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BQ24250: Vsys outputs 0,9V rather than 3,5V or 4,35V when no battery is plugged.

carlosgdj07
Prodigy 240 points
Part Number: BQ24250

Dear all,

I am issuing a strange behaviour. It is supposed that if you dont have any battery connected, but you plug-in a main power source (5V for instance), Vsys is going to be Vsysmin (3.5V) or Vbatreg+3.5% (4.35V).

It is not my case. In my board, Vsys = 0,9V.

The point is bq24250 is supplying Vsys=0.9V when only main power is attached and no battery is present... This voltage is only a reference because if I attach a load to that 0.9V, Vsys drops to 0V quickly and no current is provided to the load.

Is this behaviour expected? What should i do to obtain that 3.5V or 4.35V when only main power is attached to bq24250?

My schematic is the fone which follows:

Thank you,

  • 0
    TI__Guru**** 166596 points
    Are you running in standalone mode or host controlled mode? If in standalone mode, is R2 really 0 ohm? If so then the input current limit is reduced to 0 A and the converter will not be able to provide an output at SYS. At what voltage are EN1 and EN2? If both high then the IC is in HiZ and will not be able provide an output at SYS.
  • 0 in reply to Jeff F
    Prodigy 240 points
    Dear Jeff,

    By the moment, we are in standalone.

    R2 is 0 ohm, yes, but datasheet says that if pin 23 Vdmp is shorted to GND, then Vdpm will be default, what is the same, 4.68V.

    EN1 is pulled-up and EN2 is pulled-down, so we have a configuration of "Externally programmed by ILIM (up to 2.0A)".

    Chip is working okay when a battery is plugged. It charges at desired current and when battery is removed, system is powered from main input. The problem is when the first power-up occurs and only main power supply is present, without any battery plugged.

    Best regards,
  • 0 in reply to carlosgdj07
    TI__Guru**** 166596 points

    What is the load SYS?  Can you send a scope shot of IN, SW, SYS and REGN?

  • 0 in reply to Jeff F
    Prodigy 240 points

    The load of Vsys is formed by a Modem SoC and a LDO which performs a conversión from Vsys to 3V3.

    I cannot monitor in my oscilloscope those 4 channels, but I have measured the following:

    - Vin = 5V, very stable (from laboratory power source).

    - Vsw = I cannot access to that signal.

    - Vsys = 0.9V.

    What is REGN?

    What would be the purpose of measuring that signals? As I said before, It works properly when a battery is plugged, so DC/DC converter is working properly sometimes...

  • 0 in reply to carlosgdj07
    TI__Guru**** 166596 points

    When the battery is attached, it could be supplementing the load on SYS.  Is it possible the load on SYS is higher than you think? Even if the output of the source shows 5V, what is the voltage that the VBUS pin?  I need to know the voltages on those pins to tell you how the part is operating (i.e. input current limit, VINDPM, etc).  Alternatively, if you can provide the I2C register settings, I might be able to debug the problem.