Datasheet

Figure 43 : 5.1V/2A Power Supply using External
Limiting Current Resistor and Crow-
bar Protection on the Supply Voltage
(L296P only)
SOFT-START AND REPETITIVE POWER-ON
When the device is repetitively powered-on, the soft-
start capacitor, C
SS
, must be discharged rapidly to
ensure that each start is "soft". This can be achieved
economically using the reset circuit, as shown in Fig-
ure 44.
In this circuit the divider R1, R2 connected to 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 approximate discharge times obtained with this
circuit are :
CSS (
µ
F) tDIS (
µ
s)
2.2
4.7
10
200
300
600
If these times are still too long, an external PNP tran-
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
Figure 46 illustrates how it is possible to obtain at the
same time both the power fail and reset functions
simply by adding one diode (D) and one 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 the hysteresis resistor it is possible to 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
automatically locked to the soft-start. Soft-start and
delayed reset 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
19/22