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AFE5818: CONFIGURING REGISTERS FOR LNA, PGA, VCAT IMPLEMENTATION

Nikhila S K
Prodigy 10 points
Part Number: AFE5818


Tool/software:

I am working with the AFE5818, including the LNA, PGA, and VCAT, but it seems that the LNA, PGA and VCAT is not changing as expected, even after reviewing the datasheet and writing the specific register bits.

Could you suggest the correct registers that need to be updated to properly reflect this change?

  • 0
    TI__Expert 7725 points

    Hi,

    How are you checking this ?

    Did you read the corresponding  register to verify the spi is working correctly ?

  • 0 in reply to Sachin H K
    Prodigy 10 points

    Hi, 

    We have a GUI that displays the peak-to-peak voltage of the ADC output. The SPI is functioning correctly.

    We're configuring the gain settings by writing to the registers, C3, C4, and CB. 

  • 0 in reply to Nikhila S K
    TI__Expert 7725 points

    Ok,

    Can you tell what is your original PGA/LNA /DTGC setting and expected output at ADC ?

    Now what did you change and what is the output ?

    What is the signal you are feeding into this AFE ?

  • 0 in reply to Sachin H K
    Prodigy 10 points

    We are feeding a 500 kHz, 250 mVpp signal into the AFE using a signal generator. The input into AFE has also been physically probed to ensure that the correct signal is going into the AFE. The initial AFE configuration set is as follows: 010014, 032012, 040011, 020080, 020380, 020100. Then, we updated the configuration register to 020000 in order to achieve a sine wave output.

    The LNA is configured to 12 dB, the PGA to 24 dB, and the VCAT to 36 dB using configuration registers C3, C4, and CB; the register configuration is C30000, C44000, CB00E0. Ideally, the overall gain should be 0 dB (LNA + PGA - VCAT).

    However, the ADC output shows a Vout of 76 mVpp, whereas we are expecting 250 mVpp. 

    Can you confirm if there is any additional register to be configured for the gain setting?

  • +1 in reply to Nikhila S K
    TI__Expert 7725 points

    To check the gain programmed correctly->  change the gain by 6dB and accordingly the output should change by a factor of 2 . This way you can check whether gain programmability is working fine or not .

    To match absolute gain -> Datasheet condition is at 5MHz input signal. In the device there is HPF so 500KHz signal might have some effect on this.

    Since this is NDA restricted device we can continue further in mail . Please reach out to ultrasound_rx-support@list.ti.com