E
7/96
TOP100-4
5
PI-1119-110194
VIN
VOUT
0
IOUT
0
1
2
1
4
3
DRAIN
0
VIN
VC
0
1
2
1
2
8
1
0
IC
1
2
8
8
1
2
8
1
VC(reset)
45 mA
Shutdown/Auto-restart
To minimize
TOPSwitch
power
dissipation, the shutdown/auto-restart
circuit turns the power supply on and off
at a duty cycle of typically 5% if an out
of regulation condition persists. Loss of
regulation interrupts the external current
into the CONTROL pin. V
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, V
regulation returns
to shunt mode, and normal operation of
the power supply resumes.
Latching Shutdown
The output overvoltage protection latch
is activated by a high-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.
V
is regulated in hysteretic mode when
the power supply is latched off.
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 145
°
C).
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.
V
is regulated in hysteretic mode when
the power supply is latched off.
High-voltage Bias Current Source
This current source biases
TOPSwitch
from the DRAIN pin and charges the
CONTROL pin external capacitance
(C
) 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 (I
C
) and discharge currents
(I
and I
). This current source is
turned off during normal operation when
the output MOSFET is switching.
Figure 6. Typical Waveforms for (1) Normal Operation, (2) Auto-restart, (3) Latching Shutdown, and (4) Power Down Reset.