minimum input voltage applied, v out is the regulator output voltage, i load is the load current. the dynamic switching losses during turn on and turn off can be neglected if a proper type catch diode is used. packages (free standing) for a free standing application when no heatsink is used, the junction temperature can be determined by the following expression: t j = ( ja ) (p d ) + t a where ( ja )(p d ) represents the junction temperature rise caused by the dissipated power and t a is the maxi- mum ambient temperature. some aspects that can influence thermal design it should be noted that the package thermal resistance and the junction temperature rise numbers are all approxi- mate, and there are many factors that will affect these numbers, such as pc board size, shape, thickness, physical position, location, board temperature, as well as whether the surrounding air is moving or still. other factors are trace width, total printed circuit copper area, copper thickness, single or double sided, multilayer board, the amount of solder on the board or even color of the traces. the size, quantity and spacing of other components on the board can also influence its effectiveness to dissipate the heat. figure 8. inverting buck-boost regulator using the tc2575 (12v) develops 12v @ 0.35a d1 1n5822 l1 68 h output gnd 2 5 4 feedback 12 to 40v unregulated dc input 1 3 r247k on/off +v in 12v @ 700a regulated output tc2576 (12v) c out 2200 f c in 100 f /50v
17 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ? 2001 microchip technology inc. ds21398a additional applications inverting regulator an inverting buck boost regulator using the tc2575 (12v) is shown in figure 8. this circuit converts a positive input voltage to a negative output voltage with a common ground by bootstrapping the regulators ground to the negative output voltage. by grounding the feedback pin, the regulator senses the inverted output voltage and regu- lates it. in this example the tc2575 (12v) is used to generate a 12v output. the maximum input voltage in this case cannot exceed 28v because the maximum voltage appearing across the regulator is the absolute sum of the input and output voltages and this must be limited to a maximum of 40v. this circuit configuration is able to deliver approximately 0.35a to the output when the input voltage is 12v or higher. at lighter loads the minimum input voltage required drops to approximately 4.7v, because the buck boost regulator to- pology can produce an output voltage that, in its absolute value, is either greater or less than the input voltage. since the switch currents in this buck boost configura- tion are higher than in the standard buck converter topology, the available output current is lower. this type of buck boost inverting regulator can also require a larger amount of startup input current, even for light loads. this may overload an input power source with a current limit less than 1.5a. such an amount of input start-up current is needed for at least 2.0msec or more. the actual time depends on the output voltage and size of the output capacitor. because of the relatively high startup currents required by this inverting regulator topology, the use of a delayed startup or an undervoltage lockout circuit is recommended. using a delayed startup arrangement, the input capaci- tor can charge up to a higher voltage before the switch mode regulator begins to operate. the high input current needed for startup is now partially supplied by the input capacitor c in . design recommendations: the inverting regulator operates in a different manner than the buck converter and so a different design procedure has to be used to select the inductor l1 or the output capacitor c out . the output capacitor values must be larger than what is normally required for buck converter designs. low input voltages or high output currents require a large value output capacitor (in the range of thousands of f). the recommended range of inductor values for the inverting converter design is between 68 h and 220 h. to select an inductor with an appropriate current rating, the inductor peak current has to be calculated. the following formula is used to obtain the peak inductor current: i peak i load (v in i v out i ) + v in x t on v in 2l 1 where t on i v out i 1.0 , and f osc = 52khz. v in + i v out i x f osc under normal continuous inductor current operating conditions, the worst case occurs when v in is minimal. note that the voltage appearing across the regulator is the absolute sum of the input and output voltage, and must not exceed 40v. it has been already mentioned above, that in some situations, the delayed startup or the undervoltge lockout features could be very useful. a delayed startup circuit applied to a buck-boost converter is shown in figure 9. figure 15 in the "undervoltage lockout" section describes an undervoltage lockout feature for the same converter topology. figure 9. inverting buck-boost regulator with delayed startup d1 1n5819 l1 100 h output gnd 2 3 4 feedback 12 to 25v unregulated dc input 1 c1 0.1 f 5 r1 47k r2 47k on/off +v in 12v @ 0.35a regulated output tc2575 (12v) c out 1800 f/16v c in 100 f /50v tc2575 1 3 5 gnd on /off +v in r2 47k c in 100 f note: this picture does not show the complete circuit. r1 47 k r3 470 shutdown input moc8101 v out off on 5.0v 0 +v in figure 10. inverting buck-boost regulator shutdown circuit using an optocoupler
tc2575 1.0a step-down switching regulator 18 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a design recommendations the same design rules as for the previous inverting buck boost converter can be applied. the output capacitor c out must be chosen larger than what would be required for a standard buck converter. low input voltages or high output currents require a large value output capacitor (in the range of thousands of f). the recommended range of inductor values for the negative boost regulator is the same as for inverting converter design. another important point is that these negative boost converters cannot provide any current limiting load protec- tion in the event of a short in the output so some other means, such as a fuse, may be necessary to provide the load protection. delayed startup there are some applications, like the inverting regulator already mentioned above, which require a higher amount of start-up current. in such cases, if the input power source is limited, this delayed start-up feature becomes very useful. to provide a time delay between the time when the input voltage is applied and the time when the output voltage comes up, the circuit in figure 13 can be used. as the input voltage is applied, the capacitor c1 charges up, and the voltage across the resistor r2 falls down. when the voltage on the on/off pin falls below the threshold value 1.4 v, the regulator starts up. resistor r1 is included to limit the maximum voltage applied to the on/off pin. it reduces the power supply noise sensitivity, and also limits the capacitor c1 discharge current, but its use is not mandatory. when a high 50hz or 60hz (100hz or 120hz respec- tively) ripple voltage exists, a long delay time can cause some problems by coupling the ripple into the on/off pin, the regulator could be switched periodically on and off with the line (or double) frequency. negative boost regulator this example is a variation of the buck boost topology and it is called negative boost regulator. this regulator experiences relatively high switch current, especially at low input voltages. the internal switch current limiting results in lower output load current capability. the circuit in figure 12 shows the negative boost configuration. the input voltage in this application ranges from 5.0 to 12v and provides a regulated 12v output. if the input voltage is greater than 12v, the output will rise above 12 v accordingly, but will not damage the regulator. with the inverting configuration, the use of the on/off pin requires some level shifting techniques. this is caused by the fact, that the ground pin of the converter ic is no longer at ground. now, the on/off pin threshold voltage (1.4v approximately) has to be related to the negative output voltage level. there are many different possible shutdown methods, two of them are shown in figures 10 and 11. figure 11. inverting buck-boost regulator shutdown circuit using a pnp transistor note: this picture does not show the complete circuit. r2 5.6 k q1 2n3906 tc2575 1 3 5 gnd on /off r1 12k v out +v in shutdown input off on +v 0 +v in c in 100 f figure 12. negative boost regulator 1n5819 output 2 4 feedback v out = 12v load current from 200ma for v in = 5.2v to 500ma for v in 7.0v v in d1 c out 1000 f/16v c in 100 f/ 50v tc2575 (12v) 1 5 3 gnd +v in unregulated dc input v in = 5.0v to 12v on/off l1 150 h regulated output
19 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ? 2001 microchip technology inc. ds21398a undervoltage lockout some applications require the regulator to remain off until the input voltage reaches a certain threshold level. figure 14 shows an undervoltage lockout circuit applied to a buck regulator. a version of this circuit for buck boost converter is shown in figure 14. resistor r3 pulls the on/off pin high and keeps the regulator off until the input voltage reaches a predetermined threshold level, with re- spect to the ground pin 3, which is determined by the following expression: v th v z1 + ( 1.0 + r2 ) v be (q1) r1 figure 14. undervoltage lockout circuit for buck converter r2 10k z1 1n5242b r1 10k q1 2n3904 r3 47k c in 100 f tc2575 (5v) 1 3 5 gnd v th 13v on /off +v in +v in note: this picture does not show the complete circuit. figure 15. undervoltage lockout circuit for buck-boost converter r2 15k z1 1n5242b r1 15 k q1 2n3904 r3 68k c in 100 f tc2575 (5v) 1 3 5 gnd v th 13v on /off +v in +v in v out = 5.0v note: this picture does not show the complete circuit figure 13. delayed startup circuitry r1 47k lm2575 1 3 5 gnd on /off r2 47k +v in +v in c1 0.1 f c in 100 f note : : this picture does not show the complete circuit. adjustable output, low-ripple power supply a 1.0a output current capability power supply that features an adjustable output voltage is shown in figure 16. this regulator delivers 1.0a into 1.2 to 35v output. the input voltage ranges from roughly 8.0 to 40v. in order to achieve a 10 or more times reduction of output ripple, an additional l-c filter is included in this circuit.
tc2575 1.0a step-down switching regulator 20 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a figure 17. schematic diagram of the 8.0v at 1.0a step-down converter using the tc2575-adj d1 1n5819 l1 330mh l2 25 h output 2 4 feedback r2 10k r1 1.8k regulated output filtered v out v out 2 = 8.0v @ 1.0a regulated output filtered = 8.0v @ 1.0a unregulated dc input c2 330 f/16v c3 100 f/16v c1 100 f /50v tc2575-adj 1 5 on/off gnd +v in 3 +v in = +10v to + 40v the tc2576-adj step-down voltage regulator with 8.0v @ 1.0a output power capability. typical application with through-hole pc board layout c1 100 f, 63v, aluminum electrolytic c2 330 f, 16v, aluminum electrolytic c3 100 f, 16v, aluminum electrolytic d1 1.0a, 40v, schottky rectifier, 1n5819 l1 330 h, tech 39: 77 458 bv, toroid, through-hole, pin 3 = start, pin 7 = finish l2 25 h, tdk: sft52501, toroid core, through-hole r1 1.8k r2 10k v out = v ref + ( 1.0 + r2 ) r1 v ref = 1.23v r1 is between 1.0k and 5.0k figure 16. adjustable power supply with low ripple voltage d1 1n5819 l1 150 h output 2 4 feedback r2 50k r1 1.1k l2 20 h output voltage 1.2v to 35v @1.0a optional output ripple filter unregulated dc input c out 2200 f c1 100 f c in 100 f/50v tc2575-adj 1 gnd +v in 5 3 on/off
21 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ? 2001 microchip technology inc. ds21398a figure 18. pc board component side figure 19. pc board copper side +v out1 +v in gnd in c1 l1 c2 d1 j1 u1 tc2575 l2 c3 +v out2 r2 r1 gnd out note: not to scale. note: not to scale .
tc2575 1.0a step-down switching regulator 22 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a typical characteristics (circuit of figure 2) 0 20 50 3.0 0 50 2.0 0 1.2 50 i q , quiescent current (ma) v in input voltage (v) i o , output current (a) t j , junction temperature ( c) v in input voltage (v) input-output differential (v) t j , junction temperature ( c) switch current (a) , v out output voltage change (%) v sat saturation voltage (v) v out output voltage change (%) figure 20. normalized output voltage t j , junction temperature ( c) figure 21. line regulation v in = 20 v i load = 200ma normalized at t j = 25 c figure 22 switch saturation voltage figure 23. current limit figure 24. dropout voltage figure 25. quiescent current i load = 200ma t j = 25 c 3.3 v, 5.0 v and adj 12v 25 c v in = 25v measured at ground pin t j = 25 c i load = 200ma i load = 1.0a ? v out = 5% r ind = 0.2 ? 125 c 40 c 5.0 25 10 0 20 15 25 25 75 50 35 30 40 100 125 0.8 0.4 0.4 0 0 0.2 0.4 0.6 0.2 1.0 0.6 0.2 0.2 0.6 2.5 1.5 0.5 0 2.0 1.0 14 10 6.0 4.0 18 12 8.0 16 1.1 0.9 0.7 0.5 1.0 0.8 0.6 1.2 0.8 0.4 1.0 0.6 1.8 1.4 1.6 0.4 25 0.1 0 0.2 25 0.3 50 0.4 75 0.5 100 0.6 125 0.7 5.0 5 10 0 15 25 20 50 25 75 30 100 35 125 0.8 0.9 1.0 40 i load = 200ma i load = 1.0a v out = 5.0v
23 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ? 2001 microchip technology inc. ds21398a typical characteristics (circuit of figure 2 cont.) output voltage (pin 2) output current (pin 2) output ripple voltage i stby , standby quiescent current ( a) 100 50 50 10 v 0 0 i fb , feedback pin current (na) t j , junction temperature ( c) t j , junction temperature ( c) 5.0 sec/div 100 sec/div normalized frequency (%) t j , junction temperature ( c) i stby , standby quiescent current ( a) figure 26. standby quiescent current v in , input voltage (v) figure 27. standby quiescent current figure 28. oscillator frequency figure 29. feedback pin current figure 30. switching waveforms figure 31. load transient response v in = 12v v on /off = 5.0v t j = 25 c 100 1.0 a 1.0 40 0 2.0 0.5 20 1.0 a 0 120 0 0 100 0.5 a 2.0 100 40 80 4.0 60 40 20 mv 8.0 20 0 10 0 0 0 40 80 120 60 20 6.0 /div i load load current (a) v out output voltage 20 25 25 25 5.0 0 0 0 10 25 25 25 15 50 50 50 20 75 75 75 25 100 100 100 30 125 125 125 40 35 v in = 12v normalized at 25 c adjustable version only change (mv) current inductor
tc2575 1.0a step-down switching regulator 24 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a typical characteristics (circuit of figure 2 cont.) v in , maximum input et, voltage time (v sec) voltage (v) i l , maximum load current (a) i l , maximum load current (a) 0.2 60 0.2 note: this inductor value selection guide is applicable for continuous mo d 200 0.2 60 0.2 60 i l , maximum load current (a) v in , maximum input voltage (v) v in , maximum input voltage (v) figure 32. tc2575 ( v out = 3.3v) i l , maximum load current (a) figure 33.tc2575 ( v out = 5.0v) figure 34. tc2575 ( v out = 12.0v) figure 35. tc2575-adj h1500 h1000 l680 l470 l330 l150 h1000 l100 l680 l470 l330 l220 l150 h1500 h1000 h680 h470 h680 h2200 h2200 h1500 h1000 h470 l330 l220 l150 l680 l680 l470 l470 l100 l220 l330 40 150 20 25 125 40 15 20 100 30 10 15 80 25 8.0 12 70 20 7.0 10 60 18 6.0 9.0 50 17 8.0 40 16 7.0 20 14 5.0 0.3 0.3 0.3 0.3 0.4 0.4 0.4 0.4 0.5 0.5 0.5 0.5 0.6 0.6 0.6 0.6 0.7 0.7 0.7 0.8 0.8 0.8 0.8 0.9 0.9 0.9 1. 0 1 . 1.0 1.0 15 30 l220
25 tc2575 tc2575-1 3/13/00 1.0a step-down switching regulator ? 2001 microchip technology inc. ds21398a printed in the u.s.a. 5-pin to-220 .273 (6.93) .263 (6.68) .037 (0.95) .025 (0.64) .117 (2.97) .103 (2.62) .415 (10.54) .390 (9.91) .156 (3.96) .140 (3.56) dia. .293 (7.44) .204 (5.18) .590 (14.99) .482 (12.24) .072 (1.83) .062 (1.57) pin 1 .185 (4.70) .165 (4.19) .055 (1.40) .045 (1.14) .613 (15.57) .569 (14.45) .115 (2.92) .087 (2.21) .025 (0.64) .012 (0.30) 3 - 7.5 5 plcs. package dimensions dimensions: inches (mm)
tc2575 1.0a step-down switching regulator 26 tc2575-1 3/13/00 ? 2001 microchip technology inc. ds21398a information contained in this publication regarding device applications and the like is intended through suggestion only and ma y be superseded by updates. it is your responsibility to ensure that your application meets with your specifications. no representation or warrant y is given and no liability is assumed by microchip technology incorporated with respect to the accuracy or use of such information, or infringement of patent s or other intellectual property rights arising from such use or otherwise. use of microchip ? s products as critical components in life support systems is not authorized except with express written approval by microchip. no licenses are conveyed, implicitly or otherwise, except as maybe explicitly expressed herein, under any intellec- tual property rights. the microchip logo and name are registered trademarks of microchip technology inc. in the u.s.a. and othe r countries. all rights reserved. all other trademarks mentioned herein are the property of their respective companies. all rights reserved. ? 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