for technical support and more information, see inside back cover or visit www.ti.com pt series suffix (pt1234 x ) case/pin order package configuration suffix code vertical n (ene) horizontal a (enf) smd c (eng) (reference the applicable package code drawing for the dimensions and pc board layout) PT7681?5v 30-a programmable isr with margin up/down controls slts177a - december 2002 - revised march 2003 features ? 5v input voltage ? 30a output current ? 4-bit programmable output: 2v to 3.5v ? 95% efficiency ? margin up/down controls ? differential remote sense description the PT7681 excalibur? is a high performance integrated switching regu- lator (isr), which is housed in a 27-pin space-saving solderable copper pack- age. operating from a +5v input source, the PT7681 delivers up to 30a of out- put current over the adjustable output voltage range of 2v to 3.5v. the high output current and relatively small size makes the PT7681 suitable for power- ing high-end dsp, microprocessor, and asic circuits requiring core or i/o logic supply voltages as low as 2v. the output voltage is programmable via a 4-bit input code. ? over-current protection ? over-temperature protection ? 27-pin solderable copper case ? 1.57in2 pcb area (n suffix) ? ipc lead-free 2 standard application c in = required 1500f electrolytic c out = required 330f electrolytic l 1 = optional 1h input choke PT7681 4321 26 20-25 12 5 13-19 7-11 l o a d c out + c in + programming pins v in v out gnd sense(+) sense(?) stby vid0 vid1 vid2 vid3 l1 1h gnd 27 6 margup margdn ordering information PT7681 = 2 to 3.5 volts a special feature of the PT7681 is the margin up and margin down controls. these controls provide a convenient method for testing the load circuit over its supply voltage margins during production and quali- fication test programs. other features include output short- circuit and over-temperature protection, a standby on/off control, and a differ- ential remote sense to compensate for voltage drop between the regulator and load.
for technical support and more information, see inside back cover or visit www.ti.com * for stby pin: open =output enabled ground =output disabled. pin-out information pin function 1vid0 2vid1 3vid2 4vid3 5 stby * 6 margdn 7v in 8v in 9v in 10 v in 11 v in 12 sense(C) 13 gnd 14 gnd pin function 15 gnd 16 gnd 17 gnd 18 gnd 19 gnd 20 v out 21 v out 22 v out 23 v out 24 v out 25 v out 26 sense(+) 27 margup PT7681 ? 5v programming information vid3 vid2 vid1 vid0 vout 1111 2.00v 1110 2.10v 1101 2.20v 1100 2.30v 1011 2.40v 1010 2.50v 1001 2.60v 1000 2.70v 0111 2.80v 0110 2.90v 0101 3.00v 0100 3.10v 0011 3.20v 0010 3.30v 0001 3.40v 0000 3.50v logic 0 = pin 12 potential (rem sense gnd) logic 1 = open circuit (no pull-up resistors) vid 3 must not be changed while the unit is operating. pin descriptions vin: the positive input voltage power node to the mod- ule, which is referenced to common gnd. gnd: this is the common ground connection for the v in and v out power connections. it is also the 0vdc reference for the stby control input. stby: the stby pin is an open-collector/drain nega- tive logic input that is referenced to gnd. applying a ground signal to this input will disable the modules output and place the regulator in standby m ode. when in standby, the input current drawn by the regula- tor is significantly reduced. if the stby input is left open circuit, the module will produce an output when- ever a valid input source is applied. vid0?vid3: selects the set-point output voltage of the regulator according to the applicable program code (see programming information). each input, vid0 through vid3, must either be connected to sense(C) or left open circuit. vout: the regulated positive power output with respect to the gnd node. the set point voltage at this node is defined by the status of the pins vid0 through vid3. sense(+): provides the regulator with the capability to regulate the set-point voltage at the load. when used with sense(C), the regulation circuitry will compensate for voltage drop between the converter and the load. this pin may be left open circuit, but connecting it to vout will improve load regulation. sense(?): this is the logic 0 reference for the inputs vid0 through vid3. it also provides the regulator with a differential remote sense capability when used with the sense(+) input. for optimum output voltage accuracy this pin should always be connected to gnd. margdn: this is an open-collector/drain negative logic input. applying a ground signal to this input increases the output voltage of the module by up to 5%. the con- trol provides a convenient method for testing the operation of the load circuit over its supply voltage tolerance mar- gins. margup: an open-collector/drain negative logic input that operates similar to the margdn control. applying a ground signal to this input automatically decreases the output by up to 5%. 30-a programmable isr with margin up/down controls slts177a - december 2002 - revised march 2003
for technical support and more information, see inside back cover or visit www.ti.com PT7681 ? 5v typical characteristics specifications (unless otherwise stated, t a =25c, v in =5v, c in =1,500f, c out =330f, v o =3.3v, and i o =i o max) PT7681 characteristics symbols conditions min typ max units output current i o t a = 60c, 200lfm, pkg n 0 30 a t a = 25c, natural convection 0 29 input voltage range v in over i o range 4.5 5.5 v set-point voltage tolerance v o tol all output voltages 10 25 (1) mv temperature variation reg temp C40c t a +85c, i o =i o min 1 %v o line regulation reg line over v in range 5 mv load regulation reg load over i o range 5 mv total output voltage variation ? v o tol includes set-point, line, load, 1.5 3 %v o C40c t a +85c efficiency i o =15a v o =3.3v 93 v o =2.5v 92 % v o =1.8v 89 i o =30a v o =3.3v 90 v o =2.5v 87 % v o =1.8v 83 v o ripple (pk-pk) v r 20mhz bandwidth 40 mv pp transient response t tr 1a/s load step, 50% and 100% i o max 25 sec v os v o over/undershoot 200 (2) mv over-current threshold i trip reset followed by auto-recovery 38 a output margin adjust v o adj pin 6 or 26 connected to pin 12 5 % switching frequency ? s over v in range 250 300 350 khz stby* input requirements input high voltage v ih referenced to gnd 2.0 open (3) v input low voltage v il -0.2 0.8 input low current i il pin 5 to gnd 0.3 ma standby input current i in standby pin 5 to gnd 6 ma external capacitance c out 330 (4) 15,000 f operating temperature range t a over v in range C40 85 (5) c solder reflow temperature t reflow surface temperature of module pins or case 215 (6) c storage temperature t s C40 125 c mechanical shock per mil-std-883d, method 2002.3 500 gs 1 msec, half sine, mounted to a fixture mechanical vibration mil-std-883d, method 2007.2 suffix a 20 (7) gs 20-2000 hz suffixes n,c tbd (7) weight vertical/horizontal 36 grams flammability materials meet ul 94v-0 notes: (1) if the remote sense ground is not used, pin 12 must be connected to pin 13 for optimum output voltage accuracy. (2) the transient response may be improved by placing additional capacitors with low equivalent series resistance (esr) on the o utput. (3) the stby* control (pin 5) has an internal pull-up. if it is left open-circuit, the module will operate when input power is a pplied. a low-leakage (<1a) mosfet must be used to control this pin. the open-circuit voltage may be as high as vin. (4) for operation below 0c, cin and cout must have stable characteristics. use either low esr tantalum or oscon? capacitors. (5) see safe operating area curves or consult factory for the appropriate derating. (6) during reflow of smd package version do not elevate the module case, pins, or internal component temperatures above a peak o f 215c. for further guidance refer to the application note, reflow soldering requirements for plug-in power surface products, (slta051). (7) the case pins on the through-hole package types (suffixes n & a) must be soldered. for more information see the applicable p ackage outline drawing. external capacitors: the regulator require a minimum output capacitance of 330f for proper operation. an input capacitance of 1500f is also requ ired. this must be rated for a m inimum of 1.1arms of ripple current. for transient or dynamic load applications, additional capacitance may be required. for f urther informa- tion refer to the application note regarding capacitor selection for this product. input filter: an input filter inductor is optional for most applications. the inductor must be sized to handle 30adc with a typical value of 1h. 30-a programmable isr with margin up/down controls slts177a - december 2002 - revised march 2003
for technical support and more information, see inside back cover or visit www.ti.com performance characteristics; v out =3.3v (see note a) safe operating area curves (see note b) efficiency vs output current; v in =5v ripple vs output current power dissipation vs output current; v in =5v PT7681, v in =5vdc, v out =3.3v PT7681 ? 5v typical characteristics 20 30 40 50 60 70 80 90 0 5 10 15 20 25 30 iout ( a ) ambient temperature (c) 400lfm 200lfm 60lfm nat conv airflow 20 30 40 50 60 70 80 90 0 5 10 15 20 25 30 iout ( a ) ambient temperature ( c) 400lfm 200lfm 60lfm nat conv airflow PT7681, v in =5vdc, v out =2.5v note a: all characteristic data in the above graphs has been developed from actual products tested at 25c. this data is considered ty pical for the isr. note b: soa curves represent operating conditions at which internal components are at or below manufacturers maximum rated operating temperatures. 50 60 70 80 90 100 0 5 10 15 20 25 30 iout ( a ) efficiency - % 0.00 2.00 4.00 6.00 8.00 10.00 12.00 0 5 10 15 20 25 30 iout ( a ) pd - watts 0 10 20 30 40 50 60 0 5 10 15 20 25 30 iout ( a ) ripple - mv 5.5v 5.0v 4.5v v in 30-a programmable isr with margin up/down controls slts177a - december 2002 - revised march 2003
application notes for technical support and more information, see inside back cover or visit www.ti.com pt7680 series used it is important to at least connect the sense(C) pin to gnd locally, as this provides a return path for the regulators internal bias currents. with the sense leads connected, the difference between the voltage measured between the v out and gnd pins, and that measured between the sense(+) and sense(C) pins, is the amount of ir drop being compensated by the regulator. this should be limited to 0.6v. (0.3v maximum between pins 25 & 26, and also between pins 12 & 13). note: the remote sense feature is not designed to compensate for the forward drop of non-linear or frequency dependent components that may be placed in series with the converter output. examples include or-ing diodes, filter inductors, ferrite beads, and fuses. when these components are enclosed by the remote sense connections they are effectively placed inside the regulation control loop, which can adversely affect the stability of the regulator. margin up/margin down the margup / margdn controls allow up to a 5% momentary adjustment of the regulators output voltage set point. this adjustment is independent of the vid control inputs and provides a convenient method for testing the load circuits supply voltage margins. a 5% adjustment is made by simply connecting either control input directly to the remote sense ground. adjustments of less than 5% can be accommodated by grounding the input through a suitably sized padding resistor. note: these inputs must be controlled with a low-leakage (<1a) open-collector/open-drain transistor. do not add pull- up resistors or use a push-pull logic gate to drive these pins. over-temperature protection the pt7680 series of isrs incorporates an on-board temperature sensor, which protects the modules internal circuitry against excessively high temperatures. a rise in the temperature of the internal components may be the result of a drop in air flow, or a high ambient temperature. if the modules internal temperature exceeds its otp threshold (see data sheet specifications), the regulator output is disabled and the output voltage is reduced to zero. the re covery is automatic, and begins with a soft- start power up. it occurs when the the sensed temperature decreases by about 10c below the trip point. note: the over-temperature protection is a last resort mecha- nism to prevent thermal stress to the regulator. operation at or close to the thermal shutdown temperature is not r ecom- mended and will reduce the long-term reliability of the module. always operate the regulator within the specified safe operating area (soa) limits for the worst-case conditions of ambient temperature and airflow. over-current protection to protect against load faults, the pt7680 series of regula- tors incorporates output over-current protection. applying a load that exceeds the r egulators over-current threshold (see data sheet specifications) will cause the regulated output to shut down. following shutdown the isr will periodically attempt to recover by initiating a soft-start power-up. this is often described as a hiccup mode of operation, whereby the module continues in a cycle of shutdown and power up until the load fault is removed. during this period, the average current flowing into the fault is significantly reduced. once the fault is rem oved, the converter automatically recovers to normal operation. differential remote sense connecting the sense(+) and sense(-) pins to the load circuit allows the regulator to compensate for limited amounts of ir voltage drop. this voltage drop is caused by current flowing through the trace resistance between the power converter and the point of regulation some distance away. although not recommended, leaving the sense pins disconnected will not damage the regulator. an internal 15 ? resistor, connected between each sense pin and its corresponding output node, keeps the output voltage in regulation. if the remote sense feature is not operating features and system considerations for the pt7680 series of isrs power up & soft-start timing following either the application of a valid input source voltage, or the removal of a ground signal to the stby control pin (with input power applied), the regulator will initiate a soft-start power up. the soft start slows the rate at which the output voltage rises, and also introduces a short time delay of approx. 10ms. figure 1-1 shows the power-up characteristic of a PT7681 with a 15-a load, and with the output voltage programmed to 3.3v. vo (2v/div) iin (10a/div) vin (2v/div) horiz scale: 10ms/div figure 1-1
for technical support and more information, see inside back cover or visit www.ti.com application notes application notes table 2-1: input/output capacitors capacitor recommendations for the pt7680 series of 30-a switching regulators input capacitor: the recommended input capacitance is determined by 1.1a minimum ripple current rating and 1500f mini- mum capacitance. ripple current and <100m ? equivalent series resistance (esr) values are the major considerations, along with temperature, when designing with different types of capacitors. tantalum capacitors have a recommended minimum voltage rating of twice the maximum dc voltage + ac ripple. this is necessary to insure reliabil- ity for input voltage bus applications. output capacitors: the esr of the required capacitors is less than 100m ? . electrolytic capacitors have marginal ripple performance at frequencies greater than 400khz but excellent low frequency transient response. above the ripple frequency, ceramic capacitors are necessary to im prove the transient response and reduce any high frequency noise components apparent during higher current excursions. preferred low esr type capacitor part numbers are identified in table 2-1. pt7680 series tantalum capacitors( optional output capacitors) tantalum type capacitors can be used for the output but only the avx tps series, sprague 593d/594/595 series or kemet t495/t510 series. these capacitors are rec- ommended over many other tantalum types due to their higher rated surge, power dissipation, and ripple current capability. as a caution the taj series by avx is not recommended. this series has considerably higher esr, reduced power dissipation, and lower ripple current ca- pability. the taj series is also less reliable than the avx tps series when determining power dissipation capa- bility. tantalum or oscon? types are recommended for applications where ambient temperatures fall below 0c. capacitor table table 2-1 identifies the characteristics of capacitors from a number of vendors with acceptable esr and ripple cur- rent (rms) ratings. the number of capacitors required at both the input and output buses is identified for each capacitor type. this is not an extensive capacitor list. capacitors from other vendors are available with comparable specifications. those listed are for guidance. the rms ripple current rating and esr (equivalent series resistance at 100khz) are critical parameters necessary to insure both optimum regulator performance and long capacitor life. r o t i c a p a c / r o d n e v s e i r e s s c i t s i r e t c a r a h c r o t i c a p a cy t i t n a u q g n i k r o w e g a t l o v ) f ( e u l a vt n e l a v i u q e ) r s e ( e c n a t s i s e r s e i r e s m u m i x a m c 5 0 1 e l p p i r ) s m r i ( t n e r r u c l a c i s y h p ) m m ( e z i s t u p n i s u b t u p t u o s u b r e b m u n r o d n e v c i n o s a n a p ) t m s ( k f ) l a i d a r ( c f v 5 2 v 5 3 v 6 1 v 6 1 0 0 2 2 0 3 3 0 7 4 0 0 5 1 8 3 0 . 0 ? 0 8 0 . 0 ? 0 9 0 . 0 ? 3 4 0 . 0 ? a m 0 0 8 1 a m 0 5 8 a m 5 5 7 a m 0 9 6 1 5 . 6 1 x 6 1 2 . 0 1 x 0 1 5 . 2 1 x 0 1 5 1 x 6 1 1 1 1 1 1 1 m 2 2 2 e 1 k f v e e p 1 3 3 v 1 k f v e e 1 7 4 c 1 c f u e e s 2 5 1 c 1 c f u e e z x l d e t i n u n o c - i m e h c x f v 5 2 v 6 1 v 0 1 0 3 3 0 0 5 1 0 8 6 0 9 0 . 0 ? 8 3 0 . 0 ? 5 1 0 . 0 ? a m 0 6 7 a m 0 6 6 1 a m 5 3 7 4 5 . 2 1 x 0 1 0 2 x 5 . 2 1 5 . 0 1 x 0 1 1 2 1 1 1 l l 2 1 x 0 1 m 1 3 3 b v 5 2 z x l l l 0 2 x 2 1 m 2 5 1 b v 6 1 z x l m 0 8 6 x f 0 1 n o c i h c i n s e i r e s l p ) m s ( x n v 5 2 v 0 1 v 0 1 0 9 3 0 0 5 1 0 3 3 0 8 0 . 0 ? 0 5 0 . 0 ? 4 2 0 . 0 ? a m 0 2 7 a m 0 3 3 1 a m 0 7 7 3 5 1 x 5 . 2 1 5 1 x 6 1 8 x 0 1 1 5 1 1 1 6 h h m 1 9 3 e 1 l p u 6 h h m 2 5 1 a 1 l p u s g 1 r c m 1 3 3 a 1 x n p n o c s o ) l a i d a r ( p s ) t m s ( p v s v 0 1 v 0 1 0 7 4 0 3 3 5 1 0 . 0 ? 7 1 0 . 0 ? a m 0 1 5 4 > a m 0 5 9 3 > 5 . 0 1 x 0 1 3 . 8 x 2 1 x 9 3 4 1 1 m 0 7 4 p s 0 1 m 0 3 3 p v s 0 1 x v a m u l a t a n a t s e i r e s - s p t v 0 1 v 0 1 0 3 3 0 3 3 0 1 . 0 ? 0 6 0 . 0 ? a m 4 1 4 1 a m 6 2 8 1 x l 3 . 7 x w 3 . 4 h 1 . 4 5 5 1 1 0 0 1 0 r 0 1 0 m 7 3 3 v s p t 0 6 0 0 r 0 1 0 m 7 3 3 v s p t e u g a r p s m u l a t n a t d 4 9 5 / d 5 9 5 v 0 1 v 0 1 0 3 3 0 8 6 5 4 0 . 0 ? 1 1 0 . 0 = 4 ? 9 0 . 0 ? a m 0 0 5 4 > a m 0 1 5 1 > x l 3 . 7 x w 7 . 5 h 0 . 4 5 2 1 1 t 2 r 0 1 0 0 x 7 3 3 d 4 9 5 t 2 r 0 1 0 0 x 7 8 6 d 5 9 5 ) t n u o m e c a f r u s ( t e m e k m u l a t n a t 5 9 4 t / 0 1 5 t s e i r e s v 0 1 v 0 1 0 3 3 0 2 2 5 3 0 . 0 ? 7 0 . 0 ? 5 3 0 . 0 = 2 ? a m 0 0 0 2 a m 0 0 0 2 > l 3 . 7 x w 3 . 4 h 0 . 4 x 5 6 1 2 s a 0 1 0 m 7 3 3 x 0 1 5 s a 0 1 0 m 7 2 2 x 5 9 4 t ) t n u o m e c a f r u s ( p a c s o p o y n a s b p t v 0 10 2 24 0 . 0 ? a m 0 0 0 3x l 2 . 7 x w 3 . 4 h 1 . 3 62 m 0 2 2 b p t 0 1 ) t n u o m e c a f r u s (
application notes for technical support and more information, see inside back cover or visit www.ti.com pt7680 series using the standby function on the pt7680 series of 30-a switching regulators for applications requiring on/off control of the output voltage, the 30-a rated pt7680 series of excalibur isrs incorporate an on/off standby function. this feature may be used for power-up/shutdown sequencing, or to change the output voltage while input power is applied. see r elated notes: pin-coded output voltage adjustment of the pt7680 series of 30-a isrs. the standby function is provided by the stby* control, pin 5. if pin 5 is left open-circuit the regulator operates normally, providing a regulated output whenever a valid supply voltage is applied to v in (pins 7-11) with respect to gnd (pins 13-19). connecting pin 5 to ground 1 will disable the regulator output 2 . this places the regulator in standby mode, and reduces the input current to typically 6ma. if a ground signal is applied to pin 5 prior to power- up, the regulator output will remain inactive during the period that input power is applied. the standby input must be controlled with an open- collector (or open-drain) discrete transistor (see figure 3-1). t able 3-1 gives the input requirements. table 3-1 standby control input requirements parameter min typ max enable 2v open cct. 1 disable C0.2v 0.8v i stby (low) 0.5ma vstby (o/c) v in turn-on time: turning q 1 in fig. 3-1 off, removes the low-voltage signal at pin 5 and enables the output 3 . af- ter a delay of less than 5ms, the output voltage rises to full regulation within 30ms 4 . fig. 3-2 shows the typical output voltage waveform of a PT7681 following the turn-off of q 1 at time t =0 secs. in the circuit of fig. 3-1, the output voltage is set to 3.3v. the waveform was measured with a +5v input source voltage, and 15-a output load. figure 3-1 figure 3-2 c out + c in + 5v com inhibit l o a d PT7681 43 1 26 20 ? 25 12 513 ? 19 7 ? 11 vo vin gnd senes(+) stby vid3 - vid0 senes( ? ) v o =3.3v com q 1 bss138 2 iin (5a/div) vo (2v/div) vstby (5v/div) horiz scale: 5ms/div notes: 1. the standby input of the pt7 680 series of regulators must be controlled using an open-collector (or open-drain) discrete transistor. do not use a pull-up resistor. the control input has an open-circuit voltage equal to v in . to set the regulator output to zero, the control pin must be pulled to less than 0.8vdc with a 0.5ma sink to ground. 2. in the standby mode the output of the regulator is tri- state, and the output voltage falls at the rate that the load circuit discharges the output filter capacitors. 3. when the ground signal to the standby pin is removed, the regulator output initiates a soft-start cycle by first asserting a low impedance to ground. if an external voltage is applied to the output bus, it will sink current and possibly over-stress the part. 4. the turn-off time of q 1 , or rise time of the standby input is not critical. turning q 1 off slowly will not affect regulator operation. however, a slow turn-off time will increase both the initial delay and rise-time of the output voltage.
for technical support and more information, see inside back cover or visit www.ti.com application notes pt7680 series pin-coded output v oltage adjustment of the pt7680 series of 30-a switching regulators the pt7680 excalibur? family of converters use a pin code to adjust the output voltage. this feature uses the control inputs, vid0Cvid3 (pins 1C4). when these pins are left open-circuit, the isr regulates at its default output voltage. each of the programming pins are internally connected to a precision resistor, and when pulled low 1 applies a weighted change to the output voltage. by selectively connecting vid0Cvid3 to sense(C) 2 , the output voltage of these isrs can be programmed in incremental steps over their specified output voltage range. the program codes and output voltages offered by these isrs are compatible with the voltage id specifications used by popular microprocessors. see figure 4-1 for the connection schematic, and the respective device data sheet for the programming code information. notes: 1. the programming convention is as follows:- logic 0: connect to pin 12; sense(C). logic 1: open circuit/open drain (see note 2) 2. for optimal output voltage accuracy sense(C) (pin 12) should always be used as the logic 0 reference. the input/output ground (pins 13-19) can also be used if pin 12 is connected to pin 13 external to the module. 3. do not connect pull-up resistors to the voltage programming pins. figure 4-1 4. if active devices are used to ground the voltage control pins, low-level open drain mosfet devices should be used over bipolar transistors. the inherent v ce (sat) in bipolar devices introduces errors in the devices internal divider network. discrete transistors such as the bss138, 2n7002, or irlml2402 are examples of appropriate devices. active voltage programming: special precautions should be taken when making changes to the output voltage progam code while the unit is powered. this activity can induce current transients through the device as a result of the electrolytic output capacitors being either charged or discharged to the new output voltage set-point. the transient current can be minimized by making only incremental changes to the binary code, i.e. one lsb at a time. a m inimum of 100s settling time between each program state is also recom- mended. making non-incremental changes to vid3 is discouraged. when active devices are used to program the output voltage, their state should be asserted prior to the input power being applied. one approach is to pull stby (pin 5) control to gnd prior to power up. after the host board has then asserted the program code, the ground signal to pin 5 can be removed. this will allow the regulator to intiate a clean soft-start power-up to the desired pr ogram voltage. for more information on the use of the standby function, consult the related application note, using the standby function on the pt7680 series of 30-a switching regulators. c out + c in + 1h (optional) +5v com stby l o a d q 1 l 1 sense( ? ) v out power gnd PT7681 43 1 26 20 ? 25 12 513 ? 19 7 ? 11 v out v in gnd sns(+) sns( ? ) stby vid3 - vid0 2
application notes for technical support and more information, see inside back cover or visit www.ti.com using the up/down margin adjust controls on the pt7680 series of 30-a regulators the pt7680 series of integrated switching regulator modules incorporate margup (pin 27) and margdn (pin 6) control inputs. these controls allow the output voltage set point to be momentarily adjusted 1 , either up or down, by a nominal 5%. the adjustment is in- dependent of the vid control inputs and provides a convenient method for dynamically testing the load circuits power supply voltage over its operating margin or range. the 5% adjustment is made by driving the appropriate margin control input to the ground reference at sense(-) (pin 12) 2 . an open drain, low-leakage (<1a), logic-level mosfet or p-channel jfet is recommended for this purpose. adjustments of less than 5% are also possible using a series resistor (see figure 5.1). the value of the resistor can be selected from table 5.1, or calcu- lated using the following formu las. resistor value calculation to reduce the margin adjustment to a value less than 5%, series padding resistors are required (see r d and r u in figure 5.1). for the same amount of adjustment, the resistor value calculated for r u and r d will be different. r u = 100 ( 6 C 1.2 ? %) k ? ? % r d = 4.99 (100 C ? %) C94.81 k ? ? % where: ? % = the required margin adjust in percent notes: 1. the margup and margdn controls were not intended to be activated simultaneously. if they are their affects on the output voltage may not completely cancel, resulting in a slight shift in the output voltage set point. 2. when possible use the sense(-) (pin 12) as the ground reference. this will produce a more accurate adjustment of the output voltage at the load circuit terminals. gnd (pins 13-19) can be used if the sense(-) pin is connected to gnd near the regulator. c out + c in +5v pwr gnd margin dn l o a d q 2 sense( ? ) +v out power gnd PT7681 43 1 26 20 ? 25 12 513 ? 19 7 ? 11 v out v in gnd sns(+) sns( ? ) stby vid3 - vid0 2 q 1 6 27 marg dn marg up + margin up 0v +v o r d r u 0v figure 5.1; margin up/down application schematic table 5.1; margin up/down adjust resistor values padding resistor values % adjust r u (margin up) r d (margin dn) 5 0.0k ? 0.0k ? (no resistor) 4 30.0k ? 24.9k ? 3 80.0k ? 66.5k ? 2 180.0k ? 150.0k ? 1 480.0k ? 399.0k ? pt7680 series
important notice texas instruments incorporated and its subsidiaries (ti) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. all products are sold subject to ti?s terms and conditions of sale supplied at the time of order acknowledgment. ti warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with ti?s standard warranty. testing and other quality control techniques are used to the extent ti deems necessary to support this warranty. except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. ti assumes no liability for applications assistance or customer product design. customers are responsible for their products and applications using ti components. to minimize the risks associated with customer products and applications, customers should provide adequate design and operating safeguards. ti does not warrant or represent that any license, either express or implied, is granted under any ti patent right, copyright, mask work right, or other ti intellectual property right relating to any combination, machine, or process in which ti products or services are used. information published by ti regarding third?party products or services does not constitute a license from ti to use such products or services or a warranty or endorsement thereof. use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from ti under the patents or other intellectual property of ti. reproduction of information in ti data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. reproduction of this information with alteration is an unfair and deceptive business practice. ti is not responsible or liable for such altered documentation. resale of ti products or services with statements different from or beyond the parameters stated by ti for that product or service voids all express and any implied warranties for the associated ti product or service and is an unfair and deceptive business practice. ti is not responsible or liable for any such statements. mailing address: texas instruments post office box 655303 dallas, texas 75265 copyright ? 2003, texas instruments incorporated
|
