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Original question:

BQ25120A: After setting system voltage to 3.2 V, I2C Communication fails and system voltage drops back to 1.8 V after starting...

BQ25120A: I2C does not ACK without VIN present on evaluation board

John Condon55
Prodigy 160 points
Part Number: BQ25120A
Other Parts Discussed in Thread: EV2400

Greetings,

We're working with the BQ2520AEVM (Evaluation Board) interfaced with the EV2400 and Battery Management Studio v1.3.86. It is attached to both a 4.2V LiPo battery (VBat) and a power supply (VIn). We also attached a simulated load to the VSys. We noticed a couple issues.

1.) If there is no load present on VSys and VIn is removed, VSys goes from 1.8V to 3.0V. What is the minimum load for a stable output on VSys? Is there a minimum load on VLDO as well?

2.) During our testing we found that the Battery Management Studio only reports "Device ACK OK" when the charging voltage is present on VIN. Looking at the schematics, the I2C lines should be pulled up to VSys, not VIn. Does the I2C communications require VIN? Could it be a limitation of the EV2400 I2C interface?

Thanks!

  • 0
    TI__Genius 12485 points

    John,

    Can you plot a register dump of all the registers so that we can verify what is happening?

    There is no requirement on minimum load for the VSYS or VLDO. Without any load, we should still be regulating to 1.8V (or what target was programmed on I2C)

    On the battery only mode, /CD pin has to be pulled up high. You can short the jumper on /CD to VSYS. 

    Also make sure the VPULLUPI2C jumper is removed as the EV2400 pulls the bus in the box itself. 

    let us know if you have any questions. 

    Regards,

    Gautham

  • 0 in reply to Gautham
    TI__Mastermind 21590 points

    Hello John,

    Any updates on this?