IR3898MTR1PBF International Rectifier, IR3898MTR1PBF Datasheet - Page 30
IR3898MTR1PBF
Manufacturer Part Number
IR3898MTR1PBF
Description
6A Highly Integrated Single-Input Voltage, Synchronous Buck Regulator in a PQFN package.
Manufacturer
International Rectifier
Datasheet
1.IR3898MTR1PBF.pdf
(42 pages)
Specifications of IR3898MTR1PBF
Part Status
Active and Preferred
Package
PQFN / 4 x 5
Circuit
Single Output
Iout (a)
6
Switch Freq (khz)
0 - 1500
Input Range (v)
1.0 - 16
Output Range (v)
0.5 - 12
Pbf
PbF Option Available
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
3
2
Gain (dB)
Z
Figure 27: Type III Compensation network
0
2 *
2 *
IN
sR C
C4
R4
30
in
5
R
R C
1
and Z
(
and its asymptotic gain plot
3
4
F
V
*
V
V
Z
2
1
out
C
C C
(1
1
OUT
e
FEBRUARY 02, 2012 | DATA SHEET | Rev 3.2
R5
2
R6
4
2
f
C
,
*
according to Fig. 27, the transfer
3
sR C
C
) 1
F
H
3
3
3
Z
V
(
2
Fb
REF
3
s
) 1
)
sR
2 *
3
R3
sC
C
C
E
F
R C
Z
1
Z
P
2
2
3
/
IN
4
2
f
*
*
Single‐Input Voltage, Synchronous Buck Regulator
A
C
R
C
C2
C3
3
2
4
3
F
R
P
(1
5
3
Comp
(28)
(30)
(29)
Frequency
sR C
Z
Ve
4
(27)
f
4
- 30 -
)
6A 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
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 22uF
capacitor used in this design is 10uF at 1.2 V DC bias and
600 kHz frequency. It is this value that must be used for all
ABLE
Compensator
F
F
F
V
V
V
section)
V
L
C
Z
Z
o
o
o
in
o
osc
ref
1
=1.0uH
2
Type III
3:
=1.2V
=4x22uF, ESR≈3mΩ each
Type II
=12V
Type
=0.5V
=1.8V (This is a function of Vin, pls. see feed forward
o
D
R C
for overall stability.
2 *
2 *
IFFERENT TYPES OF COMPENSATORS
3
*
R C
C
4
1
3
*
4
*
* (
V
V
1
osc
F
in
F
R
3
LC
o
o
4
< F
*
) is selected such that:
F
LC
2 *
F
< F
ESR
ESR
1/5
R
5
< F
vs F
O
)
< F
L C
~
1
O
o
< F
1/10
ESR
O
2 *
*
TM
S
/2
o
C
1
*
4
F
*
s
IR3898
R
Typical Output
SP Cap, Ceramic
5
Electrolytic
Capacitor
PD‐97662
(33)
(31)
(32)