AMC1306M25: EVM R3 Function

Joyce Gao

Intellectual 1730 points

Part Number: AMC1306M25

Tool/software:

Hi expert,

We found in AMC1306 EVM, there's an 0ohm R3 shorted to AGND from AINN, what's the function? Why need this?

Many thanks!

Joyce

2 months ago

0 Eva Mason 2 months ago

TI__Expert 4955 points

Hi Joyce,

This is to establish the common-mode input voltage. One of the inputs must be tied to ground to do this.

Best regards,

Eva

0 Joyce Gao 2 months ago in reply to Eva Mason

TI__Intellectual 1730 points

Hi Eva,

Why don't directly connect to GND but add a 0R resistor like this?

Joyce

0 Eva Mason 2 months ago in reply to Joyce Gao

TI__Expert 4955 points

Hi Joyce,

This gives users the option to not connect to ground if there's an application where that is necessary.

Who is your customer and what is their application?

Best regards,

Eva

0 Joyce Gao 2 months ago in reply to Eva Mason

TI__Intellectual 1730 points

Eva,

Customer is INFO CONVERGENCE with servo drives end use. They met similar issue with this e2e post((+) AMC1306M25: The Current sampling is not accurate of AMC1306M25. - Data converters forum - Data converters - TI E2E support forums). It's similar that if they use 0R resistor, noise will be huge, but if change to 1R resistor, noise will be gone. Customer wonders why should add the 0R resistor shorted to GND and why 0R resistor leads to noise.

Joyce

0 Eva Mason 2 months ago in reply to Joyce Gao

TI__Expert 4955 points

Hi Joyce,

The 0 Ohm resistor should not be a source of noise. It's probably a layout concern. I can take a look if that would be helpful. The resistor is not a requirement, so if removing it from their system or using a different resistor leads to better results, that is suggestable too.

Best regards,

Eva