Oscillator

11

12

13

6

CLKSYNC

ION

IOFF

VOUT

10

CT

+

–

3.5V

3V

V

REF

14

8.8X

SYNCEN

3.5V

1.5V

S

Q

Q

R

SYNCEN

3.0V

+

–

CLK

V

REF

1.5V

UCC2884

UCC3884

The oscillator has charge and discharge currents programmed with resistors to ground from ION and IOFF

respectively, as seen on the Oscillator Block Diagram.(Figure 1). This generates a linear sawtooth waveform on

CT. Frequency foldback is accomplished by the level shifted output voltage controlling the VOUT voltage which

decreases the discharge current and the frequency.

Synchronization is accomplished by coupling the fastest oscillator CLKSYNC signal as shown on the Oscillator

Synchronization Diagram (Figure 2). The fastest (master) CLKSYNC pin couples a negative pulse into the slower

(slave) CLKSYNC pins forcing the slaves’ CT pins to quickly discharge as shown on the Oscillator Waveform

diagram (Figure 3).

Figure 1. UCC3884 Oscillator

Copyright © 1999–2008, Texas Instruments Incorporated

Submit Documentation Feedback

9

Product Folder Link(s): UCC2884 UCC3884