SG2524, SG3524

REGULATING PULSEWIDTH MODULATORS

SLVS077D – APRIL 1977 – REVISED FEBRUARY 2003

7

POST OFFICE BOX 655303

The SG2524 is a fixed-frequency pulse-width-modulation (PWM) voltage-regulator control circuit. The regulator

comparator, providing linear control of the output pulse duration (width) by the error amplifier. The SG2524 contains

an onboard 5-V regulator that serves as a reference, as well as supplying the SG2524 internal regulator control

circuitry. The internal reference voltage is divided externally by a resistor ladder network to provide a reference within

the common-mode range of the error amplifier as shown in Figure 6, or an external reference can be used. The output

is sensed by a second resistor divider network and the error signal is amplified. This voltage is then compared to the

appropriate output pass transistor (Q1 or Q2) by the pulse-steering flip-flop, which is synchronously toggled by the

oscillator output. The oscillator output pulse also serves as a blanking pulse to ensure both outputs are never on

outputs may be applied in a push-pull configuration in which their frequency is one-half that of the base oscillator, or

paralleled for single-ended applications in which the frequency is equal to that of the oscillator. The output of the error

amplifier shares a common input to the comparator with the current-limiting and shut-down circuitry and can be

overridden by signals from either of these inputs. This common point is pinned out externally via the COMP pin, which

can be employed to either control the gain of the error amplifier or to compensate it. In addition, the COMP pin can

be used to provide additional control to the regulator.

oscillator

f

[ 1.30

R

T

C

T

f is in kHz

This results in a frequency range typically from 130 Hz to 722 kHz.

blanking

The output pulse of the oscillator is used as a blanking pulse at the output. This pulse duration is controlled by

be maintained by applying a shunt capacitance from OSC OUT to ground.

synchronous operation

When an external clock is desired, a clock pulse of approximately 3 V can be applied directly to the oscillator

output terminal. The impedance to ground at this point is approximately 2 k

be selected for a clock period slightly greater than that of the external clock.

† Throughout these discussions, references to the SG2524 apply also to the SG3524.