I found application note TI Designs: TI TIDU361A

In the attached diagram taken from TI TIDU361A. The Vin- of INA is connected to the negative power supply. The same Vin- is also connected to GND_INA in the diagram, which is the ground pin of the INA device. This look like the GND pin of INA is connected to negative power supply.

I have marked two circles in red in the attached diagram. The red circle on the top is Vbus of INA. What will be the voltage of Vbus connected to Zener diode ? The resistors R1 and R2 making voltage divider also connected to Vbus. Do we need to make Vbus positive ? What is Vbus voltage ?

The other red circle on the bottom in the diagram. Is that "Vs" of INA ? With Zener diode (+4.7 V) and resistor Rz on the bottom, are we making Vs positive ?

 

Hi eng,
This is the d/s circuit diagram, for +36V supply, where did you get circuit?

It will be Vs, for the Logic
E
BTW: The top 'Zener' is a transorb device

 

Hi,

The circuit diagram in the original post is taken from the link below. Also attach as PDF.

https://www.ti.com/lit/ug/tidu361a/tidu361a.pdf?ts=1732962313012&ref_url=https%3A%2F%2Fwww.google.com%2F

 

Hi eng,
This is the d/s circuit diagram, for +36V supply, where did you get circuit?

It will be Vs, for the Logic
E
BTW: The top 'Zener' is a transorb device
View attachment 337017View attachment 337019

Yes that is true. The bus voltage in INA226 is from 0V to 36V. But the application note I also provided in attachment is monitoring the negative bus and shunt voltage. I am still wondering my questions in original post. Kindly have a look again.

 

hi.

What will be the voltage of Vbus connected to Zener diode ?

It is NOT a Zener diode, it is a 24V limit transient absorber.

The other red circle on the bottom in the diagram. Is that "Vs" of INA ? With Zener diode (+4.7 V) and resistor Rz on the bottom, are we making Vs positive ?

You are making Vs 4.7v positive RELATIVE to the GNA GND [which is at -48v]

E

 

Thanks for your comment. I got it we are making Vs 4.7v positive with respect to INA GND and the INA GND is -48 V.

According to datasheet Vs power supply has to stay between 2.7 V to 5.5 V with respect to INA GND. If the INA GND is -48 V then the zener diode will make the Vs 4.7v positive with respect to INA GND. What should be the optimum value of Rz, in the diagram posted in original post ?

I am not getting the calculation for Vbus.

According to datasheet of INA 226, the Vbus has to stay between 0 and 40 V. Kindly explain the calculation of Vbus.

 

Hi eng,

What should be the optimum value of Rz, in the diagram posted in original post ?

If we assume a regular 4.7V Zener from a 48V supply with say a 10mA operating current.

That would be (48V-4.7V)/0.01A= 4k3

According to datasheet of INA 226, the Vbus has to stay between 0 and 40 V. Kindly explain the calculation of Vbus.

I would read that as being less than 40V.
Use the R1/R2 as shown in the d/s image, theVbus, will be 48V/(12k1/(12k1+35k7))= 35.8V

E

 

@ericgibbs

Thank you very much for your comments. I learn a lot from your comments. This help to understand the circuit diagram I posted in the original post taken from an application note in which INA226 was used as bus and shunt monitor for negative power supply -48 V.

In my application, I have -5 V instead -48 V. The negative power supply -5 V is connected to a load. The load current is not more then 10 mA.

The power supply pin of INA226 is Vs and according to datasheet Vs has to be within 2.7 V and 5.5 V with respect to ground.

If I connect the INA_GND to -5 V and Vs to the 0 V which is PCB_GND (the signal and power ground for positive power supply on the PCB).

If the Vs pin is connected to 0 V (PCB_GND) and the INA_GND is connected to -5 V, then Vs is INA_GND + 5V already. Do I need to connect a diode, marked as "D2" red in the attached circuit ? Do I need Rz ?

Regarding Vbus, if I also connect Vbus to 0 V (PCB_GND) then then Vbus is also INA_GND + 5V already. Do I need to connect a diode, marked as "D1" red in the attached circuit ? Do I need R1 and R2 ?

 

hi ng,
Is this image showing what you are asking, check the connections.
Mark up the image, showing any corrections.
E

Check the ISO1541 supply c0onnections.