TOP264VG datasheet(10/40 Pages) POWERINT

10 / 40 page

Rev. E 08/12

TOP264-271

www.powerint.com

the clamp circuit and the output rectifier during start-up. This

feature also helps minimize output overshoot and prevents

saturation of the transformer during start-up.

Shutdown/Auto-Restart (for OCP, SCP, OPP)

To minimize TOP264-271 power dissipation under fault

conditions such as over current (OC), short-circuit (SC) or over

power (OP), the shutdown/auto-restart circuit turns the power

supply on and off at an auto-restart duty cycle of typically 2% 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 as described in CONTROL pin operation section.

When the fault condition is removed, the power supply output

becomes regulated, V

C regulation returns to shunt mode, and

normal operation of the power supply resumes.

Hysteretic Over-Temperature Protection (OTP)

Temperature protection is provided by a precision analog circuit

that turns the output MOSFET off when the junction temperature

exceeds the thermal shutdown temperature (142 °C typical).

When the junction temperature cools to below the lower

hysteretic temperature point, normal operation resumes, thus

providing automatic recovery. A large hysteresis of 75 °C

(typical) is provided to prevent overheating of the PC board due

to a continuous fault condition. V

C is regulated in hysteretic

mode, and a 4.8 V to 5.8 V (typical) triangular waveform is

present on the CONTROL pin while in thermal shutdown.

Bandgap Reference

All critical TOP264-271 internal voltages are derived from a

temperature-compensated bandgap reference. This voltage

reference is used to generate all other internal current references,

which are trimmed to accurately set the switching frequency,

MOSFET gate drive current, current limit, and the line OV/UV/

OVP thresholds. TOP264-271 has improved circuitry to

maintain all of the above critical parameters within very tight

absolute and temperature tolerances.

High-Voltage Bias Current Source

This high-voltage current source biases TOP264-271 from the

DRAIN pin and charges the CONTROL pin external capacitance

during start-up or hysteretic operation. Hysteretic operation

occurs during auto-restart, remote-off and over-temperature

shutdown. In this mode of operation, the current source is

switched on and off, with an effective duty cycle of approxi-

mately 35%. This duty cycle is determined by the ratio of

CONTROL pin charge (I

C) and discharge currents (ICD1 and ICD2).

This current source is turned off during normal operation when

the output MOSFET is switching. The effect of the current

source switching will be seen on the DRAIN voltage waveform

as small disturbances and is normal.

TOP264VG Datasheet(PDF) 10 Page - Power Integrations, Inc.

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