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PGA460: INN better connection

Koyo Asaishi
Intellectual 1960 points
Part Number: PGA460

Hi team,

I have questions about INN connection.

This device is used for ultrasonic application, then SNR is important.
When we tested with same connection as datasheet, SNR is not good but when we connect to GND, SNR looks better.

Questions are;

  1. Can we connect INN to GND directly without capacitor?
    We are wondering if gain decrease or it will be unstable etc.
  2. Can we connect as differential connection without capacitor?
  3. For LNA in the device, is this such a differential amp circuit or any other? I observed 0.9V at INN.
    If you can open the info, could you share it?

Best regards,
Koyo

  • 0
    TI__Mastermind 27950 points

    Hi Koyo-san,

    Responding to your questions:

    1. We do not recommend connecting INN directly to ground because the C_INN capacitor is used to help limit current and is part of the filter network of the analog front end. Did the customer calculate and update the value of C_INN based on the C_INN equation using transducer frequency in the PGA460 datasheet (see "Table 101. Recommended Component Values for Typical Applications")?
    2. The PGA460 is a single ended input device, whereby INP is the input pin, and the INN should be treated as an auxiliary filter/ground pin, not an input. It is not possible to connect as a differential without the capacitor.
    3. The analog front end is biased to 0.9V to allow for the positive and negative voltage swing of the transducer. The INP/INN network is still a single ended circuit internally, not a differential.

    Can the customer provide the echo data dump capture of their performance envelope with C_INN and with INN connected directly to ground?

  • 0 in reply to Akeem Whitehead
    TI__Intellectual 1960 points

    Hi Akeem,

    Thanks for the answers.
    We solve the issue because we found the issue comes from DCDC converter.

    The converter has PSM function, then this PSM freq interfere to the signal.

    Thanks 
    Koyo