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PGA900: DAC loop back

Part Number: PGA900

Hi,

i tried to unterstandthe DAC Loop back function and calculation of the ADC output.

  • Could someone please confirm/correct the following calculation:

DAC output: 0x0666 or 0,5VDC

Voltage after loop back amplifier: 0,1V (0,5V/5=0,1)

ADC input voltage / Out put AFE Amplifier (4V/V): 0,4 (0,1V*4=0,4)

  • Is it possible to use the loop back for an ADC DAC function or integrity check?

Regards

Mario

  • Hi Mario,

    Those calculations look correct, although the minimum available gain for the PGAIN is 5 V/V instead of 4 V/V. The DAC loop back can be used for an integrity or function check, and it can be fully controlled through firmware in the integrated M0.

    Regards,

  • Hi Scott,

    thanks for the response.

    I`ve got some additional question about the Loop back function.

    How I have to setup the AFE for an Loop back measurement in an normal resitive application?

    - Switch off the bridge supply?

    - Set the relevant bits in the DAC_LPBK_CTRL

    - some thing more?

  • Hi Scott,

    thanks for the response.

    I`ve got some additional question about the Loop back function.

    How I have to setup the AFE for an Loop back measurement in an normal resitive application?

    - Switch off the bridge supply?

    - Set the relevant bits in the DAC_LPBK_CTRL

    - some thing more?

  • Hi Mario,

    It isn't strictly necessary to switch off the external bridge supply since the VCM for the DAC loopback gain is set at VBRDG/2 internally.

    You will need to set the EN_LB, LB_AMP_EN, and LB_CONNECT bits in the DAC_LPBK_CTRL register and adjust the PGAIN value appropriately. That's all that is needed for the loopback setup.

    Regards,