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  • Resolved

BQ25890: Why VSYS is only 1.87V with a 4.7Om load?

Part Number: BQ25890

I use the schematic just as the BQ25890evm.

The system works well with battery. The Ilimit is 1.6A. And I did not program the chip through I2C.

When I remove the battery and only connect the VBUS:

1. When the VSYS is connect to a 10Om load, the VSYS is 3.65V.

2. When the VSYS is connect to a 4.7Om load, the VSYS is only 1.87V.

Question: Is that normal? Why the VSYS drops below 3.5V (VSYS MIN)?

Question: What is the maximum current that VSYS can provide when battery is removed? I didn't find the value in the datasheet.

The Figure 5 and Figure 6 in the datasheet only show the SYS Voltage Regulation vs System Load Current when the battery is on.

Thank you.

Frank

  • Guru 62745 points

    In reply to FrankXu:

    Frank,

    Can you remove the USB meter and short D+=D- and retry?

     

  • In reply to Jeff F:

    Hi Jeff,

         Thank you.

          I ordered a BQ25890EVM-664 from TI and today I got it.

          TEST1. I use a 4.7Om load for test.

          1. When no load is put at the VSYS, the VSYS is 4.2V. (D+ D- not shorted)

           2. Then, I put the load onto the SYS while keeping the board powered by the VSOURCE. The VSYS drops to 1.82V which is similar to the phenonmen that happened on my board (1.75V). Here now, the VSOURCE keeps on 5.08V and the current is 0.18A.

     

       3. I also repeat the above experiment with D+ D- shorted. The exactly same phenonmen happened, the VSYS droops to 1.82V.

      4. You can see that the Vsource did not drop. And the Vsource is a 2A charger and as I said, when the battery is put on, the meter shows the current is 1.08A.

          And I also tried the experiment without the meter. The exact phenonmen happened.

    5. If a 10Om load is used. The VSYS is 4.19V and everything is OK.

        So, I think the bq25890 VSYS can not provide > 4.2/4.7=893mA current when battery is off.

        Question1. What is the maximum current that the VSYS can provide when the battery is off?

        TEST2.  Compare my board with BQ25890EVM-644.

        Both the boards can not drive a 4.7Om load.

        When the load is 10Om, the VSYS on my board is 3.64V while the VSYS on EVM is 4.19V.

        Question2 : What is the difference between my board and EVM?

        Question3 : The STATE LED on my board blink once at a time, while the STATE LED on the EVM blinks much quickly. Why?

     

         B.R.

    Frank

  • Guru 62745 points

    In reply to FrankXu:

    Frank,

    I have used the bq25890 to provide well above 2A from 5V/3A input so I know it is capable. To summarize:
    1. At startup with SYS < ~2.0V, input current is limited to 200mA so the charger will not startup into 4.7ohm.
    2. After startup, the input current limit is clamped to the lower of the setting per the ILIM resistor or setting in the IINDPM register. With the 890, the IINDPM register is configured by D+/D- pins. With D+/D- shorted, IINDPM is 3A but, unless you disable ILIM resistor via I2C or also change resistor to set it to 3A, the ILIM resistor clamps the input current below 3A. If I recall correctly, the EVM ILIM resistor has a potentiometer in parallel with fixed resistor. If you increase the potentiometer to the maximum, so that help?
    3. If the load transient caused by quickly added such a large load causes the SYS voltage to drop <~ 2.0V, the charger could get confused and think it is in startup, which returns you to condition one above. In that case, you will need to add additional capacitor from SYS to GND that can absorb more of the transient and prevent such a droop.

    With the EVM, you can use the bqStudio I2C software to read the charger's status register, which might tell you the problem. Do you have an EV2300 or EV2400 I2C box to use with the software?

     

  • In reply to Jeff F:

    Hi Jeff,

        Thank you very much.

        I find that the JP10 is shorted with a jumper on the EVM, and the VSYS is 4.2V. Remove the jumper in JP10, the VSYS become 3.65V.

        In my test, the RLIM is 130Om on the EVM (the R19 potentiometer is set to 0Om). So the ILIM is 355/130=2.73A.

        In my test, the 4.7Om load is in parrel with a 1uF cap. With the 4.7Om load, the VSYS is 3.13V.

        And with the 10Om load, the VSYS is 3.65V, when I open the power first, and then connect the load to VSYS manually.

        

    With the 4.7 Om load:

    The adapter is recognized as a SDP, and the current limit is 500mA. 3.65/4.7*3.65/0.9/5=0.63A.0.5A. 

    That's why the VSYS drops. And if I set the current limit to 3.25A, the VSYS can be 3.65V even with the 4.7Om load.

    Thank you for your advice.

    But I still have some problem with the EVM:

    Problem1: With a 2A adapter and D+/D- shorted on the EVM board, the adapter is still recognized as a SDP. (current meter is not used). But on my board, I did the experiment many days ago and it's recognized as DCP.

    Problem2: With the battery on, the adapter never charges the battery. But with my board, the adapter charges the battery with 1.08A.

    For the above 2 problems, I've also tried other adapters, but always SDP and never charge.

    I have not found the reason from the registers, could you help. Thank you so much.



    B.R.


    Frank

  • Guru 62745 points

    In reply to FrankXu:

    Frank,

    First, please check the EVM to ensure that it has a bq25890 installed and not a bq25892.  Then, confirm that JP1 shunt is not installed and JP2 shunt is connected between pins 1 and 2.  If you are using a power supply, you can install the shunt on JP5 to short D+=D- and simulate a DCP.  If you are plugging in a DCP adapter, use J5.  If that doesn't work, try flipping the S2 switch.

     

  • In reply to Jeff F:

    Hi Jeff,

            I use a power supply, set 5V output and 2A current limit. The S2 is switched to the right position which makes D+ D- shorted. The battery and a 10Om load is connected to the VBAT and VSYS receptively. The Rlimit is adjusted to the smallest value 130Om, so the Ilimit set by the Rlimit is 335/130=2.577A.

    The connection is shown below:

    The Vsource is recognized as a DCP, and the regisiters are shown below:

    If the power supply is off, the VSYS is 3.7V which means the power now is supplied by the battery (VBATT is about 3.7V for this half full battery).

    Question 1: Why the Input Current limit is only 500mA?

    Question 2: Why the state is still not charging? The Isource shown in the power supply is 320mA, but if the battery is removed, the Isource is 297mA. So the power supply drives 20mA into the battery. I wait for 10 minutes, the Isoure is still 320mA and the state is still not charging.

     

    Then I change another battery and switch the power supply off and on. This battery is nearly full, the VBATT is about 4.124V as shown below,

    The state is still not charging, and the input current limit is still 500mA.

    But this time, the Isource is 370mA, which means about 70mA is driven into the battery. But the state is still not charging.

    Please help. Thank you.

    B.R.

    Frank

  • In reply to FrankXu:

    Please note that battery charging is enabled when CHG_CONFIG = 1 and CE pin = Low. CE pin must be Low to charge. Please install JP7 shunt: JP7 CE pin setting: pull low to enable the charge.

    The input current limit detection is correct because REG00[5:0]=3.25A (top-left corner on the GUI) for DCP.
    For REG13[5:0] (shows Input Current Limit=500mA), it is the input Current Limit in effect while Input Current Optimizer (ICO) is enabled. Since REG14[6] (Input Current Optimizer (ICO) Status) shows “In Progress”, ICO current limit is not finalized, i.e. REG13[5:0] does not show the final ICO current limit yet. To avoid confusion, please set Enable ICD (REG02[4])=0 (i.e. disable ICD) and read registers again.

    Thanks!
  • In reply to Ning T:

    Hi Ning T,

           Thank you very much. Now I have no problem with the EVM board.

           But with my own board, there is still a strange phenonmen.

           I use a 5V2A power supply and with D+D- shorted.

           When the battery is on, the bq25890 can recognize the source as DCP when power up.

           But when the battery is not connect, the bq25890 recognize the source as "Unknown adapter (500mA)".

           This is the registers in the two conditions with my board. I did the same experiments with the EVM, it can recognize the source correctly in both condition.

           Can you help me to find the problem with my board?

           Thank you.

    Condition

    No Battery

    With Battery

    ISource

    268mA

    557mA

    REG00

    0x48

    IINLIM=500mA

    0x7F

    IINLIM=3.25A

    REG01

    0x6

     

    0x6

     

    REG02

    0x5D

     

    0x5D

     

    REG03

    0x1A

     

    0x1A

     

    REG04

    0x20

     

    0x20

     

    REG05

    0x13

     

    0x13

     

    REG06

    0x5E

     

    0x5E

     

    REG07

    0x9D

     

    0x9D

     

    REG08

    0x3

     

    0x3

     

    REG09

    0x44

     

    0x44

     

    REG0A

    0x73

     

    0x73

     

    REG0B

    0xA7

    101:Unknownadpter

    (500mA)

    NotCharging

    In VSYSmin regulation

    0x76

    011:DCP(3.25A)

     

    FastCharging

    Not In VSYSmin regulation

    REG0C

    0x5

    TS Cold

    0x0

     

    REG0D

    0x12

     

    0x12

     

    REG0E

    0x0

    VBAT=0V

    0x4D

    VBAT=3.844V

    REG0F

    0x44

    VSYS=3.664V

    0x4D

    VSYS=3.844V

    REG10

    0x7F

     

    0x49

     

    REG11

    0x96

    VBUS=4.8V

    0x93

    VBUS=4.5V

    REG12

    0x0

    IBAT=0mA

    0x5

    IBAT=250mA

    REG13

    0x8

    Not in IINDPM

    IDPM_LIM=500mA

    0x4A

    IINDPM

    IDPM_LIM=600mA

    REG14

    0x1D

    Optimization is in progress

    0x5D

    Maximum Input Current Detected

  • In reply to Ning T:

    And the following table shows the difference between my board and EVM board, when battery is not on.‘

    It's strange that, although the battery is not on, the EVM still get VBAT=4.184V and VSYS=4.224V. And I checked the voltage with  multimeter, that is true. 

    And the STAT LED blinks very very quickly on the EVM, about 5Hz, not 1Hz. Why?

    I think when the battery is removed, the VBAT should cut off, and the VSYS would be 3.65V according to the datasheet.

    Condition

    My board

    EVM board

    REG00

    0x48

    IINLIM=500mA

    0x7F

    IINLIM=3.25A

    REG01

    0x6

     

    0x6

     

    REG02

    0x5D

     

    0x1D

     

    REG03

    0x1A

     

    0x1A

     

    REG04

    0x20

     

    0x20

     

    REG05

    0x13

     

    0x13

     

    REG06

    0x5E

     

    0x5E

     

    REG07

    0x9D

     

    0x9D

     

    REG08

    0x3

     

    0x3

     

    REG09

    0x44

     

    0x44

     

    REG0A

    0x73

     

    0x73

     

    REG0B

    0xA7

    101:Unknownadpter

    (500mA)

    NotCharging

    In VSYSmin regulation

    0x7E

    011:DCP

    (3.25A)

    Charging TerminationDone

    Not in VSYSmin regulation

    REG0C

    0x5

    TS Cold

    0x80

     

    REG0D

    0x12

     

    0x12

     

    REG0E

    0x0

    VBAT=0V

    0x5E

    VBAT=4.184V

    REG0F

    0x44

    VSYS=3.664V

    0x60

    VSYS=4224V

    REG10

    0x7F

     

    0x51

     

    REG11

    0x96

    VBUS=4.8V

    0x98

    VBUS=

    REG12

    0x0

    IBAT=0mA

    0x0

    IBAT=0mA

    REG13

    0x8

    In VINDPM

    Not in IINDPM

    IDPM_LIM=500mA

    0x3F

    Not in VINDPM

    Not in IINDPM

    IDPM_LIM=3.25A

    REG14

    0x1D

    Optimization is in progress

    0x1D

    Optimization is in progress

    I think the only difference between my board and EVM is that I use a bq27441 to monitor the volume of the battery.

  • In reply to FrankXu:

    I removed the bq27441 from my board, but it doesn't change anthing.

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