LT1431 Programmable Reference U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ Guaranteed 0.4% Initial Voltage Tolerance 0.1Ω Typical Dynamic Output Impedance Fast Turn-On Sink Current Capability, 1mA to 100mA Low Reference Pin Current UO APPLICATI ■ ■ Linear Regulators Adjustable Power Supplies Switching Power Supplies A simplified three pin version, the LT1431Z/IZ, is available for applications as an adjustable reference and is pin compatible with the TL431. UO ■ S The LT1431 is an adjustable shunt voltage regulator with 100mA sink capability, 0.4% initial reference voltage tolerance, and 0.3% typical temperature stability. On-chip divider resistors allow the LT1431 to be configured as a 5V shunt regulator, with 1% initial voltage tolerance and requiring no additional external components. By adding two external resistors, the output voltage may be set to any value between 2.5V and 36V. The nominal internal current limit of 100mA may be decreased by including one external resistor. TYPICAL APPLICATI Isolated 5V Regulator + 5V + COLL VIN COMP V + RTOP SWITCHING REGULATOR REF + gm = 4mA/V – – RMID 2.5V LT1431 GND-F GND-S LT1431 • TA01 1 LT1431 W W W AXI U U ABSOLUTE RATI GS V+, VCOLLECTOR ....................................................... 36V VCOMP, RTOP,RMID,VREF ............................................ 6V GND-F to GND-S .................................................... 0.7V Ambient Temperature Range LT1431M ........................................ – 55°C to 125°C LT1431I ............................................ – 40°C to 85°C LT1431C .............................................. 0°C TO 70°C JunctionTemperature Range LT1431M ........................................ – 55°C to 150°C LT1431I .......................................... – 40°C to 100°C LT1431C ............................................. 0°C to 100°C Storage Temperature Range ................ –65°C to 150°C Lead Temperature (Soldering, 10 sec)................ 300°C W U U PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW COLLECTOR 1 8 REF COMP 2 7 RMID V+ 3 6 GND-F RTOP 4 5 GND-S J8 PACKAGE 8-LEAD CERAMIC DIP COLLECTOR 1 LT1431MJ8 LT1431CN8 LT1431IN8 N8 PACKAGE 8-LEAD PLASTIC DIP TJ MAX = 150°C, θJA = 100°C/W (J) TJ MAX = 100°C, θJA = 130°C/W (N) ORDER PART NUMBER TOP VIEW 8 7 RMID V+ 3 6 GND-F RTOP 4 5 GND-S S8 PACKAGE 8-LEAD PLASTIC SOIC TJ MAX = 100°C, θJA = 170°C/W LT1431CS8 LT1431IS8 PART MARKING 2 3 REF COMP 2 ORDER PART NUMBER BOTTOM VIEW 1 LT1431CZ LT1431IZ REF ANODE CATHODE Z PACKAGE 3-LEAD TO-92 PLASTIC TJ MAX = 100°C, θJA = 160°C/W LT1431 LT1431I ELECTRICAL CHARACTERISTICS TA = 25°C, IK = 10mA, unless otherwise specified (Note 1). LT1431M/I MIN TYP MAX SYMBOL PARAMETER CONDITIONS VREF Reference Voltage VKA = 5V, IK = 2mA, (Note 2) ● ∆VREF/∆T Reference Drift LT1431C MIN TYP MAX UNITS 2.490 2.500 2.510 2.490 2.500 2.510 2.465 2.535 2.480 2.520 VKA = 5V, IK = 2mA ● 50 ∆VREF/∆VKA Voltage Ratio, Reference to Cathode (Open-Loop Gain) IK = 2mA, VKA = 3V to 36V ● 0.2 0.5 0.2 0.5 mV/V |IREF| VKA = 5V, TA = 25°C 0.2 1.0 1.5 0.2 1.0 1.2 µA µA 0.6 1.0 0.6 1.0 mA Reference Input Current ● IMIN Minimum Operating Current VKA = VREF to 36V |IOFF| Off-State Cathode Current VKA = 36V, VREF = 0V |ILEAK| Off-State Collector Leakage Current Dynamic Impedance VKA = VREF, IK = 1mA to 100mA, f ≤ 1kHz ILIM Collector Current Limit VKA = VREF + 50mV 5V Reference Output Internal Divider Used, IK = 2mA The ● denotes specifications which apply over the operating temperature range. Note 1: VKA is the cathode voltage of the LT1431CZ/IZ and corresponds to V + of the LT1431CN8/MJ8. IK is the cathode current of the LT1431CZ/IZ and corresponds to I(V +) + ICOLLECTOR of the LT1431CN8/MJ8/IN8. 2 ppm/°C ● 1 15 1 2 µA µA ● 1 5 1 2 µA µA 0.2 0.2 Ω 260 mA VCOLL = 36V, V + = 5V, VREF = 2.4V |ZKA| 30 V V ● 80 360 100 4.950 5.000 5.050 4.950 5.000 5.050 Note 2: The LT1431 has bias current cancellation which is effective only for VKA ≥ 3V. A slight (≈2mV) shift in reference voltage occurs when VKA drops below 3V. For this reason, these tests are not performed at VKA = VREF. V LT1431 U W TYPICAL PERFOR A CE CHARACTERISTICS VREF and IREF vs V + 2.5V Reference IK vs VKA 2.505 3.5 900 2.504 3.0 800 2.503 2.5 700 2.502 2.0 IMIN VREF (V) 600 500 400 2.501 1.5 VREF 2.500 2.499 1.0 0.5 IREF 300 2.498 200 2.497 –0.5 100 2.496 –1.0 0 0 0 –1.5 2.495 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 + V (V) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 VKA (V) LT1431 • TPC01 LT1431 • TPC02 VREF and IREF vs Temperature 3.0 2.503 2.5 2.502 2.0 2.501 1.5 1.0 VREF 0.5 2.499 2.498 0 IREF 2.497 –0.5 2.496 2.495 2.5025 1.00 VREF 2.5000 0.33 IREF 2.4950 0 2.4925 –0.33 2.4900 –0.66 –1.0 0 4 8 12 16 20 24 28 32 36 40 V + (V) –1.5 2.4875 –50 –25 50 25 75 0 TEMPERATURE (°C) LT1431 • TPC03 ILIMIT vs Temperature with External Resistor Propagation Delay vs Overdrive PROPAGATION DELAY (µs) 1.00 ICOLL = 100mA 1.000 0.80 0.875 0.750 0.60 ICOLL = 50mA 0.40 0.625 0.500 –50 –25 0.20 50 25 75 0 TEMPERATURE (°C) 100 5V 1k 3 135 VSAT (V) ILIMIT (NORMALIZED) 0.7 AT 25°C RLIM + 3.6 –1.00 125 150 1.20 ILIMIT = 100 LT1027 • TPC04 COLLECTOR VSAT vs Temperature vs Current 1.250 1.125 0.66 2.4975 VREF (V) 3.5 2.504 IREF (µA) 2.505 IREF (µA) VREF (V) VREF and IREF vs V + 2.500 IREF (µA) IK (µA) 1000 125 LT1431 • TPC05 0 –50 –25 ICOLL = 20mA VREF ± OVERDRIVE 105 100 125 LT1431 • TPC06 1 OUTPUT LT1431 5 6 90 75 60 45 OUTPUT HIGH-TO-LOW 30 OUTPUT LOW-TO-HIGH 15 ICOLL = 10mA 50 25 75 0 TEMPERATURE (°C) 120 0 0 50 150 100 OVERDRIVE (mV) 200 250 LT1431 • TPC07 3 LT1431 U W TYPICAL PERFOR A CE CHARACTERISTICS Voltage Gain and Phase vs Frequency Transconductance and Phase vs Frequency (REF to COLL) PHASE AV 135 9 10 90 108 Ω 100 1010 45 60 0 40 –45 1M 107 45 gm 105 –45 104 –90 –135 103 –135 –180 10M 102 0 10k 100k FREQUENCY (Hz) 90 0 –90 1k 135 PHASE 106 20 –20 100 180 100 1k 10k 100k FREQUENCY (Hz) 1M Transconductance and Phase vs Frequency (Ref to Comp) 20 1.4 0 1.2 3.0 IK ≤ 100mA PHASE –20 –60 –80 3 × 102 2.0 1M 0.6 –140 10M 1.5 ICOLL = 10mA 0.5 0 100 1k 10k FREQUENCY (Hz) LT1431 • TPC10 0 –50 –25 100k 50 25 75 0 TEMPERATURE (˚C) LT1431 • TPC11 ICOMP vs VCOMP vs VREF 100 125 LT1431 • TPC12 Noise vs Frequency 0.1Hz to 10Hz Noise 1000 600 NOISE VOLTAGE (50µV/DIV) 500 NOISE (nV/√Hz) VREF = 5V 400 ICOMP (µA) ICOLL = 100mA 1.0 0.2 –120 10k 100k FREQUENCY (Hz) 0.8 0.4 –100 1k VCOMP (V) 103 2.5 1.0 ZKA (Ω) –40 PHASE (DEG) REF-TO-COLL gm (µ ) Ω 3 × 103 0.1 100 VCOMP vs Temperature vs ICOLL Dynamic Impedance vs Frequency gm –180 10M LT1431 • TPC09 LT1431 • TPC08 104 PHASE (DEG) 80 PHASE (DEG) REF-TO-COLL 1k LOAD AV (dB) 120 180 REF-TO-COLL gm (m ) 140 VREF = 4V 300 VREF = 3V 200 500 VREF = 2.53V 100 0 0 0 0.5 1.0 1.5 2.0 VCOMP (V) 2.5 3.0 3.5 LT1431 • TPC13 4 1 10 100 1k FREQUENCY (Hz) 10k 100k LT1431 • G14 0 1 4 3 2 TIME (MINUTES) 5 6 LT1431 • TPC15 LT1431 U U U PI FU CTIO S COLL (Pin 1): Open collector of the output transistor. The maximum pin voltage is 26V. The saturation voltage at 100mA is approximately 1V. RMID (Pin 7): Middle of the on-chip resistive divider string between RTOP and GND-S. The pin is tied to REF for selfcontained 5V operation. It may be left open if unused. COMP (Pin 2): Base of the driver for the output transistor. This pin allows additional compensation for complex feedback systems and shutdown of the regulator. It must be left open if unused. REF (Pin 8): Control pin of the shunt regulator with a 2.5V threshold. If V + > 3V, input bias current cancellation reduces IB to 0.2µA typical. V + (Pin 3): Bias voltage for the entire shunt regulator. The maximum input voltage is 36V and the minimum to operate is equal to VREF (2.5V). The quiescent current is typically 0.6mA. COMP, RTOP, RMID, and REF have static discharge protection circuits that must not be activated on a continuous basis. Therefore, the absolute maximum DC voltage on these pins is 6V, well beyond the normal operating conditions. RTOP (Pin 4): Top of the on-chip 5k-5k resistive divider that guarantees 1% accuracy of operation as a 5V shunt regulator with no external trim. The pin is tied to COLL for self-contained 5V operation. It may be left open if unused. See note on parasitic diodes below. As with all bipolar ICs, the LT1431 contains parasitic diodes which must not be forward biased or else anomalous behavior will result. Pin conditions to be avoided are RTOP below RMID in voltage and any pin below GND-F in voltage (except for GND-S). GND-S (Pin 5): Ground reference for the on-chip resistive divider and shunt regulator circuitry except for the output transistor. This pin allows external current limit of the output transistor with one resistor between GND-F (force) and GND-S (sense). The following pin definitions apply to the Z package. CATHODE (Pin 1): Corresponds to COLL and V + tied together. GND-F (Pin 6): Emitter of the output transistor and substrate connection for the die. REF (Pin 3): Corresponds to REF. ANODE (Pin 2): Corresponds to GND-S and GND-F tied together. W BLOCK DIAGRA RTOP V 4 + 3 COMP 2 COLLECTOR 1 5k REF RMID 8 + gm = 4mA/V 7 – 5k 2.5V 5 GND-SENSE 6 GND-FORCE LT1431 • BD01 5 LT1431 U U W U APPLICATIO S I FOR ATIO Frequency Compensation pole-zero compensation. This can be accomplished with a capacitor or series resistor and capacitor between COLL and COMP. As a shunt regulator, the LT1431 is stable for all capacitive loads on the COLL pin. Capacitive loading between 0.01µF and 18µF causes reduced phase margin with some ringing under transient conditions. Output capacitors should not be used arbitrarily because output noise is not necessarily reduced. The compensation schemes mentioned above use voltage feedback to stabilize the circuits. There must be voltage gain at the COLL pin for them to be effective, so the COLL pin must see a reasonable AC impedance. Capacitive loading of the COLL pin reduces the AC impedance, voltage gain, and frequency response, thereby decreasing the effectiveness of the compensation schemes, but also decreasing their necessity. Excess capacitance on the REF pin can introduce enough phase shift to induce oscillation when configured as a reference >2.5V. This can be compensated with capacitance between COLL and REF (phase lead). More complicated feedback loops may require shaping of the frequency response of the LT1431 with dominant pole or U TYPICAL APPLICATIO S 2.5V Reference 8-Pin Package 2.5V Reference 3-Pin Package RL 5V Reference RL VIN RL VIN 2.5V 2.5V V+ CATHODE VIN REF REF LT1431Z 5V V+ COLL RTOP LT1431 COLL REF LT1431 RMID ANODE GND-S GND-F LT1431 • TA04 LT1431 • TA03 LT1431 • TA02 Programmable Reference with Adjustable Current Limit Increasing 5V Reference RL RL VIN R 5V + ∆ V+ RTOP COLL VIN V+ REF COLL R1 REF LT1431 LT1431 GND-F ∆ = R × (0.5mA) ±25% PROCESS TOLERANCE ∆ ≤ 500mV R2 GND-F GND-S LT1431 • TA05 6 ( ) VOUT = 1 + R1 VREF R2 RMID GND-S GND-F GND-S RLIM ILIMIT = 0.7 AT 25°C RLIM + 3.6 LT1431 • TA06 LT1431 U TYPICAL APPLICATIO S PNP Low Dropout 5V Regulator* VIN 0.1µF 20Ω** 2W 47Ω MJE2955 1k 2N2219 0.015µF 150Ω 3 4 2 COMP 1 COLL V+ REF LT1431 RTOP RMID GND-S 5 8 7 GND-F 6 5V + MEASURED DROPOUT VOLTAGE 420mV AT 4A 190mV AT 2A 95mV AT 1A 60mV AT 0.5A 330µF LT1431 • TA07 *NO SHORT-CIRCUIT PROTECTION **MAY BE INCREASED AT LOWER WATTAGE FOR LOWER OUTPUT CURRENTS FET Low Dropout 5V Regulator with Current Limit 12V MTP50N05EL MTM25N05L VIN ≥ 5.2V D + 47µF 0.002Ω* 5V, 2.5A S 2 + – G 1.5V 7 + 3 4 47µF LT1006 5 1N4148 6 1 COLL Measured Dropout Voltages ILOAD 2A 1A 0.5A MTP50N05EL 47mV 22mV 11.5mV MTM25N05L 145mV 73mV 37mV 3 4 V+ REF LT1431 RTOP GND-S 5 RMID 8 7 GND-F 6 LT1431 • TA08 *1.5" #23 SOLID COPPER WIRE ~0.002Ω → 3A LIMIT 7 LT1431 U TYPICAL APPLICATIO S 12V to 5V Buck Converter with Foldback Current Limit* Buck Converter Efficiency 80 PULSE ENGINEERING #PE-51515 LOGIC IN 4 70 MBR735 GND 5k 3 VIN = 9V VOUT LT1089 HI-SIDE SWITCH 100Ω 0.5W EFFICIENCY (%) VIN VIN 1500pF 2 COMP 1 COLL V+ REF RMID GND-S 5 60 VIN = 15V 50 40 LT1431 RTOP VIN = 12V 8 30 7 0 1 2 4 3 5 6 8 7 ILOAD (A) GND-F 6 LT1431 • TA10 5V, 7A + *CONTACT LTC FOR HIGH EFFICIENCY SWITCHING REGULATORS 3300µF LT1431 • TA09 Isolated 5V to ±15V Flyback Converter Fully Loaded Output Ripple vs Filtering COILTRONICS CTX02-11934 6, 7 4.5V TO 5.5V 0.47µF C* MUR105 9 + C* LT1072 30mVP-P 40mVP-P 6mVP-P 8mVP-P + –15V, 70mA 3k LT1172 210µF 15k L* MUR105 • 4, 5 + 50µF VOUT VIN • LT1172 OR LT1072 GND + • VC MUR105 15V, 70mA + C* 1.5k 4N36 2.4k 0.68µF 0.1µF 1 20k 2 3 V+ 8 REF COLL LT1431 COMP GND-S 5 13.3k 2.7k GND-F 6 LT1431 • TA11 8 100µF *L BELL INDUSTRIES J.W. MILLER DIVISION 9310-36 10µH, 450mA 1 MEASURED EFFICIENCY LT117267.8% AT 2.2W OUT LT107268.6% AT 2.2W OUT LT107161.1% AT 4.4W OUT + 100µF 2 10 LT1431 • TA12 LT1431 U TYPICAL APPLICATIO S 5V Power Supply Monitor with ±500mV Window and 50mV Hysteresis Transfer Function 6 1k 6k* 1k 4k* V+ COLL REF LT1431 COLL REF 3 LT1431 5k 2 5k GND-F GND-S 4 VOUT V+ 5 “HIGH” FOR OVER VOLTAGE OR UNDER VOLTAGE 1N4148 GND-S GND-F 1 10Ω** *DETERMINES WINDOW SIZE V = (R – 5)(0.5mA) **SETS HYSTERESIS 10Ω** 0 0 2 1 3 VIN LT1431 • TA13 4 5 6 LT1431 • TA14 High Efficiency Buck Converter E = 85% to 89% VIN 1 + D1 BAT85 C1 220µF 35V BOLD LINE INDICATES HIGH CURRENT PATHS * = 1% FILM RESISTORS C1 = NICHICON-UPL1V221MPH C6 = NICHICON-UPL1C471MPH6 D1, D2 = PHILIPS-BAT85 D3 = MOTORALA-MBR330 L1 = COILTRONICS CTX50-3-MP C3, C4, C5 = WIMA-MKS-2 5 VIN VSW 4 C5 0.047µF LT1170 R1 470k + C2 4.7µF 35V TANTALUM GND 3 D4 BAT85 VC FB 2 1 R2 1k C3 0.1µF C4 0.033µF D3 MBR330 L1 50µH 3A 0.12mΩ ESR + 5V 2.5A D2 BAT85 OFF 1 RUN = 0 SHUTDOWN > 3V R3 10k RTN R6* 23.7k Q2 2N3904 2 Q1 VN2222LL Q3 2N3904 3 4 R4 100Ω C6 470µF 16V R5 680Ω R8* 24.9k COMP V+ 1 COLL REF VR2 LT1431CN8 RTOP GND-S 5 RMID GND-F 8 7 R7* 24.9k 6 2 NOTES: UNLESS OTHERWISE SPECIFIED 1. ALL RESISTANCES ARE IN Ω, 0.25W, 5% 2. ALL CAPACITANCES ARE IN µF, 50V, 10% 3. SHUTDOWN LOGIC STATE MUST BE DEFINED BY A LOGIC GATE OR BY TYING TO GND LT1431 • TA15 9 LT1431 W W SCHE ATIC DIAGRA Q5 R1 35k 4X R2 35k Q2 Q1 Q7 3 Q13 V + Q17 3X Q11 Q3 Q10 Q12 Q6 2X Q9 8 REF Q14 C1 22pF R12 1k R11 11k C2 65pF R13 6.5k Q8 7 R9 2.5k Q20 2X Q22 45X Q18 Q19 Q15 R16 11Ω Q16 10X R4 5k GND-SENSE COLLECTOR 1 R7 2.5k 4 R3 5k R MID R17 1.5k C4 1pF Q4 RTOP C3 6pF R15 5k 5X R6 8.5k COMP 2 R5 5k R8 600Ω R10 340Ω R21 100k R14 11Ω R20 5k Q21 2.5X R18 50k R19 3.6Ω 5 6 GND-FORCE LT1431 • SD01 10 LT1431 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. J8 Package 8-Lead Ceramic DIP 0.405 (10.287) MAX 0.005 (0.127) MIN 8 7 6 5 0.025 (0.635) RAD TYP 0.220 – 0.310 (5.588 – 7.874) 1 0.290 – 0.320 (7.366 – 8.128) 2 3 4 0.200 (5.080) MAX 0.055 (1.397) MAX 0.015 – 0.060 (0.381 – 1.524) 0.008 – 0.018 (0.203 – 0.460) 0° – 15° 0.038 – 0.068 (0.965 – 1.727) 0.385 ± 0.025 (9.779 ± 0.635) 0.125 3.175 0.100 ± 0.010 MIN (2.540 ± 0.254) 0.014 – 0.026 (0.360 – 0.660) J8 0392 N8 Package 8-Lead Plastic DIP 0.400 (10.160) MAX 8 7 6 5 0.250 ± 0.010 (6.350 ± 0.254) 1 0.300 – 0.320 (7.620 – 8.128) 0.009 – 0.015 (0.229 – 0.381) ( +0.025 0.325 –0.015 +0.635 8.255 –0.381 ) 2 0.045 – 0.065 (1.143 – 1.651) 3 4 0.130 ± 0.005 (3.302 ± 0.127) 0.065 (1.651) TYP 0.045 ± 0.015 (1.143 ± 0.381) 0.100 ± 0.010 (2.540 ± 0.254) 0.125 (3.175) MIN 0.018 ± 0.003 (0.457 ± 0.076) Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of circuits as described herein will not infringe on existing patent rights. 0.020 (0.508) MIN N8 0392 11 LT1431 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic SOIC 0.189 – 0.197 (4.801 – 5.004) 8 7 6 5 0.228 – 0.244 (5.791 – 6.197) 0.150 – 0.157 (3.810 – 3.988) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 2 0.016 – 0.050 0.406 – 1.270 4 0.053 – 0.069 (1.346 – 1.752) 0.004 – 0.010 (0.101 – 0.254) 0.008 – 0.010 (0.203 – 0.254) 0°– 8° TYP 3 0.014 – 0.019 (0.355 – 0.483) 0.050 (1.270) BSC SO8 0392 Z Package 3-Lead TO-92 0.060 ± 0.005 (1.524± 0.127) DIA 0.180 ± 0.005 (4.572 ± 0.127) 0.90 (2.286) NOM 0.180 ± 0.005 (4.572 ± 0.127) 0.500 (12.79) MIN 0.060 ± 0.010 (1.524 ± 0.254) 0.050 (1.270) MAX 0.140 ± 0.010 (3.556 ± 0.127) 5° NOM 10° NOM UNCONTROLLED LEAD DIA 0.020 ± 0.003 (0.508 ± 0.076) 0.050 ± 0.005 (1.270 ± 0.127) 12 0.015 ± 0.02 (0.381 ± 0.051) Z3 1191 0.016 ± 0.03 (0.406 ± 0.076) Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LT/GP1292 5K REV B LINEAR TECHNOLOGY CORPORATION 1992