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BQ25606: Failure to provide enough current

Part Number: BQ25606

I bought and assembled a 3A battery charger with this IC but when testing with a half charged LiPo cell (it was at 3.4V) the charger didn't behave as expected.  Both the STAT and the PG leds were high,  and the current going into the battery was only 0.2A. Now I'm trying to figure out if either my assembly, as the schematic shown bellow, is wrong, or if I made a mistake while soldering the components, can anyone help me?

I'm feeding it with a lab power supply and monitoring the batteries temperature, and applying  thermal and  over/under voltage protection with an external circuit , is there any problem with how i handled the supposed USB interface and the TS?

Thanks in advance

  • The schematic looks Okay. Looks like the BAT is not in charging mode according to STAT pin
    1. What are the resistance value connected on ILIM pin? The resistance value determines charge current.
    2. Check if you TS voltage is in the operation percentage
    3. Do you have correct SYS voltage? 3.68V?
    4. Can you disconnect your external circuit? Why do you need external over/under voltage protection?
  • Hi,
    1 - The resistance connected to ILIM is 1kΩ
    2 - The TS voltage is 3.62 V
    3 - The SYS voltage is 4.23 V
    4 - Right now we have no external circuit connected to the charger.
  • According to VSYS voltage, the battery is fully charged. Please check if the battery is a good battery.
  • I've changed the battery, now I'm getting 0.5A charging current, 4.11V on the SYS pin, 2.676V on the TS pin, both leds are still high and 3.98V on the battery.

  • It looks about right. You get higher current 0.5A now and SYS and BAT voltage is correct. Do you have long wire from battery pin to battery? In that case, you may not get full charge current. Can you try to discharge your battery to lower level and see if you can get higher charge current at lower battery voltage level? By the way, how did you measure battery current? It is measured on VBUS side or BAT pin side?

    Can you check the STAT pin voltage instead? When a battery is charging, the pin voltage should be low.

  • Ok, I've discharged the battery a bit, now I have the following values:

    1. The resistance connected to ILIM is 154Ohm and not 1kOhm, to get 3A from the equation Kilim/Rilim.

    2. The disconnected voltage of the battery is 3,299V

    3. After connecting to the charger, and powering it on, i get 3,61V on the battery connectors.

    4. Both the LEDS are at max

    5. The current being drawn by the charger from my power supply, which is limited to 3.5A, is 0,5A.

    6. The STAT pin is at 23mV, measured at the end of R5 connected to it.

    7. The SYS pin is at 3.858V

    8. The TS pin is at 2,234V

    9. The cables connecting the battery to the charger are around 20cm

    As you can see, since the battery is at a low level of charge, but I'm still not getting the full current.

  • Correction

    4.Both Leds are HIGH

  • Please confirm the following:
    1. You confirmed RILIM=154 Ohm, what is the resistance value you connected at ICHG pin, both resistor values determine charge current.
    2. What is your input voltage? From schematic, I saw 12V input. If it is 12V, 0.5A at VBUS is 6W. The charge current is not equal to VBUS current depending on VBUS and VBAT.
    3. 20cm is long connection in real application that may cause oscillation some cases
  • 1.RICHG is 240 Ohm
    2.Input voltage is 12V, is there a problem with that? I can redesign the circuit to work on 5V or 3.3V input also.
    The charge current can never be higher than VBUS current, am I correct?

    Some questions:
    1.One thing that came to mind, is the d+ and d- being handled correctly?
  • OK. The charge current is about 3 times the VBUS current that you were measuring. D+/D- connection is correct. The charger is charging correctly.
  • I don't understand how you say the charger is working correctly if:
    1. The charging current is 1 A (measured with a current sensor) instead of the 3 A that it should be with a ICHG resistance of 240 Ω.
    2. The STAT and PG LED's are both ON and as far as I understand from the datasheet they should be both OFF during charging.

    Can you please confirm again my schematic? (I have edit the first post with a version of the schematic where everything is visible)

  • I would like to bump the thread since I have got no answer.

  • Hey Sebastian,

    Concerning 1) what is the voltage at the BAT pin of the charger when you are measuring 1A of current?
    Concerning 2) the STAT and PG LED's should be ON during charger. These pins are open-drain outputs that internally pull LOW when active. When a valid input is applied, /PG pulls LOW. When charging, STAT pulls LOW. In other words, current will start sinking into the charger through your connected LEDs.


    Regards,
    Joel H
  • Hi,

    The voltage at the BAT pin was 3,7 V and the battery cell voltage prior to charging has 3,5 V

    Also can you please confirm that my schematic is correct for a 3 A charging.


    Regards,
    Sebastião Beirão

  • Sebastian,

    With 12V input, you can get around 2.8A charge current(the current into the battery) according to your ICHG resistor. With 12V input, battery charge current is much higher than charger's input current. Battery charger current is estimated as: (VBUS*IVBUS *efficiency)/VBAT, if you measured 1A current at input, efficiency is 87%, the real charge current into battery is calculated as: 12V*1A*0.87/3.7V=2.82A. For switching charger, charge current could be higher than charger's input current.
  • I have measure the 1 A with a multimeter with the plus probe on the charger BAT pin and the negative probe on the battery plus so I was measuring 1 A on the battery input....

    Trust me, I'm studying Electrical Engineering, so if I say the current is on the Battery I know what I'm saying. 

    The thing here is trying to validate the schematic if you can guarantee me that the schematic is ok, than the problem could be either the PCB Layout or the Soldering... 

    By the way in order to have exactly 3 A of charging current witch ICHG resistor should I use?

    Best regards,

    Sebastião Beirão 

  • OK. When you measured the battery charge current, do you have another multimeter to measure voltage at BAT pin on the same setup? Could you measure VBUS voltage on the same setup as well?
  • Yes I had. As I said to Joel Hernandez, the Battery voltage while charging was 3,7 V and the VBUS was 12 V.

    This 12 V were coming from a LAB power supply limited at 3,5 A.
  • The schematic is correct. Check if the IC is soldered well with thermal pad solidly connected to PCB. Te charger has thermal regulation that may foldback charge current. You may estimate the charge current by the equation: ICHG=677/RICHG.
  • Thank you. We will review our PCB design and resolder the chip! Thanks for all the help.

  • Since I last posted I've updated the PCB design, and after testing with different RICH values I came across another issue. When I'm using a RICH resistor with 430Ohms, I get the expected 1,5A current, but when I try a resistor with a lower value, I've tried with 240-330-360-390 Ohms, to get higher charge currents, the charger doesn't work and the STAT pin starts blinking really fast, so fast that it doesn't even have time to light up completely, It's way above 1Hz, why is this happening? Why can't I reach higher currents? Isn't this IC supposed to give upwards of 3A of charging current?

    Below is my PCB design.

  • I would like to bump the thread since I got no answer...

  • Hello,

    Based on your most recent response, I believe there may be some connection issue between your battery and the charger's BAT and GND pins. This may cause the STAT pin to oscillate at much faster pace or behave erratically. Another common reason is battery to BAT pin trace/line impedance. If this is significant, changing your resistors to higher charge current setting may force the charger into early CV/Termination, while not actually charging the battery fully. Try this test without a real battery first; i.e. using a power supply with the ability to sink current, or a constant voltage E-Load.

    You may also want to consider the power capability of your input source. Do you have this information?

    Additionally, please verify that the GND net in your first post's schematic is actually tied to the rest of the board grounds.

    I would also ask you to monitor the BAT pin voltage, rather than the cell voltage itself. This gives us a better approximation of what the charger is seeing.



    Regards,
    Joel H
  • 1. The battery connection can't be the issue, I've double checked everything and even tried changing cables, but it didn't yield better results.

    2. The BAT pin trace impedance is insignificant, since the track is very large, as you can see in the attached design.

    2. My input source was powerful enough, since i was using a 200W Lab PSU.

    4. All the grounds are connected in the PCB.

    5. I've checked the BAT pin voltage and it showed me the correct battery voltage.

    The big issue here is why the charger works with an higher RICH, which results in a smaller current, and fails to work with a lower RICH, which would provide a higher current. The charger is working perfectly with 1,5A, but it should also work with 3A when I swap the RICHG resistor.

  • Hey Sebastian, 

    The reason I asked about the BAT pin voltage and the line impedance (which includes board trace impedance, contact resistance from the battery connection point, and battery lead resistance) is because when you are trying to push more current into the battery, you could be artificially pushing the battery voltage to the battery regulation point. 

    Have you been able to take a waveform of both the BAT pin voltage and the current going into the battery? My thought is that the lower RICHG resistance is pushing the charger in and out of charging due to the higher current and higher battery voltage. If you are measuring battery voltage DC-wise, then you will only see average battery voltage. If you are measuring DC-current, again you will only see average current. This would also explain the erratic oscillation of the STAT pin as it attempts to charge, BAT voltage rises and immediately enters the termination threshold condition, stops charging, BAT voltage drops down to ~3.4V, and repeat. 

    You will likely want to add the STAT pin as a channel in the waveform you provide.

    Regards,

    Joel H