TLE 4267

Semiconductor Group

2

1998-11-01

Design Notes for External Components

The input capacitor

C

circuit consisting of lead inductance and input capacitance can be damped by a resistor

of approx. 1

regulating circuit. Stability is guaranteed at values of

≥ 22 µF and an ESR of ≤ 3 Ω within

the operating temperature range.

Circuit Description

The control amplifier compares a reference voltage, which is kept highly accurate by

resistance adjustment, to a voltage that is proportional to the output voltage and drives

the base of the series transistor via a buffer. Saturation control as a function of the load

current prevents any over-saturating of the power element.

A comparator in the reset-generator block compares a reference that is independent of

the input voltage to the scaled-down output voltage. If this reaches a value of 4.5 V, the

reset-delay capacitor is discharged and then the reset output is set Low. As the output

voltage increases again, the reset-delay capacitor is charged with constant current from

V

reset goes High again. The reset delay can be set within wide range by selection of the

external capacitor.

With the integrated turn-ON/turn-OFF logic it is simple to implement delayed turn-OFF

without external components.

Truth Table for Turn-ON/Turn-OFF Logic

Pin 2: (Inhibit, E2) Enable function, active High

Pin 6: (Hold, E6) Hold and release function, active Low

Pin 2

Pin 6

V

Q

Remarks

L

X

OFF

Initial state, pin 6 internally pulled up

H

X

ON

Regulator switched on via pin 2, by ignition for example

H

L

ON

Pin 6 clamped active to ground by controller while pin 2 is still

high

X

L

ON

Previous state remains, even ignition is shut off: self-holding

state

L

L

ON

Ignition shut off while regulator is in self-holding state

L

H

OFF

Regulator shut down by releasing of pin 6 while pin 2 remains

Low, final state. No active clamping required by external self-

holding circuit (

µC) to keep regulator shut off.