UCC28C40, UCC28C41, UCC28C42, UCC28C43, UCC28C44, UCC28C45

UCC38C40, UCC38C41, UCC38C42, UCC38C43, UCC38C44, UCC38C45

SLUS458E -- AUGUST 2001 -- REVISED OCTOBER 2010

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APPLICATION INFORMATION

oscillator synchronization

The UCC38C4x oscillator has the same synchronization characteristics as the original bipolar devices. Thus,

the information in the Application Note U--100A, UC3842/3/4/5 Provides Low-Cost Current-Mode Control, (TI

Literature No. SLUA143) still applies. The application note describes how a small resistor from the timing

capacitor-to-ground can offer an insertion point for synchronization to an external clock, (see Figures 2 and 3).

Figure 2 shows how the UCC38C42 can be synchronized to an external clock source. This allows precise

control of frequency and dead time with a digital pulse train.

UDG--01069

8

4

VREF

RT/CT

UCC38C42

PWM

RT

CT

24 Ω

SYNCHRONIZATION

CIRCUIT INPUT

Figure 2. Oscillator Synchronization Circuit

LOW

LOW

HIGH

CLOCK

INPUT

PWM

OUT

UPPER THRESHOLD

LOWER THRESHOLD

OUTPUT A

COMBINED

UPPER THRESHOLD

LOWER THRESHOLD

V

CT

V

V

UDG--01070

Figure 3. Synchronization to an External Clock