Datasheet

2
8
5
+
+
+
S Q
QR
Latched
Fault
150 mV
VDD
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-HT
www.ti.com SGLS400C –OCTOBER 2009–REVISED DECEMBER 2012
Current-Limit Resistor Selection
As shown in Figure 29, 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 theISNS pin, an overcurrent condition is declared.
When this happens, the FET is turned off and, as shown in Figure 30, 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 29), another overcurrent condition is declared and the process repeats indefinitely.
Figure 29 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 27. Typical Soft-Start Capacitor and V
OUT
During Overcurrent
Figure 28. Current-Limit Reset
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