IR3895MPBF IRF [International Rectifier], IR3895MPBF Datasheet - Page 29

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

The ESR zero of the output capacitor is expressed as
follows:
H (s) dB
The transfer function (V
The (s) indicates that the transfer function varies as a
function of frequency. This configuration introduces a
gain and zero, expressed by:
First select the desired zero‐crossover frequency (F
F
o

V
V
out
Z
e
F
Figure 26: Type II compensation network
F
IN

ESR
G ain (dB )
ESR
H s
F
29
H s
z

( )
and its asymptotic gain plot
and F

 
F
2
V
Z
2 *
 
π * ESR* C
O U T

AUGUST 08, 2012 | DATA SHEET| Rev 3.1
R 5
R 6

Z
Z
o
R
1
IN
R
R
1
f
e
3

/V
5
V
3
*
 
Fb

R E F
out
C

3
1/5~1/10 *
) is given by:
1

F

o
sR C
R 3
P O LE

sR C
5 3
E /A
3 3
(20)
(21)
Single‐Input Voltage, Synchronous Buck Regulator
C

C 3

(18)
P O LE
F
(19)
s
C om p

F requency
(22)
o
Z
):
V e
f
- 29 -P
16A Highly Integrated SupIRBuck
Use the following equation to calculate R3:
Where:
To cancel one of the LC filter poles, place the zero before
the LC filter resonant frequency pole:
Use equation 21 to calculate C3.
One more capacitor is sometimes added in parallel with
C3 and R3. This introduces one more pole which is mainly
used to suppress the switching noise.
The additional pole is given by:
The pole sets to one half of the switching frequency
which results in the capacitor C
For a general solution for unconditional stability for any
type of output capacitors, and a wide range of ESR
values, a type III compensation network can be used, as
shown in Fig. 27.
C
F
POLE
V
V
F
F
F
R
o
ESR
LC
P
5
in
osc
= Crossover Frequency
= Feedback Resistor
= Maximum Input Voltage
= Resonant Frequency of the Output Filter

= Amplitude of the oscillator Ramp Voltage
= Zero Frequency of the Output Capacitor
F
F

z
z
R
2 *


3


75 % *
0.75*

* R * F
V
R
osc
3
3
*
2
F
*

1
C
1
C C
V
LC
F F
3
in
3
s
o
L C
1

*
*
*
o

*
C
F
C
1
POLE
POLE
LC
ESR
2
o
3


*

POLE

R
5
* R * F

:
1
3
IR3895
s
(23)
PD‐97746

(24)
(25)
(26)