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INA213: Inquiry about "Swing to V+ power-supply rail"

ArTzy
Genius 13999 points
Part Number: INA213

Hi Experts,

Good day. I have a question about  max value of "Swing to V+ power-supply rail" for the orderable part:

  • INA213AIDCKR

Table of "6.5 Electrical Characteristics" show "Swing to V+ power-supply rail" is Maximum value "(V+) – 0.2" in case of output current 0.5mA.
Please tell me the maximum value when the output current value is lower, for example 100uA or 10uA.
0.5mA is excessive because my application carries very little current. I understand that the typical characteristics refer to Figure 10.

Thank you.

Regards,
Archie A.

  • +1
    Guru 244020 points

    MOSFETs behave like resistors. So you can assume a worst-case output impedance of 0.2 V / 0.5 mA = 400 Ω.

    400 Ω × 100 µA = 40 mV
    400 Ω ×  10 µA =  4 mV

  • +1
    TI__Mastermind 26485 points

    Hello Archie,

    I would not assume that you will get higher voltage just because you limit your output current.  This is because there are other circuitry involved and the temperature variation is a factor.  I would normally design to the Swing High value as good practice.  You will see improvement with less current but that number will vary from device to device.

  • 0 in reply to Javier Contreras4
    Guru 140200 points

    Hi Archie,

    I agree with Javier. Figure 10 is only showing the typical performance and it really looks like the output MOSFETs present their drain source "on" resistance when being fully turned-on. But this need not necessarily be true. Another mechanism could limit the output voltage independently of the output current, the driver circuit of output stage, for instance.

    There's another trap: When the INA213 is emitting this specified maximum output voltage, the output stage is sitting in saturation and no longer works in linear operation. The INA213 is out of regulation then. The output voltage is no longer fully correct and output recovery issues can be seen. When highest precision is needed or when an ADC has to be driven it's wise to drive the output not into full saturation but to stay a bit away from the supply rails. This is no special behaviour of the INA213 but of all chips containing a rail to rail output stage.

    Kai

  • 0 in reply to Clemens Ladisch
    TI__Genius 13999 points

    Hi Experts,

    Thanks for your responses.

    Follow up query, is it appropriate to use the swing high level as “(V+) – 0.19” when the output current is 1.02uA?

    Thank you.

    Regards,
    Archie A.

  • +1 in reply to ArTzy
    TI__Mastermind 26485 points

    Archie,

    I would assume that you can think of Swing High as that value but nothing is tested in that conditions.  As Kia pointed out it could be outside the linear range and you also need to account for gain error and offset if you expect to calculate what is the minimum voltage at the input when the output is as swing high.