Datasheet

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LT1431

1413fc

Programmable Reference

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Guaranteed 0.4% Initial Voltage Tolerance

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0.1Ω Typical Dynamic Output Impedance

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Fast Turn On

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Sink Current Capability, 1mA to 100mA

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Low Reference Pin Current

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Available in N8, S8 or 3-Lead TO-92 Z Packages

The LT

1431 is an adjustable shunt voltage regulator with

100mA sink capability, 0.4% initial reference voltage tol-

erance 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 exter-

nal resistor.

A simplified 3-pin version, the LT1431CZ/LT1431IZ, is

available for applications as an adjustable reference and is

pin compatible with the TL431.

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Linear Regulators

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Adjustable Power Supplies

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Switching Power Supplies

Isolated 5V Regulator

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

, LTC and LT are registered trademarks of Linear Technology Corporation.

LT1431 • TA01

COLLCOMPV

LT1431

GND-FGND-S

TOP

REF

MID

2.5V

–

4mA/V

SWITCHING

REGULATOR

–

TEMPERATURE (°C)

–50

REF

(V)

2.4975

2.5000

2.5025

25 75

LT1431 • TA01b

2.4950

2.4925

–25 0

50 100 125

2.4900

2.4875

REF

vs Temperature

Summary of content (12 pages)

PAGE 1
LT1431 Programmable Reference U FEATURES ■ ■ ■ ■ ■ ■ DESCRIPTIO The LT®1431 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.
PAGE 2
LT1431 W W W AXI U U ABSOLUTE RATI GS (Note 1) V+, VCOLLECTOR ....................................................... 36V VCOMP, RTOP, RMID, VREF .......................................... 6V GND-F to GND-S .................................................... 0.7V Ambient Temperature Range LT1431M (OBSOLETE) ................... – 55°C to 125°C LT1431I ............................................ – 40°C to 85°C LT1431C ..............................................
PAGE 3
LT1431 ELECTRICAL CHARACTERISTICS Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: VKA is the cathode voltage of the LT1431CZ/IZ and corresponds to V + of the LT1431CN8/IN8/CS8/IS8. IK is the cathode current of the LT1431CZ/IZ and corresponds to I(V +) + ICOLLECTOR of the LT1431CN8/ IN8/CS8/IS8. Note 3: The LT1431 has bias current cancellation which is effective only for VKA ≥ 3V.
PAGE 4
LT1431 U W TYPICAL PERFOR A CE CHARACTERISTICS 120 VREF ± OVERDRIVE 105 1 OUTPUT 120 LT1431 5 6 45 OUTPUT HIGH-TO-LOW 50 0 150 100 OVERDRIVE (mV) 200 90 AV 45 60 0 40 –45 –90 20 –135 0 –20 100 250 1k 10k 100k FREQUENCY (Hz) 1M Transconductance and Phase vs Frequency (Ref to Comp) 20 1.4 0 1.
PAGE 5
LT1431 U U U PI FU CTIO S COLL (Pin 1): Open collector of the output transistor. The maximum pin voltage is 36V. 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.
PAGE 6
LT1431 U W U U APPLICATIO S I FOR ATIO Frequency Compensation response of the LT1431 with dominant pole or 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.
PAGE 7
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.
PAGE 8
LT1431 U TYPICAL APPLICATIO S Buck Converter Efficiency 12V to 5V Buck Converter with Foldback Current Limit* 80 PULSE ENGINEERING #PE-51515 VOUT LT1089 HI-SIDE SWITCH LOGIC IN 3 4 MBR735 GND 5k VIN = 9V 70 100Ω 0.
PAGE 9
LT1431 U TYPICAL APPLICATIO S 5V Power Supply Monitor with ±500mV Window and 50mV Hysteresis Transfer Function 6 1k 6k* 1k 4k* LT1431 VOUT V+ COLL REF COLL REF 3 LT1431 5k GND-S 4 2 5k GND-F GND-S GND-F 1 10Ω** *DETERMINES WINDOW SIZE V = (R – 5k)(0.
PAGE 10
LT1431 W W SCHE ATIC DIAGRA Q5 R1 35k 3 Q13 V + Q17 3X 4X R2 35k Q2 Q1 Q7 Q10 Q11 Q3 Q12 Q6 2X Q9 8 REF Q14 C1 22pF COMP 2 R12 1k R15 5k 5X R6 8.5k R11 11k C2 65pF R13 6.5k Q20 2X Q22 45X 7 Q18 Q19 R9 2.5k Q8 Q15 R20 5k R16 11Ω Q16 Q21 2.5X 10X R4 5k GND-SENSE COLLECTOR 1 R7 2.5k 4 R3 5k R MID R17 1.5k C4 1pF Q4 RTOP C3 6pF R5 5k R8 600Ω R10 340Ω R14 11Ω R21 100k R18 50k R19 3.
PAGE 11
LT1431 U PACKAGE DESCRIPTIO N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .300 – .325 (7.620 – 8.255) .065 (1.651) TYP +0.889 –0.381 8 7 6 5 1 2 3 4 .255 ± .015* (6.477 ± 0.381) +.035 .325 –.015 8.255 .130 ± .005 (3.302 ± 0.127) .045 – .065 (1.143 – 1.651) .008 – .015 (0.203 – 0.381) ( .400* (10.160) MAX .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 .100 (2.54) BSC ) N8 1002 (0.457 ± 0.076) NOTE: 1.
PAGE 12
LT1431 U PACKAGE DESCRIPTIO Z Package 3-Lead Plastic TO-92 (Similar to TO-226) (Reference LTC DWG # 05-08-1410) .180 ± .005 (4.572 ± 0.127) .060 ± .005 (1.524± 0.127) DIA .90 (2.286) NOM .180 ± .005 (4.572 ± 0.127) .500 (12.70) MIN .050 UNCONTROLLED (1.270) LEAD DIMENSION MAX .016 ± .003 (0.406 ± 0.076) .050 (1.27) BSC 5° NOM .015 ± .002 (0.381 ± 0.051) Z3 (TO-92) 0801 .060 ± .010 (1.524 ± 0.254) 3 2 .098 +.016/–.04 (2.5 +0.4/–0.