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BQ25890 Charging Issue

Jeff Lam55
Intellectual 420 points
Other Parts Discussed in Thread: BQ25890

Hi,

I just did a prototype using TI BQ25890 charger, there are some issues that I am encountering and I hope to hear your suggestions.

When I connect the Quick Charge USB adapter to the input of BQ25890, the handshake can successfully initiate and the voltage would change from 5V to 12V (which is good). 

I also can measure good output (12V) at the PMID and good output (around 6.7V) at the REGN. 

____________________________________________________________________

However, the voltage at the System Output and Battery + is completely off.....

The voltage at the Batt+ is 1.75V and Sys_out is around 2.4V.

Also I noticed that the Sys_out is very noisy.

Below is the my circuit schematic:

Since the Batt+ voltage is lower than the voltage of my battery, the battery isn't charging.

Also, another observation is that the Vin would switched to 5V as soon as I connect a 3.6V battery to the circuit.

If I remove Vin and the battery stays connected to the charger, I get a healthy and clean output at Vsys and PMID.

Seems like the problem is with the buck converter of the charger. Any thought on what I should do to isolate the problem?

Thank you so much,

Jeff

  • 0
    TI__Guru**** 153546 points
    What is your input current limit setting? In standalone mode, it is set by D+/D- pins. In I2C host mode, it is set by I2C register value.
  • 0 in reply to Jeff F
    Intellectual 420 points

    Hi,

    In the circuit, the RIlim = 130 ohm, so the current should be limited to around 2.4A.

    I also attached a screenshot of the I2C register setting below:

    Thanks!!

  • 0 in reply to Jeff Lam55
    TI__Guru**** 153546 points
    Input current limit register is reporting 100mA and VSYS is reporting in VSYSMIN so something is up with your input. D+/D- has control of input current until you write something different via I2C. If D+ is shorted to D- then ILIM resistor sets the default; otherwise, the D+/D- algorithm determines the input current limit.
  • 0 in reply to Jeff F
    Prodigy 170 points

    Hi,

    I have BQ25890EVM on my hand, I dindt connect the host because I want it to run stand alone (Default Mode) I short R18 on the EVB so that the Rilim is 130ohm, therefore I should expect A=355/130=2.7A and I connect it to a DCP usb adaptor (where D+ and D- are shorted) but I can charge the battery only upto 1.5A.

    Basically I want this BQ25890EVM when in default mode to charge upto 3A on a DCP mode.

    Any insight why the BQ25890EVM is acting like this?

    Thanks,

    Jay

  • 0 in reply to jay claro
    TI__Guru**** 153546 points

    Jay,

    What is the load on SYS?  The charger prioritizes the load on SYS over battery charge current.  If no load on SYS, what is the voltage at BAT and VBUS pins relative to the IC GND pins?  If V(BAT) is close to VBATREG=4.20V then the charge current will be reduced as the charger moves from constant charging (CC) to constant voltage (CV) mode.  If V(VBUS) is drooping by ~600mV from the applied voltage (due to resistive connection from power source), then the charger will have used its ICO feature to reduce the input current limit to prevent further droop.

  • 0 in reply to Jeff F
    Prodigy 170 points
    Hi Jeff,

    I check my condition with no load situation, I discharge first the battery such that the voltage is around 3.8V because I thought the battery maybe full charge, after I plug the USB to a DCP charger the voltage jump immediately to 4.2V and the current charging to battery with no load on VSYS is 1.5A.

    On your comment that the VBUS drop is more than 600mV I tried external PSU and slowly increase the voltage until I reach 7V but still the current I see on the battery is 1.5A maximum.

    Appreciate if you have the EVB you can try on your side as well my test condition default mode Rilim =130R.

    Thanks,

    Jay
  • 0 in reply to Jeff F
    Prodigy 170 points
    Hi Jeff,

    No Load on the VSYS, I discharge the battery before I charged is the battery voltage is 3.8V, when I plug the VBUS to a dcp wall adaptor the VBAT jump to 4.2V.

    I suspect initially that the 5V supply was dropping so I use a PSU short the D+ and D- then plug the 5V, and slowly increase the voltage upto 8V but I am still getting 1.5A consistently.

    Appreciate if you can check on your side as well.

    Thanks,

    jay
  • 0 in reply to jay claro
    TI__Guru**** 153546 points

    Jay,

    If the voltage at the BAT pin is at 4.2V, the charger thinks the battery is fully charged and is in CV mode. The current has started to taper down.  Either the connections from the BAT pin to battery are highly resistive or the battery itself is highly resistive (4.2V-3.8V)/1.5A = 0.267ohm).  Are you measuring the battery current through an multi-meter?  Generally, that is not recommended due to its high resistance.

  • 0 in reply to Jeff F
    Prodigy 170 points

    Hi Jeff,

    Initially that's my set up I measure the current by inserting a multimeter on the battery GND. I changed the set up and measure the current on the Vbus but I still get 1-1.5A.

    On a default mode (No Host intervention) and using a DCP I should be able to suck 3A theoretically right?

    Thanks,

    Jay

  • 0 in reply to jay claro
    TI__Guru**** 153546 points

    Jay,

    In default mode, ICHRG=2A and input current limit is limited by the resistance on ILIM pin.  What is the resistance on the ILIM pin?

  • 0 in reply to Jeff F
    Prodigy 170 points

    Hi Jeff,

    I set the Ilim to 130R technically I should be limiting the current to 355/130=2.7A but I can draw only 1.5A, and the vbus status says DCP input.

    If its 2A I think I am just short by 500mA only its just easy work around, because initially I thought I can draw 3.25A on a default mode.

    Thanks,

    Jay

  • 0 in reply to Jeff F
    Prodigy 170 points
    Hi Jeff,

    Thanks for your info.

    Just curious if this BQ25890 IC enumerates to the USB wall charger to take 12V /1.5A (18W), but the battery cannot handle 12V maximum is just 4.25V, Does it safe to say that this IC convert the power (18W) to 4.2V/4.28A to charge fast the battery?

    Or should I say how does this BQ25890 makes the battery charging charge fast?

    Thanks,

    Jay
  • 0 in reply to jay claro
    TI__Guru**** 153546 points

    Jay,

    The bq2589x does not enumerate USB but can automatically negotiate with certain high voltage DCP adapters to change their output voltage to 9V or 12V.  The charger core is a buck converter that steps down the input voltage to the 4.2V battery voltage.  Fast charging is achieved by allowing higher input power with higher input voltage and input current below the charger's maximum input current limit.  Higher input power allows for higher output power, specifically higher charge current.

  • 0 in reply to Jeff F
    Prodigy 170 points
    Hi Jeff,

    You are right the maximum I can draw without HOST is 2A.

    One more question, This BQ25890 uses Dp and Dm to enumerate, can I still use the DP/DM for USB 3.0?
    What I meant by that I will connect the DP/DM in parallel to USB3.0 and to this DP/DM of BQ25890?

    Appreciate if you can feedback before I start my design.

    Thanks,

    Jay
  • 0 in reply to jay claro
    TI__Guru**** 153546 points
    Jay,

    The bq25890 D+/D- feature does not enumerate but does follow the primary and secondary level USB detections per the USB BC1.2 spec. You can connect the D+/D- lines together as long as nothing else on the USB D+/D- bus attempts to communicate for the first 2 seconds after input power is applied to the charger. If you can't guarantee that, then you will be a USB switch, similar to the one on the bq25890EVM.