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TIDA-01513: How to modify schematic with chassis is not connect to low voltage GND

Part Number: TIDA-01513

Hi TI,

According to customer's requirement, chassis will not connect to high voltage or low voltage GND.

Is it OK to modify the circuit from "Addendum to TIDA-01513" below?

If this modifiation is wrong, is there other way (or design guide) to meet customer's requirement?

One more question.

Why voltage measurement circuit need to to be isolated, but isolation leakage current or isolation resistance don't?

  • Hi Sky,

    It depends on which insulation status you want to monitor.

    As the connection shown in your figure, it measures the resistance between chassis and low voltage GND.

    If you want to measure the HV ground to LV ground insulation, move the connection from chassis to HV GND.

    About the second question, voltage measurement should be galvanic isolated, because the high voltage and low voltage side doesn't share the same ground, and typically you don't want to break the isolation here for just measuring the voltage.

    But the insulation detection is to measure the resistance between HV ground and LV ground, so when you want to take the measurement, S1 & S2 toggles, creating controlled leakage path to "break" the isolation a little bit, and use these additional leakage, which have known values, to calculate the original insulation resistance. When we don't do the measurement, S1 & S2 are both open to retain the galvanic isolation.

  • Hi Robin,

    Requirement from customer is to measure RisoP/N between TVB and chassis as figure1 below.

    Is the block diagram which I modified as figure 2 correct?

    Another question, as you mentioned "creating controlled leakage path to "break" the isolation a little bit".

    Is there any risk if I want to measure IR continuously and always turn on S1 & S2?

     figure 1

     figure 2

  • For figure 1 you need an extra isolated amplifier to pass your signal from referencing to TVB-, to referencing  to MCU GND.

    Not easy to get rid of it, because there are three grounds in the circuit, you are measuring insulation between Chassis(1) and TVB-(2), But need that measured on MCU GND(3).

    Insulation measurement  path shouldn't be always on since it adds extra leakage, which typically you don't want. Also per the equations in the addendum, switches need to be toggled to build the two formula, for solving the Risop and Rison

  • Hi Robin,

    "For figure 1 you need an extra isolated amplifier to pass your signal from referencing to TVB-, to referencing  to MCU GND."

    Could you provide some diagram to help me to understand your description?

  • Your figure2 is accurate. Two isolated op needed there.

  • Hi Robin,

    In your figure above, Rps/ns -> S1/2 -> amp -> iso amp -> MCU ADC.

    In my figure2,            Rps/ns -> S1/2 -> iso amp -> amp -> MCU ADC.

    What is the difference between these two topology?