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BQ24650: BQ24650 not charging

Jan Drexler
Prodigy 86 points
Part Number: BQ24650

Hello,
I would like to ask you for help with battery charge controller BQ24650. We have problem with battery charging, when we connect battery to output, then charger output voltage goes down.

.Before we connect battery, we have following behavior:

  • Feedback is 1.6V – 2.08V
  • V ripples are around 1.4V
  • Negative spikes 5.6V

After we connect battery, charger not charging.

  • Battery has 13.6V
  • Feedback 2.00V
  • Voltage before diode: 0.85V

We followed TI reference schema (Preventing BQ24650 Leakage Current When Using Shaded Solar Panels - slva829.pdf, page 9.):

 

R1 = 16.9kOhm

R2 = 97.6kOhm

C (after diode) = 1uF

Diode PDS1040-13

Please can you help me with this issue?

Thank you,

Jan

  • 0
    TI__Mastermind 24075 points

    Hi Jan,

       Scope capture 2 shows BQ24650 undergoing battery absent detection, which is correct operation when no battery is connected. R2 and R1 set charge regulation voltage according to 2.1*(1+R2/R1) so witth R2 = 499k and R1 = 100k which would give a charge regulation voltage of 12.58V. The battery you are connecting is 13.6V so this would result in BAT OVP. 

  • 0 in reply to Kedar Manishankar
    Prodigy 86 points

    Hello Kedar,

    thank you for your message. Schema was taken from reference design with default values, our values I wrote bellow picture.

    Our R1 = 16.9kOhm, R2 = 97.6kOhm, so it will be: 2.1 * (1 + R2/R1) = 2,1 * (1 + 97.6/16.9) = 14.22V.

    Our current voltage level of battery is 13.6V, but still doesn't charging. Do you want send our scheme?

    Thank you,

    Jan

  • 0 in reply to Jan Drexler
    TI__Mastermind 24075 points

    Hi Jan,

        Yes I can take a look at the schematic.

  • 0 in reply to Kedar Manishankar
    Prodigy 86 points

    Hello Kedar,

    thank you, I just sent you our schematic. Please for your review, if is everyting ok.

    Thank you,

    Jan

  • 0 in reply to Kedar Manishankar
    Prodigy 86 points

    I would like to ask you for review.

    Thank you,

    Jan

  • 0 in reply to Jan Drexler
    TI__Mastermind 24075 points

    Hi Jan,

        Looking at the schematic you have here, you have R34 = 1k, and R35 = 5.86k. From above schematic you have the resistors swapped (Right now your charge regulation would be set for 2.46V). If R35 = 1k, and R34 = 5.86k, then yes you will have a charge regulation voltage of 14.406V. You can review section 8.3.1 Battery Voltage Regulation of the BQ24650 datasheet for the formula.

  • 0 in reply to Kedar Manishankar
    Prodigy 86 points

    Hello Kedar,

    sorry, I overlooked this. It was old schematic. Here is current schema with R35 = 16.9kOhm, R34 = 97.6kOhm

    Current schematic:

    Thank you,

    Jan

  • 0 in reply to Kedar Manishankar
    Prodigy 86 points

    Hello,

    for debug propose, we build new PCB without other circuits and we got following behavior:

    Picture 1 - Vout without inserted battery 

    Picture 2 - SRN Voltage after input turn on. Vout voltage after output diode is constantly on battery voltage level.

    Currently measured values with battery:

    Vreg = 5.93

    VCC = 23V

    Vref= 1.94V

    TS = 3.29V

    MPPset= 1.52V

    RSN = 0.85V

    Thank you,

    Jan

  • 0 in reply to Jan Drexler
    Prodigy 86 points

    Hello Kedar,

    we solved it, charging is now working correctly! Problem was with wrong TS input (correct values are from range VLTF - VTCO = 2.43V - 1.49V) and we had 3.29V due wrong resistor in TS resistor network. Now TS is 1.72V and charging working fine.

    Thank you,

    Jan