LT1431 Просмотр технического описания (PDF) - Linear Technology

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LT1431

Programmable Reference

Linear Technology 

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.

COMP (Pin 2): Base of the driver for the output transis-

tor. This pin allows additional compensation for complex

feedback systems and shutdown of the regulator. It must

be left open if unused.

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.

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.

GND-S (Pin 5): Ground reference for the on-chip resis-

tive 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).

GND-F (Pin 6): Emitter of the output transistor and sub-

strate connection for the die.

RMID (Pin 7): Middle of the on-chip resistive divider string

between RTOP and GND-S. The pin is tied to REF for self-

contained 5V operation. It may 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.

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.

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).

The following pin definitions apply to the Z package.

CATHODE: Corresponds to COLL and V+ tied together.

ANODE: Corresponds to GND-S and GND-F tied together.

REF: Corresponds to REF.

Block Diagram

RTOP

4

5k

8

REF

7

RMID

5k

V+

3

+

gm =

4mA/V

–

2.5V

COMP

2

COLLECTOR

1

5

GND-SENSE

LT1431 BD

6

GND-FORCE

1431fd



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