FAN2013B Fairchild Semiconductor, FAN2013B Datasheet - Page 7

• Manufacturer Part Number: FAN2013B
• Description: The FAN2013B is a high-efficiency, low-noise, synchronous Pulse Width Modulated (PWM) current-mode DC-DC converter designed for low-voltage applications
• Manufacturer: Fairchild Semiconductor

© 2008 Fairchild Semiconductor Corporation
FAN2013B • Rev. 1.0.2
∆ I
Applications Information
Setting the Output Voltage
The internal voltage reference is 0.8V. The output is
divided down by a voltage divider, R1 and R2 to the FB
pin. The output voltage is:
V
According to this equation, assuming desired output
voltage of 1.2V, and given R2 = 10KΩ as the
recommended resistance for any output voltage setting,
the calculated value of R1 is 5KΩ. Maximum V
Inductor Selection
The inductor parameters directly related to device
performance are saturation current and DC resistance.
The FAN2013B operates with a typical inductor value of
2.2µH. The lower the DC resistance, the higher the
efficiency. For saturation current, the inductor should be
rated higher than the maximum load current, plus half of
the inductor ripple current, calculated by:
where:
ΔI
f = Switching Frequency
L = Inductor Value
Recommended inductors are listed in Table1.
Table 1. Recommended Inductors
Capacitor Selection
For best performance, a low-ESR input capacitor is
required. A ceramic capacitor of at least 10µF, placed
as close to the V
recommended.
The output capacitor determines the output ripple and
the transient response. A minimum of 20µF output
capacitor is required for the FAN2013B to operate in
stable conditions.
Table 2. Recommended Capacitors
Inductor Value
O UT
L
L
Capacitor
= Inductor Ripple Current
=
Value
10µF
=
2.2µH
2.2µH
V
O U T
V
REF
×
1
1
- -- -- -- -- --- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -
+
–
R
- -- -- -
R
(
1
2
V
O U T
L
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and AGND pins as possible is
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Part Number
Part Number
SD25 2R2
OUT
= 2.5V.
(2)
(3)
7
PCB Layout Recommendations
The inherently high peak currents and switching
frequency of power supplies require a careful PCB
layout design. For best results, use wide traces for high-
current paths and place the input capacitor, the
inductor, and the output capacitor as close as possible
to the integrated circuit terminals. To minimize voltage
stress to the device resulting from ever-present
switching spikes, use an input bypass capacitor with low
ESR. Note that the peak amplitude of the switching
spikes depends upon the load current; the higher the
load current, the higher the switching spikes.
The resistor divider that sets the output voltage should
be routed away from the inductor to avoid RF coupling.
The ground plane at the bottom side of the PCB acts as
an
recommended PCB layout is shown below in Figure 11.
electromagnetic
Figure 11.
Recommended PCB Layout
shield
to
reduce
www.fairchildsemi.com
EMI.
The