PRINCIPLES OF OPERATION

The SG2524/3524 is a fixed frequency pulse-

with-modulation voltage regulator control circuit.

The regulator operates at a frequency that is pro-

tor providing linear control of the output pulse

width by the error amplifier. the SG2524/3524

contains, an on-board 5V regulator that serves as

a

reference

as

well

as

powering

the

SG2524/3524’s internal control circuitry and is

also useful in supplying external support functions.

This reference voltage is lowered externally by a

resistor divider to provide a reference within the

common mode range the error amplifier or an ex-

ternal reference may be used. The power supply

output is sensed by a second resistor divider net-

work to generale a feedback signal to error ampli-

fier. The amplifier output voltage is then com-

resulting modulated pulse out of the high-gain

comparator is then steered to the appropriate out-

steering flip-flop, which is synchronously toggled

by the oscillator output. The oscillator output

pulse also serves as a blanking pulse to assure

both output are never on simultaneously during

the transition times. The width of the blanking

may be applied in a push-pull configuration in

which their frequency is half that of the base oscil-

lator, or paralleled for single-ended applications in

which the frequency is equal to that of the oscilla-

tor. The output of the error amplifier shares a

common input to the comparator with the current

limiting at shutdown circuitry and can be overrid-

den by signals from either of these inputs. This

common point is also available externally and

may be employed to control the gain of, or to

compensate, the error amplifier, or to provide ad-

ditional control to the regulator.

RECOMMENDED OPERATING CONDITIONS

8 to 40V

Reference Output Current

0 to 20mA

- 0.03 to -2mA

1.8 to 100K

Ω

0.001 to 0.1

µF

TYPICAL APPLICATIONS DATA

OSCILLATOR

The oscillator controls the frequency of the

cording to the approximate formula:

f

where:

Ω

µF

f is in KHz

0.1

100K

Ω. This results in a frequency range typically

from 120Hz to to 500KHz.

BLANKING

The output pulse of oscillator is used as a blank-

ing pulse at the output. This pulse width is con-

required for frequency control, the oscillator out-

put pulse width may still be increased by applying

a shunt capacitance of up to 100pF from pin 3 to

ground. If still greater dead-time is required, it

should be accomplished by limiting the maximum

duty cycle by clamping the output of the error am-

plifier. This can easily be done with the circuit be-

low:

SYNCRONOUS OPERATION

When an external clock is desired, a clock pulse

of approximately 3V can be applied directly to the

oscillator output terminal. The impedance to

ground at this point is approximately 2K

Ω. In this

period slightly greater than that the external clock.

If two more SG2524 regulators are to be operated

synchronously, all

oscillator output terminals

nected to a single timing capacitor, and timing re-

Figure 6.

SG2524 - SG3524

5/9