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BQ24295: BQ24295-Power switching problem

user3486585
Prodigy 20 points
Part Number: BQ24295

I am using BQ24295 chip, encounter the problem of disconnecting VBUS voltage, sys voltage power off. VBUS input voltage is 5V, BAT voltage is 3.9V, sys output voltage is about 4V. There is no use of boost external charging and USB function.I want to know how the two voltages of VBUS and BAT are switched.

1. VBUS Voltage Drop How Much Start Switching Battery Voltage Supply

2. How long will it take for VBUS to switch to battery voltage?

Is it the 30ms mentioned in the screenshot?

3. When VBUS rises, what conditions will be satisfied to switch back to VBUS? Is the switching time the same as the 30ms shown above?

4. The minimum voltage of sys pin is determined by REG01. At present, we have 3.7V on this side and 3.9V on the upper limit of battery voltage charging. How to improve the output voltage of sys? What I understand is that the maximum charge voltage of the battery set (the battery charged to the maximum set voltage) +150 mV. For example, I now upgrade the battery voltage ceiling to 4.2V. When the battery is full, the sys pin output voltage is 4.35V?

thanks a lot.

  • 0
    TI__Mastermind 25800 points
    Hello,

    For 1) and 2) The answer is similar in that the power to the charger is similar to an ideal diode OR'ing control between VBUS and VBAT power rails. Effectively the voltage and switch over between the two rails is almost instantaneous and the higher of the two rails will bias the charger internally.

    For 3) You can refer to section 8.3.1.4 Power Up from DC Source of the datasheet. As I mentioned for 1) and 2), the biasing of the internal elements of the charger will be dictated by that OR'ing control, but VSYS regulation requires that steps in the aforementioned datasheet section.

    For 4) I don't understand your question about "improve the output voltage of sys?". What do you mean by this specifically. You understanding is correct: once charging has terminated the system voltage will be VBAT + 150mV (typical).


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 20 points

    Hello Joel

    thanks for your reply.

    When i remove my DC adapter from the charger board, sometimes the system voltage drops and leads to reset .I don't know how to explain this phenomenon. 

  • 0 in reply to user3486585
    TI__Mastermind 25800 points

    Hello,

    Can you provide some more test setup information?

    Do you have a schematic of your charging system that you can provide?

    Are you programming any of the registers of the charger? If so, what is being programmed? A register dump of all registers would be preferred.

    Is there any system load applied, either transiently or not?

    Is charging enabled?

    For reference, I have performed a similar test using our BQ24295EVM board to test if there is a VSYS drop issue, but I could not duplicate it.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    TI__Genius 10240 points
    Hi there,

    We haven’t heard back from you. We are assuming you were able to resolve the issue. If not, just post a reply below or create a new thread if the thread has locked due to time-out.