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INA219 I2C communication problem

AFM
Intellectual 560 points
Other Parts Discussed in Thread: INA219

Hi All,

i have a strange behaviour on our prototypes using ina219 as a current monitor: 

the situation is that we can communicate with the ina219 only if we have a load. when there is no charge over Rshunt, in this case we can't commuicate with the chip.

is that normal ? do we miss some configuration for the ina219 ?

Thanks for help

  • 0
    TI__Expert 4595 points

    Hi,

    When you say can't communicate with the chip, do you mean that INA219 doesn not acknowledge to its address? If the power supply exists and the Address pins are configured correctly, the device should recognize it's slave address and acknowledge. Can you provide a schematic and what changes between load and no load conditions.

  • 0 in reply to Rabab Itarsiwala
    Intellectual 560 points

    hi,

    in fact, the chip is well configured since we can read from it in the presence of the load (Vin-).

    when the VDD is present and there is no load on Vin- (5V), there is no acknowledge from the chip.

    note: the I2C bus is shared with other modules.   

  • 0 in reply to AFM
    TI__Expert 4595 points
    Hi,
    Is VDD = 3.3 V? Do you have a scopeshot of the communication (SCL and SDA) when there is no load?
  • 0 in reply to Rabab Itarsiwala
    Intellectual 560 points

    VDD is also 5V. i will try to get the I2C graphs.

    is this about the smbus timeout feature ?

  • 0 in reply to AFM
    TI__Expert 4595 points
    Hi,
    SMBus timeout in the INA219 resets the interface any time SCL is low for more than 28 ms. I do not believe this is the case here.
  • 0 in reply to Rabab Itarsiwala
    Intellectual 560 points

    Hi,

    after tests, we found that the VDD of ina219 is the problem: in fact, the bus I2C is shared between different modules,

    The VDD of the MCU is 2.5V and the I2C bus is pulled up to this voltage.

    in our case, the ina219 is powerd by Vs=5V and the MCU is 2.5V. in this situation the ina219 is not stable.

    in the datasheet, the Vih min mentioned as  0.7 (Vs) is that mean that Vihmin = 0.7 x Vs = 0.7 x 5 = 3.5V ?!

    can we leave this configuration for I2C (ina219 5V and MCU 2.5V) or should we add a shiftlevel ?

    thanks for help

  • 0 in reply to AFM
    TI__Expert 4595 points
    Hi,
    Vih (min) = 3.5 for Vs = 5 V and if the bus is pulled to only 2.5 V then that will be a problem. Can you use 3 V supply on both INA219 and the MCU?
  • 0 in reply to Rabab Itarsiwala
    Intellectual 560 points

    Thanks.

    it's stable now. we will fix this on the coming run.