L4902A 데이터 시트보기 (PDF) - STMicroelectronics

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L4902A

DUAL 5V REGULATOR WITH RESET AND DISABLE

STMicroelectronics 

L4902A

TEST CIRCUIT

APPLICATION INFORMATION

In power supplies for µP systems it is necessary to

provide power continuously to avoid loss of infor-

mation in memories and in time of day clocks, or to

save datawhen the primary supply is removed.The

L4902A makes it very easy to supply such equip-

ments ; it provides two voltage regulators (both 5V

high precision) with common inputs plus a reset

output for the data save function and a Reg. 2

disable input.

CIRCUIT OPERATION (see Figure 1)

After switch on Reg. 1 saturates until V01 rises to

the nominal value.

When the input reaches VIT and the output 1 is

higher than VRT the output 2 (V02) switches on and

the reset output (VR) also goes high after a pro-

Figure 1

grammable time TRD (timing capacitor).

V02 and VR are switched togetherat low level when

one of the following conditions occurs :

- a high level ( VDT) is applied on pin 3 ;

- an input overvoltage ;

- an overload on the output 1 (V01 VRT) ;

- a switch off (VIN VIT - VITH) ;

and they start again as before when the condition

is removed.

An overload on output 2 does not switch Reg. 2,

and does not influence Reg. 1.

The V01 output features :

- 5V internal reference without voltage divider be-

tween the output and the error comparator

- very low drop series regulator element utilizing

current mirrors

permit high output impedance and then very low

leakage current even in power down condition.

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