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INA193A-Q1: Output Voltage of amplifier is not having lower saturation as mentioned in Datasheet for Vsense<20mV . We are able to sense less than 0.3V at the Vout corresponding to drop across Shunt.

Asha Chandrashekar
Intellectual 320 points
Part Number: INA193A-Q1

2 Queries:

1. Output Voltage of amplifier is not having lower saturation as mentioned in Datasheet for Vsense<20mV . We are able to sense less than 0.3V at the Vout corresponding to drop across Shunt.

2. Also , we are able to see a drop across a filter resistor which is used ie drop across shunt is not equal to input to amplifier . There is a drop in the input voltage fed to Amplifier . Do you have a suggestion for this?

Below is our design , and drop is found in R25 and R26.

  • 0
    Guru 140200 points

    Hi Asha,

    your schematic didn't come through. Please try again and use the "Insert File" button (paperclip) in the header of text box :-)

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 18790 points

    Asha,

    As Kai mentioned, can you please post the schematic. I cannot understand your second question without this. 

    Regarding your first question, is your common mode above or below the supply voltage in this case? Regardless, I would believe that you could realistically have a device that performs better than the datasheet test limit. This is a test limit, so I would expect that the "bottom-out" voltage might vary from part to part. Are you seeing this behavior across multiple devices, or just a single unit? I would advise the customer that although they happen to be seeing better than listed performance in a single device, they would still need to design to the worst case possibility for a solid design. 

  • 0 in reply to Carolus Andrews
    Intellectual 320 points

    Hello Andrews,

    We havent tested the lower limit voltage in multiple devices . It has been measured only on a single device . 

    Also , lower threshold limit for Vout seems to be 0,3V as mentioned in DS . But , we are able to sense even 80mV at the Vout . There is a large delta right .

    Regarding the common mode voltage was both lower and higher than the supply voltage in this case . Means in both the case we are able to see the same.

  • 0 in reply to Asha Chandrashekar
    TI__Mastermind 18790 points

    Asha,

    The most likely explanation is that you simply have a device that performs better than the typical device. The datasheet shows expected behavior at sense voltages below 20mV, and I would advise that this behavior will most likely not be repeatable across multiple devices. 

    I took the liberty of simulating the given conditions, and the sim shows expected behavior as per the datasheet:

    Regarding the drop you are seeing over the filter, this will occur, and add additional error, not only from the voltage drop, but by actually shifting the gain of the device as well. We typically advise that the resistors of the input filter be less than 10Ω's to minimize this. If you want to keep the same cutoff frequencies, simply reduce the resistors from 100Ω's to 10Ω's, and then recalculate the capacitors based on this value. 

  • 0 in reply to Carolus Andrews
    Intellectual 320 points

    Hello Andrews,

    Thank you very much for your suggestion .

    1.We have changed the Fllter resistor to 10ohm, and now not observing high error at the input.

    But could you please elaborate on how this will effect the gain of the amplifier . It will be of much help.

    2.But regarding lower saturation , eve after checking many devices we are able to see lower saturation of 0.028V and not 0.3Volts as mentioned.

  • 0 in reply to Asha Chandrashekar
    TI__Mastermind 18790 points

    Asha,

    1. Regarding the gain, check out section 7.4.1 of the datasheet. The internals of the device are a set of resistors that are matched to each other, but can exhibit a +/-30% tolerance to the absolute value. This means that the actual resistance of the 5kΩ resistors can be anywhere from 3.5kΩ to 6.5kΩ. With these values, you can calculate the worst case effects of your gain error alongside your chosen filter resistor, as well as the typical gain error at 5kΩ.

    I got the following values for 10Ω: Min(Rint = 6.5kΩ): .153%, typ (Rint = 5.0kΩ): .199%, Max (Rint = 3.5kΩ): .285%

    As to your second question, as I said in my prior post, it might be feasible that the parts you are testing come from the same lot and perform better, but taking lot to lot variance into consideration, this is the expected operation of the device when applying a Vsense < 20mV. Also, note there are two separate cases for Low Vsense, and the performance is slightly better in this case (–16 V ≤ VCM < 0 or VS < VCM ≤ 80 V) than in the other (0 V ≤ VCM ≤ VS).