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LT1161 Datasheet(PDF) 8 Page - Linear Technology

Part No. LT1161
Description  Quad Protected High-Side MOSFET Driver
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Maker  LINER [Linear Technology]
Homepage  http://www.linear.com
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LT1161 Datasheet(HTML) 8 Page - Linear Technology

 
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8
LT1161
APPLICATIONS INFORMATION
Low Voltage/Wide Supply Range Operation
When the supply is <12V, the LT1161 charge pumps do
not produce sufficient gate voltage to fully enhance stan-
dard N-channel MOSFETs. For these applications, logic-
level MOSFETs can be used to extend operation down to
8V. If the MOSFET has a maximum VGS rating of 15V or
greater, then it can also be used up to the 60V (absolute
maximum) rating of the LT1161. MOSFETs are available
from both Motorola and Siliconix which meet these
criteria.
Protecting Against Supply Transients
The LT1161 is 100% tested and guaranteed to be safe
from damage with 60V applied between the V+ and ground
pins. However, when this voltage is exceeded, even for a
few microseconds, the result can be a catastrophic failure.
For this reason
it is imperative that the LT1161 not be
exposed to supply transients above 60V.
For proper current-sense operation, the V+ pins are re-
quired to be connected to the positive side of the drain
sense resistors (see Drain Sense Configuration). There-
fore, the best way to prevent supply transients is to ensure
that the supply is adequately decoupled at the point where
the V+ pins and drain sense resistors meet. Several
hundred microfarads may be required with high current
switches.
When operating voltages approach the 60V absolute maxi-
mum rating of the LT1161, local supply decoupling be-
tween the V+ pins (11, 20) and ground pins (1, 10) is highly
recommended. A small ferrite bead between the supply
connection and local capacitor can also be effective in
suppressing transients. Note however, that resistance
should not be added in series with the V+ pins because it
will cause an error in the current sense threshold.
Fault Feedback
Two methods can be used to derive switch status. First,
the timer pin voltage can be monitored to indicate when
the switch is turned off due to current limit. During normal
operation (ON or OFF), the timer voltage is 3.5V and only
during current limit does the voltage drop below 3V.
The second method shown in Figure 8 uses a quad
exclusive-NOR gate to indicate when the output of the
switch has not obeyed the input command (i.e., output low
when it should be high or vice versa). In addition to current
limit, this gives a fault indication if the switch is shorted or
if the load is open.
Figure 8. Fault Feedback Using Exclusive-NOR Gate
24V
RS
ROL
ADD FOR
OPEN-LOAD
DETECTION
1161 F08
FAULT
INPUT
1/4 MM74HC266A
100k
LT1161
V+
V+
DS
G
IN
+
LOAD
Low-Side Driving
Although the LT1161 is primarily targeted at high-side
(grounded load) switch applications, it can also be used
for low-side (supply-connected load), or mixed high- and
low-side switch applications. Figures 9a and 9b illustrate
LT1161 switch channels driving low-side power MOSFETs.
Because the LT1161 charge pump tries to pump the gate
of the N-channel MOSFET
above supply, a clamp zener is
required to prevent the VGS (absolute maximum) of the
MOSFET from being exceeded. The LT1161 gate drive is
current limited for this purpose so that no resistance is
needed between the gate pin and zener.
Figure 9a. Low-Side Driver with Load Current Sensing
100
µF
IRFZ44
1
µF
RS
0.01
(PTC)
1161 F09a
15V
1N4744
LT1161
12V TO 48V
V+
V+
DS
G
+
4A
LOAD
T


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