TOP221-227
V
IN
V
IN
0
DRAIN
V
OUT
0
0
I
OUT
• • •
• • •
V
V
C
C(reset)
0
0
• • •
• • •
I
C
Figure 6. Typical Waveforms for (1) Normal Operation, (2) Auto-restart, and (3) Power Down Reset.
The leading edge blanking circuit inhibits the current limit
comparator for a short time after the output MOSFET is
turned on. The leading edge blanking time has been set so
that current spikes caused by primary-side capacitances
and secondary-side rectifier reverse recovery time will not
cause premature termination of the switching pulse.
Overtemperature Protection
Temperature protection is provided by a precision analog
circuit that turns the output MOSFET off when the junction
temperature exceeds the thermal shutdown temperature
(typically 135 °C). Activating the power-up reset circuit by
removing and restoring input power or momentarily pulling
the CONTROL pin below the power-up reset threshold resets
the latch and allows TOPSwitch to resume normal power
supply operation. VC is regulated in hysteretic mode and a
4.7 V to 5.7 V (typical) sawtooth waveform is present on the
CONTROL pin when the power supply is latched off.
The current limit can be lower for a short period after the
leading edge blanking time as shown in Figure 12. This is
due to dynamic characteristics of the MOSFET. To avoid trig-
gering the current limit in normal operation, the drain current
waveform should stay within the envelope shown.
High-Voltage Bias Current Source
This current source biases TOPSwitch from the DRAIN pin
and charges the CONTROL pin external capacitance (CT)
during start-up or hysteretic operation. Hysteretic opera-
tion occurs during auto-restart and overtemperature latched
shutdown. The current source is switched on and off with an
effective duty cycle of approximately 35%. This duty cycle
is determined by the ratio of CONTROL pin charge (IC) and
discharge currents (ICD1 and ICD2). This current source is
turned off during normal operation when the output MOSFET
is switching.
Shutdown/Auto-restart
To minimize TOPSwitch power dissipation, the shutdown/
auto-restart circuit turns the power supply on and off at an
auto-restart duty cycle of typically 5% if an out of regulation
condition persists. Loss of regulation interrupts the external
current into the CONTROL pin. VC regulation changes from
shunt mode to the hysteretic auto-restart mode described
above. When the fault condition is removed, the power sup-
ply output becomes regulated, VC regulation returns to shunt
mode, and normal operation of the power supply resumes.
5
Rev. G 08/16
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