TOP412/414
V
IN
V
IN
0
DRAIN
V
OUT
0
0
I
OUT
1
1
2
2
8
8
1
1
2
2
8
8
1
1
• • •
• • •
• • •
• • •
V
C(reset)
V
C
0
0
45 mA
I
C
3
4
1
1
2
PI-1119-110194
Figure 6. Typical Waveforms for (1) Normal Operation, (2) Auto-restart, (3) Latching Shutdown, and (4) Power Down Reset.
CONTROL pin. VC regulation changes from shunt mode to
the hysteretic auto-restart mode described above. When the
fault condition is removed, the power supply output becomes
regulated, VC regulation returns to shunt mode, and normal
operation of the power supply resumes.
temperature exceeds the thermal shutdown temperature
(typically 145 °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 when the power
supply is latched off.
Latching Shutdown
Theoutputovervoltageprotectionlatchisactivatedbyahigh-
current pulse into the CONTROL pin. When set, the latch
turns off the TOPSwitch output. 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 when the power supply is latched off.
High-voltage Bias Current Source
ThiscurrentsourcebiasesTOPSwitch fromtheDRAINpinand
charges the CONTROL pin external capacitance (CT) during
start-up or hysteretic operation. Hysteretic operation occurs
during auto-restart and 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.
Over-Temperature Protection
Temperature protection is provided by a precision analog
circuit that turns the output MOSFET off when the junction
A
4/99
5
POWERINT [ Power Integrations ]
