TIDA-00835: AMC1301 common mode or bias resistance?

Marvin Cantos

Expert 6630 points

Part Number: TIDA-00835
Other Parts Discussed in Thread: AMC1301, AMC3330, AMC1350

Tool/software:

Hi Team,

Good day. I am posting this inquiry on behalf of the customer.

I am looking at isolated voltage measurement circuit: Reference Design Guide

There is a voltage measurement circuit on page 19, however, I cannot understand the purpose of resistors R65 or R50. One of the assumptions is to provide an offset of 20 mV with resistors R50 and R55, but for what? Current flowing through R50 will cause a voltage drop across R55. Accordingly, the inputs will be shifted. Without resistor R50, the input common-mode voltage will be set relative to GND_VCC through the low-resistance resistors of the input divider whatever. Help please understand this design.

Thank you for your help.

Kind regards,

Marvin

7 months ago

0 Alexander Smith 7 months ago

TI__Guru 55232 points

Hi Marvin,

I'm not one of the designers of TIDA-00835, but the only reason I can think for this is that Delta-sigma ADCs are subject to deadzone's around 0V input. This is sometimes done for customers requiring highest accuracy with very high levels of averaging, not a normal application.

However I would also not recommend using AMC1301 for voltage measurement, not all of the external diodes due to additional leakage and inaccuracy they may cause.

This document has more up to date recommendations and circuit designs for voltage measurement: https://www.ti.com/lit/eb/slyy234/slyy234.pdf

Please consider AMC3330 or AMC1350 as recommended devices.