L4903 查看數據表（PDF） - STMicroelectronics

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L4903

DUAL 5V REGULATOR WITH RESET AND DISABLE FUNCTIONS

STMicroelectronics 

L4903

TEST CIRCUIT

Figure 1 : P.C. Board and Components Layout of the 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

savedata when the primary supply is removed. The

L4903 makes it very easy to supply such equip-

ments ; it provides two voltage regulators (both 5 V

high precision) with separate inputs plus a reset

output for the data save function and Reg. 2 disable

input.

CIRCUIT OPERATION (see Figure 2)

After switch on Reg. 1 saturates until V01 rises to

the nominal value.

When the input 2 reaches VIT and the output 1 is

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

on and the reset output (VR) goes low after a

programmable time TRD (timing capacitor).

V02 is switched at low level and VR at high level

when one of the following conditions occurs ;

- a high level (> VDT) is applied on pin 5 ;

- 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

4/8

is removed.

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

and does not influence Reg. 1.

The V01 output features :

- 5 V internal reference without voltage divider

between 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 conditions.

This output may thereforebe used to supply circuits

continuously, such as volatile RAMs, allowing the

use of a back-up battery.

The V02 can supply other non essential 5 V circuits

which may be powered down when the system is

inactive, or that must be powered down to prevent

uncorrect operation for supply voltages below the

minimum value.

The reset output can beused as a ”POWER DOWN

INTERRUPT”, permitting RAM access only in cor-

rect power conditions, or as a ”BACK-UP ENABLE”

to transfer data into in a NV SHADOW MEMORY

when the supply is interrupted.

The disable function can be used for remote on/off

control of circuits connected to the V02 output.

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