TLE 4470

Semiconductor Group

16

1998-11-01

Figure 5

Early Warning

The early warning function compares a voltage defined by the user to an internal

reference voltage. Therefore the voltage to be supervised has to be scaled down by an

external voltage divider in order to compare it to internal sense threshold (reference

voltage) which is typically 1.35 V. The sense out pin is set to low when the user defined

voltage falls below this threshold.

A typical example where this circuit can be used is to supervise the input voltage

V

give the microprocessor a prewarning of a low battery condition.

Calculation of the voltage divider can be easily done since the sense input current can

be neglected.

To minimize transient influences the use of a capacitor in parallel to

R

Like the reset output pin, the sense out pin SQ is internally connected to the stand-by

output Q1 via a 30 k

Ω pull-up resistor. The sense out LOW signal at pin SQ is generated

down to an input voltage

V

AES02505

1

Band-Gap

Reference

Reference

Band-Gap

+

_

RADJ

RO

Q1

V

GND

R

1

2

R

30 k

Ω

1.35 V

1.35 V

_

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TLE 4470 G