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AMC1350-Q1: three phase Ac voltage sensing

Mohammed Khan
Intellectual 380 points
Part Number: AMC1350-Q1
Other Parts Discussed in Thread: AMC1350, AMC1200

AMC1350_sim_no_diff.TSC

1. The above circuit is used in AC voltage sensing. The output is finally fed to the controller. Please do share review comments and precautions to be taken.

2. If i connect the INN in to ground, what will be the difference ? Please explain.

  • 0
    TI__Mastermind 49261 points

    Hi Mohammed,

    This looks like two line-line voltage measurements in a wye system with a neutral. With the power supply and all measurements made with respect to neutral - this looks OK. 

    INN could not be tied to GND in this configuration as it would short a phase measurement voltage to neutral.  

    This application note is for line-line measurements in a delta configuration, it may help:

    https://www.ti.com/lit/an/sbaa553/sbaa553.pdf

  • 0 in reply to Alexander Smith
    Intellectual 380 points

    Thanks for the info. that helps..

    Although i have few queries:

    1. Nonlinearity and Drift 0.02% (max), ±0.4 ppm/°C (typ), how to consider these in final calculations. Should i subtract it from output voltage or what do you recommend ?

    2. Also this is a board-board connection, meaning, my resistor divider is on one board, the rest signal conditioning circuitry on the other board. Does the IC have any internal protection ? I'm thinking to add some TVS diodes. What all protection components do you recommend to add external to the IC? The whole purpose is to protect the input lines of the Isolator Amplifier.  Note: Input Voltage range : ±1.3 V

  • 0 in reply to Mohammed Khan
    TI__Mastermind 49261 points

    Hi Mohammed,

    Similar to gain error & drift they represent a scalar error where they will contribute a percentage of error to either the input/output - depending on how you are calculating. Subtracting or adding is not important as long as you are consistent with the other error sources. This excel calculator may help: https://www.ti.com/lit/zip/sbar013

    There are internal ESD diodes that can handle up to 10mA with voltage down to -6V or +500mV with respect to the high side supply voltage as listed in the absolute maximum ratings table. The downside of additional TVS diodes is that they can contribute to a leakage current error, especially over temperature. 

  • 0 in reply to Alexander Smith
    Intellectual 380 points

    Thanks for the update Smith. The only concern is as this is board-board , i'm little worried as there will be too much Human interaction. What if i add a Unity gain circuit and then  add TVS protection and other protections before this circuit. Please see the sim file and comment.

     AMC1350_sim_protected.TSC

  • 0 in reply to Mohammed Khan
    TI__Mastermind 49261 points

    Hi Mohammed,

    The resistor divider and AMC1350 should be on the same board, then the board connection to another board can be made with the differential output of the AMC1350. 

    The board to board connection should not be made between the resistor divider and AMC1350, as the connection will be exposed to high voltage and potentially human interaction as you said. 

  • 0 in reply to Alexander Smith
    Intellectual 380 points

    Thanks for the inputs Smith.

    Few more queries:

    1. In the given simulation file below, I have added an RC filter. Also i'm planning to use those two resistors bigger and Surge protected. Is that RC filter ok or do i need to do some tweaking ?

    2. In the same simulation file, i'm planning to connect the differential output of isolator directly to ADC (Differential mode). Please give out some suggestion here on how to do it.

    FYI, ADC positive is referenced to +3V, Negative to ground. I have +1.5V reference available. 

    Note: Input Voltage range : ±1.3 V

    3.I have added an image taken from AMC1200 (TIDRMS9) for the protection purpose. can i use the same protections on my circuit ?

    Discussion.TSC

  • 0 in reply to Mohammed Khan
    TI__Mastermind 49261 points

    Hi Mohammed,

    The RC filter is fine - of course it can be tweaked if necessary during testing after board manufacture. 

    This document should help with differential connection to an ADC: https://www.ti.com/lit/an/sbaa312/sbaa312.pdf

    The protection should be OK. But as I said in my last post - it is not safe to make the board to board connection on the high voltage side if human interaction is possible.