• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 79 subscribers
  • Views 500 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

MSP430F67791A: Regarding Isolation of AC input and battery Power

vijayanarayana ramamoorthy
Prodigy 220 points
Part Number: MSP430F67791A
Other Parts Discussed in Thread: LM5576

Dear All

I am currently designing a E-Meter which is powered by a 12V battery i have used the analog front end design as per the application note i have a few doubts here 

1) I am powering the micro controller from a 12V car battery (since i need to operate a few high power relay based on the readings ) 

2) I am measuring the power of the  a POLYPHASE  

As per my design i have connected the neutral to AGND using a ferite  bead, and for the digital gnd i am using the battery gnd. My point is since i am powering the micro controller with the battery + and  - through  an  LM5576 LD0 ,  should i need to completely isolate  the AVDD  using  a ferrite bead to isolate the DVDD(Output of LM5576 ) ,  or should i need to use any isolation transformers.

 

  • 0
    TI__Genius 14875 points
    Hi Vijayanarayana,
    We are working on this and will have a response to you shortly.
  • 0
    TI__Mastermind 49692 points

    Hello,

    If you're using Current Transformers (CT's) in your poly-phase design, these current sensors are inherently isolated. Current flowing through them induces a voltage on the output wires, which requires the appropriate burden resistor.

    On the other hand, shunts are essentially low-resistance resistors capable of high temperature and large currents. However, these are NOT isolated. If you use these current sensors in a poly-phase design, they must be isolated (e.g. using isolators for each channel).

    With regards to ferrite beads, these do NOT isolate, but only filter noise instead. I'd strongly recommend isolators between any Human Machine Interfaces (HMI) and between any host or wireless microcontrollers/processors. Assuming CT's are used as the current sensors, the only point where High Voltage (HV) will be physically connected to the MSP430 will be through the voltage divider (resistor ladder) for measuring the RMS Voltage signal (a scaled down version). Be very careful to add TVS diodes and/or varistors to the analog front end to ensure no voltage spikes on the inputs could damage the MSP430.

    Please read through the following threads as well, since they have some good discussion about these topics.

    Regards,

    James

    MSP Customer Applications

**Attention** This is a public forum