INA226: Positive and negative voltages with common grounds

Hi Ewald,

You are correct. It should be connected to GND_INA. That is a mistake on the TI design drawing and customer replicated it. Actually, we are currently fixing the TI design document this month. 

The connections should look like this:

Hi Mayrim,

you are showing the example TIDA-00313 (-48V Telecom Current/Voltage/Power Sense with Isolation). In this case, I think the originally shown circuit (at https://www.ti.com/lit/ug/tidu361/tidu361.pdf ) was right, because you are measuring Vin+ at load-side (this is what user wants to know) and Vbus is referenced to GND (I mean GND at R1) via a voltagedivider. You changed the circuit to measure at -48V source-side.

Anyway voltage at load-side can be calculated (R_SHUNT and current is known) and the advantage of measuring at source-side (Vin-) is to measure current without the current which flows across R1, R2 and INA226-internal R_Vbus (830k).

Back to the example of Mrs. Rabab (e2e.ti.com/.../426430):

I would change the circuit like this:

.

Only disadvantage of this circuit is to measure Vbus at -28V source-side (because this is U6-GND) and not at load-side (-28V_OBOX_OUT). If you want to know voltage at load-side you must calculate -Vbus + R22 * I_load in software. In this case and under assumption of 1A current: -28V + 0.002R * 1A = -27.998V.

Advantage is, like mentioned above, you do not measure the current which flows through INA226-internal R_Vbus (830k). This is 0.00337mA at 28V.

Is this correct?

I am looking forward to realise a circuit similar to Mrs. Rabab's circuit. I think +/-15V power-supplies are very common and this is simple a way to monitor this such power-sypplies. Maybe you pick up this circuit (if it is correct) to your _datasheets

Best regards,

Ewald

Current/Power Monitor

Hi Mayrim,

I've seen my ciruit-modification is wrong. U6 Vbus shoud be connected to GND!

Kind regards,

Ewald

Hi Mayrim,

I have a further question:
I want to connect the Alert Pin of INA226. The INA226 at negetive Power-Supply is referenced to -15V in my case. I want to bring the Alert Output to my 2.5V digital System. Is the Alert Open-Drain-Output of INA226 capable to withstand a Drain-Source Voltage of 17.5V (15V + 2.5V)?
How high is the maximum Drain-Source Voltage of the Alert Open-Drain-Output Transistor?

Kind Regards,
Ewald

Hi Ewald,

Yes, but you will need to limit the current. I would recommend a pull up resistor greater than 10k ohms.

Hi Mayrim,

are you sure?

The yellow tagged Alert V_OL value says the max. voltage, when the Open-Drain Output pulls-down respectively the transistor is connected through and when a current I_OL = 3mA is flowing through the transistor.

I want to know the maximum pull-up voltage (when the transistor is switched off). This value is missing in the datasheet. At section 6.1 "Absolute Maximum Ratings" I find the I_OUT (Open-drain digital output current) = 10mA max. and the V_VS (Supply voltage) = 6V max. only. I cannot find any statements relating to the maximum pull-up voltage of ALERT Open-Drain-Output.

For me it is quite clear to limit the current below 10mA max. which is flowing through the alert transistor. I have to adjust the pull-up resistor accordingly.

Kind regards,

Ewald

Hi Mayrim,

thank you for your prompt answers to my questions! I think all my issues are solved now.

Kind regards,
Ewald