Datasheet

ADP1877HC-EVALZ
Rev. A | Page 3 of 12
COMPONENT DESIGN
For information in selecting power components and calculating
component values, see the ADP1877 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 for each input.
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 in Size 0805 are selected.
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 significantly reduce the switching power loss. As for the
synchronous rectifier (low-side MOSFET), select a MOSFET
with low R
DSON
because switching speed is not critical and there
is no switching 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). As for the low-side MOSFET, the
BSC030N03LS, with R
DSON
of 4.7 mΩ at a V
GS
of 4.5 V, is
selected.
SWITCHING NOISE AND OVERSHOOT REDUCTION
In reducing the overshoot voltage and ringing at the SWx
node, gate resistors of 3 Ω and RC snubbers of 4 Ω and 1.2 nF
are added.