TK83854 データシートの表示（PDF） - Toko America Inc

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TK83854

HIGH POWER FACTOR PREREGULATOR

Toko America Inc  

TK83854

PIN DESCRIPTION (CONT.)

VOLTAGE AMPLIFIER INVERTING OUTPUT (VSENSE)

This is normally connected to a feedback network and to

the boost converter output through a divider network.

interaction between the gate impedance and the GTDRV

output driver that might cause the GTDRV output to

overshoot excessively. Some overshoot of the GTDRV

output is always expected when driving a capacitive load.

OSCILLATOR CHARGING CURRENT AND MULTIPLIER

LIMIT SET (RSET)

A resistor from RSET to ground will program oscillator

charging current and maximum multiplier output. Multiplier

output current will not exceed 3.75 V divided by the resistor

from RSET to ground.

SOFT-START (SS)

SS will remain at GND as long as the IC is disabled or VCC

is too low. SS will pull up to over 8 V by an internal 14 µA

current source when both VCC becomes valid and the IC is

enabled. SS will act as the reference input to the voltage

amplifier if SS is below Vref. With a large capacitor from SS

to GND, the reference to the voltage regulating amplifier

will rise slowly, and increase the PWM duty cycle slowly.

In the event of a disable command or a supply dropout, SS

will quickly discharge to ground and disable the PWM.

OSCILLATOR TIMING CAPACITOR (CT )

A capacitor from CT to GND will set the PWM oscillator

frequency according to this relationship:

fOSC = 1.25 / (RSET x CT)

POSITIVE SUPPLY VOLTAGE (VCC)

Connect VCC to a stable source of at least 20 mA above 17

V for normal operation. Also bypass VCC directly to GND to

absorb supply current spikes required to charge external

MOSFET gate capacitances. To prevent inadequate

GTDRV signals, these devices will be inhibited unless VCC

exceeds the upper undervoltage lockout threshold and

remains above the lower threshold.

GATE DRIVER (GTDRV)

The output of the PWM is a totem pole MOSFET gate

driver on GTDRV. This output is internally clamped to

15 V so the IC can be operated with VCC as high as 35 V.

Use a series gate resistor of at least 5 ohms to prevent

Page 8

January 1999 TOKO, Inc.

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