LTC3553-2_15 Datasheet, PDF (32/36 Pages) Linear Technology – Micropower USB Power Manager with Li-Ion Charger, Always-On LDO and Buck Regulator

LTC3553-2
OPERATION
Printed Circuit Board Layout
When laying out the printed circuit board, the following
list should be followed to ensure proper operation of the
LTC3553-2:
1. The Exposed Pad of the package (Pin 21) should connect
directly to a large ground plane to minimize thermal
and electrical impedance.
2. The traces connecting the regulator input supply pins
(BVIN and V_INLDO) and their respective decoupling
capacitors should be kept as short as possible. The
GND side of each capacitor should connect directly to
the ground plane of the part. This capacitor provides
the AC current to the internal power MOSFETs and their
drivers. It is important to minimize inductance from this
capacitor to the pin of the LTC3553-2. Connect BVIN
to V_OUT and V_INLDO to its input supply through short
low impedance traces.
3. The switching power trace connecting the SW pin to
its inductor should be minimized to reduce radiated
EMI and parasitic coupling. Due to the large voltage
swing of the switching node, sensitive nodes such as
the feedback nodes should be kept far away or shielded
from the switching nodes or poor performance could
result.
4. Connections between the buck regulator inductor and
its output capacitor should be kept as short as possible.
The GND side of the output capacitor should connect
directly to the thermal ground plane of the part.
5. Keep the feedback pin traces (BUCK_FB and LDO_FB)
as short as possible. Minimize any parasitic capacitance
between the feedback traces and any switching node
(i.e., SW and logic signals). If necessary, shield the
feedback nodes with a GND trace.
6. Connections between the LTC3553-2 PowerPath pins
(V_BUS and V_OUT) and their respective decoupling ca-
pacitors should be kept as short as possible. The GND
side of these capacitors should connect directly to the
ground plane of the part.
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