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Original question:

PGA460-Q1: PGA460 Frequently Asked Questions (FAQ) & EVM Troubleshooting Guide

PGA460: Connection transformer-pin DECPL MOSFET

Asael7
Intellectual 270 points
Part Number: PGA460

Hi.

I'm not sure if I should connect the transformer to the MOSFET connected to DECPL pin or not.

In datasheet the connection is like in the first image but in the EVM boards connection is like in the second image.

So, when should be used the first connection and when the second connection?

  • 0
    TI__Mastermind 27950 points
    Hi Martin,

    The time and temperature decouple features of the PGA460 are advanced/optional features. If you have no need for the decoupling features (i.e. your system is not temperature or noise sensitive), you can keep the DECPL pin floating, and connect the transformer and tuning capacitor directly to ground as shown in the following simplified reference design:
    "PGA460 Mono-static Transducer Transformer Driver Small Form Factor Design File": www.ti.com/.../slac754
  • 0 in reply to Akeem Whitehead
    Intellectual 270 points

    Ok. But if the system is noise sensitive, which circuit is it OK?
    I understand that the MOSFET is to decoupling the transformer but in the second circuit, the transformer is not connected to the decoupling MOSFET like in the first circuit. So, I think that first circuit is the correct but the second is used in EVM boards, that's why I don't know which one use.

  • 0 in reply to Asael7
    TI__Mastermind 27950 points

    Hi Martin,

    If you are to use the decouple feature, then use the schematic from the datasheet. The EVM schematic is modular such that the transformer and tuning capacitor can either be decoupled through the FET or grounded directly depending on the R39/40 resistor configuration.

  • 0 in reply to Akeem Whitehead
    TI__Genius 11015 points
    Hello Martin,

    Hope Akeem's response has answered your question. I will close this thread for now. Please start a new thread if you have any further questions.