Optimize High-Current Sensing Accuracy by Improving Pad Layout of
Low-Value Shunt Resistors

When current sense resistors in the order of milli-Ohms are used,
significant errors can be introduced by bad choice of sense trace
locations on the resistor pad and by poor pad design.

This article is a useful contribution to "how to do it right".

http://www.analog.com/library/analogDialogue/archives/46-06/shunt_resistors=
..pdf

My very recent experience is that even resistprs in the 0.1 Ohm range
can cause problems if poorly managed.
I installed two x 0.1 Ohm SR's (sense resistors) in a product to
measure current. Currents were <150 mA and < 500 mA in each case
giving 0.015V and 0.05V drop in 0.1R. Acceptable in the context.

I was using 1% through hole parts. To use these in 4 wire sense mode I
added a measurement wire to each lead, wrapped it around the lead
several times, slid it along the lead to make body contact and
soldered it in place so the solder joint was against the resistor
body. Should be perfect, right ? :-).
While this method is not 'approved' and cannot easily be replicated
using a PCB it should work very well indeed. I thought. The resistors
are about 10% low. By making connection at the lead copper where it
would enter a PCB at minimum approved lead length the results would
have been almost correct. Calibrating a resistor so the minimum lead
length is a necessary part of the calibration seems "strange". BUT the
0.9 Ohm reading suggests this MAY have been done, as it is well
outside the 1% tolerance.
Readings shall be multiplied by 1.1 in this case.


 Russell
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.