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BQ25700A: ChargeOption1 AUTO_WAKEUP_EN bit not configured as default claims

Zane Hovey
Prodigy 20 points
Part Number: BQ25700A

Tool/software:

In the datasheet, ChargeOption1 AUTO_WAKEUP_EN bit shows that a binary value of "1b: Enable <default at POR>, however, we're finding that the default is actually "0b", or, disabled. We can prove this by setting the bit high and the charger starts normal operation.

What's happening is that in our device, batteries are in shutdown mode by default. This means absolutely 0V coming out of the battery. To bring the battery out of shutdown, there needs to be at minimum, of +5 VDC presented to the battery + terminal. If we configure the BQ charger and doing nothing further, no voltage appears from the charger. However, if I then write the ChargeOption1 AUTO_WAKEUP_EN bit to "1", we see the output voltage from the charger.

So, couple questions.

1. Is there an errata for this part, if so, could we get a copy?

2. What would cause the ChargeOption1 AUTO_WAKEUP_EN bit to be LOW instead of HIGH, which is the opposite of the datasheet?

3. Have you seen this issue before for this part?

4. Setting the number of cells, voltage, and other parameters don't seem to make any difference (the default ChargeOption1 AUTO_WAKEUP_EN bit remains LOW until we set it.

  • 0
    TI__Mastermind 23585 points

    HI, Zane,

    I just connected the adapter on the BQ25700AEVM, then read the register map. 

    It shows AUTO_WAKEUP_EN=1, with charge current =128mA. 

    Regards,

    Tiger

  • 0 in reply to Tiger Zhou
    Prodigy 20 points

    Other than writing this bit/register to '0', what else could change this back to a zero? The issue we're facing is  resolved by simply setting this bit to 1, but apparently somewhere in our boot-up, it's getting reset to zero but definitely not by directly writing to it or the ChargeOption1 register (this has already been verified with an analyzer). 

  • 0 in reply to Zane Hovey
    TI__Mastermind 23585 points

    When this bit is HIGH, if the battery is below minimum system voltage (REG0x3E()), the device will automatically enable 128 mA charging current for 30 mins. When the battery is charged up above minimum system voltage, charge will terminate and the bit is reset to LOW.

  • 0 in reply to Tiger Zhou
    Prodigy 20 points

    If a  battery has a standby mode, which requires at least a trickle charge to bring it out of standby, AND the charger requires at least REG0x3E volts, or it won't charge, we end up in a voltage deadlock.

    Is there a way to force the BQ25700A to charge, regardless of what voltages it senses long enough the break this deadlock?

  • 0 in reply to Zane Hovey
    TI__Mastermind 23585 points

    Hi, Zane,

    I don't see a deadlock here. The min system voltage REG0X3E is generated by the charger, regardless of the battery voltage. You can always enable charge by set the charge current register REG0X14. 

    Regards,

    Tiger

  • 0 in reply to Tiger Zhou
    Prodigy 20 points

    Here's our setup and conditions:

    ==> Set charge in REG0X14 (tried various bit options from 64 mA to 2A),  

    ==> Set voltage in REG0X3E to a min of 7 v to 12.3 V

    <== 0V input from the battery (CELL_BATPRESS = 0 volts)

    <== We can get a supply voltage to the drain of BAFET

    ==> But no drive to BAFET gate* 

    * Until we write b0 of Options1, after a few seconds after initialization of the BQ25700A, and at that point we immediately see the drive to the BAFET gate, which triggers voltage on the battery terminal, which then pulls the batteries out of shutdown and normal operation proceeds. 

    Are you saying that if you set all of this up, without a battery present, you can see the BAFET gate enabled and voltage output across the Sense resistor between pins SRP and SRN in Figure 40 from the datasheet?

     

  • 0 in reply to Tiger Zhou
    Prodigy 20 points

    One other point to make. There is a difference between schematics of what we're using and the ref design (fig 40 from the datasheet). Our Vsys is the same as the external source (labeled "Adapter" in the ref design), so unlike the ref design, where VSYS connects near Q4, we do not. "SYS" still connects to Q4 and BAFET though. With that diff, is there any issues you see that would prohibit operation? The temp of the charger also gets quite warm.

  • 0 in reply to Zane Hovey
    TI__Mastermind 23585 points

    Hi, Zane,

    Figure 40 schematic is a standard implementation of TI charger BQ25700A. Most customers follow the schematic, or directly copy the schematic. Could you share your schematic here?  

    My suggestion is to refer to the BQ25700AEVM as a starting point. 

    https://www.ti.com/tool/BQ25700AEVM-732

    Regards,

    Tiger