Datasheet

+
2
150 mV
S Q
QR
+
8
5
V
SS
UDG-10077
TPS40200
Reset Fault
+
100 mV
7
VDD
ISNS
Fault
SS
Latched
Fault
GND
Enable
Error Amplifier
300 kW
100 kW
+
SS Reference
Error Amplifier
300 mV
+
TPS40200
SLUS659F –FEBRUARY 2006–REVISED MARCH 2012 www.ti.com
Current Limit Resistor Selection
As shown in Figure 27, a resistor in series with the power MOSFET sets the overcurrent protection level. Use a
low-inductance resistor to avoid ringing signals and nuisance tripping. When the FET is on and the controller
senses 100mV 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 25, 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 26), another overcurrent condition is declared and the process repeats indefinitely. Figure 26 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 25. Current Limit Reset
Figure 26. Typical Soft-Start Capacitor and V
OUT
During Overcurrent
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