LT1158CS LINER [Linear Technology], LT1158CS Datasheet - Page 13

• Manufacturer Part Number: LT1158CS
• Description: Half Bridge N-Channel Power MOSFET Driver
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
from 2 to 5 times the final value will be present for a few
spike is normally well within the safe operating area (SOA)
of the MOSFET, but can be further reduced with a small
(0.5 H) inductor in series with the output.
If neither the enable nor input pins are pulled low in
response to the fault indication, the top MOSFET current
will recover to a steady-state value I
LT1158 as shown in Figure 8:
The time for the current to recover to I
initial current spike is approximately Q
Q
set higher than the required start-up current for motors
(see Starting High In-Rush Current Loads). Note that the
s, followed by an interval in which I
GS
I
R
I
R
r current
SC
SC
is the MOSFET gate-to-source charge. I
SENSE
SENSE
Figure 8. Top MOSFET Short-Circuit Turn-On current
r 150mV
150mV
R
R
SENSE
SENSE
r 150mV
150mV
sense ratio, V = V
I
SC
I
SC
U
1
150mV
INFORMATION
1
Standard 3-Lead
MOSFET
5 s/DIV
U
V
150mV
V
2
GS
W
I
SC
DS
SC
2
GS
regulated by the
V
SC
= 0. The current
GS
/0.5mA, where
LT1158 F08
SC
following the
5-Lead
MOSFET
need not be
V
U
T
value of R
current sensing ratio (typically 1000 – 3000), thus elimi-
nating the need for a low valued shunt. V is in the range
of 1V to 3V in most applications.
Assuming a dead short, the MOSFET dissipation will rise
to V
= 10A, the dissipation would be 240W. To determine how
long the MOSFET can remain at this dissipation level
before it must be shut down, refer to the SOA curves given
in the MOSFET data sheet. For example, an IRFZ34 would
be safe if shut down within 10ms.
A Tektronix A6303 current probe is highly recommended
for viewing output fault currents.
If Short-Circuit Protection is Not Required
In applications which do not require the current sense
capability of the LT1158, the sense pins 11 and 12 should
both be connected to pin 13, and the fault pin 5 left open.
The enable pin 4 may still be used to shut down the device.
Note, however, that when unprotected the top MOSFET
can be easily (and often dramatically) destroyed by even a
momentary short.
Self-Protection with Automatic Restart
When using the current sense circuits of Figures 6 and 7,
local shutdown can be achieved by connecting the fault pin
through resistor R
An optional thermostat mounted to the load or MOSFET
heatsink can also be used to pull enable low.
An internal 25 A current source normally keeps the en-
able capacitor C
to V
charged to below the enable low threshold (1.15V typ.)
which shuts down both MOSFETs. When the fault pin or
thermostat releases, C
threshold where restart is attempted. In a sustained short
circuit, fault will again pull low and the cycle will repeat
until the short is removed. The time to shut down for a DC
input or thermal fault is given by:
t
SHUTDOWN
SUPPLY
+
, for V
SENSE
+
I
SC
< 7.5V). When a fault occurs, C
= (100 + 0.8R
EN
. For example, with a 24V supply and I
for the 5-lead MOSFET increases by the
F
charged to the 7.5V clamp voltage (or
to the enable pin as shown in Figure 9.
EN
recharges to the upper enable
F
) C
EN
DC input
LT1158
EN
13
is dis-
SC