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Original question:

BQ25505: BQ25505 is not Working without solar when connected Battery?

BQ25505RGRR input solar issues?

ram chinni
Prodigy 245 points

Dear Sir/Madam,

I have been working on this boost charger chip to charge my 3.7V 2600mah li-ion battery from the last 5 months.

Issues i have been facing

1) Without solar battery is not connecting to my load circuit due to internal FET.

2) I am using 5V 55ma solar panel to charge my battery. Is it okay?

Battery capacity: 5V 2600mah

3) What will happen if i connect 3.7V 2600 mah in the place of solar input when solar is not present? Will the chip damage?/Will it be okay?

4) When light is present battery is connecting to the load circuit. when there is no light internal FET automatically turning off.

I want to charge my battery at the same time i want it to connect to my load circuit directly without interference of VSTOR.

I am at very crucial position. I need your response at the earliest. Please give me your valuable suggestions.

Regards,

Ram.

. 

  • 0
    TI__Guru**** 166896 points

    Hi Ram,

    Regarding 1, when no VIN_DC is applied (i.e. no solar panel), the battery at VBAT must be connected when both VBAT and VSTOR are < 100mV in order for the FET to turn on.  If VBAT falls below the VBAT_UV voltage (2.2V typical), the FET automatically shuts off to prevent battery under-voltage.

    Regarding 2 and 3, the boost charger requires the VIN_DC = MPP of panel (typically 80% of panel open circuit voltage) < VBAT_OV=final battery voltage.  If VIN_DC>VBAT_OV, the charger turns on a pull down FET at VIN_DC to prevent overcharging the battery.  I am assuming your MPP = 80%*5V = 4.0V and VBAT_OV=5.0V so I see no issue.  However, if you change to VBAT_OV=3.7V with the same panel, the charger will turn on the pull down FET and not charge.

    Regarding 4, I am assuming the load circuit is attached at VSTOR.  Current can flow from VSTOR to VBAT through the internal FET body diode when the charger is charging.  With only 55mA from the panel, all of the panel power may be going to the load on VSTOR.  For example, with a 5V, 55mA panel, your max input power is 5V*80%*55mA = 220mW.  Assuming boost charger efficiency of 85% at VIN_DC=4V, your output power is 220mW*85%=187mW.  That gives only 187mW/5V = 37.4mA of current to split between the load on VSTOR and charge the battery at BAT.  I fear your battery will never charge if your load is >37.4mA.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 245 points

    Hi Jeff,

    Thank you for your reply and valuable valuable. 

     In my circuit VSTOR is connected to my load circuit.

    i)As per below circuit we have designed like when solar is present battery wont connect to the load.

    ii)When solar is not there battery will connect to he load.

    Can't we connect VBAT_SEC directly to my load circuit instead of Vstor. My circuit needs battery all the time. Will it charge if i connect VBAT_SEC?

    In the morning my circuit is working fine. In the evening my circuit is not getting the power. I am not getting where i am doing the mistake? 

    I want to turn on internal fet between VBAT_SEC and VSTOR permanently. Will it be okay? Will it charge my battery ? 

    Please help me out. Waiting for your valuable response. 

    Regards,

    Ram.

  • 0 in reply to ram chinni
    Prodigy 245 points

    Dear Jeff,

    I am requesting you to respond on this at the earliest.

    Regards,

    Ram.

  • 0 in reply to ram chinni
    TI__Guru**** 166896 points

    Ram,

    I do not understand the circuit above.  Is the solar panel output going directly to the system load or battery, in addition to the input of the charger? 

    You can connect your load directly to the battery at BAT_SEC.  In either configuration, the load and battery are parallel loads from VSTOR.  The system load is lower resistance so it will pull the most current, with the remainder (if any) going to charge the battery.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 245 points

    Jeff,

    Thank you for your valuable response.

    Actually what happened we have connected load circuit at VSTOR.

    when VIN_DC applied by solar panel the VBAT_SEC and VSTOR is connecting and after some time internal FET is getting turned OFF. So at VSTOR i am getting zero volts.

    So i have shorted both VSTOR and VBAT_SEC on my PCB to give continuous power to my load circuit. 

    Is is okay?

    Regards,

    Ram.

  • 0 in reply to ram chinni
    TI__Guru**** 166896 points

    Ram,

    Yes.  The internal PFET between VBAT_SEC and VSTOR only turns off when V(VSTOR)<2.2V.  Is your load too much for solar panel and therefore causing your battery to get depleted?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 60 points

    Jeff,

    If my circuit is getting the Power from Battery   In a few Minutes in per day and rest of time it will , Let me know , what is My Battery Charging status.

    My battery is getting chagrining or Not?

    Ram

  • 0 in reply to NIPUN NET SOLUTIONS PVT LTD
    TI__Guru**** 166896 points

    Ram,

    If your system runs only a few minutes per day but you get light for more minutes than that, then the battery will charge when there is no system load.  If you know your exact system load and operating time and light time per day, you can calculate the time using the design spreadsheet at the link:

    www.ti.com/.../sluc463.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Prodigy 60 points

    Jeff,

    thank you

    i will test and Come back to you.

    Ram

  • 0 in reply to NIPUN NET SOLUTIONS PVT LTD
    Prodigy 60 points

    Jeff,

    Can I connect VBAT_SEC to System Load Without connecting to VSTOR(no connection Between VSTOR and  System Load).

    Ram

  • 0 in reply to NIPUN NET SOLUTIONS PVT LTD
    TI__Guru**** 166896 points

    Ram,

    Yes.   However, the benefit to connecting system load to VSTOR is the PFET preventing the battery from going below the undervoltage threshold (2.2V).  However, if you are certain that your input power availability is enough to power the system and charge the battery, this will not be an issue.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 60 points

    Jeff,

    thank you,

    I will back to you after testing My circuit.

    Ram

  • 0 in reply to NIPUN NET SOLUTIONS PVT LTD
    Prodigy 60 points

    Hi Jeff,

     

    Find   My Final  Circuit Below  and  whenever required Power to load it supplies and also  Battery is charging. Give me yours valuable suggestions if any.

    Ram

    My_Testing Circuit_BQ25505.pdf

  • 0 in reply to NIPUN NET SOLUTIONS PVT LTD
    Prodigy 60 points

    Jeff,

    Please Reply ,on the Above Query,

    Ram

  • 0 in reply to NIPUN NET SOLUTIONS PVT LTD
    TI__Guru**** 166896 points

    Ram,

    Again, the charger will function but, by shorting the charger's undervoltage prevention PFET, you run the risk of over-discharging your battery unless it has an internal protector to prevent overdischarge.

    Regards,

    Jeff