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Right now I'm picking a current sense amplifier for my application, and I'm looking for for amplifiers with maximum offset voltage of below 50uV (and offset and bias currents in nA/pA range).

Luckily, I have found a few of them at a reasonable price, but they all seem to have GND pin and REF pin. GND pin is always marked in datasheets as ground (who could imagine).

For example: TSC212 Datasheet or NCV214 Datasheet

These amplifiers have a GND pin, and can work over wide supply voltage range. Since I want true zero output, I want to supply them with 3.3V at their Vcc and -3.3V at their GND pin, as well as GND (0V) at their REF pin to produce MCU ADC readable values referenced to 0V. However, the GND (negative supply pin) is marked as "Ground" in the datasheets, there is no explicit indication that I can use negative supply with them.

My electrointuition and familiarity with amplifier structure (to a certain degree) suggests, that I should have no problem using them with negative supply rails, since voltages are relative and bla-bla (excuse my scientific language). Nevertheless, I would want someone smart to confirm it for me (or maybe I'm wrong?). It's suspicious that negative supply voltages are not mentioned in datasheets.

Question: can current sense amplifiers with negative supply pin marked as GND work with negative voltage on GND pin, given supply voltage (V+ - V-) doesn't exceed the spec?

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    \$\begingroup\$ with maximum offset voltage of below 50uA o_O ??? \$\endgroup\$ Nov 4, 2021 at 11:46
  • \$\begingroup\$ yeah there are a few of them with max offset of 25-35uV. Not the point tho \$\endgroup\$
    – Ilya
    Nov 4, 2021 at 11:49
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    \$\begingroup\$ I meant, maximum offset voltage of below 50 microamps? \$\endgroup\$ Nov 4, 2021 at 11:50
  • \$\begingroup\$ Ah didn't notice a typo, apologies. Will fix. \$\endgroup\$
    – Ilya
    Nov 4, 2021 at 11:51

2 Answers 2

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However, the GND (negative supply pin) is marked as "Ground" in the datasheets, there is no explicit indication that I can use negative supply with them.

That is because VCC voltage is given as the voltage at VCC pin w.r.t. the voltage at GND pin. So, what the IC sees is the difference between VCC and GND (For example, look at Note.1 at p.4 of TCS21x datasheet). So, if you apply -3.3V at GND pin and 3.3V at VCC then the supply of the chip will be 6.6V. If this is not a problem for the chip (i.e. does not exceed the voltage given under ABS MAX RATINGS) then there'll be no problems. Normally, in practice, a small negative voltage (e.g. -0.1V as Andy suggests in his answer) could be enough for zeroing.

What you should take into account are:

  • Offset voltage: It'll reflect to the output with gain factor. For A = 200V/V the zero-voltage of the amplifier can be as high as 7mV.

  • Common-Mode Voltage: This is quite important if you are to go for hi-side (a.k.a. positive-side) sensing. The voltage at positive side w.r.t. the voltage at return path (could be GND or whatever) should not exceed the common-mode voltage.

Remember to make zero-calibration on your ADC side.

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  • \$\begingroup\$ My logic was exactly that. Thanks for confirming it. \$\endgroup\$
    – Ilya
    Nov 4, 2021 at 12:06
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It's suspicious that negative supply voltages are not mentioned in datasheets.

That's probably because the output on both chips can typically swing to within 5 mV of GND but, if you want to apply a small negative supply to GND of -100 mV that would be fine - tie REF to 0 volts.

Even a negative supply of -3.3 volts will be fine providing the whole supply rail (positive and negative together) do not exceed the maximum stated in their respective data sheets.

can current sense amplifiers with negative supply pin marked as GND work with negative voltage on GND pin, given supply voltage (V+ - V-) doesn't exceed the spec?

The ones you have listed can but if you want some global answer that covers all possible existing and future candidates then no.

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  • \$\begingroup\$ Thank you for your reply. I think I saw this right. I'm using an inverting charge pump to make a negative supply with literally 1 IC and 3 caps. Is there some simpler way to make -0.1V? \$\endgroup\$
    – Ilya
    Nov 4, 2021 at 12:07
  • \$\begingroup\$ There's probably nothing simpler than a chip and 3 caps. If you had a spare inverter you could wire as an oscillator you might save a small amount of room and a few pennies. \$\endgroup\$
    – Andy aka
    Nov 4, 2021 at 12:09

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