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  • TI Thinks Resolved

AFE58JD18: Supply bypass caps

Intellectual 2170 points

Replies: 8

Views: 128

Part Number: AFE58JD18

In the AFE58JD18 datasheet, it says "Bypass all supply pins with 0.1-μF ceramic chip capacitors (size 0603 or smaller)." I read that as, for every supply pin, one should add a bypass capacitor. However, in the EVM design, this doesn't seem to be the case. For example, the 5VA rail has 7 pins on the device, but only 4 capacitors on the EVM Decoupling schematic. 

Given the EVM is a reference design, is it OK follow this example? 

On a similar note, I see there isn't a via for every power or ground pin of the device, but instead power and ground pins are grouped together with traces or polygon pours sharing a subset of vias. Again, I want to be sure it's ok to follow this example.

  • Hi,

    We will reply to your question very soon.

    Thank you!

    Best regards,

    Chen

  • In reply to Chen Kung:

    Any update on this?

  • In reply to Gregory Duperon:

    Hi,

    Thank you for all your comments.

    Yes, you are correct!

    Our EVM board needs to follow the datasheet mentioned on Figure 133 and Page 112.

    Also I will check these details with our group and engineers.

    Thank you again!

    Have a very nice day!

    Best regards,

    Chen

  • In reply to Chen Kung:

    Thanks for this. I'd be curious what the engineers opinions are about this. Following the example of the EVM greatly simplifies my design, and if its performance meets spec, I'd be inclined to try it. 

  • In reply to Matthew Coolidge:

    Hi,

    sorry, could you please let us know where you receive the AFE58JD18 datasheet?

    could you please let us know?

    Thank you!

    Best regards,

    Chen

  • In reply to Chen Kung:

    Hi,

    If you have found the datasheet on your side,

    then please refer to the datasheet page 127 Figure 146.

    Notice 1. it explains that Placing at least capacitor for one every three supply pins.

    Therefore, for your example, 5VA has 7 pins on the device,

    then you can place at least 7/3 = 2 or 3 capacitors as close as possible to the device.

    Thank you!

  • In reply to Chen Kung:

    Hi Chen,

    Thank you! I see, not on p127, but on p112 the note of one capacitor for every three pins. I had missed this before. I had been referencing the paragraph under table 33 that says "bypass all supply pins". 

    This is very helpful, thank you. 

    Best regards,

    Matthew

  • In reply to Matthew Coolidge:

    Hi,

    Thank you for the correction.

    Yes, you are right. This is referred to the AFE58JD18 datasheet on page 112

    Figure 133. Application Circuit

    Thank you again!

    Best regards,

    Chen

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