LT1158CS datasheet(12/20 Pages) LINER

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LT1158

Figure 5. Adding Zero Current Shutdown

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.

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

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.

100k

V+

LT1158

VP0300

RGS

1158 F05

LOAD

GND

TO OTHER

CONTROL

CIRCUITS

CMOS

ON/OFF

100k

V+

T GATE DR

T GATE FB

T SOURCE

B GATE DR

B GATE FB

2N2222

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

Figure 7. Short-Circuit Protection with Current-Sensing MOSFET

T GATE DR

T GATE FB

T SOURCE

SENSE+

SENSE–

FAULT

LT1158

V+

1158 F07

10k

RSENSE

KELVIN

SENSE

OUTPUT

Figure 6. Short-Circuit Protection with Standard MOSFET

T GATE DR

T GATE FB

T SOURCE

SENSE+

SENSE–

FAULT

LT1158

RSENSE

V+

1158 F06

10k

APPLICATIONS INFORMATION

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