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INA180: INA180 vs OPA365 current sensing results

Hasan Talasci
Prodigy 20 points
Part Number: INA180
Other Parts Discussed in Thread: OPA2365, OPA365, INA296B, INA240

Hi all

I was doing some simulation about low side current sensing circuit using high speed opamp and current sense amplifiers. Since INA180 has high market rank i decided to use it to simulate result of each device.Since im new at current sense ic family but i was using opamp based circuit many years.

You can see below result and circuit diagrams.Current source is sine wave 2amps peak rating and 10kHz. Same current wave has been used for each circuit as described VF2 probe. INA180A1(gain=20)doesnt start to sense until current source reaches at 1.6Amps. At that point inaout equals to 1.6mV . Otherwise opa2365 (gain set by 20 as well ) does the job great and it starts to sense around 1Amp of current thought the shunt resistor 5milliohms. Actually my expectation was ina180 has better performance. Also as i said before im not familiar with current sense ic and maybe im missing some points on the datasheet. Can you please explain them ? What do you think about performance of each ic , which one better for operation ? Do you recommend higher performance low cost current sense ic's such as ina180 ?

Thanks.

Hasan.

  • 0
    Prodigy 20 points
    Hasan Talasci said:
    At that point inaout equals to 1.6mV

    sorry.  it must be 20mv which is lowest voltage of the inaout. It doenst sit to ground level. it has 20mV offset even at negative transient.

  • 0
    TI__Mastermind 31915 points

    Hello Hasan,

    I am looking this over and will respond shortly.

    Sincerely,

    Peter

  • +1 in reply to Peter Iliya
    TI__Mastermind 31915 points

    Hey Hasan,

    There are several things happening here. 

    First, you are sensing bidirectional current (positive and negative) with unidirectional amplifier circuits. Thus you will see an inverting overload recovery every half cycle. Also, these delays are usually going to be proportional to the amplitude of the overdrive (the more negative the current, the longer the delay).

    See the inverting overload recovery (~30µs) for INA180 from datasheet below:

    This behavior is not exactly covered in OPA365 datasheet, but it's reasonable to assume it will be faster given that it shows a fast non-inverting overload recovery time (<0.1µs) specification and will have faster closed-loop bandwidth (2.5 MHz) and slew rate.

    The other factor here is that the input voltages are small and may be affected by comparable offset voltages.

    When choosing between an op amp and current sense amplifier, it depends upon system requirements.

    First thing is to determine if you can use a mid-supply bias voltage (Vs/2) given that you are sensing bidirectional current. This would be a voltage (equal to Vs/2) at INA180 REF pin or at R7 of the op amp circuit. This would remove any overload recovery delay times and simplify overall measurement. See this document for more information: https://www.ti.com.cn/cn/lit/an/sboa551/sboa551.pdf 

    If you need high bandwidth and short settling times, then there are other faster current sense amplifiers (e.g., INA240 or INA296B), but if you have REF = Vs/2, then you probably would not even need a faster amplifier.

    Op amps in a differential network are nice because you tune the gain and frequency roll off to what you need, but you need very accurate gain setting resistors (~0.1%) in order to achieve gain error performance of most CSAs. With a CSA, the internal gain setting resistors are precisely matched and final test screened for tolerance and drift over temperature. Resistor tolerance in differential networks also play a role in the device CMRR. This document explains more about this: https://www.ti.com/lit/an/sboa582/sboa582.pdf?ts=1707779898178&ref_url=https%253A%252F%252Fwww.google.com%252F 

    So this all to say that you need to understand what resistors would be used, what the tolerances and 6-sigma temperature coefficients would be and what would the worst-case gain error and drift over temperature would. Then compare this (and total cost) to INA180.

    Sincerely,

    Peter