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ADS8584S: Power Supply for AVDD

Intellectual 2675 points

Replies: 2

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Part Number: ADS8584S

Hi Team,

ADS8584S is used in our application, for the power supply for AVDD, can TLV759P(http://www.ti.com/product/TLV759P)(High noise, low PSRR) meet the requirements of ADS8584S?

The input of TLV759P is the output of a buck with 500kHz switching frequency and 29mV ripple. 

LP38798(www.ti.com/product/LP38798)(Low noise, high PSRR) works good for AVDD, now we want to evaluate if TLV75901 can work well without any effect on ADS8584S. Could you please help confirm?

Thanks and Best Regards!

Hao

  • Hi Hao,

    The PSRR on TLV759P is 30dB at 1MHz and 45dB at 100kHz, let's assume that the PSRR is 35dB at 500kHz, based on the equation below:

    PSRR=20∙log (Ripple_input / Ripple_output )

    It can attenuate a 29mV ripple at the input to 516uV at the output of TLV759P. When your ADS8584S is set to +/-10V input, one LSB will be 20/2^16=20/65536=305uV, hence this noise equals to 1.7 code. This effect will be worse if the ADC is configured to +/-5V input range.

    However, ADS8584S has higher PSRR (lower than -100dB when >100kHz) with decoupling capacitor shown below, so this 0.5mV ripple at the power supply of ADC should not have a significant impact to the performance.

     I hope this information is helpful to you. Below is an application note about the LDO PSRR, for your reference.

    http://www.ti.com/lit/an/slaa414a/slaa414a.pdf

    For the circuit design for power supply, you may check on the power management E2E forum. Thanks.

    Best regards,

    Dale


  • In reply to Dale Li:

    Thanks, Dale!