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| 0.5A Step-Down Switching Regulator TC2574 TC2574 0.5A Step-Down Switching Regulator FEATURES s s s s s s s s s s 3.3V, 5.0V, 12V and Adjustable Output Versions Adjustable Version Output Voltage Range, 1.23 to 37 V 4% Max Over Line and Load Conditions Guaranteed 0.5 A Output Current Wide Input Voltage Range: 4.75 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 GENERAL DESCRIPTION The TC2574 series of regulators are monolithic integrated circuits ideally suited for easy and convenient design of a step-down switching regulator (buck converter). All circuits of this series are capable of driving a 0.5A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5.0V, 12V and an adjustable output version. These regulators were designed to minimize the number of external components to simplify the power supply design. Standard series of inductors optimized for use with the TC2574 are offered by several different inductor manufacturers. Since the TC2574 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 most cases, the power dissipated by the TC2574 regulator is so low, that the copper traces on the printed circuit board are normally the only heatsink needed and no additional heatsinking is required. The TC2574 features include a guaranteed 4% tolerance on output voltage within specified input voltages and output load conditions, and 10% on the oscillator frequency (2% over 0C to +125C). External shutdown is included, featuring 60A (typical) standby current. The output switch includes cycle-by-cycle current limiting, as well as thermal shutdown for full protection under fault conditions. APPLICATIONS s s s s s s Simple and High-Efficiency Step-Down (Buck) Regulator Efficient Pre-Regulator for Linear Regulators On-Card Switching Regulators Positive to Negative Converters (Buck-Boost) Negative Step-Up Converters Power Supply for Battery Chargers PIN CONFIGURATIONS 16-Pin SOIC (Wide) NC 1 NC 2 FB 3 SIG GND 4 ON/OFF 5 16 NC 15 NC 14 OUTPUT ORDERING INFORMATION Part Number TC2574-3.3VPA TC2574-5.0VPA TC2574-12.0VPA TC2574-VPA* TC2574-VOE* Package 8-Pin PDIP (Narrow) 8-Pin PDIP (Narrow) 8-Pin PDIP (Narrow) 8-Pin PDIP (Narrow) 16-Pin SOIC (Wide) Temperature Range -40 to +125C -40 to +125C -40 to +125C -40 to +125C -40 to +125C TC2574 13 NC 12 VIN 11 NC 10 NC 9 NC PWR GND 6 NC 7 NC 8 Note: *ADJ = 1.23 To 37V. 8-Pin PDIP (Narrow) FB 1 SIG GND 2 ON/OFF 3 PWR GND 4 8 NC 7 OUTPUT TC2574 6 NC 5 VIN TC2574-1 1/6/00 1 TelCom Semiconductor reserves the right to make changes in the circuitry and specifications of its devices. 0.5A Step-Down Switching Regulator TC2574 ABSOLUTE MAXIMUM RATINGS* Maximum Supply Voltage ................................ VIN = 45V ON/OFF Pin Input Voltage ..................... -0.3V V +VIN Output Voltage to Ground (Steady State) ............... -1.0 V Max Power Dissipation (SOIC) ........... (Internally Limited) Thermal Resistance, Junction-to-Ambient ..... 145C/W Max Power Dissipation (PDIP) ............ (Internally Limited) Thermal Resistance, Junction-to-Ambient ... 100C/W Thermal Resistance, Junction-to-Case ........ 5.0C/W Storage Temperature Range ................. -65C to +150C Minimum ESD Rating .............................................. 2.0kV (Human Body Model: C = 100 pF, R = 1.5 k) Lead Temperature (Soldering, 10 seconds) .......... 260 C Maximum Junction Temperature............................. 150C Operating Junction Temperature Range .... -40 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, VIN = 12V for the 3.3V, 5.0V, and Adjustable version,VIN = 25V for the 12V version. ILOAD = 100mA. For typical values TJ = 25C, for min/max values TJ is the operating junction temperature range that applies (Note 2), unless otherwise noted. Symbol VOUT Parameter Output Voltage Test Conditions VIN = 12V, ILOAD = 100mA, TJ = 25C 4.75V VIN 40V, 0.1A ILOAD 0.5AV TJ = 25C TJ = -40C to +125 VIN = 12V, ILOAD = 0.5 A VIN = 12V, ILOAD = 100mA, TJ = 25C 7.0V VIN 40V, 0.1A ILOAD 0.5A TJ = 25C TJ = -40C to +125C VIN = 12V, ILOAD = 0.5 A VIN = 25V, ILOAD = 100mA, TJ = 25C 15V VIN 40V, 0.1A ILOAD 0.5A TJ = 25C TJ = -40C to +125C VIN = 15V, ILOAD = 0.5 A VIN = 12V, ILOAD = 100mA, VOUT = 5.0V, TJ = 25*C 7.0V VIN 40V, 0.1A ILOAD 0.5A VOUT = 5.0V TJ = 25C TJ = -40C to +125C VIN = 12V, ILOAD = 0.5A, VOUT = 5.0V Min 3.234 3.168 3.135 -- 4.9 4.8 4.75 -- 11.76 11.52 11.4 -- 1.217 Typ 3.3 3.3 -- 72 5.0 5.0 -- 77 10 12 -- 88 1.23 Max 3.366 3.432 3.465 -- 5.1 5.2 5.25 -- 12.24 12.48 12.6 -- 1.243 Units V TC2574-3.3 [( Note 1) Test Circuit Figure 2] VOUT Efficiency Output Voltage % V TC2574-5 [( Note 1) Test Circuit Figure 2] VOUT Efficiency Output Voltage % V TC2574-12 [( Note 1) Test Circuit Figure 2] VFB VFBT Efficiency Feedback Voltage Feedback Voltage % V TC2574-Adjustable Version [( Note 1) Test Circuit Figure 2] Efficiency 1.193 1.18 -- 1.23 -- 77 1.267 1.28 -- % NOTES: 1. External components such as the catch diode, inductor, input and output capacitors can affect the switching regulator system performance. When the TC2574 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 TC2574: TLOW = -40C THIGH = +125C TC2574-1 1/6/00 2 0.5A Step-Down Switching Regulator TC2574 ELECTRICAL CHARACTERISTICS: Unless otherwise specified, VIN = 12V for the 3.3V, 5.0V, and Adjustable version,VIN = 25V for the 12V version. ILOAD = 100mA. For typical values TJ = 25C, for min/max values TJ is the operating junction temperature range that applies (Note 2), unless otherwise noted. Symbol Ib Parameter Feedback Bias Current Test Conditions Min Typ Max Units nA TC2574-ADJUSTABLE VERSION [(Note 1) Test Circuit Figure 2] VOUT = 5.0V (Adjustable Version Only) TJ = 25C TJ = -40C to +125C Oscillator Frequency (Note 3) TJ = 25C TJ = 0 to +125C TJ = -40 to +125C Saturation Voltage IOUT = 0.5 A, (Note 4) TJ = 25C TJ = -40 to +125C Max Duty Cycle ("on") [Note 5] Current Limit Peak Current (Notes 3 and 4) TJ = 25C TJ = -40 to +125C Output Leakage Current (Notes 6 and 7), TJ = 25C Output = 0 V Output = - 1.0 V Quiescent Current (Note 6) TJ = 25C TJ = -40 to +125C Standby Quiescent Current ON/OFF Pin = 5.0 V ("off") TJ = 25C TJ = -40 to +125C ON/OFF Pin Logic Input Level VOUT = 0V TJ = 25C TJ = -40 to +125C Nominal Output Voltage TJ = 25C TJ = -40 to +125C ON/OFF Pin Input Current mA ON/OFF Pin = 5.0V ("off"), TJ = 25C ON/OFF Pin Input Current mA ON/OFF Pin = 0 ("on"), TJ = 25C -- -- -- 47 42 -- -- 93 0.7 0.65 -- -- -- -- -- -- 25 -- 52 52 - 1.0 -- 98 1.0 -- 0.6 10 5.0 -- 60 -- 100 200 -- 58 63 1.2 1.4 -- 1.6 1.8 mA 2.0 30 mA 9.0 11 A 200 400 V 2.2 2.4 -- -- -- -- 1.4 -- 1.2 -- 15 0 -- -- 1.0 0.8 A 30 A 5.0 fO kHz VSAT V DC ICL % A IL IQ ISTBY VIH VIL IIH IIL NOTES: 1. External components such as the catch diode, inductor, input and output capacitors can affect the switching regulator system performance. When the TC2574 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 TC2574: TLOW = -40C T high = +125C 3. The oscillator frequency reduces to approximately 18kHz in the event of an output short or an overload which causes the regulated 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 0 V. 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 version, to force the output transistor OFF. 7. VIN = 40 V. TC2574-1 1/6/00 3 0.5A Step-Down Switching Regulator TC2574 PIN DESCRIPTION Pin No. 8-Pin PDIP 5 Pin No 16-Pin SOIC 12 Symbol VIN Description This pin is the positive input supply for the TC2574 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 (CIN in Figure 1). This is the emitter of the internal switch. The saturation voltage VSAT 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. Circuit signal ground pin. See the information about the printed circuit board layout. Circuit power ground pin. See the information about the printed circuit board layout. 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 TC2574 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. It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total input supply current to approximately 80A. The input threshold voltage is typically 1.5V. Applying a voltage above this value (up to +VIN ) shuts the regulator off. If the voltage applied to this pin is ower than 1.5 V or if this pin is left open, the regulator will be in the "on" condition. 7 14 Output 2 4 1 4 6 3 SIG Gnd PWR GND FB 3 5 ON/OFF REPRESENTATIVE BLOCK DIAGRAM AND TYPICAL APPLICATION Unregulated DC Input CIN +VIN + 5 TC2574 1 3.1V Internal Regulator ON/OFF ON/OFF 3 Output Voltage Versions Fixed gain Error Amplifier Current Limit Comparator R2 () Feedback R1 + - Driver 3.3V 5.0V 12V 1.7k 3.1k 8.84k + R2 1.0k - Freq. Shift 18kHz 1.235V Band-Gap Reference + - Latch For Adjustable version R1 = open, R2 = 0 Output 1.0 Amp Switch 7 PWR GND 4 D1 L1 VOUT SIG GND 2 52kHz Oscillator Reset Thermal Shutdown + COUT Load TC2574-1 1/6/00 4 0.5A Step-Down Switching Regulator TC2574 Feedback 7.0 - 40V Unregulated DC Input +VIN CIN 22F 1 TC2574 2 Sig 4 GND Output L1 330H 5.0V Regulated Output 0.5A Load D1 COUT 220F + 5 7 PWR 3 ON/OFF GND Figure 1. Block Diagram and Typical Application: Fixed Output Versions Test CIrcuit and Layout Guidelines 1 TC2574 Fixed Output 4 PWR 2 GND Sig 3 GND Output 7 ON/OFF D1 1N5819 L1 330H VIN 5 7.0 - 40V Unregulated DC Input +C IN 22F VOUT COUT 220F + Load CIN COUT D1 L1 R2 - 22F, 60V, Aluminum Electrolytic - 220F, 25V, Aluminum Electrolytic - Schottky, 1N5819 - 2.0k,0.1% - 6.12k, 0.1% Adjustable Output Voltage Versions 1 TC2574 Adjustable 4 + CIN 22F PWR 2 GND Sig 3 GND Output 7 ON/OFF + D1 1N5819 COUT 220F L1 330H VIN 5 7.0 - 40V Unregulated DC Input VOUT 5.0V R2 6.12k Load R2 6.12k VOUT = VREF (1.0 + R1) R1= R2 (VOUT - 1.0) VREF Where VREF = 1.23V, R1 between 1.0k and 5.0k R2 Figure 2. Test Circuit and Layout Guidelines TC2574-1 1/6/00 5 0.5A Step-Down Switching Regulator TC2574 PCB LAYOUT GUIIDELINES As with 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 electromagnetic interferences (EMI) and affect the desired operation. 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 7 (emitter of the internal switch) of the TC2574 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 nearto the regulator, when using the adjustable version of the TC2574 regulator. 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: (VOUT - VD ) tOFF 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: IL (OFF) = d = tON ,where T is the period of switching. T For the buck converter with ideal components, the duty cycle can also be described as: d = VOUT VIN Figure 4 shows the buck converter idealized waveforms of the catch diode voltage and the inductor current. VON (SW) DESIGN PROCEDURE Buck Converter Basics The TC2574 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: (VIN - VOUT ) tON 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. IL (ON) = Power Switch + VIN - D1 COUT+ RLOAD L Diode Voltage Power Switch Off Power VD/(FWD) Switch On Power Switch Off Power Switch On Time Inductor Current IPK ILOAD (AV) IMIN Diode Power Switch Diode Power Switch Time Figure 4. Buck Converter Idealized Waveforms Figure 3. Basic Buck Converter TC2574-1 1/6/00 6 0.5A Step-Down Switching Regulator TC2574 Procedure (Fixed Output Voltage Version) In order to simplify the switching regulator design, a step-by-step design procedure and examples are provided. Procedure Given Parameters: VOUT = Regulated Output Voltage (3.3V, 5.0V or 12V) VIN(max) = Maximum Input Voltage ILOAD(max) = Maximum Load Current 1. Controller IC Selection According to the required input voltage, output voltage and current select the appropriate type of the controller IC output voltage version. 2. Input Capacitor Selection (CIN ) To prevent large voltage transients from appearing at the input tantalum electrolytic bypass capacitor is needed between the pin +VIN 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) A. Since the diode maximum peak current exceeds the regulator maximum load current. For a robust design the diode should have a current rating equal to the maximum current limit of the TC2574 to be able to withstand 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. According to the required working conditions, select the correct inductor value using the selection guide from Figures 39 to 41. B. From the appropriate inductor selection guide, identify the inductance region intersected by the Maximum Input Voltage 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 manufacturers part numbers listed in Table 2. The 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: Example Given Parameters: VOUT = 5.0 V VIN (max) = 15 V ILOAD (max) = 0.4 A 1. Controller IC Selection According to the required input voltage, output voltage, polarity and current value, use the TC2574-5 controlller IC. 2. Input Capacitor Selection (CIN ) A 22F, 25V aluminium electrolytic capacitor located near to the input and ground pins provides input sufficient bypassing. 3. Catch Diode Selection (D1) A. For this example the current rating of the diode is 1.0A B. Use a 20V 1N5817 Schottky diode, or any of the suggested fast recovery diodes shown in Table 1. 4. Inductor Selection (L1) A. Use the inductor selection guide shown in Figure 38. B. From the selection guide, the inductance area intersected by the 15V line and 0.4A line is 330. C. Inductor value required is 330H. From Table 2, choose an inductor from any of the listed manufacturers. IP (max) = ILOAD (max)+ (VIN - VOUT ) tON 2L where tON is the "on" time of the power switch and tON = VOUT 1.0 x VIN fOSC For additional information about the inductor, see the inductor section in the "EXTERNAL COMPONENTS" section of this data sheet. TC2574-1 1/6/00 7 0.5A Step-Down Switching Regulator TC2574 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 5. Output Capacitor Selection (COUT) A. Since the TC2574 is a forward-mode switching regulator with voltage mode control, its open loop 2-pole-1-zero frequency characteristic has the dominant pole-pair deter mined by the output capacitor and inductor values. For stable operation and an acceptable ripple voltage, (approximately 1% of the output voltage) a value between 100F and 470F 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 5.0Vregulator, a rating at least 8.0V is a appropriate, and a 10Vor 16V rating is recommended. Example 5. Output Capacitor Selection (COUT ) A. COUT = 100F to 470F standard aluminium electrolytic. B. Capacitor voltage rating = 20V. Procedure (Adjustable Output Version: TC2574-ADJ) Procedure Given Parameters: VOUT = Regulated Output Voltage VIN (max) = Maximum DC Input Voltage ILOAD (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: VOUT = VREF Given Parameters: VOUT = 24V VIN (max) = 40V ILOAD (max) = 0.4A 1. Programming Output Voltage (selecting R1 and R2) Select R1 and R2 R2 VOUT = 1.23 + Select R1 = 1.0k R1 Example (1.0 ) (1.0 + R2 ) where V R1 REF = 1.23V R2 = R1 V (V OUT - 1.0) = 1.0k REF 10V ( 1.23V - 1.0) Resistor R1 can be between 1.0k and 5.0k. (For best temperature coefficient and stability with time, use 1% metal film resitors). VOUT R2 = R1 - 1.0) VREF R1 = 18.51k, choose a 18.7k metal film resistor. ( 2. Input Capacitor Selection (CIN ) 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 +VIN 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. 2. Input Capacitor Selection (CIN ) A 22F aluminium electrolytic capacitor located near the input and ground pin provides sufficient bypassing. TC2574-1 1/6/00 8 0.5A Step-Down Switching Regulator TC2574 Procedure (Adjustable Output Version): (TC2574-ADJ) (Continued) Procedure 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 TC2574 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 = ( VIN - VOUT) VOUT 10 x [V x sec] VIN F[Hz] 6 Example 3. Catch Diode Selection (D1) A. For this example, a 1.0A current rating is adequate. B. Use a 50V MBR150 Schottky diode or any suggested fast recovery diodes in Table 1. 4. Inductor Selection (L1) A. Calculate E x T [V xsec] constant: E x T = (40 - 24) x 24 1000 x = 105[V x sec] 40 52 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 39. 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 8. D. From the inductor code, identify the inductor value. Then select an appropriate inductor from Table 2. The inductor chosen must be rated for a switching frequency of 52kHz and for a current rating of 1.15 x ILOAD . The inductor current rating can also be determined by calculating the inductor peak current: IP (max) = ILOAD(max) + (VIN - VOUT) tON 2L B. E x T = 185 [V x sec] C. ILOAD(max) = 0.4 A Inductance Region = 1000 D. Proper inductor value = 1000H Choose the inductor from Table 2. where tON is the "on" time of the power switch and tON = (VOUT 1.0 ) x VIN fOSC For additional information about the inductor, see the inductor section in the "EXTERNAL COMPONENTS" section of this data sheet. TC2574-1 1/6/00 9 0.5A Step-Down Switching Regulator TC2574 Procedure (Adjustable Output Version: TC2574-ADJ) (Continued) Procedure 5. Output Capacitor Selection (COUT ) A. Since the TC2574 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: V COUT 13,000 IN(max) [F] VOUT x L[F] B. Capacitor values between 10F and 2000F 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 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 of at least 8.0V is appropriate, and a 10V or 16V rating is recommended. Example 5. Output Capacitor Selection (COUT ) A. 40 COUT 13,300 x 22.2F 24 x 1000 To achieve an acceptable ripple voltage, select COUT 100F electrolytic capacitor. Table 1. Diode Selection Guide gives an overview about through-hole diodes for an effective design. 1.0 Amp Diodes VR 20V 30V 40V 50V 60V Schottky 1N5817 MBR120P 1N5818 MBR130P 1N5819 MBR140P MBR150 MBR160 Fast Recovery MUR110 (rated to 100V) TC2574-1 1/6/00 10 0.5A Step-Down Switching Regulator TC2574 Table 2. Inductor Selection Guide Inductor Value 68H 100H 150H 220H 330H 470H 680H 1000H 1500H 2200H Pulse Engineering * * 52625 52626 52627 52628 52629 52631 * * Tech 89 55 258 SN 55 308 SN 55 356 SN 55 406 SN 55 454 SN * 55 504 SN 55 554 SN * * Renco RL-1284-68 RL-1284-100 RL-1284-150 RL-1284-220 RL-1284-330 RL-1284-470 RL-1284-680 RL-1284-1000 RL-1284-1500 RL-1284-2200 NPI NP5915 NP5916 NP5917 NP5918/5919 NP5920/5921 NP5922 NP5923 * * * Table 3. Example of Several Inductor Manufacturers Phone/Fax Numbers Pulse Engineering Inc. Pulse Engineering Inc. Europe Renco Electronics Inc. Tech 39 NPI/APC Phone Fax Phone Fax Phone Fax Phone Fax Phone Fax + 1-619-674-8100 + 1-619-674-8262 + 353-9324-107 + 353-9324-459 + 1-516-645-5828 + 1-516-586-5562 + 33-1-4115-1681 + 33-1-4709-5051 + 44-634-290-588 TC2574-1 1/6/00 11 0.5A Step-Down Switching Regulator TC2574 EXTERNAL COMPONENTS Input Capacitor (CIN) The Input Capacitor Should Have a Low ESR For stable operation of the switch mode converter a lowESR (Equivalent Series Resistance) aluminium or solid tantalum bypass capacitor is needed between the input pinand 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 -25C larger values of the input capacitor may be needed. Also paralleling a ceramic or solid tantalum capacitor will increase the regulator stability at cold temperatures. RMS Current Rating of CIN 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 electrolytic capacitor beyond the RMS current rating is a shortened operating life. In order to assure maximum capacitor operating lifetime, the capacitor's RMS ripple current rating should be: IRMS > 1.2 x d x ILOAD where d is the duty cycle, for a continuous mode buck regualor t V d = ON = OUT T VIN and d = tON IVOUTI = for a buck-boost regulator. T IVOUTI + VIN 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 0.03 ), 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 temperatures below -25C. The ESR rises dramatically at cold temperatures and typically rises 3 times at -25C and as much as 10 times at -40C. Solid tantalum capacitors have much better ESR spec at cold temperatures and are recommended for temperatures below -25C. 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 TC2574 The TC2574 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 TC2574 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 rectifier 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. 12 Output Capacitor (COUT) 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 reTC2574-1 1/6/00 0.5A Step-Down Switching Regulator TC2574 A fast-recovery diode with soft recovery characteristics can better fulfill some quality, low noise design requirements.Table 1 provides a list of suitable diodes for the TC2574 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 transitions 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 semiconductors 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 TC2574 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 conditions, the circuit will be forced to the discontinuousmode 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 Continuous Mode Switching Current Waveforms VERTICAL RESOLUTION 200mADV 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 TC2574 regulator was added to this data sheet (Figures 39 through 41). 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 0.2A) 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 Interference) shielding that the core must provide. There are many different styles of inductors available, 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 Continuous Mode Switching Current Waveforms VERTICAL RESOLUTION 100mADV 0.5A Inductor Current Waveform 0A 0.5A Power Switch Current Waveform 0A Inductor 0.1A Current Waveform 0A Power 0.1A Switch Current Waveform 0A HORIZONTAL TIME BASE: 5.0sec/DIV HORIZONTAL TIME BASE: 5.0sec/DIV Figure 5. Continuous Mode Switching Current Waveforms TC2574-1 1/6/00 Figure 6. Continuous Mode Switching Current Waveforms 13 0.5A Step-Down Switching Regulator TC2574 within the core, it generates less EMI, reducing noise problems in sensitive circuits. The least expensive is the bobbin core type, which consists of wire wound on a ferrite rod core. 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. these transients, all these contribute to the amplitude of these spikes. To minimize these voltage spikes, low inductance 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. Voltage spikes caused by switching action of the output switch and the parasitic inductance of the output capacitor Unfiltered Output Voltage 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 TC2574 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 TC2574. Different inductor types have different saturation characteristics, and this should be kept in mind when selecting an inductor. Filtered Output Voltage HORIZONTAL TIME BASE: 5.0sec/DIV Figure 7. Output Ripple Voltage Waveforms 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 (20H, 100F), 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 15. 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. GENERAL RECOMMENDATIONS Output Voltage Ripple and Transients Source of the Output Ripple Since the TC2574 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. Heatsinking and Thermal Considerations The TC2574 is available in both 8-Pin PDIP (narrow) and 16-Pin SOIC (wide) packages. When used in the typical application the copper lead frame conducts the majority of the heat from the die, through the leads, to the printed circuit copper. The copper and the board are the heatsink for this package and the other heat producing components, such as the catch diode and inductor. For the best thermal performance, wide copper traces should be used and all ground and unused pins should be soldered to generous amounts of printed circuit board copper, such as a ground plane. Large areas of copper provide the best transfer of heat to the surrounding air. One 14 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 TC2574-1 1/6/00 VERTICAL RESOLUTION 20mV.DIV 0.5A Step-Down Switching Regulator TC2574 exception to this is the output (switch) pin, which should not have large areas of copper in order to minimize coupling to sensitive circuitry. Additional improvement in heat dissipation can be achieved even by using of double sided or multilayer boards which can provide even better heat path to the ambient. Using a socket for the 8-Pin PDIP (narrow) package is not recommended because socket represents an additional thermal resistance, and as a result the junction temperature will be higher. Since the current rating of the TC2574 is only 0.5 A, the total package power dissipation for this switcher is quite low, ranging from approximately 0.1 up to 0.75 under varying conditions. In a carefully engineered printed circuit board, the through-hole PDIP package can easily dissipate up to 0.75 , even at ambient temperatures of 60C, and still keep the maximum junction temperature below 125C. IQ (quiescent current) and VSAT can be found in the TC2574 data sheet, VIN is minimum input voltage applied, VO is the regulator output voltage, ILOAD is the load current. 8.0 to 25 V Unregulated DC Input +VIN CIN* 22F Feedback 1 TC2574 (12V) 4 Pwr 2 GND Sig 3 GND Output 7 ON/OFF L1 68 mH 5 D1 MBR150 COUT 680F -12 V @ 100mA Regulated Output Thermal Analysis and Design The following procedure must be performed to determine the operating junction temperature. First determine: 1. PD(max) - maximum regulator power dissipation in the application. 2. TA(max) - maximum ambient temperature in the application. 3. TJ (max) - maximum allowed junction temperature (125C for the TC2574). For a conservative design, the maximum junction temperature should not exceed 110C to assure safe operation. For every additional +10C temperature 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 page 2 of this data sheet or JC and JA values). The following formula is to calculate the approximate total power dissipated by the TC2574: PD = (VIN x IQ ) + d x ILOAD x VSAT where d is the duty cycle and for buck converter d= TC2574-1 1/6/00 Figure 8. Inverting Buck-Boost Develops -12V The dynamic switching losses during turn-on and turn-off can be neglected if a proper type catch diode is used. The junction temperature can be determined by the following expression: TJ = (JA )(PD ) + TA where (JA )(PD ) represents the junction temperature rise caused by the dissipated power and TA is the maximum 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 approximate, 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. At higher power levels the thermal resistance decreases due to the increased air current activity. 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. Some of them, like the catch diode or the inductor will enerate some additional heat. tON VO = T VIN 15 0.5A Step-Down Switching Regulator TC2574 ADDITIONAL APPLICATIONS Inverting Regulator An inverting buck-boost regulator using the TC2574 (12V) 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 regulates it. In this example the TC2574 (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 0.1 A to the output when the input voltage is 8.0 V or higher. At lighter loads the minimum input voltage required drops to approximately 4.7V, because the buck-boost regulator topology 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 configuration 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 0.6A. 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. While using a delayed startup arrangement, the input capacitor 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 CIN. 12 to 25V Unregulated DC Input CIN C1 22 mF /50 V 0.1F Feedback +VIN 5 3 R1 47k TC2574 (12V) ON/OFF 4 R2 47k Pwr 2 GND L1 1 H Output 68 7 Sig GND D1 MBR150 COUT 680F /16V -12V @ 100mA Regulated Output Figure 9. Inverting Buck-Boost Regulator with Delayed Startup The following formula is used to obtain the peak inductor current: IPEAK ILOAD (VIN - IVOUTI) VIN x tON + VIN 2L1 IVOUTI VIN + IVOUTI 1.0 , and fOSC = 52kHz. fOSC where tON Under normal continuous inductor current operating conditions, the worst case occurs when VIN is minimal. It has been already mentioned above, that in some situations, the delayed startup or the undervoltage 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. 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 (1.3V 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. 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 COUT. 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 68H and 220 H. To select an inductor with an appropriate current rating, the inductor peak current has to be calculated. TC2574-1 1/6/00 +VIN +VIN 5 CIN 22F R1 47 k TC2574-XX 5.0 V 0 On Shutdown Input Off R3 470 3 ON/OFF 2 and 4 R2 47 k GNDs Pins -VOUT MOC8101 NOTE: This picture does not show the complete circuit. Figure 10. Inverting Buck-Boost Regulator Shutdown Circuit Using an Optocoupler 16 0.5A Step-Down Switching Regulator TC2574 +V 0 On R2 5.6 k +VIN Cin 22F Q1 2N3906 3 ON/OFF 2 GNDs and Pins 4 R1 12 k -VOUT +VIN 5 TC2574 Off Shutdown Input Another important point is that these negative boost converters cannot provide any current limiting load protection 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 1.3 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 respectively) 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. +VIN +VIN 5 TC2574 NOTE: This picture does not show the complete circuit. Figure 11. Inverting Buck-Boost Regulator Shutdown Circuit Using a PNP Transistor 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. 1 +VIN 5 CIN 22F 4 TC2574 (12V) Feedback Output Pwr 2 GND Sig 3 GND 7 ON/OFF D1 1N5817 VOUT = -12V VIN -5.0 to -12 V L1 330H Load Current 60mA for VIN = -5.2V 120mA for VIN = -7.0V COUT 1000F C1 0.1 F C IN 22mF 3 ON/OFF 2 GNDs and and Pins 4 R2 47 k R1 47 k NOTE: This picture does not show the complete circuit. Figure 13. Delayed Startup Circuitry Figure 12. Negative Boost Regulator 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 15. Resistor R3 pulls the ON/OFF pin high and keeps the regulator off until the input voltage reaches an predetermined threshold level, which is determined by the following expression: 17 Design Recommendations: The same design rules as for the previous inverting buck-boost converter can be applied. The output capacitor COUT 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. TC2574-1 1/6/00 0.5A Step-Down Switching Regulator TC2574 VTH VZ1 + 1.0 + ( R2 R1 )V BE (Q1) Adjustable Output, Low-Ripple Power Supply A 0.5 A output current capability power supply that features an adjustable output voltage is shown in Figure 16. This regulator delivers 0.5 A into 1.2 to 35 V output. The input voltage ranges from roughly 3.0 to 40 V. In order to achieve a 10 or more times reduction of output ripple, an additional L-C filter is included in this circuit. GNDs Pins +VIN +VIN 5 TC2574 (5V) 3 ON/OFF 2 and 4 GNDs Pins +VIN +VIN 5 TC2574 (5V) 3 ON/OFF 2 and 4 R1 10k R3 47k CIN 22F Z1 1N5242B Q1 2N3904 R2 10k R2 15 k R3 68 k Cin 22mF Z1 1N5242 Q1 2N3904 R1 15 k -VOUT NOTE: This picture does not show the complete circuit. Figure 14. Undervoltage Lockout Circuit for Buck Converter NOTE: This picture does not show the complete circuit (see Figure 8). Figure 15. Undervoltage Lockout Circuit for Buck-Boost Converter 40V Max Unregulated DC Input Feedback +VIN 5 1 TC2574-ADJ Output 4 Pwr 2 GND Sig 3 GND 7 ON/OFF D1 1N5819 COUT 1000F R1 1.1 k L1 150H R2 50 k C1 100F L2 20H Output Voltage 1.2 to 35V @ 0.5 A CIN 22F Optional Output Ripple Filter Figure 16. 1.2 to 35V Adjustable 500mA Power Supply with Low Output Ripple TC2574-1 1/6/00 18 0.5A Step-Down Switching Regulator TC2574 The TC2574-5 Step-Down Voltage Regulator with 5.0V @ 0.5A Output Power Capability. Typical Application with Through-Hole PC Board Layout Feedback Unregulated DC Input +VIN = 7.0 to 40 V +VIN 5 4 1 TC2574 (5V) Output 7 ON/OFF L1 330H Regulated Output +VOUT = 5.0V @ 0.5 A Pwr 2 GND Sig 3 GND C1 220F D1 1N5819 C2 220F GND GND C1 - 22F, 63V, Aluminum Electrolytic C2 - 220F, 16V, Aluminum Electrolytic D1 - 1.0A, 40V, Schotty Rectifier, 1N5819 L1 - 330H, RL-1284-330, Renco Electronics Figure 17. Schematic Diagram of the TC2574 (5V) Step-Down Converter TC2574-5.0 + +VIN C1 U1 D1 L1 GND NOTE: Not to scale. Figure 18. PC Board Layout Component Side NOTE: Not to scale. GND C2 + VOUT Figure 19. PC Board Layout Copper Side TC2574-1 1/6/00 19 0.5A Step-Down Switching Regulator TC2574 The TC2574-ADJ Step-Down Voltage Regulator with 5.0V @ 0.5A Output Power Capability. Typical Application with Through-Hole PC Board Layout Feedback Unregulated DC Input +Vin = 7.0 to 40 V +VIN 5 4 C1 22F 1 TC2574-ADJ Output Pwr 2 GND Sig 3 GND 7 ON/OFF L1 330H L2 22H Regulated Output Filtered VOUT = 5.0 V @ 0.5 A R2 6.12 kW D1 1N5819 C2 220F C3 100F R1 2.0 kW GND GND C1 - 22F, 63V, Aluminum Electrolytic C2 - 220F, 16V, Aluminum Electrolytic C3 - 100F, 16V Aluminum Electrolytic D1 - 1.0A, 40V, Schotty Rectifier, 1N5829 L1 - 330H, RL-1284-330, Renco Electronics L2 - 25H, SFT52501, TDK R1 - 2.0k, 0.1%, 0.25W R2 - 6.12k, 0.1%, 0.25W Output Ripple Filter Figure 20. Schematic Diagram of the 5.0V @ 0.5A Step-Down Converter Using the TC2574-ADJ (An additional LC filter is included to achieve low output ripple voltage) TC2574 + +VIN C1 U1 D1 GND R1 R2 L2 L1 VOUT C2 + C3 + GND NOTE: Not to scale. NOTE: Not to scale. Figure 21. PC Board Layout Component Side Figure 22. PC Board Layout Copper Side TC2574-1 1/6/00 20 0.5A Step-Down Switching Regulator TC2574 TYPICAL CHARACTERISTICS (Circuit of Figure 2) Figure 23. Normalized Output Voltage VOUT,OUTPUT VOLTAGE CHANGE (%) 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -50 -25 0 25 60 75 100 125 VIN = 20V ILOAD = 100mA Normalized at TJ = 25C Figure 24. Line Regulation VOUT,OUTPUT VOLTAGE CHANGE (%) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 0 5.0 10 15 20 25 30 35 40 12V 3.3V , 5.0V and ADJ ILOAD = 100mA TJ = 25C 1.0 TJ JUNCTION TEMPERATURE (C) VIN, INPUT VOLTAGE (V) Figure 25. Dropout Voltage INPUT- OUTPUT DIFFERENTIAL (V) 2.0 1.4 Figure 26. Current Limit IO, OUTPUT CURRENT (A) 1.3 1.2 1.1 1.0 0.9 0.8 0.7 -50 -25 0 25 60 75 100 125 L = 300H 1.5 ILOAD = 500mA VIN = 25 V 1.0 ILoad = 100mA 0.5 0 -50 -5 0 25 60 75 100 125 TJ JUNCTION TEMPERATURE (C) TJ JUNCTION TEMPERATURE (C) Figure 27. Quiescent Current 18 16 14 12 10 8.0 6.0 4.0 0 5.0 10 15 20 25 VIN INPUT VOLTAGE (V) 30 35 40 ILOAD = 100mA ILOAD = 500mA VOUT = 5.0 V Measured at Ground Pin TJ = 25C Figure 28. Standby Quiescent Current ISTBY, STANDABY CURRENT (A) 200 180 160 140 120 100 80 60 40 20 0 -50 VIN = 12 V VIN = 40 V VON/OFF = 5.0 V 20 IQ, QUIESCENT CURRENT (mA) -25 0 25 60 75 100 125 TJ JUNCTION TEMPERATURE (C) TC2574-1 1/6/00 21 0.5A Step-Down Switching Regulator TC2574 TYPICAL CHARACTERISTICS (Circuit of Figure 2 Cont.) Figure 29. Oscillator Frequency 8.0 VSAT, SATURATION VOLTAGE (V) NORMALIZED FREQUENCY (%) Figure 30. Switch Saturation Voltage 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0 0.1 0.2 0.3 0.4 0.5 SWITCH CURRENT (A) 125C -40C 25C 6.0 4.0 2.0 0 -2.0 -4.0 -6.0 -8.0 10 -50 VIN = 12 V Normalized at 25C -25 0 25 50 75 100 125 TJ JUNCTION TEMPERATURE (C) Figure 31. Minimum Operating Voltage 5.0 4.5 VIN, INPUT VOLTAGE (V) IFB, FEEDBACK PIN CURRENT (nA) Figure 32. Feedback Pin Current 100 80 60 40 20 0 -20 -0 -60 -80 -25 0 25 50 75 100 125 Adjustable Version Only Adjustable Version Only 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 50 VIN = 1.23V ILOAD = 100mA 25 0 25 50 75 100 125 -100 -50 TJ JUNCTION TEMPERATURE (C) TJ, JUNCTION TEMPERATURE (5C) Figure 33. Continuous Mode Switching Waveforms VOUT = 5.0V, 500mA Load Current, L = 330H 20V A 10V 0 0.6A B 0.4A 0.2A 0 C 20mV AC 5 sec/DIV A: Output Pin Voltage 10V/DIV. B: Inductor Current, 0.2 A/DIV. . C: Output Ripple Voltage, 20mV/DIV, AC-Coupled TC2574-1 1/6/00 Figure 34. Discontinuous Mode Switching Waveforms VOUT = 5.0V, 100mA Load Current, L = 100H 20V 10V 0 0.6A B 0.4A 0.2A 0 C 20mV AC 5 sec/DIV A: Output Pin Voltage 10V/DIV. B: Inductor Current, 0.2 A/DIV. . C: Output Ripple Voltage, 20mV/DIV, AC-Coupled 22 A 0.5A Step-Down Switching Regulator TC2574 TYPICAL CHARACTERISTICS (Circuit of Figure 2 Cont.) Figure 35. 500mA Load Transient Response for Continuous Mode Operation, L = 330 H, COUT = 300F 50mV AC A 50 mV AC Figure 36. 250mA Load Transient Response for Disontinuous Mode Operation, L = 68H, COUT = 470F A 500mA B 0 B 200 mA 100 mA 0 200sec/DIV A: Output Pin Voltage 50V/DIV, AC Coupled B: 100mA to 500mA Load Pulse . 200sec/DIV A: Output Pin Voltage 50V/DIV, AC Coupled B: 50mA to 250mA Load Pulse TYPICAL CHARACTERISTICS (Circuit of Figure 16 Cont.) 60 20 15 12 10 9.0 8.0 7.0 6.0 Figure 37. TC2574 (VOUT = 3.3V) VIN, MAXIMUM INPUT VOLTAGE (V) 680 470 330 220 150 100 Figure 38. TC2574 (VOUT = 5.0V) 60 30 20 15 12 10 9.0 220 8.0 150 1000 680 470 330 VIN, MAXIMUM INPUT VOLTAGE (V) 5.0 0.1 0.15 0.2 0.3 0.4 0.5 7.0 0.1 0.15 0.2 0.3 0.4 0.5 IL, MAXIMUM LOAD CURRENT (A) IL, MAXIMUM LOAD CURRENT (A) 60 Figure 39. TC2574 (VOUT = 12.0V) 1500 1000 Figure 40. TC2574-ADJ ET, VOLTAGE TIME (sec) 250 200 150 100 80 60 50 40 30 20 15 10 0.1 23 VIN, MAXIMUM INPUT VOLTAGE (V) 40 30 25 20 18 17 16 15 2200 2200 1500 1000 680 470 330 220 150 100 68 680 470 330 220 14 0.1 0.15 0.2 0.3 0.4 0.5 0.15 0.2 0.3 0.4 0.5 IL, MAXIMUM LOAD CURRENT (A) TC2574-1 1/6/00 IL, MAXIMUM LOAD CURRENT (A) 0.5A Step-Down Switching Regulator TC2574 TAPE AND REEL DIMENSIONS Component Taping Orientation for 16-Pin SOIC User Direction of Feed PIN 1 User Direction of Feed W = Width of Carrier Tape PIN 1 Standard Reel Component Orientation for TR Suffix Device P = Pitch Reverse Reel Component Orientation for RT Suffix Device Carrier Tape, Reel Size, and Number of Components Per Reel Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size 16-Pin SOIC 16 mm 8 mm 2500 13 in TC2574-1 1/6/00 24 0.5A Step-Down Switching Regulator TC2574 PACKAGE DIMENSIONS 8-Pin PDIP (Narrow) PIN 1 .260 (6.60) .240 (6.10) .045 (1.14) .030 (0.76) .400 (10.16) .348 (8.84) .200 (5.08) .140 (3.56) .150 (3.81) .115 (2.92) .070 (1.78) .040 (1.02) .310 (7.87) .290 (7.37) .040 (1.02) .020 (0.51) .015 (0.38) .008 (0.20) .400 (10.16) .310 (7.87) 3MIN. .110 (2.79) .090 (2.29) .022 (0.56) .015 (0.38) 16-Pin SOIC (Wide) PIN 1 .299 (7.59) .419 (10.65) .290 (7.40) .398 (10.10) .413 (10.49) .398 (10.10) .104 (2.64) .097 (2.46) .050 (1.27) TYP. .019 (0.48) .014 (0.36) .012 (0.30) .004 (0.10) 8 MAX. .050 (1.27) .015 (0.40) .013 (0.33) .009 (0.23) Dimensions: inches (mm) Sales Offices TelCom Semiconductor, Inc. 1300 Terra Bella Avenue P.O. Box 7267 Mountain View, CA 94039-7267 TEL: 650-968-9241 FAX: 650-967-1590 E-Mail: liter@telcom-semi.com TC2574-1 1/6/00 TelCom Semiconductor, GmbH Lochhamer Strasse 13 D-82152 Martinsried Germany TEL: (011) 49 89 895 6500 FAX: (011) 49 89 895 6502 2 25 TelCom Semiconductor H.K. Ltd. 10 Sam Chuk Street, Ground Floor San Po Kong, Kowloon Hong Kong TEL: (011) 852-2350-7380 FAX: (011) 852-2354-9957 |
Price & Availability of TC2574-VPA
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