Datasheet
COMP
OL
COMP_POLE
1 gmea
C = -
A
2 × × BW
2 × × ×
gmea
p
p f
Acomp
20
PRI
COMP_POLE CO
REF
OL
V
= ×
10 × A × V
f f
( )
PRI
LM
OPN CO
COMP
i
POLE
V
R +
I x 1 - D 2 × ×
A = 20 × log - 20 × log
R 2 × ×
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f
f
POLE POLE
CO
w w
< f < 20 ×
2 × 2 ×p p
( )
2
POLE
OPOS ONEG SEC1 SEC2
PRI
PRI
PRI
OPN OPOS ONEG
1
=
C x C N + N
V
1
2 × × × × 1 - D × × + C
I (1 D) C + C N
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2
x
PRI PRI
LM
OPN SEC
PRI
C
i
POLE
V N
R + ×
I (1 - D) N
ˆ
V
ˆ
V
s
R × 1 +
2 × x
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TPS55010
SLVSAV0A –APRIL 2011–REVISED JUNE 2011
www.ti.com
capacitor ripple voltage is < 1%. Type 2 or 3 compensation should be considered if a low primary ripple design is
preferred. To get started, the modulator pole frequency, f
POLE
, determined from Equation 61 should be used to
select the crossover frequency, f
CO
. In this example, 0.4 kHz is selected as the crossover frequency. The next
step is to determine the compensation gain, A
COMP
, at the crossover frequency to compensate the loop.
Equation 64 uses the dc gain of the power stage, modulator pole, and crossover frequency to estimate the gain.
R
i
is the current sense gain which is the inverse of the C
COMP
to I
PH
transconductance, which is 7.5 A/V. 11.58
dB is calculated for A
COMP
. The compensation pole frequency f
COMP_POLE
can be calculated using Equation 65.
A
OL
in Equation 65 is the open loop gain of the error amplifier and is 500 V/V. f
COMP_POLE
is calculated as 0.49
Hz. Using Equation 66, C
COMP
is calculated to be 0.159 µF. A 0.1 µF capacitor will be used for C
COMP
.
(61)
Spacer
(62)
Spacer
(63)
Spacer
(64)
Spacer
(65)
Spacer
(66)
CHARACTERISTICS
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