LT1158CS LINER [Linear Technology], LT1158CS Datasheet - Page 14

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

APPLICATIONS
LT1158
Note that for the first event only, t
mately twice the above value since C
all the way from its quiescent voltage. Allowable values for
R
t
output is shorted with a PWM input. This is because the
fault pin only conducts when fault currents are actually
present in the MOSFET. Fault does not conduct while the
input is low in Figures 6 and 7 or during the interval I
0 in Figure 8. Thus t
the duty cycle of the current in the top MOSFET is low,
maintaining the average MOSFET current at a relatively
constant level.
The length of time following shutdown before restart is
attempted is given by:
In Figure 9, the top MOSFET would shut down after being
in DC current limit for 0.9ms and try to restart at 60ms
intervals, thus producing a duty cyle of 1.5% in short
circuit. The resulting average top MOSFET dissipation
during a short is easily measured by taking the product of
the supply voltage and the average supply current.
Starting High In-Rush Current Loads
The LT1158 has a V
than I
14
SHUTDOWN
F
are from zero to 10k.
t
RESTART
1.15V
7.5V
SC
OPTIONAL THERMOSTAT
CLOSE ON RISE
AIRPAX #67FXXX
to flow in the top MOSFET providing that the
Figure 9. Self-Protection with Auto Restart
C
1 F
becomes more difficult to analyze when the
EN
+
25
1 5
DS
U
V
SHUTDOWN
A
sensing function which allows more
R
1k
F
INFORMATION
C
U
ENABLE
FAULT
EN
will safely increase when
6 10
25 A
7.5V
SHUTDOWN
EN
W
is being discharged
LT1158
4
C
EN
is approxi-
U
1158 F09
DS
=
This calculation gives the minimum current which could
be delivered with the IRFZ34 at T
ing the fault pin on the LT1158. If more start current is
required, using an IRFZ44 (R
increase I
short-circuit current remains at 5A.
In order for the V
supply pins for the LT1158 must be connected at the drain
of the top MOSFET, which must be properly decoupled
(see Ugly Transient Issues).
Driving Lamps
Incandescent lamps represent a challenging load because
they have much in common with a short circuit when cold.
The top gate driver in the LT1158 can be configured to turn
on large lamps while still protecting the power MOSFET
sense
tions the current is limited only by the R
with R
R
Figure 7). Again adjusting R
worst-case start currents are:
Properly sizing the MOSFET for I
loads with long time constants, such as motors with high
mechanical inertia, to be started.
Returning to the example used in Power MOSFET Selec-
tion, an IRFZ34 (R
operation at 5A. If the short-circuit current is also set at 5A,
what start current can be supported? From the equation
for R
worst-case start current to be calculated:
DS(ON)
I
I
I
START
START
START
SENSE
–
SENSE
pin is within 1.2V of supply. Under these condi-
alone, since R
START
, a 0.03 shunt would be required, allowing the
. For a 5-lead MOSFET the current is limited by
1
1
1 7 0 05
to over 15A at T
DS
1 2
R
R
DS(ON)
sensing function to work properly, the
DS ON
DS ON
V
1 2
1 2
SENSE
V
V
= 0.05 max.) was selected for
0 03
DS(ON)
R
is not in the output path (see
DS(ON)
SENSE
J
J
= 110 C, even though the
= 125 C without activat-
START
= 0.028 max.) would
for temperature, the
10
A
3-Lead MOSFET
5-Lead MOSFET
allows inductive
DS(ON)
in series