Datasheet

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 s mall 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
V
REF
R
T
/C
T
UCC38C42
PWM
R
T
C
T
24
Ω
SYNCHRONIZATION
CIRCUIT INPUT
Figure 2. Oscillator Synchronization Circuit
ON .
LOW LOWHIGH
ON .OFF .
CLOCK
INPUT
PWM
OUT
UPPER THRESHOLD
LOWER THRESHOLD
OUTPUT A
COMBINED
UPPER THRESHOLD
LOWER THRESHOLD
V
CT
V
CT
(ANALOG)
V
SYNC
(DIGITAL)
UDG--01070
Figure 3. Synchronization to an External Clock