Datasheet

UCC25705, UCC25706, UCC35705, UCC35706
HIGH-SPEED VOLTAGE MODE PULSE WIDTH MODULATOR
SLUS473B -- NOVEMBER 1999 -- REVISED OCTOBER 2010
6
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FUNCTIONAL DESCRIPTION
45
RC DISCH
3
VFF
R
FF
2*I
DISCH
R
DISCH
R
T
C
T
V
IN
30 * I
DISCH
VDD
I
DISCH
Figure 2. Duty Cycle Clamp (MODE = 1)
The on-time is approximately:
T
ON
=∝ × R
T
× C
T
where ∝=
V
FF
V
IN
≈
2 × R
FF
R
DISCH
Theoff-timeis:
T
OFF
=∝ ×
C
T
×

R
T
× R
DISCH


30 × R
T
− R
DISCH

The frequency is:
f =

1
∝×R
T
× C
T

×
1
1 +
R
DISCH

30×R
T
−R
DISCH

The maximum duty cycle is:
Duty Cycle =
T
ON
T
ON
+ T
OFF
=

1 −
R
DISCH
30 × R
T
