Datasheet

Figure 43 : 5.1V/2APower Supply using External
Limiting Current Resistor and Crow-
bar Protection on the Supply Voltage
(L296P only)
SOFT-START AND REPETITIVE POWER-ON
Whenthe deviceisrepetitivelypowered-on,thesoft-
start capacitor, C
SS
, must be discharged rapidly to
ensurethateachstartis ”soft”.Thiscanbeachieved
economicallyusingtheresetcircuit, asshownin Fig-
ure 44.
In this circuit thedivider R1, R2 connectedto pin 12
determines the minimum supply voltage, below
which the open collector transistor at the pin 14 out-
put discharges C
SS
.
Figure 44
Figure 45
Figure 46
The approximatedischargetimes obtainedwith this
circuit are :
CSS (µF) tDIS (µs)
2.2
4.7
10
200
300
600
If thesetimes arestilltoolong,anexternalPNPtran-
sistor may be added, as shown in Figure 45 ; with
this circuit discharge times of a few microseconds
may be obtained.
HOW TO OBTAIN BOTH RESET AND
POWER FAIL
Figure46illustrates how it ispossibleto obtainatthe
same time both the power fail and reset functions
simply by addingone diode(D) andone resistor(R).
In this case the Reset delay time (pin 13) can only
start when the output voltage is V
O
≥ V
REF
- 100mV
and the voltage accross R2 is higher than 4.5V.
With thehysteresisresistor itis possibleto fix the in-
put pin 12 hysteresis in order to increase immunity
to the 100Hz ripple present on the supply voltage.
Moreover, the power fail and reset delay time are
automaticallylocked to the soft-start.Soft-start and
delayedreset are thus two sequential functions.
The hysteresis resistor should be In the range of
aboit 100kΩ and the pull-up resistor of 1 to 2.2kΩ.
L296 - L296P
19/21