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BQ25120 operation

Other Parts Discussed in Thread: BQ25120, BQ25120A

Hi TI Team .

We are using BQ25120 in one of our designs.

Below is the observation , 

Without the battery connected ,

  1. When USB is plugged in PMID_1 and PMID_0 comes up.
  2. When USB is plugged out and plugged in suddenly PMID_1 and PMID_0 does not  come up.
  3. Plug out the USB and wait for 10-12 seconds and then plug in the USB then PMID_1 and PMID_0 comes up.

Is this because PMID_1 and PMID_0 has to ramp down completely before the next power on.I have a 4.7uF CAP on the output of PMID_1 and PMID_0.

I even removed 4.7uF CAP and now it works most of the times but still PMID_1 and PMID_0 doesn't come up sometimes.

Could you please help me in understanding what is happening.

I have attached the SHC for your reference.

Thanks in Advance.

Awaiting your earliest response.

Thanks ,

Rajesh N

  • Rajesh,

    I believe you are using the earlier version of the silicon where we had a requirement of BAT to be >1V or less than 0.2V for PMID to come up. 

    When you unplug and re-plugin, can you plot the BAT voltage at this point? The capacitor on that node might be just charged enough to be on this voltage range. 

    Is your planned use case with a real battery?

    Regards,

    Gautham

  • Hi Gautham,

    Thanks for the response.
    Our end use case will be always with battery.
    Only during debug and testing we would use the device without battery.

    I shall monitor BAT volatage during 5V plug in and plu out .

    Can you point it out in the datasheet where the below mentioned spec is specified,
    "BAT to be >1V or less than 0.2V for PMID to come up"

    What is the new spec for the current version of BQ25120 IC?

    Regards,
    Rajesh N
  • Gautham,

    I have experienced similar phenomena as Rajesh. With nothing connected to BAT, sometimes PMID and SYS do not come up when I apply 4.7V to IN. I adjust the voltage at IN up, down, up, and down again (using a bench-top power supply, roughly one volt in each direction), and suddenly PMID and SYS will turn on. If I turn off the board and repeat, PMID and SYS turn on immediately.

    Can you explain the precise conditions that are required for PMID and SYS to start up?

    Sam
  • Sam,

    On the older revision of the IC- We would want to avoid VIN plug when you are having BAT from >0.2V and <1V. 

    Regards,

    Gautham

  • Gautham,

    Where can we find out what versions of this device exist? In another thread you had mentioned the A variant coming out, but I can't find any reference to that on the TI website and an Applications Engineer I spoke to couldn't find any reference to it either.

    Andrew
  • Andrew,

    We have the BQ25120 and then the BQ25120A which are the two versions of BQ25120 for mass-release.

    The BQ25120A will appear on the web very soon (early next month)- we are in the last stages of the release.

    Regards,
    Gautham
  • Thanks! Is it possible to get samples sooner? We need to decide if this device is going to work for us or not.
  • Gautham,

    If I apply power to VIN with no battery connected (open circuit @ BAT), is PMID supposed to come up (VIN - dropout voltage)? I am relying on the 1.8V buck supply to turn on even when the battery is completely dead, in order to program the BQ25120 using I2C.

    I am not seeing anything turn on when no battery is connected.
  • To clarify, in normal operation I do not plan to use the BQ25120 with no battery connected, however I am troubleshooting the IC.

    I have connected a battery with open-circuit voltage of 2.967 V to BAT, and I have applied 4.958 V to IN. However, PMID is only 1.342 V, and the buck converter output is 0V.

    In your earlier post, you mentioned "We would want to avoid VIN plug when you are having BAT from >0.2V and <1V. ". Since my battery is > 1 V, why is PMID not coming up?


    Thanks,

    Sam
  • Sam,

    Feel free to open a new post and share scheamtics if you can. the PMID at 1.3V seems to be a different issue. Possibly loading or a weak short somewhere. 

    Once you share the schematic, we might be able to troubleshoot it. 

    regards,

    Gautham

  • Andrew,

    I will contact you on email regarding this.
  • Gautham,
    Do you have a updated estimate for when the new silicon will be available?

    Thanks,
    Matt