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BQ2002C: Can't enter permanently in Trickle Charge Mode

Yulian Sokolovski89
Prodigy 40 points
Part Number: BQ2002C
Other Parts Discussed in Thread: BQ2002E

Hi guys,

Currently we are working on 7 pcs. NiMh standalone battery charger based on BQ2002C (it is part of a bigger project).

The issue which we have - the charger switching between Fast Charge and Trickle Charge Modes and can't  remain permanently in Trickle Mode. 

As attachments you can find the schematic and oscilogram of CC pin (Ch2) and Battery voltage (Ch1).

I'll be very grateful if someone can help me with this issue.

Best regards,

Yulian

BATTERY_CHARGER_SCH.pdf

  • 0
    TI__Guru 56650 points
    I saw Q10 and U24 on the schematic. Where do you find that reference design?
  • 0 in reply to Yulian Sokolovski89
    TI__Guru 56650 points

    According to the trickle charge time, the CC should stay high about 1s. So, your waveform doesn't seem run between fast charge and trickle charge.  CC pin output is pulled to low for some reason. 

    If we compare your schematic and DV2002L2 schematic, you can find DV2002L2 has a 1000uF input capacitor. Would you add a capacitor at your input.

    Also, would you order an DV2002L2 evaluation board to compare with your board?

  • 0 in reply to Wang5577
    Prodigy 40 points

    I think that the times and levels are ok according trickle charge mode descrepted in the datasheet.

    In first oscillogram you can see that the CC pin is in low level (if we ignore the spikes) for around 1s. In second one CC pin is high for around 73ms. 

    I tried with 1000uF on Vcc pin but situation is the same.

    What I think as possible reason causing the spikes is voltage drop of battery pack and lack of hysteresis on CC pin. When charging the voltage is around 9.66V and when it is inhibit the voltage drops to 9.48V. It is around 180mV on the battery pack (around 27mV per cell) respectively 40mV drop on CC pin. What do you think, is it possible to be the reason and if yes how can I solve it?

  • 0 in reply to Yulian Sokolovski89
    TI__Guru 56650 points
    In that case, if we move 1000uF to BAT side which make the charger voltage drop slow. Does the CC pin still have those spikes? Please help me check it. That can help us understand it.
  • 0 in reply to Wang5577
    Prodigy 40 points
    I've tested your suggestion, but situation is the same. If I leave it in this semi-trickle mode, the spikes density decrease with the time and after .. arhm ... , let say 4-5 hours, the controller enters permanently in trickle mode.

    Anyway, I've tested BQ2002E on the same board and there isn't such kind of behaviour. It seems that something missing in C version.