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PGA281: Replace PGA281

zhang ping
Genius 3505 points
Part Number: PGA281
Other Parts Discussed in Thread: PGA280, PGA206, INA851

My circuit function is to measure 0-7.4A current. Pga281 is used for current sampling, and the accuracy shall not be higher than 500uA. Since pga281 is out of stock, I hope to use instrument operational amplifier or general operational amplifier to build a circuit to replace the function of pga281. I hope to have a reference scheme, please help me; I need high-precision sampling circuit;

  • 0
    TI__Guru 53566 points

    HI Zhang,

    We do not have a direct pin-to-pin replacement for the PGA281.  The closest device would be the PGA280 which is currently out of stock.  Unfortunately, we do not offer a reference design to replace  PGA281 since this would be a very complex, expensive discrete circuit.  The PGA281 is a highly integrated device offering low offset, low gain error and ultra low drift offering 8 binary gains ranging for 128-V/V to attenuation of 1/8-V/V.  

    One possibility is to use an instrumentation amplifier and switch a couple of different RG gain resistors using low on-resistance, low capacitance photo-mos relays.   Keep in mind, the circuit will become expensive as you add more gain options. 

    There is also the PGA206 offering binary gains 1 to 8, that may or may not fit your application depending on your common-mode voltage and gain requirements. If you require fully-differential output, you could follow the PGA206 with a fully-differential amplifier.

    You have mention that the circuit is to measure 0-7.4A current.  What is the value of the shunt resistor to measure current?  What is the common-mode voltage? Do you require a fully-differential output?  What is the full-scale range of the ADC?

    Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    TI__Guru 53566 points

    Hi Zhang,

    There are several possibilities, but if you require differential output, below find a couple of suggestions.

    1) One possible solution requires to drive a fully-differential ADC, one possibility is to use the INA851, a number of analog switches, 4- precision amplifiers and a number of high precision, low-drift resistors or matched resistor networks. The number of resistors and channels on each switch depends on the number of gains required.  The accuracy of the solution will be directly related to the drift matching of the resistor network. Below is a block diagram.  

    2) Another simpler solution is using the PGA206 followed with a Fully-differential amplifier to perform single-ended to differential conversion; this may meet the requirement depending on your gain and/or common-mode voltage needs.

    If you require more detailed answer, please answer the following questions: 

    A) You have mention that the circuit is to measure 0-7.4A current.  What is the value of the shunt resistor to measure current?  What is the common-mode voltage? Do you require a fully-differential output?  What is the full-scale range of the ADC?

    B) The absolute accuracy of the shunt sense resistor to measure the current typically dominates on the capability of the measurement.  A 500uA on a 7.4A full-scale corresponds to an absolute accuracy of 0.006%.  Shunt sense resistors available in the market do not meet this accuracy requirement.  Do you mean 500uA accuracy, or do you mean 500uA resolution?  Please let me know which part number you plant to use for a shunt resistor.

    Thank you and Regards,

    Luis