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BQ24075 is not charging the discharge battery

Embionics Technololgy
Prodigy 190 points
Other Parts Discussed in Thread: BQ24075, BQ24075EVM

Dear All

I am using BQ24075 battery charger and power path managment IC. Initially when discharge battery is connected to board it charge the battery to the 4.1Volt. LD1 red led indicates the charging status.  But after plugging new discharge battery to the same board it would not charge the battery, as LD1 red led on board remain off. Please suggest! Snap shot of the Schematic is below!

  • 0
    TI__Guru**** 166696 points

    The /CHG indicator only shows charging for the 1st charge cycle.  Recharge cycles are not shown.  A recharge cycle occurs if a battery reaches full charge, charging stops, the battery voltage bleeds down to the recharge voltage and charging resumes without power being removed. So it is possible that the battery is charging but the indicator is not on.  Is charge current flowing?  If you remove and replace the input power, does the charge indicator turn on?

  • 0 in reply to Jeff F
    Prodigy 190 points

    Thanks for your reply!

    I checked board, the charge current is zero and replaced the input power but it is still not charging the battery. and charge indicator is also off! So there might be other reason for this. Because the /CHG pin showing 3.7V (high) which indicates charging is disabled. why this is happening? Please suggest!

  • 0 in reply to Embionics Technololgy
    TI__Guru**** 166696 points

    Can you resend the schematic?  It is not viewable from the first post. 

    What is the voltage on the TS pin?

  • 0 in reply to Jeff F
    Prodigy 10 points

    Hi,

    Please find attached Schematic

    5516.Battery Charger Sche.pdf

    Hope you can view it

  • 0 in reply to vihang sapale
    TI__Guru**** 166696 points

    The charger has several loops that can reduce charge current including

    1.  TS loop - what is the voltage on TS?

    2.  VINDPM - what is the voltage on IN?

    3.  DPPM - what is the voltage at SYS?

    or it could be that the battery detect circuit is not working as expected.  Do you see the waveforms in datasheet Figs 2 and 3?

  • 0 in reply to Jeff F
    Prodigy 190 points

    3005.VBAT_WF.pdf

    1. TS PIN VOLTAGE - 0.57V

    2. VIN PIN VOLTAGE - 5.05V

    3. SYSOFF PIN VOLTAGE - 0V

    These are the voltages at respective pins. I checked the waveforms at VBAT  (Pin 2 & 3), and the waveforms are attached here. Waveform shows the difference in peak to peak voltage levels when compared with datasheet waveforms.

  • 0 in reply to Embionics Technololgy
    TI__Guru**** 166696 points

    I misstated earlier.  I meant OUT not SYS voltage.

    Also, on the pdf, is that the BAT voltage?  What is happening when this is taken? At the point of battery un-attach and then re-attach?  Seems a bit fast. 

  • 0 in reply to Jeff F
    Prodigy 190 points

    OUT Voltage - 5.05V

    Yes the pdf shows the BAT voltage. Pls check the updated PDF. When batter is inserted & removed; the IC works properly in battery detection mode (refer attached waveform). But the charging cycle is not initiated at that time. Also the /CHG pin goes low for very short duration approximately for 50ms and again high.6175.BAT_Removed.pdf6874.BAT_Attached.pdf

  • 0 in reply to Embionics Technololgy
    TI__Guru**** 166696 points

    If the voltage in the scope plot is the voltage at the charger's BAT pin, /CE = 0, /PG=0, EN1=EN2 =/= 1, safety timer not expired and the load on OUT < the input current limit set by EN1 & EN2 then the IC should be charging.  The safety timer should have been reset when you removed the first battery and replaced it.

    Try toggling /CE. If that doesn't work, try toggling EN1=EN2=1.  

    The charger senses the voltage at its BAT pin.  If there is any additional resistance in series with the BAT pin (like a current meter), then the voltage at the BAT pin could be higher than the voltage at the battery itself.  The charger terminates when V(BAT) > VBATREG - VRCH (as low as 4.02V) and ICHRG < ITERM. 

    Does a slightly more discharged battery start charging?

  • 0 in reply to Jeff F
    Prodigy 190 points

    Thank you for your valuable reply!

    We tried for more discharged battery of 1.5V, we observed that battery is charged upto 3.4V in 3 hours. Charging is continued for 5 to 6 hours but battery voltage remains same as 3.4V but there is no battery charging indication. Also we toggle /CE and EN1=EN2=1 but no LED indication (RED LED off). 

    what may be the reason for battery not charging above 3.4V? Please suggest!

  • 0 in reply to Embionics Technololgy
    TI__Guru**** 166696 points

    What is the battery capacity?  How much charge current is flowing? Do you have the capability to measure VOUT, V(BAT), V(IN) and I(IN) on an oscilloscope scope over a long time period so the I can see battery attach and then start of charging?  If you can't measure I(IN) then V(ISET)

    In addition, I suggest you order the bq24075EVM, modify it to match your circuit and test with the EVM.

  • 0 in reply to Jeff F
    Prodigy 190 points

    Battery capacity is 3000mAH, 3.9V.

    We observed that pin 5(EN2) & 6(EN1) of BQ24075 are short to each other. There is no assembly mistake like solder metal between two pins & pins are electrically short. So we think that this may be the reason for battery is not being charged upto 3.9V. Comment on this whether this is the only reason for not charging the battery upto 3.9V.

  • 0 in reply to Embionics Technololgy
    TI__Guru**** 166696 points

    If EN2=EN1=0, then the IC is in the 100mA mode.  With the charge current limited to 100mA max, a 3000mAh battery would need 30 hours to charge which is longer than the safety timer allows.

    If EN2=EN1=1, then the IC is in the standby mode and will not charge.  The battery will provide the OUT voltage.