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BQ25883: Switching Noise Coupling into I2C SDA Signal Line Issue

Jayce Luo
Prodigy 590 points
Part Number: BQ25883

Hello, TI expert,

Urgent help is need right now. This is a case from our customer.

When using BQ25883, will find a switching nosie coupling into I2C SDA signal when the I2C finished 8 bits transmit and transmitter releases the SDA line to accept ACK signal. The SDA waveform is show as below (red for SDA, and blue for SCL).

The design is on a 6-layer board with 2 complete GND plane.

Can be seen that noise switching frequency about 1.56MHz, match boost switching frequency inside BQ25883.

Max negative voltage is about -900mV.

Could you please help analysis

1. the possible course of the problem

2. possible ways to solve the problem

3. if cannot be solved, possible influence, for example, will -900mV damage other devices

You can email me at:

jayce-luo@ti.com

  • 0 in reply to Jayce Luo
    TI__Guru**** 165886 points

    Hi Jayce,

    Although not required, it is best practice to route the SDA and SCL lines away from the power carrying pins (VBUS, PMID, BAT, SYS and GND).  As long as the IC pins do go more than 1 V below ground for a sustained time, there should be no damage.  If concerned, you can add a TVS or fast Schottky diode clamp on the SDA and SCL pins.  Last idea would be to improve the power capacitor placement and routing in order to minimize switching noise.  I recommend 0.1uF capacitors placed as close as possible to IC PMID and SYS pins, followed by the larger bulk capacitors on PMID and SYS.  Then, the REGN capacitor and BTST capacitor should be placed close to their respective pins and for REGN capacitor GND.  Last would be the VBUS and BAT capacitors.  The inductor can be further away.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Prodigy 590 points

    Hi Jeff, 

    Thanks for your advice, and please check my email, thanks.

    Best Regards,

    Jayce

  • 0 in reply to Jayce Luo
    TI__Guru**** 165886 points

    Jayce,

    Since we have moved this to email, I am closing this thread.

    Regards,

    Jeff