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OUT

IN

GND

FAULT

ILIM

EN

Input

TPS2551

PowerPad

Output

10kW

STAT

ExternalLogic

EnableSignal

SN74HC00D

0.1 F

m

0.1 F

m

R

10k

FAULT

W

15kW

TWO-LEVEL CURRENT-LIMIT CIRCUIT

OUT

IN

GND

FAULT

ILIM

EN

ControlSignal

Input

TPS2550/51

FAULT Signal

PowerPad

Output

CurrentLimit

ControlSignal

0.1 F

m

R

100k

FAULT

W

R1

80.6kW

R2

20kW

Q1

2N7002

TPS2550

TPS2551

SLVS736 – FEBRUARY 2008

Figure 24. Overcurrent Latch-Off Using a Quad-NAND Gate

Some applications require different current-limit thresholds depending on external system conditions. Figure 25

shows an implementation for an externally controlled, two-level current-limit circuit. The current-limit threshold is

set by the total resistance from ILIM to GND (see previously discussed "Programming the Current-Limit

Threshold" section). A logic-level input enables/disables MOSFET Q1 and changes the current-limit threshold by

modifying the total resistance from ILIM to GND. Additional MOSFETs/resistor combinations can be used in

parallel to Q1/R2 to increase the number of additional current-limit levels.

NOTE:

ILIM should never be driven directly with an external signal.

Figure 25. Two-Level Current-Limit Circuit

22

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