A

8/97

TOP209/210

5

PI-1742-011796

VIN

VOUT

0

IOUT

0

1

2

1

DRAIN

0

VIN

VC

0

•••

•••

12

12

81

0

IC

•••

•••

12

8

81

2

8

1

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

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.

Hysteretic 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). When the junction temperature cools past

the hysteresis temperature, normal operation resumes. V

regulated in hysteretic mode while the power supply is turned

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. 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

source is turned off during normal operation when the output

MOSFET is switching.

Figure 6. Typical Waveforms for (1) Normal Operation, (2) Auto-restart.