The sense lines should be connected to a point on the resistor that is not shared with the main current path, as shown in Figure 7-6. For lowest drift, the amplifier must be mounted away from any heat generating devices, which may include the sense resistor. The traces should be one continuous trace of copper from the sense resistor pad to the amplifier input pin pad, and ideally on the same copper layer with minimal vias or connectors. This can be important around the sense resistor if it is generating any significant heat gradients. Vias in the sense lines should be formed from continuous plated copper and routing through mating connectors or headers should be avoided. It is better to extend the sense lines than to place the amplifier in a hostile environment.

To minimize noise pickup and thermal errors, the input traces should be treated like a high-speed differential signal pair and routed tightly together with a direct path to the input pins on the same copper layer. They do not need to be impedance matched, but should follow the same matching rules about vias, spacing and equal lengths. The input traces should be run away from noise sources, such as digital lines, switching supplies, or motor drive lines.

Remember that these input traces can contain high voltage (up to 76 V), and should have the appropriate trace routing clearances to other components, traces and layers. Because the sense traces only carry the amplifier bias current, the connecting input traces can be thin traces running close together. This can help with routing or creating the required spacings.

The negative input bias current is not in the feedback path and will not change over V_SENSE. High or miss-matched source impedances should be avoided as this imbalance will create an additional error term over input voltage.