F

7/ 09

TOP100-4

5

PI-1119-110194

VIN

VOUT

0

IOUT

0

1

2

1

4

3

DRAIN

0

VIN

VC

0

•••

•••

12

12

81

0

IC

•••

•••

12

8

81

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

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

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

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).

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

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

(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.