• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 50 subscribers
  • Views 607 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

INA214-Q1: INA214-Q1 Input Resistance

Glen Schmidt
Prodigy 140 points
Part Number: INA214-Q1
Other Parts Discussed in Thread: INA214

I am using a INA214 for a somewhat unique go/no go current detection system (essentially a current comparator) and I need to know the tolerance of the 10K ohm input resistance for the INA214.
Alternatively, I could work with knowing how closely balanced that the two input resistances are to each other.

I need to place large protective resistances in series with the inputs.  Yes, I know the gain will be strongly affected, but since I really just need to detect current = yes or no above some threshold, then I know I can put the series resistors there as long as I account for some variability.

The data sheet tells me what is effectively the gain tolerance but that only sets the ratio, not the literal input resistance.

Thanks

Glen

  • 0
    Guru 140200 points

    Hi Glen,

    I wouldn't do that. The INA214 is not designed to have large protective resistances in series with the inputs. Don't overlook the internal bias network, discussed in section 7.4.1 of datasheet.

    Kai

  • 0
    TI__Mastermind 26660 points

    Hello Glen,

    Thanks for coming to the forum with this question.

    The variation in absolute ("literal") resistance is +/-30%.  You are correct that the gain error specification is basically dominated by the ratio of RFB/Rint. So if Rint (10kOhm for INA214) is off by -30%, then so is the RFB (1MOhm).

    As Kai mentioned you should keep in mind that the INA21x and most of the current sense amplifiers are not exactly difference amplifiers in the inside. Even though many schematics in the datasheet show no input bias network, there is most always is an input bias stage for current sense amplifiers and this is seen in Figure 24 of datasheet.

    This input bias stage is usually the key difference between current sense amplifiers and difference amplifiers it allows current sensors to operate with input voltages much greater than the supply voltage. Anyway, the input bias stage is effectively a resistor of 2.5 kOhm from IN+ to IN-, thus adding the 10 kOhm to input pins is not going to reduce gain to 1M/20k as you would expect with a difference amplifier. You can calculate the effective gain from equations (1) and (2) in the datasheet to be 10V/V when Rs = 10kOhm for INA214. You can also simulate this ideally to see the difference.

    Hope this helps you out. Let us know if you have more questions.

    Best,

    Peter