Datasheet

Evaluation Board User Guide UG-204
Rev. A | Page 3 of 12
COMPONENT DESIGN
For information about selecting power components and
calculating component values, see the ADP1850 data sheet.
INDUCTOR SELECTION
A 1.2 μH inductor with a 20 A average current rating (744325120
from Würth Elektronik) is selected. This is a compact inductor
with a ferrite core, which offers high performance in terms of
low R
DC
and low core loss.
INPUT CAPACITORS
Because of the very low ESR and high input current rating of
multilayer ceramic capacitors (MLCCs), two 10 μF MLCCs in
Size 1210 are selected as the input capacitors at the input of each
channel. In addition, a 150 μF bulk OS-CON™ (aluminum solid
capacitor with conductive polymer) capacitor from Sanyo is
chosen for filtering out any unwanted low-frequency noise
from the input power supply.
OUTPUT CAPACITORS
A combination of POSCAP™ polymer capacitors and MLCCs
are selected for the output rails. Polymer capacitors have low
ESR and high current ripple rating. Connecting polymer
capacitors and MLCCs in parallel is very effective in reducing
voltage ripple. Two 330 μF POSCAP capacitors and two 22 μF
MLCCs are selected for each output.
MOSFET SELECTION
For low output or low duty cycle, select a high-side MOSFET
with fast rise and fall times and with low input capacitance
to minimize charging and switching power loss. As for the
synchronous rectifier (low-side MOSFET), select a MOSFET
with low R
DSON
because the switching speed is not critical and
there is no switching power loss in the low-side MOSFET.
For the high-side MOSFET, the BSC080N03LS from Infineon
Technologies in the PG-TDSON-8 or Super-SO8 package is
selected. This part has low input capacitance (1.2 nF) and
fast transition times (3 ns). For the low-side MOSFET, the
BSC030N03LS, with R
DSON
of 4.7 mΩ at a V
GS
of 4.5 V, is
selected.