Datasheet

Data Sheet ADP1829
Rev. C | Page 21 of 28
Type II Compensator
G
(dB)
PHASE
–180°
–270°
f
Z
f
P
0V
VRAMP
C
HF
C
I
R
Z
R
TOP
R
BOT
FROM
V
OUT
VREF
EA
COMP
TO PWM
–
1
S
L
O
P
E
–
1
S
L
O
P
E
0
6784-027
Figure 28. Type II Compensation
If the output capacitor ESR zero frequency is sufficiently low (≤1/2
of the crossover frequency), use the ESR to stabilize the
regulator. In this case, use the circuit shown in Figure 28.
Calculate the compensation resistor, R
Z
, with the following
equation:
2
LC
IN
COESRRAMP
TOP
Z
fV
ffVR
R 
(31)
where:
f
CO
is chosen to be 1/10 of f
SW.
V
RAMP
is 1.3 V.
Next choose the compensation capacitor to set the
compensation zero, f
Z1
, to the lesser of 1/4 of the crossover
frequency or 1/2 of the LC resonant frequency:
I
Z
SWCO
Z
CR
ff
f


2
1
404
1
(32)
or
I
Z
LC
Z
CR
f
f


2
1
2
1
(33)
Solving for C
I
in Equation 32 yields
SW
Z
I
fR
C


20
(34)
Solving for C
I
in Equation 33 yields
LC
Z
I
fR
C


1
(35)
Use the larger value of C
I
from Equation 34 or Equation 35.
Because of the finite output current drive of the error amplifier,
C
I
needs to be less than 10 nF. If it is larger than 10 nF, choose a
larger R
TOP
and recalculate R
Z
and C
I
until C
I
is less than 10 nF.
Next choose the high frequency pole, f
P1
, to be 1/2 of f
SW
.
SW
P1
ff
2
1
 (36)
Because C
HF
<< C
I
, Equation 29 is simplified to
HF
Z
P1
CR
f


2
1
(37)
Solving for C
HF
in Equation 36 and Equation 37 yields
Z
SW
HF
Rf
C


1
(38)
Type III Compensator
0V
VRAMP
G
(dB)
PHASE
–270°
–90°
f
Z
f
P
C
HF
C
I
R
Z
C
FF
R
TOP
R
BOT
FROM
V
OUT
VREF
EA
COMP
TO PWM
R
FF
–
1
S
L
O
P
E
–
1
S
L
O
P
E
+
1
S
LO
P
E
0
6784-028
Figure 29. Type III Compensation
If the output capacitor ESR zero frequency is greater than 1/2 of
the crossover frequency, use Type III compensator as shown in
Figure 29. Set the poles and zeros as follows:
SW
P2P1
fff
2
1
 (39)
I
Z
SWCO
Z2Z1
CR
ff
ff


2
1
404
(40)
or
I
Z
LC
ZZ
CR
f
ff


2
1
2
21
(41)
Use the lower zero frequency from Equation 40 or Equation 41.
Calculate the compensator resistor, R
Z
.
2
LC
IN
CO
Z1
RAMP
TOP
Z
fV
ffVR
R 
(42)
Next calculate C
I
.
Z1Z
I
fR
C
π2
1

(43)