LT1158
APPLICATIONS INFORMATION
Low Current Shutdown
(Figure 6). For the current-sensing MOSFET shown in
Figure 7, the sense resistor is inserted between the sense
and Kelvin leads.
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
bottomMOSFETsareactivelyheldoffagainstanytransients
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.
+
–
TheSENSE andSENSE PCtracesmustberoutedtogether
at minimum spacing to prevent stray pickup, and a Kelvin
connectionmustbeusedatthecurrentshuntforthe3-lead
MOSFET. Using a twisted pair is the safest approach and
is recommended for sense runs of several inches.
If zero standby current is required and the load returns to
ground, then a switch can be inserted into the supply path
When the voltage across R
exceeds 110mV, the
SENSE
LT1158 FAULT pin begins to conduct, signaling a fault
condition.Thecurrentinashortcircuitrampsveryrapidly,
limited only by the series inductance and ultimately the
MOSFET and shunt resistance. Due to the response time
of the LT1158 as shown in Figure 5. Resistor R ensures
GS
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
+
V
300mV, andR mustbe330korgreaterforDCoperation.
GS
Thistechniqueisnotrecommendedforapplicationswhich
+
T GATE DR
require the LT1158 V sensing function.
DS
T GATE FB
+
V
T SOURCE
5V
+
LT1158
+
SENSE
SENSE
100k
R
T GATE DR
VP0300
10k
SENSE
–
FAULT
+
T GATE FB
V
2N2222
R
GS
+
V
100k
T SOURCE
1158 F06
LT1158
CMOS
ON/OFF
+
LOAD
TO OTHER
CONTROL
CIRCUITS
Figure 6. Short-Circuit Protection with Standard MOSFET
GND
B GATE DR
B GATE FB
+
V
1158 F05
+
T GATE DR
Figure 5. Adding Zero Current Shutdown
T GATE FB
KELVIN
SENSE
Short-Circuit Protection in Bridge Applications
T SOURCE
R
5V
SENSE
LT1158
+
SENSE
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 cur-
rent-sensing5-leadMOSFETscanbeprotected.Thebottom
MOSFET is not protected from shorts to supply.
OUTPUT
10k
–
SENSE
FAULT
1158 F07
Current is sensed by measuring the voltage across a cur-
rent shunt in the source lead of a standard 3-lead MOSFET
Figure 7. Short-Circuit Protection with Current-Sensing MOSFET
1158fb
13
LINEAR_DIMENSIONS [ Linear Dimensions ]
