Datasheet

ADP1851-EVALZ User Guide UG-443
Rev. 0 | Page 3 of 12
COMPONENT DESIGN
ADIsimPower DESIGN TOOL
The ADP1851 is supported by the ADIsimPower™ design tool
set. ADIsimPower is a collection of tools that produce complete
power designs optimized to a specific design goal. The tools
allow the user to generate a full schematic, bill of materials, and
calculate performance in minutes. ADIsimPower can optimize
designs for cost, area, efficiency, and parts count while taking
into consideration the operating conditions and limitations of
the IC and all real external components. The ADIsimPower
tool can be found at www.analog.com/ADIsimPower and
users can request an unpopulated board through the tool.
For information about selecting power components and calcu-
lating component values, see also the ADP1851 data sheet.
INDUCTOR SELECTION
The selected inductor is a Coilcraft SER1408-301ME with
0.3 µH inductance, and 53 A saturation current. This shielded
inductor with a flat wire windings core provides exceptionally
low DCR of 0.5 mΩ (typical).
INPUT CAPACITORS
Because of the low ESR and high input current rating of a multi-
layer ceramic capacitor (MLCC), a 10 µF MLCC is selected as
the input capacitor close to the high-side power MOSFET. In
addition, a 150 µF bulk OS-CON™ capacitor (aluminum solid
capacitor with conductive polymer) from Sanyo is chosen for
filtering out any unwanted low frequency noise from the input
power supply.
OUTPUT CAPACITORS
A combination of the 330 µF POSCAP™ polymer capacitors
and the 47 µF MLCC is selected for the output rail. Polymer
capacitors have low ESR and high current ripple rating.
Connecting polymer capacitors and MLCCs in parallel is
very effective in reducing voltage ripple.
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 it conducts current most of the time
during the switching cycle and contributes a larger portion in
the conductive losses than the high-side MOSFET. For the
high-side MOSFET, two BSC052N03LS from Infineon in
the PG-TDSON-8 package are selected. These parts have low
input capacitance (770 pF typical) and fast transition times
(typical turn-on delay is 2.4 ns). For the low-side MOSFET,
two BSC090NS from Infineon, with the R
DSON
of 3.5 mΩ
(maximum at V
GS
of 4.5 V) are selected.