LT1158CS View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT1158CS' PDF : 20 Pages View PDF
LT1158
APPLICATIONS INFORMATION
Low Current Shutdown
The LT1158 may be shutdown to a current level of 2mA by
pulling the enable pin 4 low. In this state both the top and
bottom MOSFETs are actively held off against any tran-
sients which might occur on the output during shutdown.
This is important in applications such as 3-phase DC
motor control when one of the phases is disabled while the
other two are switching.
If zero standby current is required and the load returns to
ground, then a switch can be inserted into the supply path
of the LT1158 as shown in Figure 5. Resistor RGS ensures
that the top MOSFET gate discharges, while the voltage
across the bottom MOSFET goes to zero. The voltage drop
across the P-channel supply switch must be less than
300mV, and RGS must be 330k or greater for DC operation.
This technique is not recommended for applications which
require the LT1158 VDS sensing function.
V+
shown in Figure 7, the sense resistor is inserted between
the sense and Kelvin leads.
The sense+ and sense– PC traces must be routed together
at minimum spacing to prevent stray pickup, and a Kelvin
connection must be used at the current shunt for the 3-
lead MOSFET. Using a twisted pair is the safest approach
and is recommended for sense runs of several inches.
When the voltage across RSENSE exceeds 110mV, the
LT1158 fault pin begins to conduct, signaling a fault
condition. The current in a short circuit ramps very rapidly,
limited only by the series inductance and ultimately the
MOSFET and shunt resistance. Due to the response time
of the LT1158 current limit loop, an initial current spike of
T GATE DR
T GATE FB
V+
+
100k
VP0300
V+
2N2222
V+
100k
T GATE DR
T GATE FB
RGS
T SOURCE
CMOS
ON/OFF
+
LT1158
TO OTHER
CONTROL
CIRCUITS
GND
B GATE DR
5V
10k
T SOURCE
LT1158 SENSE+
FAULT
SENSE–
RSENSE
LOAD
1158 F06
Figure 6. Short-Circuit Protection with Standard MOSFET
B GATE FB
1158 F05
V+
Figure 5. Adding Zero Current Shutdown
+
T GATE DR
Short-Circuit Protection in Bridge Applications
The LT1158 protects the top power MOSFET from output
shorts to ground, or in a full bridge application, shorts
across the load. Both standard 3-lead MOSFETs and
current-sensing 5-lead MOSFETs can be protected. The
bottom MOSFET is not protected from shorts to supply.
5V
10k
T GATE FB
SENSE
T SOURCE
LT1158 SENSE+ RSENSE
FAULT
SENSE–
KELVIN
OUTPUT
Current is sensed by measuring the voltage across a
current shunt in the source lead of a standard 3-lead
MOSFET (Figure 6). For the current-sensing MOSFET
1158 F07
Figure 7. Short-Circuit Protection with Current-Sensing MOSFET
12
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