TIDA-00528: 40-200V Monitoring

Neel Desai

Part Number: TIDA-00528
Other Parts Discussed in Thread: INA226

Hello,

I would like to use the TIDA-00528 design for a 48-200V monitoring application.

The Rz calculation from reference guide Rz <= (205-5.1) / (50uA + 25uA) = 2.66M (must be less than 2.66M). I have chosen my Rz as 1.33M and calculated powerRz = ~29mW.

For the Vbus to the INA226, my high Vbus would be ~6.29V (with Rtop = 150k and Rbottom = 4.75k for the voltage divider), with powerR = ~26mW.

I changed the PFET out for IRFR9214TRPBF (250V rated) instead of 600V rated (to save space).

I am requesting to check my schematic work to ensure the monitoring would work for 48-200V monitoring. In my schematic, the I2C (SDA/SCL) lines are pulled up elsewhere in the schematic.

Please provide any feedback.

Thank you for your help.

over 3 years ago

0 Guang Zhou over 3 years ago

TI__Mastermind 27470 points

Hi Neel,

What is the relationship between the two grounds in your schematic? Also, what is the application’s goal, are you trying to replicate the TIDA’s circuit functionality exactly or to adapt it for something else?

The schematic looks quite different from the original circuit.

Regards, Guang

0 Neel Desai over 3 years ago in reply to Guang Zhou

Prodigy 140 points

Hello,

The relationship between GND and ISO_GND is "GND" is the 3V3 input GND and ISO_GND is isolated ground output, tied back.

The goal is to measure voltage / current on 48-200V bus voltages, the circuit should be similar to TIDA circuit, with the differences listed below (from original post):

The Rz calculation from reference guide Rz <= (205-5.1) / (50uA + 25uA) = 2.66M (must be less than 2.66M). I have chosen my Rz as 1.33M and calculated powerRz = ~29mW.

For the Vbus to the INA226, my high Vbus would be ~6.29V (with Rtop = 150k and Rbottom = 4.75k for the voltage divider), with powerR = ~26mW.

I changed the PFET out for IRFR9214TRPBF (250V rated) instead of 600V rated (to save space).

Regards,

Neel

0 Guang Zhou over 3 years ago in reply to Neel Desai

TI__Mastermind 27470 points

Hi Neel,

I gather you only need to measure the bus voltage. Even then the circuit will not work.

Regards, Guang

0 Neel Desai over 3 years ago in reply to Guang Zhou

Prodigy 140 points

Can you provide your feedback on what is incorrect.....?

0 Guang Zhou over 3 years ago in reply to Neel Desai

TI__Mastermind 27470 points

Hi Neel,

As drawn, the 200V is dropped on D8. Assuming the OPA circuit is working, then there will be 200V dropped on R26.

I assumed the three grounds are at the same potential since their relationship is not shown.

Regards, Guang

0 Neel Desai over 3 years ago in reply to Guang Zhou

Prodigy 140 points

Hello Guang,

Thank you for the comments. In the reference design - The 400V is dropped across D2i and R1i, see reference schematic snippet below:

I based my schematic on the reference design schematic shown below.

0 Guang Zhou over 3 years ago in reply to Neel Desai

TI__Mastermind 27470 points

Hi Neel,

Your schematic is not exactly identical to the reference design, please see below notes:

If you copy the schematic and only make changes to component values, you should be fine.

Regards, Guang

0 Neel Desai over 3 years ago in reply to Guang Zhou

Prodigy 140 points

Hello Guang,

"GND" is the supply input GND for the 3.3V power supply and "ISO_GND" is the 200V supply ground (which is isolated from "GND", ties back to CHASSIS).

I have followed the reference design and changed a few components - Your last comment made it seem like something was incorrect in the component selection.

Please advise.

0 Guang Zhou over 3 years ago in reply to Neel Desai

TI__Mastermind 27470 points

Hi Neel,

Looks like your component calculation followed the design guide closely, so I think you’re fine.

Please reconsider your grounding scheme. In the original design, there is only one ground.

Regards, Guang

0 Neel Desai over 3 years ago in reply to Guang Zhou

Prodigy 140 points

Hello Guang,

Are you still worried about your initial comments about 200V dropping across D8 and R26?

And all the math for the newly selected resistors / FET is okay?

Thanks for your help.

Regards,

Neel

0 Guang Zhou over 3 years ago in reply to Neel Desai

TI__Mastermind 27470 points

Hi Neel,

Sorry to say but yes I am, but not because of the math, rather because of the grounds.

Your grounding scheme is different than the reference design and it will not work. You’re exposing the OPA and associated passive components to high voltage.

The simplest to do is to just copy the schematic and change components only.

Regards, Guang

0 Neel Desai over 3 years ago in reply to Guang Zhou

Prodigy 140 points

Hello Guang,

I do not understand how the reference design does is not "exposing the OPA and associated passive components to high voltage"?

The high voltage bus (400V, reference to GND) is still being exposed to the high voltage (400V)?

Regards,

Neel

0 Guang Zhou over 3 years ago in reply to Neel Desai

TI__Mastermind 27470 points

Hi Neel,

The design guide offers detailed explanation on this question and other key aspects of the design. Please refer to section 4 for guidance, including this paragraph for system description. This should answer your question.

Regards, Guang

0 Neel Desai over 3 years ago in reply to Guang Zhou

Prodigy 140 points

That works - Thank you for your help and support.

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TIDA-00528: 40-200V Monitoring