• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 47 subscribers
  • Views 334 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AMC1302: Low frequency distortions observed in the outputs due to the improper layout

jiaxing lei
Prodigy 170 points
Part Number: AMC1302
Other Parts Discussed in Thread: AMC3302

Tool/software:

Hi TI Experts,

As shown below, I use two AMC1302s to sense the currents before and after a filter capacitor. The common ground is set as the terminal plane of the capacitor voltage. 

In the PCB layout, I improperly connected the GND pin and INN pin at the righ-side AMC1302, which created a ground loop.

Consequently, I find there are significant low frequency distortions at the outputs of both AMC1302s.

My questions are:

1) I can understand that the performance of the right-side AMC1302 will be affected by the ground loop. But why the left-side cannot work properly? Is it also because of the right-side ground loop? Due to this issue, I am not sure if the distortions will be suppressed by breaking the additional wire.

2) Will the wire length of INN and INP generate low frequency distortions. In this pcb layout, the wire length of INN and INP is up to 45mm due to the limited space, though the pcb layout is symmetric.

Thanks for your help.

  • 0
    TI__Guru 55662 points

    Hi Jiaxing,

    I would expect some difference in voltage potential between the two AMC1302 devices input connections. 

    The issue may be that they are sharing a common voltage supply and as you said there is an additional ground loop between the isolated supply that bypasses the filter capacitor. 

    The INN to GND1 connection should be made for both devices to ensure the input voltage remains within the input common-mode.

    This may require separate supplies for each device depending on the voltage potential difference between the input and output side of the filter capacitor. 

    Transition to the AMC3302 with integrated DC/DC may help simplify the design and provide a smaller layout. 

  • 0 in reply to Alexander Smith
    Prodigy 170 points

    Thanks for your reply. I will try first to break the ground loop. If this does not work, I will try the separate supply.