Datasheet

2
8
5
+
+
+
S Q
QR
Latched
Fault
150mV
V
IN
SS
GND
+
Fault
TPS40200
100mV
Reset
Fault
7
ISNS
Enable
EAMP
+
300mV
EAMP
SSRef
V
S-S
100kW
300
kW
TPS40200-EP
SGLS371A –JANUARY 2007–REVISED JANUARY 2013 www.ti.com
Current-Limit Resistor Selection
As shown in Figure 28, a resistor in series with the power MOSFET sets the overcurrent protection level. Use a
low-inductance resistor to avoid problems with ringing signals and nuisance tripping. When the FET is on and the
controller senses 100 mV or more drop from the VDD pin to the ISNS pin, an overcurrent condition is declared.
When this happens, the FET is turned off and, as shown in Figure 29, the soft-start capacitor is discharged.
When the soft-start capacitor reaches a level below 150 mV, the converter clears the overcurrent condition flag
and attempts to restart. If the condition that caused the overcurrent event to occur is still present on the output of
the converter (see Figure 28), another overcurrent condition is declared and the process repeats indefinitely.
Figure 28 shows the soft-start capacitor voltage during an extended output fault condition. The overall duty cycle
of current conduction during a persistent fault is approximately 2%.
Figure 26. Typical Soft-Start Capacitor and V
OUT
During Overcurrent
Figure 27. Current-Limit Reset
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