LTC4008 Linear Technology, LTC4008 Datasheet - Page 20

• Manufacturer Part Number: LTC4008
• Description: Multi-Chemistry Battery Charger
• Manufacturer: Linear Technology

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APPLICATIO S I FOR ATIO
LTC4008
PCB Layout Considerations
For maximum efficiency, the switch node rise and fall
times should be minimized. To prevent magnetic and
electrical field radiation and high frequency resonant prob-
lems, proper layout of the components connected to the IC
is essential. (See Figure 11.) Here is a PCB layout priority
list for proper layout. Layout the PCB using this specific
order.
1. Input capacitors need to be placed as close as possible
2. The control IC needs to be close to the switching FET’s
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to switching FET’s supply and ground connections.
Shortest copper trace connections possible. These
parts must be on the same layer of copper. Vias must
not be used to make this connection.
gate terminals. Keep the gate drive signals short for a
clean FET drive. This includes IC supply pins that con-
nect to the switching FET source pins. The IC can be
placed on the opposite side of the PCB relative to above.
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3. Place inductor input as close as possible to switching
4. Place the output current sense resistor right next to
5. Place output capacitors next to the sense resistor
6. Output capacitor ground connections need to feed
FET’s output connection. Minimize the surface area of
this trace. Make the trace width the minimum amount
needed to support current—no copper fills or pours.
Avoid running the connection using multiple layers in
parallel. Minimize capacitance from this node to any
other trace or plane.
the inductor output but oriented such that the IC’s
current sense feedback traces going to resistor are not
long. The feedback traces need to be routed together
as a single pair on the same layer at any given time with
smallest trace spacing possible. Locate any filter
component on these traces next to the IC and not at the
sense resistor location.
output and ground.
into same copper that connects to the input capacitor
ground before tying back into system ground.
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