Use 4-wire (Kelvin) connections to the sense resistor. Connect to the resistor at a point that is not within a direct high-current path (See Figure 8-3).
Do not "share" part of the sense trace path with the load current.
Maintain proper clearance and spacings around the
input traces, as the traces can be at a higher voltage (up to 76 V) than the
surrounding traces and planes.
Input traces from the sense resistor pads must
follow the same path, be spaced tightly together, and ideally on the same copper
layer.
Vias used in the input traces must be of
continuous plated copper to avoid creating thermocouples.
Avoid routing inputs through jumpers and
connectors. Even the best connectors introduce thermal errors ("thermocouples").
Each input trace must have the same number of "thermocouples" if the
"thermocouples" can not be avoided.
Keep the amplifier away from heat generating
devices. The copper-solder-lead junction on the input pins form a thermocouple.
The copper mass must be equal on both input pins.
Avoid temperature gradients across the input
pins. Input pins must be equal distance to the heat source.
Place the LMP8640 in the most temperature-stable
area possible and away from high-velocity air flows. Carefully extending the
input traces is better than to place the amplifier in a less-than-ideal
environment.
Give the sense resistor as much copper trace area
as possible to dissipate heat as the resistor value changes slightly with
temperature. Also see the resistor manufacturers data sheet or application notes
for further layout guidelines.
The power-supply bypass capacitor must be placed
as closely as possible to the supply and ground terminals. The recommended value
of this bypass capacitor is 0.1 μF. Additional decoupling capacitance can be
added to compensate for noisy or high-impedance power supplies.