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INA169: 1 MHz Current Sense

Fabio Soriano
Intellectual 2325 points
Part Number: INA169
Other Parts Discussed in Thread: INA139, LMP8645HV, , LMP8640, INA137, INA592

Hi team,

I received the following request.

Could you, please, suggest the correct device/reference designs for this application?

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I am working on an a digital DC-DC application below 48V. For the feedback loop I am looking for a convenient IC, to sense a 2mohm-3mohm resistor up to 20A. The effective frequency might be as high as 1MHz, but ideally 800kHz. 

The question is the product with the highest bandwidth is INA1x9 series which has 4400kHz bandwidth.

However, the gain for high bandwidth applications is too low, therefore an amplifier will be necessary after the shunt IC which could add errors to the feedback. Plus in the datasheet 0dB gain is not constant over 400kHz for this series of ICs. See below:

 

I would like to control the peak current, therefore accurate sensing is necessary, delays on the feedback loop should be minimized. What is the correct product for sensing the current accurately for an application up to 1MHz? Is there any other differential amplifier product available for my application. Please note that the input of the monitoring should stand 48V.

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Regards,

Fabio

  • 0
    TI__Mastermind 26710 points
    Hey Fabio,

    The highest bandwidth current-sense amplifiers are the INA139/INA169, LMP8645HV, or LMP8640 and this can be determined with product selection tool online. The BW is not constant for INA139 with RL=1kΩ because it is operating in unity gain and thus there will be some gain peaking.

    You could look into some difference amplifiers like INA592 or INA137 which can support the needed common-mode.

    Overall, it will be difficult to capture this waveform. The INA169 can have a max input offset of ±2mV over temperature and the shunt voltage you have is 2mΩ*20A = 40mV. You could just add a little gain (RL>1kΩ) to INA169 and this would flatten the gain peaking. After this yes you would probably want to amplify the voltage across RL with another op amp that drives an ADC.

    Another consideration is how low the current will drop. I assume it will drop to 0A and at this point INA169 could be saturated since it could have +2mV offset while the Vshunt would be 0mV. This means the amplifier would not be operating in linear region and the BW plot would not apply. This can be avoided by biasing the output pin to a voltage greater than 0V (discussed in datasheet section 8.2.3).

    Additionally, you could try to just measure the RMS current and not the peak, but this might not acceptable with the design.

    Sincerely,
    Peter Iliya
    Current Sensing Applications