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BQ25790: Unknown adapter

Yoshinobu Kagawa
Expert 2030 points
Part Number: BQ25790
Other Parts Discussed in Thread: BQ25792, BQ25798, BQ25798EVM

1) I want to use D + / D–Detection so that the Unknown Adapter is set to the default setting. Should I set D + / D- to open?
Or according to the table below
・ GND connection via D + = 1 MΩ resistor
・ PullUp to D- = 3.3V or higher
Should I do that?
In that case, what is the PullUp resistance value of D-?
Is it okay to pull up with REGN?

2) If VBUS is turned on with ILIM_HIZ = Low when the battery is not connected, the VSYS voltage will be about 3.2V. I thought that the output would be 0V because the converter is not operating. Could you please tell me the reason?

3) If I start charging with the battery disconnected, the following QA-like shutdown occured.

https://e2e.ti.com/support/power-management/f/power-management-forum/976601/bq25790-system-shutdown-when-removing-battery

At the end, Jeff said, "This week I will be evaluating new versions of the BQ25792 with some additional features." So I want to know what the result.

Also, Jeff has proposed adding a capacitor larger than 470uF as a countermeasure, but I would like to know the reason why 100uF is not good.

Best regards,

Kagawa

  • 0
    TI__Guru**** 169206 points

    Hi Kagawa-san,

    Leaving the D+/D- pins floating results in unknown adapter detection. 

    The BQ25798 is a spin of the BQ25792.  It has MPPT and backup mode features which can be enabled but are not enabled by default.  It also has a different startup method when battery is not attached and so does not require additional capacitance on BAT.  The additional capacitance on BAT is to prevent BATOVP and SYSOVP from causing the converter to shutdown. 

    We will have the latest pre-production BQ25798 IC samples available for sampling by end of April.  The BQ25798EVM with latest pre-production ICs will be available for order the week of April 5th.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 2030 points

    Hi Jeff-san,

    Is it okay to recognize that BQ25798 is a product in which the defects in 2) and 3) have been fixed?

    Regards,

    Kagawa

  • 0 in reply to Yoshinobu Kagawa
    TI__Guru**** 169206 points

    Hi Kagawa-san,

    Regarding 2, this behavior is the same for BQ25792 and BQ25798.  Adding a 50uA load on SYS pulls it to ground.

    Regarding 3, the BQ25792 is designed assuming a battery with thermistor is connected to the charger.  When that battery and its thermistor are removed from the charger, with charge enabled, the charger enters TS fault and stops charge.  If TS function is disabled but charge is enabled, the charger attempts to charge the small capacitance at the BAT, as fast as possible, resulting in BATOVP, followed by a SYSOVP, both of which cause the converter to stop switching.  The BQ25798 has different timing of the BATOVP and SYSOVP faults so that switching is re-enabled before SYS drops below MINSYS voltage.

    Regards,

    Jeff