UCC28180
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SLUSBQ5A –NOVEMBER 2013–REVISED NOVEMBER 2013
Over-Current Protection
Inductor current is sensed by RISENSE, a low value resistor in the return path of input rectifier. The other side of
the resistor is tied to the system ground. The voltage is sensed on the rectifier side of the sense resistor and is
always negative. The voltage at ISENSE is buffered by a fixed gain of -2.5 to provide a positive internal signal to
the current functions. There are two over-current protection features; Soft Over-Current (SOC) protects against
an overload on the output and Peak Current Limit (PCL) protects against inductor saturation.
Soft Over Current (SOC)
0.72V
SOC
ISENSE Open-Pin
Protection (ISOP)
+
LINE
INPUT
–
+
IISOP
2µA
VOUT
VISOP
0.082V
ISOP
RISENSE
+
ISENSE
CISENSEfilter
RISENSEfilter
300ns
Leading Edge
Blanking
(Optional)
PCL
1V
+
+
-2.5x
Peak Current Limit (PCL)
Figure 27. Soft Over-Current/Peak-Current Limit
Soft Over-Current (SOC)
Soft Over-Current (SOC) limits the input current. SOC is activated when the current sense voltage on ISENSE
reaches -0.285 V. This is a soft control as it does not directly switch off the gate driver. Instead a 4-kΩ resistor
connects VCOMP to ground to discharges VCOMP and the control loop is adjusted to reduce the PWM duty
cycle. The under-voltage detection (UVD) is disabled during SOC.
Peak Current Limit (PCL)
Peak Current Limit (PCL) operates on a cycle-by-cycle basis. When the current sense voltage on ISENSE
reaches –0.4 V, PCL is activated, immediately terminating the active switch cycle. PCL is leading-edge blanked
to improve noise immunity against false triggering.
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