SNVS856B – JUNE 2012 – REVISED MAY 2013
OUTPUT SHORT CIRCUIT PROTECTION
If the LED string is shorted, the voltage of AUX wiring (V
ZCD-PEAK
) will decrease, and as V
ZCD-PEAK
voltage
decrease below V
ZCD-TRIG
, the TPS92314/14A will enter low switching frequency operation. During low switching
frequency operation, power supplied from L
AUX
to V
CC
is not enough to maintain V
CC
. If the short remains V
CC
will
drop below the falling threshold of V
CC-UVLO
, the TPS92314/14A will attempt to restart at this time (Figure
When the short is removed the TPS92314/14A will restore to steady state operation.
Steady
state
Low freq
state
Low freq
state
V
SW
t
V
CC
26V
13V
t
V
ZCD
V
ZCD-OVP
V
ZCD-ARM
t
V
LED
t
Figure 18. Output Short Circuit waveforms
OVER CURRENT PROTECTION
Over Current Protection (OCP) limits the drain current of MOSFET and prevents inductor / transformer
saturation. When V
ISNS
reaches a threshold, OCP function will be triggered, controller gate drive will pull low and
OFF time will extends to 233μs, also C
COMP
capacitor will be discharged by internal switch and gate drive ON
time will force to minimum in next cycle.
THERMAL PROTECTION
Thermal protection is implemented by an internal thermal shutdown circuit, which activates at 165°C (typically).
In this case, the switching power MOSFET will turn off. Capacitor C
VCC
will discharge until UVLO. If the junction
temperature of the TPS92314/14A falls back below 145°C, the TPS92314/14A resumes normal operation.
12
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