BQ25155: Compatibility between BQ25155 and cc2642 I2C output levels of BQ25155 does not match with cc2642's input level

POTHIRAJAN KANDASAMY

Part Number: BQ25155

Hi,

In our design we are connecting I2C of CC2642 with that of bq25155's I2C. We are using 3.3v power for our controller hence VIO of battery charger is also 3.3v.

Data sheet of bq25155 states that at 1.8 volt VIO , VOL(output low) => .25*VIO => .0.825volts.

GPIO input of CC2642 states that VIL = 0.2*VDDS = 0.2*3.3 = 0.66.

above numbers reveals that VOL of charger IC > VIL of micro controller. Hence not sure how to go about interfacing them?

Any help in this regard is appreciated.

Regards,

Pothirajan.K

over 5 years ago

0 Raheem over 5 years ago

TI__Mastermind 21590 points

Hello,

This is fine. As log as the MCU is able to pull the charger pins lower than the VIL of the charger, there shouldn't be a problem. In this case, the VOL of the MCU is lower than VIL of charger which is good.

0 POTHIRAJAN KANDASAMY over 5 years ago in reply to Raheem

Intellectual 600 points

Hi Sharafadeen Raheem,

As we understand VOL range of any o/p pin should fit with in the VIL range of any input pin. Which is not true here. Hence I do see a problem in interfacing these two ICs. . You may have a look at the table below for better understanding.

Output voltage at/by charger IC (bq25155) when it is logically low i.e.VOL

(3.3volt in VIO)

Input pin voltage of CC2642 to reliably detect as Low i.e. VIL

(operating at 3.3v power)

Remarks

VOL Min = 0v

VIL Min = 0v

Acceptable

VOL Max = 0.825v

VIL Max = 0.66v

Not acceptable. Microcontroller can not detect .825v reliably as low, because of .825v delivered by charger IC is out of range for low detection by cc2642

Regards,

Pothirajan.K

0 POTHIRAJAN KANDASAMY over 5 years ago in reply to POTHIRAJAN KANDASAMY

Intellectual 600 points

Hi Sharafadeen Raheem,

Eagerly looking for your input which will help us move our design forward to next step.

Regards,

Pothirajan.K

0 Raheem over 5 years ago in reply to POTHIRAJAN KANDASAMY

TI__Mastermind 21590 points

Hello,

For the I2C communication, the MCU is the one pulling the bus low. Hence, the dominant spec will be the low voltage of the MCU.

The output pins on the charger are open drain

0 POTHIRAJAN KANDASAMY over 5 years ago in reply to Raheem

Intellectual 600 points

Hi Sharafadeen Raheem,

Even for opendrain o/p, VOL is not driven to sufficiently low microcontroller can not sense appropriate levels.

Regards,

Pothirajan.K

0 POTHIRAJAN KANDASAMY over 5 years ago in reply to POTHIRAJAN KANDASAMY

Intellectual 600 points

Hi Sharafadeen Raheem,

Sorry to bother you. We have similar issues in INT, PG pins of charger IC too.

Regards,

Pothirajan.K

0 Raheem over 5 years ago in reply to POTHIRAJAN KANDASAMY

TI__Mastermind 21590 points

Hello,

I see the issue now. The BQ25155 datasheet spec is maximum across temperature which is from -40C to 125C.

The spec you mention in the CC2462 is only at 25C. I'm certain this would be higher if this was stated across temperature.

Hence why i stated that this wont be a problem.

0 POTHIRAJAN KANDASAMY over 5 years ago in reply to Raheem

Intellectual 600 points

Hi Sharafadeen Raheem,

Now I have understood, that it will not create issue in the design.

However is there a way we can get typical values?

Want to know how much power is being dissipated wasted in 25155 while it is delivering power to the circuit? i.e. Do we have efficiency curves for various combination of VBAT, VPMID and load current of the system(i.e. current being delivered to the board through PMID pin). We are using PMID only not using LDO and power outputs.

Thanks for taking efforts to give input on this aspect.

0 Raheem over 5 years ago in reply to POTHIRAJAN KANDASAMY

TI__Mastermind 21590 points

Hello,

We don't have these curves as they will be very application dependent. However, we have the battery Iq data in the datasheet. This can be used along with application parameters to calculate efficiency since this is a linear device.

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BQ25155: Compatibility between BQ25155 and cc2642 I2C output levels of BQ25155 does not match with cc2642's input level