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PGA281: Unipolar operation

Ramkrishan Maheshwari
Prodigy 10 points
Part Number: PGA281

Hello,

We are planning to use PGA281 for high accuracy voltage measurement. The minimum input voltage is 350 mV and the signal will be unipolar. The gain of PGA281 will be selected as 4. The datasheet shows the offset voltage, offset voltage error,  and Gain error for +/-15 V input supply.

Is it possible to use PGA281 with only 5V supply? if yes, can we use same offset voltage, offset voltage error,  and Gain error for tolerance analysis as mentioned in datasheet for +/-15V?

Is it possible to use PGA281 with only +/-5V supply? if yes, can we use same offset voltage, offset voltage error,  and Gain error for tolerance analysis as mentioned in datasheet for +/-15V?

Regards,

Ram

  • 0
    Guru 140200 points

    Hi Ramkrishan,

    I recommend to look at figure 45 of datasheet and to read the associated text.

    And I don't see how the PGA281 shall work with a single supply. Keep in mind that this is an instrumentation amplifier and that these need enough headroom to both supply voltage rails, especially at the input stage.

    Kai

  • 0
    TI__Guru 55466 points

    Hi Ramkrishan,

    The PGA281 is an instrumentation amplifier.   

    The minimum (VSP-VSN) supply voltage specified in the datasheet is 10V (or ±5V).  Although the device can be used with assymetrical VSP/VSN supplies, the inputs  require a 2.5V headroom away from the supplies for the device to remain in the linear region.  

    Therefore, you will require an input stage VSP/VSN bipolar supply of minimum ±5V to measure a 350mV signal referred to GND. 

    Please refer to the input voltage range specification on p.3 and the input stage power supply specifications (VSP-VSN) on p.5 of the PGA datasheet.

    Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Prodigy 10 points

    Thanks for the clarification. If I use +/- 5 V for the input supply, can i use the same value of offset voltage and gain error which is mentioned in the datasheet for +/-15 V supply for tolerance analysis

  • 0 in reply to Ramkrishan Maheshwari
    TI__Guru 55466 points

    HI Ramkrishan,

    The PGA281 power supply rejection ratio (PSR) specification is ±0.3μV/V typ, or ±3μV/V max.  In your case, based on the PSR specification, the projected offset change seen when changing supplies from ±15V to ±5V is ±0.3μV/V*(30V-10V)= ±6μV typ or ±3μV/V*(30V-10V)= ±60μV offset change max.  Therefore, for your error analysis, use the Vos specification at ±15V, and add the additional offset change per the PSR specification. 

    The gain error is not expected to change with supply voltage change; you can use the same ±15V gain error specification when using ±5V supplies.    

    Thank you and Regards,

    Luis