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INA132: change of gain

Part Number: INA132
Other Parts Discussed in Thread: INA827, INA331, INA145, INA122, INA126, INA321, , INA500, RES11A, INA597, OPA317

Hi,
is it possible (even not recommended) to change the gain?

Regards, Holger

  • Yes. But the additional external resistors are likely to have worse characteristics than the internal precision resistor network. Also note that the internal resistors are trimmed to be equal to each other, but not to an absolute value.

  • Hi Clemens,
    understood. Customer is looking for a current sensing amplifier with gain of 5, diff voltatage of max 2.3VVAC for CT and ref volt of 1.65V.

    Regards, Holger

  • The INA145 is a difference amplifier with a programmable gain. You might also be able to use an instrumentation amplifiert like the INA331 or INA827.

  • For 5V supply you should consider using INA321 or INA331 while for 36V supply INA827, INA122 or INA126 (all specified with minimum gain of 5).

  • because of lower cost they want to use the INA500A. What do you think?

    Regards, Holger

  • The INA500 itself does not allow a gain of 5; adding external resistors is possible, but would have the same problems as the INA132.

  • Holger,

    If your customer would consider INA500A with max offset of 3.5mV, min CMRR of 62dB and max GE of 0.05%, then they are not concern with obtaining high precision.  Thus, in this case they may simply use any low cost op amp and add four resistors (with 5:1 ratio) to create their own difference amplifier with a gain of 5 - see below.  One may get low cost 0.1% matching resistors that would assure min CMRR of 54dB and max gain error of 0.2% while offset may be calibrated out.

  • Hi Marek,
    here the req for the current sensor:

    Supply Voltage

    3.3V

    Single supply

    Input voltage

    ±2V

     

    Offset voltage

    <0.5mV

     

    Gain

      1 to 5

    Should be Configurable

    Gain Error

    <0.1%

     

    Output Voltage drift

    <10mV

     

    Vref

    1.65V

     

    Regards, Holger

  • It would be useful to specify IQ, GBW, Vcm and Vout ranges, and express drift in [uV/C].  In the absence of such info, there are many op amps that would meet above requirements - please click on the link to see the list:

    https://www.ti.com/amplifier-circuit/op-amps/precision/products.html#480=1&1261max=3.6%3B5.5&2max=0.002%3B0.5&

    As far as resistor matching goes, if the customer absolutely requires better than 0.1% resistor matching, they may use our recently introduced RES11A, Thin-Film Resistor Dividers with various ratios that are matched to better than 0.05% - see below. 

  • Hi,
    it is difficult to get this info from customer. They want to use
    - INA597 (with 5V supply) or
    - OPA317

    Regards, Holger

  • There is a large difference in IQ and GBW between INA597 and OPA317 (1100uA vs 21uA and 2MHz vs 0.3MHz, respectively) so I presume your customer does not have specific IQ/GBW requirements other than low cost.  In this case OPA317 together with matching resistors like RES11A may be a good choice.