Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - voltage reference Shunt Adjustable SOIC 8

LT1431

1431fe

Typical applicaTion

FeaTures DescripTion

Programmable Reference

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. The nominal internal

current limit of 100mA may be decreased by including

one external resistor.

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

available for applications as an adjustable reference and

is pin compatible with the TL431.

Isolated 5V Regulator

applicaTions

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

Available in J8, N8, S8 or 3-Lead TO-92 Z Packages

Linear Regulators

Adjustable Power Supplies

Switching Power Supplies

REF

vs Temperature

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

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property

of their respective owners.

Summary of content (14 pages)

PAGE 1
LT1431 Programmable Reference Features n n n n n n Description 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 Available in J8, N8, S8 or 3-Lead TO-92 Z Packages Applications n n n Linear Regulators Adjustable Power Supplies Switching Power Supplies L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and ThinSOT is a trademark of Linear Technology Corporation.
PAGE 2
LT1431 Absolute Maximum Ratings (Note 1) V+, VCOLLECTOR...........................................................36V VCOMP, RTOP, RMID, VREF..............................................6V GND-F to GND-S.......................................................0.7V Ambient Temperature Range LT1431M, LT1431MP.......................... –55°C to 125°C LT1431I.................................................–40°C to 85°C LT1431C...................................................
PAGE 3
LT1431 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. IK = 10mA unless otherwise specified (Note 2) LT1431I, LT1431M SYMBOL PARAMETER CONDITIONS VREF Reference Voltage VKA = 5V, IK = 2mA, (Note 3) MIN l ∆VREF/∆T Reference Drift TYP MAX LT1431C MIN TYP MAX UNITS 2.490 2.500 2.510 2.490 2.500 2.510 2.465 2.535 2.480 2.
PAGE 4
LT1431 Typical Performance Characteristics 2.5V Reference IK vs VKA 1000 2.505 VREF and IREF vs V + 3.5 2.505 VREF and IREF vs V + 3.5 2.504 3.0 800 2.503 2.5 2.503 2.5 2.502 2.0 2.502 2.0 2.501 1.5 2.501 1.5 2.500 1.0 IMIN IK (µA) VREF (V) 600 500 400 2.499 300 2.498 200 100 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 VKA (V) 0 VREF 2.500 1.0 0.5 IREF 0 2.498 2.497 –0.5 2.497 2.496 –1.0 2.496 2.495 –1.5 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 + V (V) 2.
PAGE 5
LT1431 Typical Performance Characteristics Transconductance and Phase vs Frequency (Ref to Comp) PHASE gm 1.4 0 1.2 –20 103 –60 –80 3 × 102 PHASE (DEG) –40 10k 100k FREQUENCY (Hz) 1M 2.5 2.0 0.8 0.6 0.5 1k 10k FREQUENCY (Hz) LT1431 TPC10 ICOMP vs VCOMP vs VREF LT1431 TPC11 Noise vs Frequency 50 25 75 0 TEMPERATURE (°C) 100 125 LT1431 TPC12 0.
PAGE 6
LT1431 Pin Functions 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 7
LT1431 Applications Information 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 8
LT1431 Typical Applications PNP Low Dropout 5V Regulator* VIN 0.1µF 20Ω** 2W 1k 47Ω MJE2955 2N2219 0.015µF 150Ω 3 4 2 COMP V+ RTOP 1 COLL LT1431 GND-S 5 REF RMID 8 7 GND-F 6 + MEASURED DROPOUT VOLTAGE 420mV AT 4A 190mV AT 2A 95mV AT 1A 60mV AT 0.5A 5V 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 VIN ≥ 5.2V MTP50N05EL MTM25N05L + D 47µF 0.002Ω* S – G 1.
PAGE 9
LT1431 Typical Applications 12V to 5V Buck Converter with Foldback Current Limit* Buck Converter Efficiency 80 PULSE ENGINEERING #PE-51515 VOUT LT1089 HI-SIDE SWITCH LOGIC IN 3 4 100Ω 0.
PAGE 10
LT1431 Typical Applications 5V Power Supply Monitor with ± 500mV Window and 50mV Hysteresis Transfer Function 6 1k 6k* 1k 4k* V+ V+ COLL REF LT1431 GND-S 4 VOUT 1N4148 5 “HIGH” FOR OVER VOLTAGE OR UNDER VOLTAGE COLL REF LT1431 5k GND-F GND-S 2 5k GND-F 1 10Ω** *DETERMINES WINDOW SIZE V = (R – 5k)(0.
PAGE 11
LT1431 Schematic Diagram Q5 R1 35k 4X R2 35k Q2 Q1 Q7 3 Q13 V + Q17 3X Q10 Q11 Q3 Q12 Q6 2X 8 REF Q9 Q14 C1 22pF R11 11k C2 65pF R15 5k R17 1.5k R13 6.5k COLLECTOR 1 Q20 2X C4 1pF Q22 45X Q18 Q19 R9 2.5k Q8 7 Q15 R5 5k R8 600Ω 5 R10 340Ω R20 5k R16 11Ω Q16 10X R4 5k GND-SENSE C3 6pF R7 2.5k 4 R3 5k R MID R12 1k 5X R6 8.5k Q4 RTOP COMP 2 Q21 2.5X R14 11Ω R21 100k R18 50k R19 3.
PAGE 12
LT1431 Package Description N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .300 – .325 (7.620 – 8.255) ( +.035 .325 –.015 8.255 +0.889 –0.381 .130 ± .005 (3.302 ± 0.127) .045 – .065 (1.143 – 1.651) .065 (1.651) TYP .008 – .015 (0.203 – 0.381) .400* (10.160) MAX 8 7 6 5 1 2 3 4 .255 ± .015* (6.477 ± 0.381) ) .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 .100 (2.54) BSC N8 1002 (0.457 ± 0.076) NOTE: 1.
PAGE 13
LT1431 Revision History (Revision history begins at Rev D) REV DATE DESCRIPTION PAGE NUMBER D 4/10 M-grade parts re-released. Obsolete package shading removed. E 7/11 Added LT1431MPS8 to data sheet. Changes reflected throughout. 2, 11 1 to 14 1431fe Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 14
LT1431 Package Description Z Package 3-Lead Plastic TO-92 (Similar to TO-226) (Reference LTC DWG # 05-08-1410 Rev C) .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 5° NOM .050 UNCONTROLLED (1.270) LEAD DIMENSION MAX .016 ± .003 (0.406 ± 0.076) .050 (1.27) BSC .015 ± .002 (0.381 ± 0.051) BULK PACK TO-92 TAPE AND REEL REFER TO TAPE AND REEL SECTION OF LTC DATA BOOK FOR ADDITIONAL INFORMATION .060 ± .010 (1.524 ± 0.