Datasheet

LTC3677-3
41
36773f
operaTion
Consider the previous example with an ambient tem-
perature of 55°C. The charge current will be reduced to
approximately:
I
C C
C W
W
V V
I
BAT
BAT
=
° °
°
=
110 55
45
0 3
5 3 3
1 22
–
/
– .
– .
. – 00 3
1 7
542
.
.
W
V
mA=
Printed Circuit Board Layout
When laying out the printed circuit board, the following
list should be followed to ensure proper operation of the
LTC3677-3:
1. The exposed pad of the package (Pin 45) should
connect directly to a large ground plane to minimize
thermal and electrical impedance.
2. The step-down switching regulator input supply pins
(V
IN12
and V
IN3
) 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. These capacitors provide
the AC current to the internal power MOSFETs and
their drivers. It’s important to minimizing inductance
from these capacitors to the pins of the LTC3677-3.
Connect V
IN12
and V
IN3
to V
OUT
through a short low
impedance trace.
3. The switching power traces connecting SW1, SW2,
and SW3 to their respective inductors should be mini-
mized to reduce radiated EMI and parasitic coupling.
Due to the large voltage swing of the switching nodes,
sensitive nodes such as the feedback nodes (FBx
and LDOx_FB) should be kept far away or shielded
from the switching nodes or poor performance could
result.
4. Connections between the step-down switching regu-
lator 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.
5. Keep the buck feedback pin traces (FB1, FB2, and FB3)
as 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.
6. Connections between the LTC3677-3 power path 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.