SG1731/SG2731/SG3731

4/90 Rev 1.3 9/99

Microelectronics

Inc.

Copyright

 1999

11861

Western

Avenue

∞

∞

∞

∞

∞

Garden

Grove,

CA

92841

3

(714) 898-8121

∞

∞

∞

∞

∞

FAX: (714) 893-2570

Test Conditions

Units

Min.

Typ. Max.

SHUTDOWN Section

Parameter

SG1731/2731/3731

HIGH Output Voltage

LOW Output Voltage

Driver Risetime

Driver Falltime

APPLICATION INFORMATION

SUPPLY VOLTAGE

The SG1731 requires a supply voltage for the control circuitry (V

and for the power output drivers (V

balanced positive and negative with respect to ground, or single-

ended. The only restrictions are:

1. The voltage between +V

no more than 44V.

2. The voltage between +V

no more than 44V.

3. +V

This

eliminates the combination of a single-ended positive control

supply with a single-ended negative driver supply.

SUBSTRATE CONNECTION

The substrate connection (Pin 10) must always be connected to

either -V

also be well bypassed to ground with a high quality capacitor.

OSCILLATOR

The triangle oscillator consists of two voltage comparators, a set/

reset flip-flop, a bi-directional 500

µA current source, and an

external timing capacitor C

+

)

applied to Pin 2 determines the positive peak value of the triangle,

and a negative reference voltage (2V

peak value of the triangle waveform.

Since the value of the internal current source is fixed at a nominal

±500

µA, the oscillator period is a function of the selected peak-

to-peak voltage excursion and the value of C

The theoretical

expression for the oscillator period is:

T

(Eq.1)

where C

peak-to-peak.

ERROR AMPLIFIER

The error amplifier of the SG1731 is a conventional internally-

compensated operational amplifier with low output impedance.

All of the usual feedback and frequency compensation

techniques may be use to control the closed-loop gain

characteristics. The control supply voltage ±V

input common mode range and output voltage swing; both will

extend to within 3V of the V

PULSE WIDTH MODULATION

Pulse width modulation occurs by comparing the triangle

waveform to a fixed upper (+V

and lower (-V

threshold

voltage.

A crossing above the upper threshold causes

Output A to switch to the HIGH state, and a crossing below

-V

V

V

Note 3. These parameters, although guaranteed, are not tested in production.

Note 4. Unity Gain Inverting 10K

Ω Feedback Resistance.

Note 5. V

2C

5 x 10

-4

As a design aid, the solutions to Equation 1 over the

recommended range of T

Figure 1. The lower limit on T

maximum frequency of 350 KHz. The maximum value of V

(2V

FIGURE 1 - SG1731 OSCILLATOR PERIOD VS. V

Logic Threshold

SHUTDOWN HIGH Current

SHUTDOWN LOW Current

V

400

-1.0

V

V

µA

mA

Output Drivers (Each Output)

I

I

I

I

C

C

V

V

V

V

ns

ns

19.2

19.0

-19.2

-19.0

300

300

14

6

mA

mA

Total Supply Current

V

V

V

V