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Current and Bus voltage monitor for negative voltage PSU

Steve Matthysen
Prodigy 20 points
Other Parts Discussed in Thread: INA226, ISO1541, INA220

Hi - I am wanting to use a shunt current monitor combined bus voltage monitor for each output of a dual power supply.  The device I have chosen for the positive output is the INA226 which works fine when coupled to a PIC MCU via the I2C interface.  However, I have not tried it but given that the specifications for the bus voltage input is 0 to 36V and the common mode shunt inputs have a minimum of -0.3V, then this device will no doubt not fulfill the requirement.  Is there an alternative matching device with similar capabilities available for -ve Bus voltages or another way to work around this?

The dual PSU has a common Ov rail and max outputs of + and - 25V at 3Amps.

  • 0
    TI__Expert 6930 points

    Hi Steve,

    Have you considered just using a second INA226?  It can be configured similar to the configuration shown in Figure 23 of the INA220 data sheet...in this way you will use one device for the positive output and a second for the negative output...in Figure 23 we show the bus isolation using optoisolators, but since that data sheet was released we have come out with a family of I2C isolators that would be easier and more effective to use.  Have a look at ISO1541 for the I2C isolator.  FYI...I will be out of the office until Monday with no access to thinternet so additional replies from me on this topic will be delayed.

  • 0 in reply to Edward Mullins
    Prodigy 20 points

    Hi Ed,

    Thx for this - This morning I landed on the idea of changing the design and using two independent supply modules (separate transformer secondaries) both using INA226's configured as positive channels and then connecting the pos of the one to the neg of the other but I still have to use the isolators.  I wasn't sure if opto isolators would have sufficient speed until I came across TI's ISO range which are designed perfectly for I2C buses.  The arrangement you have pointed out in the INA220 datasheet overcomes the common mode limit of -0.3 V by referencing the Gnd to the negative supply and I'll consider this option too.  Thx so much for this... ordering the ISO 1541 (and a someof the 1540's).

    regards

    Steve