FAN2011 Datasheet, PDF (8/10 Pages) Fairchild Semiconductor – 1.5A Low Voltage Current Mode Synchronous PWM Buck Regulator

Inductor Selection
The inductor parameters directly related to device performances
are saturation current and dc resistance. The FAN2011/
FAN2012 operates with a typical inductor value of 3.3µH. 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 that is calcu-
lated as follows:
∆I_L
=
V_OUT
×
1_-----–_-----(_--V_{-----O---U----T-----}⁄_---V_----I--N---)_-
L×f
where:
∆I_L = Inductor Ripple Current
f = Switching Frequency
L = Inductor Value
Some recommended inductors are suggested in the table
below:
Inductor Value
3.3µH
3.3µH
Vendor
Panasonic
Murata
Part Number
ELL6PM3R3N
LQS66C3R3M04
plane at the bottom side of the PCB acts as an electromagnetic
shield to reduce EMI. The recommended PCB layout is shown
below in Figure 5.
Figure 5. Recommended PCB Layout
Table 1: Recommended Inductors
Capacitors Selection
For best performances, a low ESR input capacitor is required. A
ceramic capacitor of at least 10µF, placed as close to the V_IN
and AGND pins of the device is recommended. The output
capacitor determines the output ripple and the transient
response.
Capacitor
Value
10µF
Vendor
Taiyo Yuden
TDK
Murata
Part Number
JMK212BJ106MG
JMK316BJ106KL
C2012X5ROJ106K
C3216X5ROJ106M
GRM32ER61C106K
Table 2: Recommended Capacitors
PCB Layout Recommendations
The inherently high peak currents and switching frequency of
power supplies require a careful PCB layout design. Therefore,
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. In order to minimize
voltage stress to the device resulting from ever present switch-
ing spikes, use an input bypass capacitor with low ESR. Use of
an external Schottky diode with its anode connected to SW
node and cathode connected to PV_IN further reduces switching
spikes. 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
FAN2011/FAN2012 Rev. 1.0.2
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