MSP430F67791A: SD24 differential input isolated towards ground?

Christian Schlink

Part Number: MSP430F67791A
Other Parts Discussed in Thread: TIDA-00601

Hi,

I want to measure the current for a 3-phase power-meter (230V 63A max). There is already a reference-design which uses current-transformers, but I want to use shunt-resistors instead. My question is: Can I connect the differential input of the SD24 to this shunt-resistor or will the isolation of the input fail at 230V and connect the main-voltage to ground? The voltage-drop over the shunt-resistor will be around 50mV which is totally fine.

Thank you in advance.

Best regards,

Chris

over 7 years ago

0 James Evans over 7 years ago

TI__Mastermind 49692 points

Hello Chris,

EDIT: This applies to single-phase only. Please see my comments in my next post for details about using shunts in multi-phase applications.

Thank you for your detailed post. The MSP430F67791A does support shunt resistors as well as current transformers, so the differential input of the SD24 can be connected across the shunt resistor. However, you'll want to refer to our shunt-based TI Designs to ensure that the circuitry is configured properly. If you're placing the shunt on the Line side versus the Neutral side, keep in mind that the MSP430F67791A will be referenced to Line. You won't need isolation between the shunt and the MSP430F67791A, but you will need isolation between the MSP430 and a host processor, user-interface, etc. If this system is entirely isolated, it wouldn't be a concern.

Hopefully this helps!

Regards,

James

MSP Customer Applications

0 James Evans over 7 years ago in reply to James Evans

TI__Mastermind 49692 points

Hello Chris,

I seem to have misunderstood your question. For a multi-phase application that uses shunts, you must have isolation between each shunt and its SD24 channel (+\-) of the MSP430F67791A. The reason for this is not because of the voltage difference observed between the differential inputs of the SD24 (let's assume 100mV), but it's because of the voltage difference between the individual SD24 channels. For example, the voltage difference between Phase 1 on Channel Ax.y (+\-) and Phase 2 on Channel Ax.z (+\-) could be 110V, which would destroy the MSP430F67791A.

Does this make sense?

The Multi-phase Energy Measurement with Isolated Shunt Sensors Reference Design (TIDA-00601) should be the perfect reference for you!