L4904A Ver la hoja de datos (PDF) - STMicroelectronics

Número de pieza

componentes Descripción

Lista de partido

L4904A

DUAL 5V REGULATOR WITH RESET

STMicroelectronics 

L4904A

TEST CIRCUIT

Figure 1 : P.C. Board and Components Layout of the Test Circuit (1:1 scale)

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

L4904A makes it very easy to supply such equip-

ments ; it provides two voltage regulators (booth 5V

high precision) with separate inputs plus a reset

output for the data save function.

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) switches on and

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

grammable time TRD (timing capacitor).

V02 and VR are switched together at low level when

one of the following conditions occurs :

- 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.

4/9

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

mirrors ;

permit high output impedance and then very low

leakage current even in power down conditions.

This output may thereforebe used to supply circuits

continuously, such as volatile RAMs, allowing the

use of a back-up battery. The V01 regulator also

features low consumption (0.6 mA typ.)to minimize

battery drain in applicationswhere the V1 regulator

is permanently connected to a battery supply.

The V02 output 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.

Thereset output can be usedas a ”POWER DOWN

INTERRUPT”, permitting RAM access only in cor-

rect powerconditions,or as a ”BACK-UPENABLE”

to transfer data into in a NV SHADOW MEMORY

when the supply is interrupted.

Share Link: