TLE 4261

Semiconductor Group

2

1998-11-01

Application Description

The IC regulates an input voltage

V

reset signal is generated for a maximum output voltage of

V

delay can be set externally with a capacitor. A connected microprocessor is monitored

by the integrated watchdog circuit. Connecting this input to the input voltage makes the

watchdog function inactive. The presence of a voltage less than 2 V on inhibit input

disables the regulator. The current consumption drops to max. 50

µA.

Design Notes for External Components

The input capacitor

C

input voltage. The IC is protected against rise times up to 100 V/

µs. It is possible to damp

the tuned circuit consisting of supply inductance and input capacitance with a resistor of

approx. 1

The output capacitor maintains the stability of the regulating loop. Stability is guaranteed

with a rating of 22

µF at an ESR of 3 Ω max. in 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 controls

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

load current prevents any over-saturation of the power element. If the output voltage

drops below 95.5 % of its typical value for more than 2

µs, a reset signal is triggered on

pin 3 and an external capacitor is discharged on pin 5. The reset signal is not cancelled

until the voltage on the capacitor has exceeded the upper switching threshold

V

positive-edge-triggered watchdog circuit monitors the connected microprocessor and

will likewise trigger a reset if pulses are missing. The IC can be disabled by a low level

on the inhibit input and the current consumption drops to < 50

µA.

The IC also incorporates a number of circuits for protection against:

q

Overload

q

Overvoltage

q

Overtemperature

q

Reverse polarity