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BQ24140: bq24140 precharge query

Star Xu
Genius 9645 points
Part Number: BQ24140
Other Parts Discussed in Thread: BQ24153A, BQ24156A, BQ25606, BQ24157

Hi

About bq24140, the range of weak battery voltage threshold (VLOWV) is 3.4V–3.7V, if the battery voltage lower than 2.9V, whether the chip go to precharge mode.

The customer simulate battery voltage 2.6V ~2.9V, and use USB charge, but could not precharge the battery. 

Waiting for your reply.

Thanks

Star

  • 0
    TI__Guru*** 146575 points

    Hi Star,

    Weak battery threshold is USB BC2.1 legacy requirement that requires the charger to stop charge if the battery is above this threshold while in default (15 minute) mode.  The assumption is that the host has not successfully powered up and enumerated the USB port.

    The "precharge" threshold for this part is VSHORT = 2.0V typical, which is not spec'd in this datasheet but is in the BQ24153A datasheet, from which the BQ24140 is derived. The "precharge" current is ISHORT=30mA typical. 

    Is the part not charging with 30mA and VBAT=2.6-2.9V and 4.0V<VIN<9.6V and/or 4.0<VBUS<6.3V?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Expert 6125 points

    Hi Jeff,

    Yes, the battery charger to regulate 3.54V output, then pull low when pass 262ms. during this time, the charge current up to 330 mA then pull down. pls see as below waveform:

    do you have any idea for this behavior?

    Best Regards,

    Mark

  • 0 in reply to Mark Chen52
    TI__Guru*** 146575 points

    Hi Mark,

    With no battery attached and in 15 minute mode, the charger is trying to determine if a battery is attached.  Top of datasheet page 21 and bottom of 22 explain battery detection.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    TI__Expert 6125 points

    Hi Jeff,

    Just like to confirm with you, so if the battery voltage during 2.6V to 2.9V, the charger concludes the battery not present, right?

    Seems the charge will be resumes after a delay of tIN(2s), that means will be start to charging after 2s, right?   

    thanks,

    Mark

  • 0 in reply to Mark Chen52
    TI__Guru*** 146575 points

    Mark,

    At power up with no battery attached, the charger should be able to detect that the battery is present as long as V(BAT)>2.0V.  If an actual battery is attached with V(BAT)>2.0V, the charger should not able to raise the voltage 3.54V so quickly as shown in the plot above.  This repeats every 262ms.  If VSHORT<V(BAT)<VLOWV, charge should start with 325mA in default mode. 

    At charge termination with no input power removal, the charger checks to see if the battery has been removed.  If it determines it has been removed then the charger resets the charging parameters to default and tries to charge after the tINT=2s delay.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Expert 6125 points

    Jeff,

    thanks for you comments, i also need you help to know as below questions:

    1. according to my attached waveform, do you know why Vout drop to 1.6V then slowly to decade? is it normal or not?

    2. you mean the charger will be regulate output voltage to 3.54V but need more startup time, do you know how much the startup time is make sense?

    3. when battery is present and voltage within 2.6V to 2.9V, the charge voltage is 3.54V and charge current is 325mA with default mode. right? 

    4. if the battery is not present, what's the behavior on the charger output?

    5. what's 15min mode? I can't to find the detail description in DS.

    Thanks,

    Mark

  • 0 in reply to Mark Chen52
    TI__Guru*** 146575 points

    Mark,

    Regarding 1, the BQ24140 is a combination of two ICs; BQ24153A and BQ24156A.  Datasheet is at http://www.ti.com/lit/ds/symlink/bq24153a.pdf.  Datasheet figures 28 to 31 on page 38 show how battery detection works when no battery is attached.  That appears to be what your scope shot is showing.  It so then this is normal.

    Regarding 2, without a battery attached, the charger will not regulate the output voltage to 3.54V.

    Regarding 3, yes.

    Regarding 4, see datasheet figures referenced in 1.

    Regarding 5, 15min or default mode happens immediately at power up, allows the charger to operate for 15min with default settings and then disables the charger unless the host writes to the charger's watchdog timer I2C bit every 32 s.

    Regards,

    Jeff    

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hi TI's team members, 

    Below table is my measure about charge, 

    they can't charge when battery cell voltage at 2.7V/2.8V/2.9V,

    I think the cause is battery cell voltage + PCM (battery protection circuit) OD side MOS internal diode forward voltage (about 0.61V) > 3.54V,

    in this condition, could BQ24140 charge to battery pack (cell + PCM) by any method?

    If can’t, do you have other charger (pin to pin) can to replace?

    Btw, I connect one Schottky Barrier Diode (MPN: DB2430100L) between U2’s pin1 and pin2,

    then it can normal charge at battery cell voltage2.7V/2.8V/2.9V, measure B- and P- voltage is 0.258V (diode forward voltage)

    So I think the cause is battery pack(cell 2.7-2.9V + PCM) need VBAT to provide > 3.54V, but BQ24140 can't provide it in default mode charge stage

    Other measure, I change to use another charger BQ25606, then measure waveform as below picture, it can normal charge at any battery cell voltage 

    Thanks

     

    Jones

  • 0 in reply to Jones Chiang
    TI__Guru*** 146575 points

    Hi Jones,

    Thank you for the table.  I now understand the issue.  I agree with your conclusion about the protector.  Unfortunately, there is no other pin to pin device with the BQ24140.  What are the exact application requirements, in other words, why was the BQ24140 chosen in the first place?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hi Jeff, 

    In VBAT 3.54V(CH1 in below picture) period(about 0.2s),

    our product had power because the MOS(Battery pack’s PCM circuit) was turn on(CH2),

    and battery also had charge current, but why charger still cut the power?

    This question’s waveform same floating (Charger no connect battery) as below picture, 
    does it means no detected battery? 
    Do you have BQ24140 detail explain about how detect the battery?

    Thanks

    Jones

  • 0 in reply to Jones Chiang
    TI__Guru*** 146575 points

    Jones,

    The battery detect circuit at power up is explained in text at the top of datasheet page 22.  In summary, the output capacitor is charged up then a discharge current (~1mA) is applied for fixed time.  If the discharge current is able to pull down the output in the fixed time, the charge assumes a battery is not present.  In theory, if you were to increase the output capacitor, you would defeat the detect circuit.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hi Jeff, 

    I added a test -> 2.8V(VIN set current limit 0.1A) as below table,

    it can charge, but the value of charge current just about 40-60mA, it is 3.54V keep about 0.1s first, then fall to 3.366V.

    Why it does not cut off VBAT in this condition? This result not same with 2.7V/2.8V/2.9V set current limit 1A(fall to 1.5-1.2V, charge current 0mA, Can't charge)

    Thanks

    Jones

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hi Jeff, 

    BQ24140 solution is TI FAE TW side suggested…

    So BQ24140 can not use on most battery pack (cell + PCM), right? Because many battery pack common design same as below,

    1. Discharge ending voltage is 3.0V

    2. PCM’s MOS internal diode forward voltage about 0.6V

    Thanks

    Jones

  • 0 in reply to Jones Chiang
    TI__Guru*** 146575 points

    Jones,

    We have seen the battery detection being an issue for some protectors.  What is the application requirement that resulted in the BQ24140 being recommended? Could we change to 2 BQ24157 in parallel?

    Regards,

    Jeff