Datasheet

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
SLUS542F − OCTOBER 2003 − REVISED JULY 2009
22
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APPLICATION INFORMATION: SETUP GUIDE
In the UCC289x controllers, slope compensation is implemented by sourcing a linearly increasing current at the
CS pin. When this current passes through the current sense filter resistor (R
F
), it is converted to a slope
compensation ramp which can be characterized by its
ǒ
dV
S
ńdt
Ǔ
. The
ǒ
dV
S
ńdt
Ǔ
of the slope compensation
current is defined by R
SLOPE
according to:
dI
S
dt
+
5 2V
t
ON
R
SLOPE
where
D 2V is the peak−to−peak ramp amplitude of the internal oscillator waveform
D 5 is the multiplication factor of the internal current mirror
The voltage equivalent of the compensation ramp
ǒ
dV
S
ńdt
Ǔ
can be easily obtained by multiplying with R
F
. After
introducing the application specific m and
ǒ
dV
L
ńdt
Ǔ
values, the equation can be rearranged for R
SLOPE
:
R
SLOPE
+
5 2V R
F
t
ON
m
ǒ
dV
L
dt
Ǔ
(25)
(26)