LTC3557 LINER [Linear Technology], LTC3557 Datasheet - Page 26

• Manufacturer Part Number: LTC3557
• Description: USB Power Manager with Li-Ion Charger and Three Step-Down Regulators
• Manufacturer: LINER [Linear Technology]

LTC3557/LTC3557-1
APPLICATIONS INFORMATION
If an external buck switching regulator controlled by the
LTC3557/LTC3557-1 V
adapter we see a signifi cant reduction in power dissipated
by the LTC3557/LTC3557-1. This is because the external
buck switching regulator will drive the PowerPath output
(V
through the example above and substitute 3.6V for V
we see that thermal regulation does not kick in until about
93°C. Thus, the external regulator not only allows higher
charging currents, but lower power dissipation means a
cooler running application.
Printed Circuit Board Layout Considerations
When laying out the printed circuit board, the following
list should be followed to ensure proper operation of the
LTC3557/LTC3557-1:
1. The Exposed Pad of the package (Pin 29) should connect
2. The trace connecting the step-down switching regulator
26
OUT
directly to a large ground plane to minimize thermal and
electrical impedance.
input supply pins (V
decoupling capacitors should be kept as short as
possible. The GND side of these capacitors should
connect directly to the ground plane of the part. These
capacitors provide the AC current to the internal power
MOSFETs and their drivers. It’s important to minimize
inductance from these capacitors to the pins of the
LTC3557/LTC3557-1. Connect V
through a short low impedance trace.
) to about 3.6V with the battery at 3.3V. If you go
C
IN1
pin is used instead of a 5V wall
and V
IN2
) and their respective
IN1
and V
IN2
to V
OUT
OUT
3. The switching power traces connecting SW1, SW2 and
4. Connections between the step-down switching regulator
5. Keep the feedback pin traces (FB1, FB2 and FB3) as
6) Connections between the LTC3557/LTC3557-1
SW3 to their respective inductors should be minimized
to reduce radiated EMI and parasitic coupling. Due to
the large voltage swing of the switching nodes, sensitive
nodes such as the feedback nodes (FB1, FB2 and FB3)
should be kept far away or shielded from the switching
nodes or poor performance could result.
inductors and their respective output capacitors should
be kept as short as possible. The GND side of the output
capacitors should connect directly to the thermal ground
plane of the part.
short as possible. Minimize any parasitic capacitance
between the feedback traces and any switching node
(i.e., SW1, SW2, SW3 and logic signals). If necessary
shield the feedback nodes with a GND trace
power path pins (V
decoupling capacitors should be kept as short as pos-
sible. The GND side of these capacitors should connect
directly to the ground plane of the part. V
decoupled with a 10μF or greater ceramic capacitor as
close as possible to the LTC3557/LTC3557-1.
BUS
and V
OUT
) and their respective
OUT
should be
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