INA219 I2C communication problem

AFM

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

over 10 years ago

0 Rabab Itarsiwala over 10 years ago

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 AFM over 10 years ago 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 Rabab Itarsiwala over 10 years ago 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 AFM over 10 years ago 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 Rabab Itarsiwala over 10 years ago 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 AFM over 10 years ago 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 Rabab Itarsiwala over 10 years ago 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 AFM over 10 years ago in reply to Rabab Itarsiwala

Intellectual 560 points

Thanks.

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

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INA219 I2C communication problem