IR3856MTRPBF International Rectifier, IR3856MTRPBF Datasheet - Page 22

• Manufacturer Part Number: IR3856MTRPBF
• Description: IC BUCK SYNC ADJ 6A 17PQFN
• Manufacturer: International Rectifier
• Series: SupIRBuck™r
• Type: Step-Down (Buck)r

Specifications of IR3856MTRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.7 ~ 18.9 V
• Current - Output: 6A
• Frequency - Switching: 250kHz ~ 1.5MHz
• Voltage - Input: 1.5 ~ 21 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 17-PowerVQFN
• Power - Output: 1.11W
• Primary Input Voltage: 21V
• No. Of Outputs: 1
• Output Voltage: 18.9V
• Output Current: 6A
• No. Of Pins: 17
• Operating Temperature Range: -40°C To +125°C
• Peak Reflow Compatible (260 C): Yes
• Rohs Compliant: Yes
• Leaded Process Compatible: Yes
• Part Status: Preferred
• Package: PQFN / 4 x 5
• Circuit: Single Output
• Iout (a): 6
• Switch Freq (khz): 250 - 1500
• Input Range (v): 1.5 - 21
• Output Range (v): 0.7 - 0.9*Vin
• Ocp Otp Uvlo Pre-bias Soft Start And: PGOOD + EN + SEQ + OVP + SYNC
• Design Tool: Yes
• Server Storage: Yes
• Routers Switches: Yes
• Base Station Telecom: Yes
• Digital Home Media: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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
Use the following equation to calculate R3:
R =
Rev2.0
o
3
):
F
F
H
z
o
V
Fig. 15. Type II compensation network
( )
=
osc
V
V
s
>
e
o
2
π
F
*
=
=
V
ESR
F
*
( H
and its asymptotic gain plot
in
o
R
R
R
1
*
*
3
8
) s
3
F
F
*
and
ESR
LC
=
2
.........
C
−
4
*
Z
F
Z
..........
R
IN
o
f
e
..........
8
/V
≤
=
..........
o
−
) is given by:
(
1/5
..........
1
+
..........
sR
sR
~
8
..........
C
1/10
3
........
C
4
.........
4
)
.......
.....
*
(21)
F
s
(19)
(20)
(22)
F
Where:
V
V
F
F
F
R
To cancel one of the LC filter poles, place the
zero before the LC filter resonant frequency pole:
Use equations (21), (22) and (23) to calculate
C4.
One more capacitor is sometimes added in
parallel with C4 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, we should implement local
feedback with a Type-III compensation network.
The typically used compensation network for
voltage-mode controller is shown in figure 16.
Again, the transfer function is given by:
By replacing Z
the transfer function can be expressed as:
F
F
.......
H
P
C
o
ESR
LC
z
z
in
osc
8
POLE
(
= Crossover Frequency
=
=
=
= Feedback Resistor
) s
= Maximum Input Voltage
= Resonant Frequency of the Output Filter
= Oscillator Ramp Voltage
75
0
2
(26)
= Zero Frequency of the Output Capacitor
=
.
π
75
=
%
sR
*
π
*
R
F
*R
8
LC
2
3
(
C
π
*
3
*F
V
V
4
C
−
C
1
1
e
o
s
+
L
in
(
4
4
1
1
o
−
C
=
*
+
+
and Z
*
C
3
H
C
C
1
sR
C
)
4
⎡
⎢
⎢
⎣
(
POLE
POLE
1
s
o
≅
3
)
+
C
..........
IR3856MPbF
=
π
sR
4
f
*R
−
)
[
according to figure 16,
1
3
Z
..........
1
Z
3
⎛
⎜ ⎜
⎝
+
IN
*F
f
C
C
sC
..........
s
4
4
..........
*
+
7
(
C
..........
C
R
3
3
8
PD-97528
..........
⎞
⎟ ⎟
⎠
+
..........
⎤
⎥
⎥
⎦
(
R
1
..........
10
+
sR
)
.......
]
POLE
..
(25)
10
22
C
.(24)
(23)
:
7
)