TK75003 Ver la hoja de datos (PDF) - Toko America Inc

Número de pieza

componentes Descripción

Fabricante

TK75003

PWM CONTROLLER

Toko America Inc  

TK75003

PIN DESCRIPTIONS

SUPPLY VOLTAGE PIN (VCC)

This pin is connected to the supply voltage. The IC is in a

low-current (500 µA typ.) standby mode before the supply

voltage exceeds 14.5 V (typ.), which is the upper threshold

of the UVLO circuit. The IC switches back to standby mode

when the supply voltage drops below 10.5 V (typ.). An

internal clamp limits the peak supply voltage to about 17.5

V (typ.). The absolute maximum supply voltage from a low

impedance source is 16 V. The device is always guaranteed

to turn on before the internal clamp turns on.

GNOUND PIN (GND)

This pin provides ground return for the IC.

DRIVE PIN (DRV)

This pin drives the external MOSFET with a totem pole

output stage capable of sinking or sourcing a peak current

of about 1 A. In standby mode, the drive pin can sink about

5 mA while keeping the drive pin pulled down to about 1 V.

The maximum duty cycle of the output signal is typically

88 %.

TIMING CAPACITOR PIN (CT)

The external timing capacitor is connected to the CT pin.

That capacitor is the only component needed for setting

the clock frequency. The frequency measured at the CT pin

is the same frequency as measured at the DRV pin. The

maximum recommended clock frequency of the device is

1.6 MHz. At normal operation, during the rising section of

the timing-capacitor voltage, a trimmed internal current of

205 µA flows out from the CT pin and charges the capacitor.

During the falling section of the timing-capacitor voltage an

internal current of about 1.8 mA discharges the capacitor.

If the voltage at the feedback pin(FB) exceeds 1.35 V (e.g.,

due to the turn-off delay during a short-circuit at the output

of a converter using the IC), the charging current is

reduced to about 59 µA, leading to a 3.2-fold reduction in

switching frequency. The frequency reduction is useful for

preventing short-circuit current runaway.

FB (FEEDBACK) PIN

The feedback pin receives the sum of three signals: the

error signal (from the external error amplifier), the switch

current signal and a voltage ramp generated across the

terminating resistance by an internal sawtooth-shaped

current with a peak value of about 200 µA. The error signal

is needed for stabilizing the output voltage or current. The

switch current signal is needed in current-mode controlled

converters and in converters with cycle-by-cycle overload

protection. Also, the switch current signal is required for

detecting impending short-circuit current runaway, and for

initiating a frequency reduction for preventing the runaway.

The voltage ramp is needed for slope compensation

(necessary for avoiding subharmonic instability in constant-

frequency peak-current controlled current- mode converters

above 50% duty ratio), or for pulse-width modulation in

voltage-mode controlled converters.

At higher clock frequencies, the bandwidth limitation of the

internally-generated sawtooth-shaped current source

becomes more apparent. The degree to which ramp

bandwidth is tolerable depends on performance

requirements at narrow pulse widths. A low impedance at

the feedback pin can effectively eliminate the internally-

generated ramp effects, and an external ramp can be

readily created to attain higher performance at high

frequencies, if desired.

January 1999 TOKO, Inc.

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