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BQ24295: VSYS stays off if PMID has load on startup, w/o battery.

Part Number: BQ24295
Other Parts Discussed in Thread: , BQ25896, BQ24296

Hello,

I have a problem with the BQ24295, in the case on the EVM (BQ24295EVM-549). It occurs in the following situation (sequence):

We use power from VSYS (~4V) and PMID (5V, from vbus/adapter or boosted).  When the Li-battery activates its safety (undervoltage-off), with no VBUS or adapter present (=all power drained) , the bq24295 loses power. The battery may stay off, as if there were no battery, or it may be defective (really no battery).

When VBUS (5V) is applied again,the bq24295 normally supplies PMID and VSYS (w/ 'In regulation"-flag).

If PMID has a load (in my case 50ohm resistive or lower, 100mA+) on startup, the BQ does not supply VSYS (0.00V, with 'In regulation"-flag active). It will also never try to precharge the battery, probably because there is no VSYS. The BQ starts with default registers, since it was a cold start. The status register flags are all normal. Changing any of the register-contents does not activate VSYS. Changing/toggling the /CE or OTG pins does not activate VSYS. Dead as a duck.

1/ Why is there no VSYS in above case ?

I would like to use BQ25896 instead because the voltages and currents can be monitored by the host, but if it exhibits the same problem it is unsuited.

2/ Can I expect the same problem with the BQ25896 ?

Regards,

 Michiel

  • Michiel,
    Just thinking there may be input current limit condition.
    Could you please help to put jumper in JP2?
    In general, if D+/D- pin are floating, our input current limit will be 100mA. If you short D+/D- each other then input current limit will be ILIM pin setting.

    I think BQ25896 won't have similar symptom because there is no D+/D- pins.

    Thanks
  • Hi Paul,

    sorry to report:

    Only the input qualification result differs, with JP2 shorted. (A functonal description of JP2 in the EVM user guide would be usefull.) In all cases VSYS stays off.

    I did look it more closely.

    On powerup from a DC source (lab supply), JP2 shorted, with a PMID load of 50ohm and a 5V-detector (w/ LED)  that adds 15mA when above 4.8V:

    • VSYS ramps up to about 1.0V in about 30µs, then stops and drops slowly.
    • The input current briefly shows about 90mA before rising to 115mA (== my load on PMID).
    • The voltage on PMID quickly (2ms) rises (C-charge curve) to 4.35V and stays there. After 272ms it rises to 5.00V.
    • With 50ohm plus an extra load of 12ohm on PMID the voltages are: 4.24V until t=272ms, 4.88V until t=422ms, 4.96V afterwards.
    • With 50ohm plus an extra load of 4.7ohm on PMID the voltages are: 4.16V until t=272ms, 4.76V until t=422ms, 4.88V afterwards.

    The event at t=272ms looks like an ideal-diode going ideal. The event at t=422ms disappears when JP2 is removed (open).

    This does not correspond with a 100mA nor 500mA current limit on PMID or I-in.

    At startup (default registers) the input current limit seems to be 500mA (readout immedately after applying power).

    At input qualification it should be 100mA.

    After input qualification it is 2A w/o JP2, and 3A w/ JP2.

    Readouts:

    JP2-open - immediately after powerup :

    JP2-open - after Iin qualification:

    JP2-shorted - immediately after powerup :

    JP2-shorted - after Iin qualification:

    Please investigate.

    Regards,

     Michiel

  • P.S.: The very short VSYS rise happens also at t=272ms.
  • PPS.: The event at t=422ms moves to t=840-860 when JP2 is removed (open), it doesnt disappear.
  • PPPS.:

    There is definately some 100mA limit in the startup sequence.

    .

    I did a lot of tests with JP2 open and shorted, different loads on PMID, and no load or a small load on VSYS.

    It is to much to post here.

    .

    I still think there is a problem with the device:

    When the combined load from the input voltage is larger than 100mA, at some point in the startup sequence, the 100mA limit keeps its influence, indefinately. Unconditionally.

    This problem makes it impossible to run a 'Phone Tablet' (Fig. 40 datasheet) from PMID.

    .

    .

    The problem is most evident with a 52 ohm resistor on PMID and a 390 ohm resistor on VSYS:

    In this case the initial current is about 85mA: VBUS (5.0V) via a real diode (RBFET/Q1)  to PMID (4.35V), which has a 52ohm load.

    VSYS and  RBFET/Q1 are switched ON at t=270ms.This causes PMID to rise from 4.35V to 5.0V, the current from PMID rises to 96mA

    VSYS is switched off immediately (30µs, only reaches 1V or so). The spike on VSYS is visible. Probable cause: The combined input current is above 100mA with the buck regulator ON.

    The input current thus drops to 96mA again.

    After input  (lab supply 5V/6A) qualification (t=420-430ms with JP2 shorted, t=840-850ms with JP2 open) , VSYS is switched ON again.

    VSYS rises to 1.65V, the input current to 98mA.

    The 100mA limit is not removeable from there on.

    IINLIM[2:0] does not indicate 100mA. "In DPM regulation"-flag is set properly. Didnt notice that.

    Reset, watchdog, changing Ilim, Q4, restarting D+/D- detection, nothing will remove the 100mA limit. 

    .

    With other loads, the problem differs. What stays is the 100mA input current limit, when tripped in the startup logic.

    .

    What would be a solution is avoiding to use 5V before VSYS.

    I am not convinced not having D+/D- (bq24296) would solve the problem. The bq24296 datasheet also mentions a 100mA limit under conditions. I'll order a bq24896 evm.

    I'll be out of office until tuesday.

    .

    Regards,

     Michiel

  • Hi,

    Referring to page 8 of the d/s, the input limit is set to 100mA when VSYS is below 2.2V.

    BQ2589x has similar spec. Please refer to https://e2e.ti.com/support/power-management/f/196/t/777459 for more details.

    Thanks,

    Ning.

    Please click "This Resolved my issue" button if this post answer your question.

  • Hello,

    i think the problem is that the datasheet does not mention the "or else" -> you will end up with device in a "totally refusing to do anything"-state.

    Regards,

    Michiel
  • Hi,

    The thread is considered solved and closed.

    Thanks,

    Ning.
    Please click "This Resolved my issue" button if this post answer your question.