Datasheet

C
HF
10 m: x 514 µF x 22 nF
27.4k: x 22 nF - 10 m: x 514 µF
=
= 189 pF
C
HF
R
ESR
x C
OUT
x C
COMP
R
COMP
x C
COMP
- R
ESR
x C
OUT
=
[F]
LOAD OUT
COMP
COMP
12 V
514 F
9 A
R C
C 25nF
R 27.4 k
æ ö
´ m
ç ÷
´
è ø
= = =
W
R
COMP
= 2Sx 7.41 m: x 10 x 514 µF x 4.99 k: x 23 kHz = 27.5 k:
R
COMP
= 2Sx R
S
x A
S
x C
OUT
x R
FB2
x f
CROSS
[:@
10
f
CROSS
=
= 23 kHz
f
SW
LM5117, LM5117-Q1
SNVS698E –APRIL 2011–REVISED MARCH 2013 www.ti.com
LOOP COMPENSATION COMPONENTS C
COMP
, R
COMP
and C
HF
R
COMP
, C
COMP
and C
HF
configure the error amplifier gain and phase characteristics to produce a stable voltage
loop. For a quick start, follow the 4 steps listed below. For detailed information, see Application Information
section.
STEP1: Select f
CROSS
By selecting one tenth of the switching frequency, f
CROSS
is calculated as follows:
(45)
STEP2: Determine required R
COMP
Knowing f
CROSS
, R
COMP
is calculated as follows:
(46)
(47)
The standard value of 27.4kΩ was selected for R
COMP
STEP3: Determine C
COMP
to cancel load pole
Knowing R
COMP
, C
COMP
is calculated as follows:
(48)
The standard value of 22nF was selected for C
COMP
STEP4: Determine C
HF
to cancel ESR zero
Knowing R
COMP
and C
COMP
, C
HF
is calculated as follows:
(49)
(50)
Half of the maximum ESR is assumed as a typical ESR. The standard value of 180pF was selected for C
HF
.
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