FAN8301MX Fairchild Semiconductor, FAN8301MX Datasheet - Page 10

• Manufacturer Part Number: FAN8301MX
• Description: IC BUCK ADJ 2A 8SOIC
• Manufacturer: Fairchild Semiconductor
• Type: Step-Down (Buck)r

Specifications of FAN8301MX

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 14 V
• Current - Output: 2A
• Frequency - Switching: 370kHz
• Voltage - Input: 4.75 ~ 16 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Output Voltage: 0.6 V to 14 V
• Output Current: 2 A
• Input Voltage: 4.75 V to 16 V
• Switching Frequency: 370 KHz
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Duty Cycle (max): 90 %
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: FAN8301MXTR

© 2008 Fairchild Semiconductor Corporation
FAN8301 • Rev. 1.0.0
Design Example
Assume the V
The maximum load current is 2A and the output voltage
is set to 2.5V at 2A maximum load. Calculate the
inductor value from the following formula:
Substituting V
f
A 15µH inductor is chosen for this application.
If the V
R3 can be calculated from:
Choose R3=5.6kΩ(1%).
In this application, the crossover frequency desired is
30kHz and the R
If R
If R
Because C
Table 1. Recommended Compensation Values
(V
1.8V
2.5V
3.3V
S
V
5V
C
L
L
R
R
=370kHz in the formula gives:
IN
O
3
C
C
=
=
C
C
=12V)
=
=
=
370
=22.72kΩ, choose 22kΩ for the design.
=22kΩ, use the following equation to get C
f
OSC
18
π
2
10µH
15µH
15µH
22µH
OUT
π
k
kHz
⋅
2
L
Ω
22
V
2
⋅
A
Δ ⋅
22
OUT
⎛
⎜
⎝
5 .
k
C
/
2
(
voltage is 2.5V, choose R2=18kΩ(1%), and
0
V
=0.965nF, choose 1nF for the design.
I
Ω
5 .
µF
L
4 .
2
0
,
⋅
⋅
OUT
MAX
MLCC
−
6 .
C
22µF
IN
A
380
30
⋅
0
)
OUT
30
C
6 .
kHz
voltage is 12V with a 10% tolerance.
=2.5V, V
⎛
⎜
⎝
1
value is calculated as follows:
µs
kHz
⎞
⎟
⎠
⎛
⎜
⎜
⎝
−
1
=
2
12
⋅
−
. 5
0
5 .
⋅
V
6 .
68
2
18kΩ
⎞
⎟
⎠
V
IN
5 .
V
R
=
OUT
k
,
IN,MAX
V
2
Ω
MAX
13
µH
⎞
⎟
⎟
⎠
=12V, ΔI
2.45kΩ
5.6kΩ
9kΩ
4kΩ
R
3
L,MAX
16kΩ
22kΩ
27kΩ
43kΩ
R
=0.4A, and
C
C
:
820pF
560pF
1.5nF
(14)
(15)
(16)
(17)
(18)
1nF
C
C
10
Layout Consideration
As for all switching power supplies careful attention to
PCB layout is important to the design. A few design
rules can be implemented to ensure good layout:
Keep the high-current traces and load connections
as short as possible.
Place the input capacitor, the inductor, the
freewheeling diode, and the output capacitor as
close as possible to the IC terminals.
Keep the loop area between the SW node, low-side
MOSFET, inductor, and output capacitor as small
as possible. Minimizing ground loops reduces EMI
issues.
Route high-dV/dt signals, such as SW node, away
from the error amplifier input/output pins. Keep
components connected to these pins close to the
pins.
To effectively remove heat from the MOSFETs, use
wide land areas with appropriate thermal vias.
Figure 17. Recommended PCB Layout
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