TOP232 datasheet(8/38 Pages) POWERINT

8 / 38 page

Rev. D 10/20

TOP232-234

www.power.com

alternate charge and discharge cycles between 4.8 V and

5.8 V (see CONTROL pin operation section above) and runs

entirely off the high-voltage DC input, but with very low power

consumption (160 mW typical at 230 VAC with M pin open).

When the TOPSwitch-FX is remotely turned on after entering

this mode, it will initiate a normal start-up sequence with

soft-start the next time the CONTROL pin reaches 5.8 V. In the

worst case, the delay from remote on to start-up can be equal

to the full discharge/charge cycle time of the CONTROL pin,

which is approximately 125 ms for a 47 µF CONTROL pin

capacitor. This reduced consumption remote off mode can

eliminate expensive and unreliable in-line mechanical switches.

It also allows for microprocessor controlled turn-on and

turn-off sequences that may be required in certain applications

such as inkjet and laser printers. See Figure 27 under

application examples for more information.

Soft-Start

An on-chip soft-start function is activated at start-up with a

duration of 10 ms (typical). Maximum duty cycle starts from

zero and linearly increases to the default maximum of 78% at

the end of the 10 ms duration. In addition to start-up, soft-

start is also activated at each restart attempt during auto-

restart and when restarting after being in hysteretic regulation

of CONTROL pin voltage (V

C), due to remote off or thermal

shutdown conditions. This effectively minimizes current and

voltage stresses on the output MOSFET, 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

To minimize TOPSwitch-FX power dissipation under fault

conditions, the shutdown/auto-restart circuit turns the power

supply on and off at an auto-restart duty cycle of typically 4%

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.

Hysteretic 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

(135 ˚C typical). When the junction temperature cools to below

the hysteretic temperature, normal operation resumes. A large

hysteresis of 70 ˚C (typical) is provided to prevent overheating

of the PC board due to a repeating fault condition. V

C is

regulated in hysteretic mode and a 4.8 V to 5.8 V (typical)

sawtooth waveform is present on the CONTROL pin when the

power supply is turned off.

Bandgap Reference

All critical TOPSwitch-FX internal voltages are derived from a

temperature-compensated bandgap reference. This reference

is also used to generate a temperature-compensated current

reference which is trimmed to accurately set the switching

frequency, MOSFET gate drive current, current limit, and the

line OV/UV thresholds. TOPSwitch-FX has improved circuitry

to maintain all of the above critical parameters within very tight

absolute and temperature tolerances.

High-Voltage Bias Current Source

This current source biases TOPSwitch-FX 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 approximately 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.

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