Sense Resistor

Load Current Path

PCB

Source

Trace

Kelvin Sense

Traces to

Amplifer

PCB

Load

Trace

LMP92064

www.ti.com

SNOSCX0A – JUNE 2013 – REVISED DECEMBER 2014

9 Power Supply Recommendations

To decouple the LMP92064 from AC noise on the power supply, it is recommended to use a 0.1-

μF bypass

capacitor between the VDD and GND pins. This capacitor should be placed as close as possible to the supply

pins. In some cases an additional 10-

μF bypass capacitor may further reduce the supply noise. In addition, the

VDIG power pin should also be decoupled to DGND with a 0.1-

μF bypass capacitor. Do not forget that these

capacitors must be rated for the full supply voltage (2x the maximum voltage is recommended for the capacitor

working voltage rating).

10 Layout

10.1 Layout Guidelines

•

Connect the sense resistor pads directly to the INCP and INCN inputs of the LMP92064 using “Kelvin” or “4-

wire” connection techniques. See the Current Input Error Sources and Layout Considerations section for more

information.

•

Bypass capacitors should be placed in close proximity to the supply pins. It is recommended to use a 0.1-

μF

capacitor on each supply pin. Additional bypass capacitors can be used.

•

A 1-

μF ceramic bypass capacitor should be placed in close proximity to the REFC pin.

•

The SPI signals traces should be routed close together.

•

Series resistors should be placed at the SPI sources.

10.1.1 Current Input Error Sources

The traces leading to and from the sense resistor can be significant error sources. With small value sense

resistors (<100 m

Ω), trace resistance shared with the load can cause significant errors. TI recommends

connecting the sense resistor pads directly to the INCP and INCN inputs of the LMP92064 using “Kelvin” or “4-

wire” connection techniques. An example is shown in Figure 28.

Figure 28. 4-Wire "Kelvin" Sensing Technique

Because the sense traces only carry the amplifier bias current, the connecting input traces can be thinner, signal

level traces. The traces should be one continuous piece of copper from the sense resistor pad to the LMP92064

input pin pad, and ideally on the same layer with minimal vias or connectors. This can be important around the

sense resistor if it is generating any significant heat. To minimize noise pickup and thermal errors, the input

traces should be treated as a signal pair and routed tightly together with a direct path to the input pins. The input

traces should be run away from noise sources, such as digital lines, switching supplies or motor drive lines.

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Product Folder Links: LMP92064