
I
NPUT SECTION
An
Input
TTL/CMOS compatible with wide voltage range
and high noise immunity (thanks to a built in hys-
teresis) are available.
and
Asynchronous RESET,
both
OVER TEMPERATURE PROTECTION (OVT)
An on-chip Over Temperature Protectionprovidse
an excellent protection of the device in extreme
conditions. Whenever the temperature - meas-
ured on a central portion of the chip- exceeds
Tmax=150 C (typical value) the device is shut off,
and the DIAG output goes LOW.
Normal operation is resumed as the chip tem-
perature (normally after few seconds) falls below
Tmax-Thys= 130 C (typical value). The hysteresis
avoid thats an intermittent behaviourtake place.
UNDER VOLTAGEPROTECTION (UV)
The supply voltage is expectedto range from 8 to
35 V. In this range the device operates correctly.
Below 8 V the overall system has to be consid-
ered not reliable. To avoid any misfunctioningthe
supply voltage is continuously monitored to pro-
vide an under voltage protection. As Vs falls be-
low Vsth-Vshys (typically 7.5 V, see
output power MOS is switched off and DIAG out-
put goes LOW. Normal operation is resumed as
soon as Vs exceeds Vsth. The hysteretic behav-
iour prevents intermittent operation at low supply
voltage.
fig.1) the
OVERCURRENT OPERATION
In order to implement a short circuit protectionthe
output power MOS is driven in linearmode to limit
the output current to the Isc value. This Isc limit is
externallysettable by means of an external1/4 W
resistor connected from Rsc pin and GND. The
value of the resistor must be chosen according to
the followingformula:
Isc (A) = 5/Rsc (kohm)
with
5 < Rsc < 30 (kohm)
For
Rsc< 5 (kohm)
Isc is limited to Isc=1.1 A (typical value).
This condition (current limited to the Isc value)
lasts for a Ton time interval, that can be set by
means of a capacitor(Cdon) connectedto the ON
DELAY pin according to the following formula:
Ton
= 1.28 msec/pF
for
50pF<Cdon<2nF
After the Ton interval has expired the output
power MOS is switched off for the Toff time inter-
val with:
Toff = 64*Ton.
OUTPUT
CURRENT
t
ON
t
ON
t
OFF
t
OFF
Time
t<t
ON
DIAG
(active low)
Time
Short Circuit
Short Circuit
Isc
Iout
D94IN105
Figure 3:
ShortCircuit OperationWaveforms
L6377
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