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BQ25898D: charger application issue

Part Number: BQ25898D

Hi,team:

   Hope everything is fine with you.

   I have three application issue about BQ25898D:

  1)datasheet describe QON could be used to enable and reset control input. it is Ok.

   Actually, we hope to connect QON (connect button to GND) and MCU to detect user action and to power up or power down Vsys.

  But QON default high voltage more than MCU GPIO voltage limit.

  could you help check what way we can achieve this function?

  2)In boost mode, we found PMID=VBUS, but VBUS is not expected. could you check whether Q1 could be controlled.

  and we found boost mode not all charger VBUS follow PMID like BQ25295.

  3) Whether BQ25898D could achieve above function, if not could you help suggest suitable device?

  Very thank for your help, hope to get your reply!

  • Hi Hailey,

    1) I want to confirm my understanding of your desire. /QON is usually implemented with a push-button to connect /QON to GND (/QON usually stays high until user activates push-button). Are you saying that you would like your MCU to detect when /QON is pulled to GND and then power up/down VSYS?

    The /QON pin is normally used to bring the charger IC out of Ship Mode or to reset VSYS by turning off the BATFET for a short time when only a battery is present. Since /QON can already handle VSYS reset, why do you need the MCU to try and reset VSYS?

    2) In Boost Mode (OTG Mode), Q1 is active and cannot be deactivated. VBUS will be connected to PMID through Q1 intentionally. Q1 is left on in order to provide overcurrent protection for safe boost mode operation.

    3) For Boost Mode on the BQ25898D, VBUS should stay at a similar voltage to PMID (slight voltage difference between PMID and VBUS due to Q1). If you need another BQ2589x device that has Boost Mode output at PMID but VBUS is isolated and Q1 is off, I would look at the BQ25895.

    Regards,

    James

  • Hi, James:

    Very thanks for your reply.

    actually, when user wants to power down(Not reset is power down for long time) system by press button, we should to detect button to GND and MCU control I2C to make BATFET off. 

  • How can I know which charger device could disable Q1 to discrete PMID and VBUS in boost mode at datasheet, could you help tell more details, very thanks!

  • Hi Hailey,

    1) If your pull-up source for SDA and SCL lines is around 1.8V, you could use this as your voltage source for the MCU GPIO pin connected to a push-button (with pull-up resistor). The BQ25898D does not have many pins that sit at lower voltage (~2V). The INT pin might be an option since the pin is active low but any external push-button implementation not recommended in the datasheet will require careful testing to make sure it does not affect the charger negatively.

    It may be better to use an external voltage source for the SYS power down function so that the control is isolated from any changes in charger behavior.

    2) Chargers that use PMID as the OTG output with Q1 disabled have applications that connect external devices to PMID, such as a phone or ear buds. Below I have included two pictures that show a VBUS output application (Figure 49) versus a PMID output application (Figure 9-1). Looking at the application diagram for a device is a quick way to tell if the OTG output is PMID or VBUS. The OTG specs should be labeled above the corresponding output line.

    Regards,

    James