IR3895MPBF IRF [International Rectifier], IR3895MPBF Datasheet - Page 30

• Manufacturer Part Number: IR3895MPBF
• Description: 16A HIGHLY INTERGRATED SUPLRBUCK
• Manufacturer: IRF [International Rectifier]

Again, the transfer function is given by:
By replacing Z
function can be expressed as:
The compensation network has three poles and two
zeros and they are expressed as follows:
H s
|H(s)| dB
( )
F
F
F
P
P
P
1
2
3
Figure 27: Type III Compensation network

 


Gain (dB)
Z
0
2 *
2 *


IN


sR C
C4
R4
30
and its asymptotic gain plot
R C
R
in
5
1
and Z
(
3
4
V



*
F
V
1
2
V
Z
out
C
C C
e
(1
1
OUT

AUGUST 08, 2012 | DATA SHEET| Rev 3.1
R5
2
4
2
R6



f
C
*

,
according to Fig. 27, the transfer
3
sR C
C
H
) 1
3
F
3



3
Z



V
(
2
Fb
REF
s


3
)
) 1
sR
2 *




3

R3




sC
C
C
R C
Z
1
E
Z
F
2
3
P
2
IN
4
/
f
*

2
*
Single‐Input Voltage, Synchronous Buck Regulator

A
C
R
C
C2
C3
2
4
3
3





F



R
P
(1
5
3
Comp

(28)
(30)

(29)


Frequency
sR C
4
(27)
Z
Ve
f
- 30 -P
4
)
16A Highly Integrated SupIRBuck
Cross over frequency is expressed as:
Based on the frequency of the zero generated by the
output capacitor and its ESR, relative to crossover
frequency, the compensation type can be different. Table
3 shows the compensation types for relative locations of
the crossover frequency.
T
The higher the crossover frequency is, the potentially
faster the load transient response will be. However, the
crossover frequency should be low enough to allow
attenuation of switching noise. Typically, the control loop
bandwidth or crossover frequency (F
that:
The DC gain should be large enough to provide high
DC‐regulation accuracy. The phase margin should be
greater than 45
For this design we have:
It must be noted here that the value of the capacitance used
in the compensator design must be the small signal value.
For instance, the small signal capacitance of the 47uf capacitor
used in this design is 29uf at 1.2V dc bias and 600 kHz
frequency. It is this value that must be used for all
computations related to the compensation.
F
F
F
ABLE
Z
Z
o
Compensator
1
2
V
V
V
forward section)
V
L
C

o

o
in
o
osc
ref

Type III
Type II
=0.4uH
3:
=1.2V
=6x47uF, ESR≈3mΩ each
=12V
R C
Type
=0.5V
=1.8V (This is a function of Vin, pls. see feed
2 *
2 *
3
D


*
IFFERENT TYPES OF COMPENSATORS
R C
C
1
4
3
*
4
*
o
* (
V
for overall stability.
V
1
osc
F
in
R
3
o
F

4
*
LC


F
2 *
< F

LC
1/5
R

F
ESR
5
< F
ESR
)
< F
L C
~
1

vs F
O
o
< F
1/10
2 *
*
O

< F
O
ESR
o
S

C
o
/2
1
) is selected such
*
4
IR3895
F
*
s
R
5
SP Cap, Ceramic
PD‐97746
Typical Output

Electrolytic
Capacitor
(33)
(31)
(32)