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L4904A
DUAL 5V REGULATOR WITH RESET
L4904ADUAL 5V REGULA TOR WITH RESET
June 2000
PIN CONNECTION OUTPUT CURRENTS : I01 = 50mA
I02 = 100mA. FIXED PRECISION OUTPUT VOLTAGE
5V ± 2 %. RESET FUNCTION CONTROLLED BY INPUT
VOLTAGE AND OUTPUT 1 VOLTAGE . RESET FUNCTION EXTERNALLY PRO-
GRAMMABLE TIMING . RESET OUTPUT LEVEL RELATED TO
OUTPUT 2. OUTPUT 2 INTERNALL Y SWITCHED WITH
ACTIVE DISCHARGING. LOW LEAKAGE CURRENT, LESS THAN 1μA T OUTPUT 1. LOW QUIESCENT CURRENT (Input 1). INPUT OVERVOLT AGE PROTECTION UP TO
60V. RESET OUTPUT NORMALL Y HIGH . OUTPUT TRANSISTORS SOA PROTECTION. SHORT CIRCUIT AND THERMAL OVER-
LOAD PROTECTION
DESCRIPTIONThe L4904A is a monolithic low drop dual 5V
regulator designed mainly for supplying microproc-
essor systems.
Reset and data save functions during switch on/off
can be realized.
1/9
BLOCK DIAGRAM
SCHEMA TIC DIAGRAM
PIN FUNCTIONS
L4904A2/9
ABSOLUTE MAXIMUM RATINGS
THERMAL DATA
ELECTRICAL CHARACTERISTICS (VIN = 14.4V , Tamb = 25o C unless otherwise specified)
L4904A3/9
TEST CIRCUIT
Figure 1 : P .C. Board and Components Layout of the Test Circuit (1:1 scale)
APPLICATION INFORMATIONIn 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 data when 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.
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 therefore be 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 applications where 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.
The reset output can be used 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.
L4904A4/9
Figure 2
APPLICATION SUGGESTIONSFigure 3 shows an application circuit for a μP
system.
Reg. 1 is permanently connected to a battery and
supplies a CMOS time-of-day clock and a CMOS
microcomputer chip with volatile memory.
Reg. 2 may be switched OFF when the system is
inactive.
Figure 4 shows the L4904A with a back up battery
on the V01 output to maintain a CMOS time-of-day
clock and a stand by type C-MOS μP . The reset
output makes sure that the RAM is forced into the
low consumption stand by state, so the access to
memory is inhibit and the back up battery voltage
cannot drop so low that memory contents are cor-
rupted.
In this case the main on-off switch disconnects both
regulators from the supply battery.
Application Circuits of a Microprocessor system
(Figure 3) or with data save battery (Figure 4). The
reset output provide delayed rising front at the
Figure 3
L4904A5/9
Figure 4
L4904A6/9
