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PGA460-Q1: How do waveforms of INP and INP change?

Yoshiki Ochi
Genius 9595 points
Part Number: PGA460-Q1
Other Parts Discussed in Thread: PGA460

Hi team, 

Could you show me the waveforms of INP-GND, INP-GND, and transformer voltage @ "Figure 136. Transformer-Driven Method Schematic" and "8.2.1.1 Design Requirements condition?"

In addition, to make sure that INP and INN is within -0.1V to 0.9V, could you tell me how to decide capacitances of CINP and CINN?

I wonder "Transformer main voltage (4-6) rating" is 200 VAC, on the other hand, recommended INP and INN are -0.1V to 0.9V.
I would like to know  how "Figure 136. Transformer-Driven Method Schematic"  operates especially for voltage waveform of INP to GND, INN to GND, and transformer voltage .

Lower figure shows my concern. 

Regards,

Ochi

  • 0
    TI__Expert 7575 points

    Hi Ochi-san,

    The PGA460’s AFE is designed to condition received ultrasonic frequency transducer signals from a few microvolts RMS to tens of millivolts RMS. The received echo is first amplified with a fixed-gain low-noise amplifier.

    The low noise amplifier (or LNA) is a single-ended input non-inverting amplifier with a low fixed gain output. As the first stage of the AFE, the device implements internal protection from the large driver voltages reaching upwards of hundreds of volts during burst. AFE protection from these large driving voltages is typically dependent on the external AC-coupling capacitor (CINP) to limit current flow at the input pin (INP).

    When choosing component values, I recommend using Table 101 in the datasheet as a guide. This table provides info on how to calculate the INP and INN capacitor values.

    Regards,

    Mekre

  • 0 in reply to Mekre Mesganaw
    TI__Genius 9595 points

    Hi Mekre-san,

    Could you modify or give your comment for lower yellow marked description?

    The PGA460’s AFE is designed to condition received ultrasonic frequency transducer signals from a few microvolts RMS to tens of millivolts RMS. The received echo is first amplified with a fixed-gain low-noise amplifier.
    "Table 100. Design Parameters" says Transducer driving voltage is 120Vpp. Then how much voltage is between INP and GND or INN and GND? I am worried that recommended INP and INN (-0.1V to 0.9V) are exceeded in this case...

    The low noise amplifier (or LNA) is a single-ended input non-inverting amplifier with a low fixed gain output. As the first stage of the AFE, the device implements internal protection from the large driver voltages reaching upwards of hundreds of volts during burst. AFE protection from these large driving voltages is typically dependent on the external AC-coupling capacitor (CINP) to limit current flow at the input pin (INP).
    Do you mention inside TVS diodes for internal protection?

    Regards,
    Ochi

  • 0 in reply to Yoshiki Ochi
    TI__Expert 7575 points

    Hi Ochi-san,

    There is internal circuitry within the device that has a diode-clipping like effect, but this effect is dependent on the value of the external AC-capacitive coupling capacitors (C_INP and C_INN).  The following post has more details on this:

     

    Regards,

    Mekre

  • 0 in reply to Mekre Mesganaw
    TI__Genius 9595 points

    Hi Mekre-san, 

    I understood that the INP voltage is clamped within recommended operating voltage by internal diode-clipping protection while driving a transducer as a transformer. External AC coupling capacitor is needed to prevent to flow large current through INP.

    Thank you for your supporting.

    Regards,
    Ochi