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BQ25121A: BQ25121A In the sleep mode powered by the battery, when awakened by MR , the chip cannot output the set 3.0V only output the default 2.5V

Star Xu
Genius 9645 points
Part Number: BQ25121A

Hi 

The customer design with bq25121A.

①Only connect the battery, turn on normally (SYS outputs 3.0V—MCU configures it through I2C at the beginning of boot);


②MCU pulls up the CD pin (MR pin can be regarded as floating at this time), and then writes to the register through I2C, then enters the ship mode;

③At this time, it operates as expected—that is, the whole machine/MCU is powered off, and the SYS output is 0V.

In the above state, press the button to pull down MR, and the Charger starts instantly, but the SYS output is 2.5V, which does not output according to the set 3.0V.

Before the MCU is started/at the beginning of the boot, the CD pin is pulled low by default. Is there any way to make the whole machine boot up normally in battery supply mode?

The pull-up resistor of the MR pin in the figure has been removed

Please give some suggestions.


Waiting for your reply.

Thanks
Star

  • 0
    TI__Genius 13885 points

    Hi Star,

    Star Xu said:
    In the above state, press the button to pull down MR, and the Charger starts instantly, but the SYS output is 2.5V, which does not output according to the set 3.0V.

    This is because shipmode results in a register reset. In order to minimize quiescent current consumption while in shipmode, the device memory is lost and the device state is reset upon shipmode exit. Because of this SYS is enabled to the default value of 2.5V. You will have to run the MCU routine that was used to program the BQ originally.

    The device schematics you provided look good.

    Star Xu said:
    Before the MCU is started/at the beginning of the boot, the CD pin is pulled low by default. Is there any way to make the whole machine boot up normally in battery supply mode?

    Can you please clarify what you mean by boot up normally? Exiting shipmode should provide conditions similar to battery-only start up. Is there any other behavior that you are seeing that is different than the battery-only start up?

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    TI__Genius 9645 points

    Hi Juan

    Thanks for your reply.

    1, When the battery is connected (there is no VBUS input at this time), SYS will normally output 3.0V;

    2, At this time, the MCU pulls up the CD pin and writes 0x00h=0x20 to enter ship mode. Then  press the switch of the MR pin (make MR=0 for a short period of time) to enable the charger to start the SYS output. Since the MCU uses the output voltage of SYS, and the MCU supports 2.5V power supply, the MCU starts normally, but the MCU fail to write the register, the SYS output does not change - it still maintains 2.5V, which does not reach the expected 3.0V.

    I2C waveform after pressing MR:

    I found that after the MCU started, I tried to configure the Charger, but I found that the Charger never responded on the SDA signal line—no ACK was sent!

    3, The register setting as below

    0x00h = 0x00；

    0x06h = 0xF8；

    0x03h = 0xC0；

    0x04h = 0xFE；

    0x08h = 0x40；

    0x09h = 0x3A；

    0x0Bh = 0x32；

    4， When the MCU detects there is no input of Vbus_5V, CD will be pulled high immediately, but in the case of normal input of Vbus_5V, CD will be pulled low by default.

    Please give some suggestions with this issue.

    Thanks

    Star

  • 0 in reply to Star Xu
    TI__Genius 13885 points

    Hi Star,

    Star Xu said:
    SYS will normally output 3.0V

    For a battery connection it will output 3.0V by default or is this after an I2C configuration? This is unexpected since the default value for the sys is 2.5V. This is why after a shipmode entry and exit the SYS returns to 2.5V, a register reset occurs and this is the default value for the SYS rail. All other registers will likely be returned to their default values as well.

    Star Xu said:

    the MCU fail to write the register, the SYS output does not change - it still maintains 2.5V, which does not reach the expected 3.0V.

    I2C waveform after pressing MR:

    I found that after the MCU started, I tried to configure the Charger, but I found that the Charger never responded on the SDA signal line—no ACK

    Can you provide battery voltage when this test is run as well as the value for register 0x09 before the shipmode is entered? Additionally, can you provide waveforms of the failed I2C interaction? Lastly, can you attempt to toggle the CD pin low then high again and reattempt the I2C communication?

    Best Regards,

    Juan Ospina