Datasheet

LM25037
RAMP
CLK + LEB
CLK
-+
Vin
C
filter
R
filter
R
CS
Current
Sense
V
REF
C
slope
R
slope
CS
Q1
Q2
C
FF
Vin
SLOPE
PROPORTIONAL
TO Vin
RAMP
COMP
Gate
Drive
1V
CLK
R
FF
V
IN
LM25037
R
FF
=
-1
F
OSC
x C
FF
x In
V
RAMP
1 -
VIN
min
LM25037, LM25037-Q1
www.ti.com SNVS572D –JULY 2008–REVISED MARCH 2013
(3)
For example, assuming a V
Ramp
of 1 volt at VIN
min
(a good compromise of signal range and noise immunity),
oscillator frequency, F
OSC
of 250 kHz, VIN
min
of 24 Volts, and C
FF
= 270 pF results in a value for R
FF
of 348 kΩ.
Figure 21. Feed-Forward Voltage Mode Configuration
CURRENT MODE CONTROL USING THE LM25037
The LM25037 can be configured in current mode control by applying the primary current signal into the RAMP
pin. One way to achieve this is shown in Figure 22, which depicts a simplified push-pull converter. The primary
current is sensed using a sense resistor and the current information is then filtered and applied to the RAMP pin
through capacitor C
slope
, for use as the modulation ramp. It can be seen that the signal applied to the RAMP pin
consists of the primary current information from the CS pin plus an additional ramp for slope compensation,
added by R
slope
and C
slope
.
Figure 22. Current Mode Configuration
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