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BQ24250EVM-150: Vsys have 3.7V~4.2V variation (33 ms cycle) when it dis-connect any battery

Gordon Liu
Intellectual 825 points
Part Number: BQ24250EVM-150
Other Parts Discussed in Thread: BQ24250C, BQ24250

Dear Sir,

I check functions of BQ24250EVM-150.

I don't use any SW to control the EVM ans set EN1=H, EN2=L.

Functions are OK when I connect the battery and Vin=5V.

When I disconnect the battery, The Vsys and Vbat become the rectangular wave form, 3.7V~4.2V, 15Hz.

Does it normal for the EVM??

  • 0
    TI__Guru*** 143940 points

    Hi Gordon,

    With charge enabled and no TS fault, the battery detection algorithm causes the SYS and BAT waveforms to modulate.  See d/s figures 1 and 2 on page 15.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 825 points

    Hi Jeff,

    I tune the TS temp > THOT (V_Ts=1V) and  the Vsys don't modulate.

    Unfortunately, I tune the   TS temp < TCOLD (V_Ts=4V)   but the Vsys still modulate.

    Could you resolve the issue??

    001 – TS temp > THOT (Charging suspended for JEITA and Standard TS)

    100 – TS temp < TCOLD (Charging suspended for JEITA and Standard TS)

  • 0 in reply to Gordon Liu
    TI__Genius 10385 points

    Gordon,

    Sorry for the delay. This is the behavior I am observing. 

    If the battery is removed in TS_OPEN, Normal, and TWARM < TS Temp < THOT, then battery detection will occur.

    Otherwise (TS Temp < TCOLD, TCOLD < TS Temp < TCOOL , and TSHOT < TS Temp ) battery detection will not occur.

    Please note if you remove the battery in normal or TWARM < TS Temp < THOT and slip into any of the other conditions battery detection will persist until a battery is connected. Verify for us that you are not setting the device into COLD from normal without a battery connected.

                    Thanks,

                                    Ricardo

  • 0 in reply to Gordon Liu
    TI__Guru*** 143940 points

    Gordon,

    If the battery is removed in TS normal and warm, then battery detection (VSYS modulation) will occur.  If the charger is in other TS faults (Cold, cool, and hot) battery detection will not occur. However if you remove the battery while normal or warm TS fault and slip into any of the other conditions battery detection will persist until a battery is connected.

    Regards,

    Jeff

  • 0 in reply to Ricardo
    Intellectual 825 points

    Hi Ricardo,

    I need 2 condition for operation, Have bettery and no battery.

    I have attached 4 waveforms. (it's only the Vin power on status)

    1: Vin=5V, No Battery, Vsys have 10ohm, load, Vts=4V

    2: Vin=5V, No Battery, Vsys have 10ohm, load, Vts=1V

    3:Vin=5V, Have Battery, Vsys have 10ohm, load, Vts=1V

    4:Vin=5V, Have Battery, Vsys have 10ohm, load, Vts=4V

  • 0 in reply to Gordon Liu
    TI__Guru*** 143940 points

    Gordon,

    Unlike our other chargers, this charger's TS function can be disabled if you take V(TS) above the disable threshold below:

    If you do not want that functionality, check out the BQ24250C.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 825 points

    Dear,

    Base on the safty issue (JEITA), We nned the Ts function.

  • 0 in reply to Gordon Liu
    TI__Genius 10385 points

    Gordon,

    Are you setting the device into cold (TS Temp < TCOLD) and then removing the battery? Also how are you setting VTS?

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Intellectual 825 points

    Hi Ricardo,

    Yes, I have set Ts=4V(85%), and I don't remove the battery.

    You can see my 1st test waveform of power-up.

  • 0 in reply to Gordon Liu
    TI__Genius 10385 points

    Gordon,

    At VTS 85% TS is disabled or otherwise known as the TS open condition. It is expected behavior for battery detection to occur in the TS open condition. There is nothing you can do to prevent this without external circuitry.

    You could try to clamp the TS pin so the open condition does not occur, but you would never be able to perform battery detection regardless of JEITA state. Unless this is what you want? I am also assuming your thermistor is attached to the battery pack.

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Intellectual 825 points

    Dear Sir,

    Design target, I only need the Vsys stable when I havn't the battery.

    Base on the datasheet (page 38),  if Ts temp < TCOLD, Charging suspended.

    I tune the R7 of bq2425xEVM-150 so that Ts=4V.

    Unfortunately, It still have charging condition so that creat the 33mS on/off signal (Vsys).

    Could you check the issue?

    Page 38 description:

    001 – TS temp > THOT (Charging suspended for JEITA and Standard TS)

    100 – TS temp < TCOLD (Charging suspended for JEITA and Standard TS)

  • 0 in reply to Gordon Liu
    TI__Guru*** 143940 points

    Hi Gordon,

    To reiterate, the charger is in TCOLD for VCOLD=60%*REGN <= V(TS) < VTS_DIS=70%*VREGN.  Because you are forcing V(TS)=4V>70%REGN, TS function is disabled and will not prevent battery detection.  I agree that the BQ24250 datasheet could be more descriptive.  You can also disable battery detection by disabling charge.  Or you can change to the pin to pin compatible BQ24250C which does not have TS pin disable function.

    Regards,

    Jeff