KSI-K003-000

5

S494

INFORMATION

The basic oscillator(switching)frequency is controlled by an external resistor (Rt) and

capacitor(Ct). The relationship between the values of Rt Ct and frequency is shown in.

The level of the sawtooth wave form is compared with an error voltage by the pulse width

modulated comparator. The output of the PWM Comparator directs the pulse steering flip

flop and the output control logic.

The error voltage is generated by the error amplifier. The error amplifier boosts the voltage

difference between the output and the 5V internal reference. See Figure7 for error amp

sensing techniques. The second error amp is typically used to implement current limiting.

The output control logic (Pin13) selects either push-pull or single-ended operation of the

output transistors (see Figure6). The dead time control prevents on-state overlap of the

output transistors as can be seen is Figure5. The dead time is approximately 3 to 5% of the

total period if the dead time control(pin4) is grounded. This dead time can be increased by

connecting the dead time control to a voltage up to 5 V. The frequency response of the

error amps can be modified by using external resistors and capacitors. These components

are typically connected between the compensation terminal (pin3) and the inverting input

of the error amps(pin2 or pin15). The switching frequency of two or more S494 circuits can

be synchronized. The timing capacitor, Ct is connected as shown in Figure8. Charging

current is provided by the master circuit. Discharging is through all the circuits slaved to

the master. Rt is required only for the master circuit.

Operating Waveform