This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

INA168-Q1: Bias Current Min/Max data + Zener on inputs

Part Number: INA168-Q1
Other Parts Discussed in Thread: INA168, INA219, , INA226

This is in regards to the input filter of the INA168:

A 0.100 ohm current sense resistor is being used as Rshunt to measure a current 0 – 500 mA. They would like to use 1K resistors for Rfilter and put a Zener diode to GND at the Vin+ and Vin- pins for protection. This is concerning to me because of bias current variability and the Zener diode leaking current off the line. Would you be willing to answer the following:

1. What is Min/Max specs of input bias current (do we have histogram data)? Also bias current delta between IN+ and IN-?

2. Is placing Zener diodes to GND on the pins a concern?

Regards,

Kevin

  • Hello Kevin,

    Thanks for reaching out on the forum. Typically for most current shunt monitors we strongly encourage to keep the filter resistors under 10 ohms, as they can provide a substantial error. This is due to resistor variation, change in gain, and as you suspected input bias current. While the zener diode may siphon some current off, that is still something we recommend if customers want to protect from large relatively long transients. They could possibly choose a rshunt value that makes their expected system Imax generate an output voltage a little lower than the swing to supply so that they can use a zener with a slighly lower breakdown voltage that will turn before the device ESD cells, to ensure that the larger external protective zeners take the brunt of the transient.

    1. This is an older part and as such we may not have done all the same tests that considered the standard now. I will check with my team tomorrow and see if I can get some information on that.

    2. That should not be a problem.
  • Hi Patrick,

    I realized I made a mistake in the part number...using the INA168-Q1 in a different opportunity. This should be the INA219 (non Q1 version).

    This is for an automotive opportunity but they dont need this to be auto qual'd necessarily. The reason they are asking about the zener + 1kohm resistor is because the INA219 cant support higher voltages. They are open to using a different part...do you think the INA226 is a better part? Their main concern is having to change their software but doing a quick pass of the datasheet it looks like the I2C timing and register map are the same so to me this looks like a good alternate.

    Do you agree?

    Regards,
    Kevin
  • Hello Kevin,
    The INA226 definitely allows for a higher common mode voltage and we do not support any bidirectional power monitor devices with a greater VCM specification. The ADC conversion times for the INA226 are slower. However, it does conform to the typical I2C standard like you say. So I do think you can pitch this part to them.

    However, one thing I would like to mention though is that with this device and any other current shunt monitor device, there is a resolution limit. Assuming a 500mA max, the smallest current that this device will be able to resolve is 15.3uA.