ncp3155a ON Semiconductor, ncp3155a Datasheet - Page 20

• Manufacturer Part Number: ncp3155a
• Description: Ncp3155a, Ncp3155b 3 A Synchronous Buck Regulator
• Manufacturer: ON Semiconductor

Compensation Type II
Components of the Type II (Figure 42) network can be
specified by the following equations:
and gm is the transconductance error amplifier gain.
Capacitor C
Compensation Type III
electrolytic, so the zero of the output LC filter goes to a
higher frequency above the zero crossover frequency. This
requires a Type III compensation network as shown in
Figure 43.
compensation network. Method I is ideal for tantalum
output capacitors, which have a higher ESR than ceramic:
This compensation is suitable for electrolytic capacitors.
V
Tantalum and ceramics capacitors have lower ESR than
There are two methods to select the zeros and poles of this
RAMP
is the peak−to−peak voltage of the oscillator ramp
R
C
C
R1 +
Figure 43. Type III Compensation
Figure 42. Type II Compensation
C2
C1
C1
C2
is optional.
+
+
+
V
2 @ p @ f
0.75 @ 2 @ p @ f
p @ R
OUT
V
ESR @ V
* V
ref
1
C1
0
@ f
ref
@ L @ V
S
1
@ R2
IN
@ V
P0
RAMP
@ R
ref
@ gm
C1
@ V
OUT
(eq. 26)
(eq. 27)
(eq. 28)
(eq. 29)
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Method II is better suited for ceramic capacitors that
typically have the lowest ESR available:
qmax is the desired maximum phase margin at the zero
crossover frequency, ƒ
degrees to radians by the formula:
q max + q max
The remaining calculations are the same for both methods.
If the equation in Equation 46 is not true, then a higher value
of R
C1
must be selected.
R1 @ R
C
R
R1 +
R2 +
FB1
FB1
+
+
FB1
degress
2 @ p @ C
V
f
f
f
f
R
C
C
Z2
P2
Z1
P3
OUT
2 @ p @ f
2p @ C
C1
C1
C2
R1 @ R2 @ R
) R2 @ R
+ f
+ f
+ 0.5 @ f
+ 0.5 @ f
V
u u
+
+
f
f
f
f
* V
ref
@ 2 @ p
Z1
Z2
P2
P3
0
0
0
2 @ p @ f
2 @ p @ f
1
. It should be 45° − 75°. Convert
FB1
1
FB1
@
+ 0.75 @ f
+ f
@
+ f
+
360
0
ref
gm
2
@ L @ V
V
f
@ f
2
@ f
@ R1
P0
FB1
Z0
S
Z2
S
1 ) sin q max
IN
1 ) sin q max
1 * sin q max
1 * sinq max
FB1
P2
Z2
1
1
: Units + radians
@ R
Z1
P3
) R1 @ R2
* R
@ R
RAMP
@ R
C1
P0
C1
C1
FB1
@ C
OUT
u
gm
1
(eq. 30)
(eq. 31)
(eq. 32)
(eq. 33)
(eq. 34)
(eq. 35)
(eq. 36)
(eq. 37)
(eq. 38)
(eq. 39)
(eq. 40)
(eq. 41)
(eq. 42)
(eq. 43)
(eq. 44)
(eq. 45)
(eq. 46)