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BQ24105 Issues

Krish Bala
Prodigy 50 points
Other Parts Discussed in Thread: BQ24105

Hello,

 

I am having some issues on getting my BQ24105 chip to start charging and I am wondering if anyone can assist me with this. We are using this IC to charge a 3 Cell 12.6V Battery.

 

The issue I am seeing is that the board we designed for the BQ24105 does not begin charging. The chip does come alive but it seems like it is stuck in the battery absent mode. The reason I believe it is stuck in this mode is because when there is no battery connected, we see the output voltage constantly jump for both our board as well as the EVM board. Once the battery is connected, the Stat1 LED on the EVM goes on, which indicates it is charging. I also notice that VIset1 and VIset2 are present on the EVM board but not on our board.

 

From what I am aware of, most of the layout as well as component values are identical to that of the bqSWITCHER EVM board. The only difference is the resistor values used for the TS line, which we are not currently using.

 

We are using a MSP430 to drive the Chip Enables and to read in the Stat1 and Stat2 pins. The only issue I can think of is that the 3.3V MSP we are using is not enough to enable and disable the chip.

 

Is there anything that we need to look for that will help us enable the bq24105?

  • 0
    TI__Prodigy 720 points

    To make it charging, /CE pin must be <0.4V,  VCC and IN pin must higher than battery voltage.

    TS function can be disabled by set TS votlage to middle of VTSB by two resistor diviver or external power supply.

    For 3cell battery,  the BAT pin resistor divider ratio should be 5:1 (from battery to ground). EVM default is 1:1 for single cell 4.2V application.

    If battery voltage is too low (2V/cell, 3cell is 6V), it considered as short circuit and use linear mode 50mA to charge, no switching action,

    If battery voltage is 2V/cell to 3V/cell, use precharge current to charge, higher than 3V/cell but lower than 4.2V/cell, fast charing.

     

  • 0 in reply to Mao Ye35
    Prodigy 50 points

    We have changed the EVM ratio to 5:1 by placing a 500K and 100K resistor. That is how we are able to charge our 3 cell battery using the EVM.

     

    The problem with out board is that VIset1 and VIset2 do not have the 1V and 0.1V respectively. Both of those voltages show 0V on our board but are present on the EVM. Another problem I have noticed is that the voltage across the 0.1 Ohm resistor is exactly the same, which indicate that there is no current being sent by the bq24105.

     

    I am also sure that the battery is not in Linear mode because I have tried the batteries with the EVM before I tested it on our board. It is performnig a fast charge on the EVM but it will does not do the same for our board.

     

    The only difference between our board and the EVM is the resistors around TS. Could the TS voltage cause the chip not to discharge if I did not disable it properly?

     

    If that is the case, what should I use as my resistor divider? The EVM has 5K and 10K as the divider.

  • 0 in reply to Krish Bala
    TI__Prodigy 720 points

    TS pin voltage must be in range 1.1-2.3V (35.1%-72.8% of VTSB) to enable charging.

    EVM use 5K and 10K resistor divider is to make TS pin voltage to get 66.7% of VTSB without thermistor, so it enables charging without thermistor connection.

     

  • 0 in reply to Mao Ye35
    Prodigy 50 points

    Thank you Mao.

     

    That was the problem. We switched to 4.87K and 10K and it works fine. I however failed to read that anywhere in the Manual for some reason. I will be more careful next time.

     

    I still do not obtain my Stat1 and Stat2 pins, eventhough the battery is being charged. Is there any reason why these would not come on? They are always showing 0V.

  • 0 in reply to Krish Bala
    TI__Prodigy 720 points

    In mid of page 4, the temperature comparater spec gives the range of TS pin.

    If you like to disable TS function, simply use two same resistor to make TS pin voltage 50% of VTSB voltage.

    STATx pin is pulled to low by internal switch, but need pulled high with external pull up voltage.

    If floating, then STATx pin always seems 0V because it can only be hi-Z or pulled low.

  • 0 in reply to Mao Ye35
    Prodigy 50 points

    Thank you for your help.

     

    One thing i noticed is that the STAT pins are behaving exactly opposite of what is shown in Table 1 (page 16) of the bq24xxx datasheet. At first I thought there was something wrong with our board, but the bqSWITCHER EVM is behaving the exact same way. Is this the normal operation for the bq24105?

  • 0 in reply to Krish Bala
    TI__Prodigy 720 points

    Datasheet ON means internal FET on, so STATx pin pull to LOW, OFF means internal FET off, so STATx pin hiz-Z, if there's pull up voltage, the pin is HIGH.