A

4/99

TOP412/414

5

CONTROL pin. V

the hysteretic auto-restart mode described above. When the

fault condition is removed, the power supply output becomes

regulated, V

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

hysteretic mode when the power supply is latched off.

Over-Temperature 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

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

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

when the output MOSFET is switching.

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

Figure 6. Typical Waveforms for (1) Normal Operation, (2) Auto-restart, (3) Latching Shutdown, and (4) Power Down Reset.