Obsolete

Product(s)

- Obsolete

Product(s)

Circuit description

TDA8139, TDA8139/D

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3

Circuit description

The TDA8139 and the TDA8139/D are dual-voltage regulators with reset and disable

functions.

The two regulation parts are supplied from a single voltage reference circuit trimmed by

zener zapping during EWS testing. Since the supply voltage of this voltage reference is

connected to pin INPUT1 (VIN1), the second regulator will not work if pin INPUT1 is not

supplied.

The adjustable voltage of pin OUTPUT2 (VO2) is defined by output bridge resistors (R1, R2):

the values of these resistors are calculated to obtain, with the targetted value for VO2, the

reference voltage (VREF = 2.5 V) on the median point connected to pin PROGRAM.

The output stages have been realized using a Darlington configuration with a typical dropout

voltage of 1.2 V.

The disable circuit will switch off pin OUTPUT2 if a voltage less than 0.8 V is applied to pin

DISABLE.

The reset circuit checks the voltage at pin OUTPUT1. If this voltage drops below VO1 -

0.25 V (4.85 V Typ.), the "a" comparator (Figure 4) rapidly discharges capacitor Ce and the

reset output immediately switches to low. When the voltage at pin OUTPUT1 exceeds VO1 -

0.2 V (4.9 V Typ.), the external capacitor voltage (VCe) increases linearly to the reference

voltage (VREF = 2.5 V) corresponding to a reset pulse delay tRD as shown in Figure 5.

Afterwards, the reset output returns to high. To avoid glitches in the reset output, the second

comparator "b" has a large hysteresis (1.9 V).

Figure 4.

Reset diagram

t

RD

C

e

2.5V

×

10

μA

---------------------------

=

OUTPUT1

REG

VREF

-

+

50

a

+

-

Ce

VREF

0.6V

b

RESET

10 µA

3

VREF = 2.5 V