LTC4100_09 datasheet(27/30 Pages) LINER

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LTC4100

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APPLICATIONS INFORMATION

PCB Layout Considerations

For maximum efﬁciency, the switch node rise and fall times

shouldbeminimized.Topreventmagneticandelectricalﬁeld

radiation and high frequency resonant problems, 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

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.

2. The control IC needs to be close to the switching FET’s

gate terminals. Keep the gate drive signals short for

a clean FET drive. This includes IC supply pins that

connect to the switching FET source pins. The IC can

be placed on the opposite side of the PCB relative to

above.

3. Place inductor input as close as possible to switching

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.

4. Place the output current sense resistor right next to

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.

5. Place output capacitors next to the sense resistor

output and ground.

6. Output capacitor ground connections need to feed

into same copper that connects to the input capacitor

ground before tying back into system ground.

Interfacing with a Selector

The LTC4100 is designed to be used with a true analog

multiplexer for the SafetySignal sensing path. Some

selector ICs from various manufacturers may not imple-

ment this. Consult LTC applications department for more

information.

Electronic Loads

The LTC4100 is designed to work with a real battery.

Electronic loads will create instability within the LTC4100

preventing accurate programming currents and volt-

ages. Consult LTC applications department for more

information.

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