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INA303: Circuit review request

MJ Jeon
Genius 5240 points
Part Number: INA303

Hi,

The customer has constructed a circuit using the INA303A2.

1. Please check if there is any problem with the configured circuit.

Current Sensing Circuit_INA303A2.pdf

The battery voltage is input at 400V, so please check whether it can be connected to the sensing part (IN+, IN-).

2. If the potential difference between both ends of the sensing resistor is 50mV or more, can a defect occur?

 

Thanks.

Regards,

MJ

  • 0
    Guru 140200 points

    Hi MJ,

    I would remove C130 and C132 or at least insert a suited isolation resistor. A cap alone at the ouput erodes the phase margin and destabilizes the INA303. If you want to connect an ADC to the output of INA303, mount the charge kick-back filter recommended in the datasheet of ADC.

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 18830 points

    MJ,

    I see a few things and have a few questions:

    First, on your positive current sensing schematic, unless I am interpreting it incorrectly, it looks as though the shunt is attempting to measure on the high side with a common mode of 400V? The INA303 cannot handle a common mode of this magnitude (VCM_max is 40V). Is the voltage on this shunt indeed 400V?

     

    Second, keep in mind that the common mode limitations in the datasheet are with respect to the ground the device is referenced to. I do not know how you tie BATTGND and GND together in the system, but if there is any deviation between these grounds, there could potentially be issues, if this deviation is more than 300mV (see above).  

    Finally, Kai is correct here. The capacitors you have connected on the outputs are within the tolerable limits of the datasheet, but only just, and any additional capacitance potentially present in the load could cause issues (such as the sample and hold capacitance in your ADC): 

    Based on the sampling rate of the system, I would either place the charge bucket filter as Kai recommends, or you may need to buffer the line if a higher sampling rate is desired here to ensure that the output settles to within 1/2 LSB inside of the ADC's acquisition time.

  • 0 in reply to Carolus Andrews
    Genius 5240 points

    Hi, Carolus

    Thank you for your answer.

    I have additional questions.

    Among the reply contents, there is a content that a problem may occur if there is a difference of more than 300mV in common mode.

    When checking the potential difference between BATTGND and GND, it is confirmed that BATTGND is higher than GND.

    During power ON/OFF, about 0.5 ~ 1.65V BATTGND is higher than GND.

    In this case, is there no problem because it is within the SPEC?

    Thanks.

    Regards,

    MJ

  • 0 in reply to MJ Jeon
    Guru 140200 points

    Hi MJ,

    how is the connection between BATTGND and GND? What is GND and what is BATTGND? How is GND generated relative to BATTGND?

    Can you show a complete schematic clearing this issue?

    Kai

  • 0 in reply to MJ Jeon
    TI__Mastermind 18830 points

    MJ,

    I also would like to see how these grounds are tied together. They do have a physical connection point somewhere in the system for these two grounds, correct?

    For cases where BATTGND > GND, they should be safe. In this condition you would simply see the common mode voltage on the inputs of the device raise by this voltage amount, which is still inside of spec of the INA303.

    For my comments above, it would be any areas where BATTGND < GND in magnitude greater than 300mV that would be of concern here (for damage survivability. the device would stop behaving linearly beyond 100mV). That said, I cannot say that this alleviates this problem entirely, because without knowing how these are referenced to one another, we can't say with confidence BATTGND will always be greater than GND. 

    Next, were you able to confirm on the voltages on the high side measurement? To refresh, it seems their schematic shows BATTERY+ = 400V, and I'm assuming HV_DC_1 = 400V - VSENSE = 400V. If this is the case, this device will break the second they energize it, also due to common mode voltage violation.