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INA223: Max speed when measuring both voltage and current using the internal mux.

Niels Leijen
Prodigy 10 points
Part Number: INA223

Hello,

For a project I want to use the INA223 in combination with an ADC to measure both the voltage and current of my load. For this I want to use the internal mux to switch at about 20khz between the "bus voltage measurement" and " shunt voltage measurement".

My question is: what is the settling time of the output if you switch betweeen the two and how fast is it possible to switch between the two?

  • 0
    TI__Mastermind 30145 points

    Hello Niels,

    Welcome to the E2E forum. Thank you for the question. We hope to address your questions promptly.

    Unfortunately we do not have any information or data about the output settling when the MUX is switched. If there is any capacitance at the OUT pin, then this will dominate any settling time. The total output capacitance will vary on your ADC and the necessary RC conditioning ("charge bucket filter" e.g.). I would suggest setting this circuit up and measuring the output disturbance and settling when switching mux from bus voltage to shunt voltage.

    I do not believe the settling time will be long when switching from shunt to bus since this is a direct connection to the bus voltage through a resistor divider.

    Anyway with a 20kHz switching this means output needs to settle within 50us and I believe is perfectly reasonable. The small-signal rise time of amplifiers can be approximated as 0.35/BW. For the 20kHz BW of the INA223, this means a rise time of 17.5us, which is well within the 50us window. For your information, I got this equation from the Analog Engineer's Pocket Reference book: http://www.ti.com/amplifier-circuit/op-amps/precision/support-training.html

    Hope this helps.

    Sincerely,

    Peter