Datasheet
SLUS542F − OCTOBER 2003 − REVISED JULY 2009
18
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FUNCTIONAL DESCRIPTION
When a wider than
ǒ
1 * D
MAX
Ǔ
T
SYNC
pulse is connected to the SYNC input, the oscillator is not able to
maintain the maximum duty cycle, originally set by the timing resistor ratio (R
ON
, R
OFF
). Furthermore, the timing
capacitor waveform has a flat portion as highlighted by the vertical marker in the timing diagram. During this
flat portion of the waveform both outputs is off which state is not compatible with the operation of active clamp
power converters. Therefore, this operating mode is not recommended .
Note that both outputs of the UCC289x controllers are off if the synchronization signal stays continuously high.
APPLICATION INFORMATION: SETUP GUIDE
1
2
3
4
16
15
14
13
VIN
LINEUV
VDD
OUT
RDEL
RTON
RTOFF
VREF
UCC2891
UCC2893
5
6
7
8
SYNC
GND
CS
RSLOPE
12
11
10
9
AUX
PGND
SS/SD
FB
POWER STAGE
1
2
3
4
16
15
14
13
LINEOV
LINEUV
VDD
OUT
RDEL
RTON
RTOFF
VREF
UCC2892
UCC2894
5
6
7
8
SYNC
GND
CS
RSLOPE
12
11
10
9
AUX
PGND
SS/SD
FB
POWER STAGE
R
IN2
R
DEL
R
ON
R
OFF
C
VREF
C
F
R
SLOPE
C
SS
R
F
R
VREF
C
BIAS
C
HF
Isolated Feedback
R
IN1
+V
IN
−V
IN
+V
IN
−V
IN
Isolated Feedback
R
IN4
R
DEL
R
ON
R
OFF
C
VREF
C
F
R
SLOPE
C
SS
R
F
R
VREF
C
BIAS
C
HF
R
IN2
R
IN1
R
IN3
R
OT
R
OT
Figure 7. UCC289x Typical Setup