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BQ24075: CHARGE CURRENT TOO LOW

Leonardo Prates
Prodigy 50 points
Part Number: BQ24075
Other Parts Discussed in Thread: LM5088

I'm using BQ24075 as a charger in my board. Conditions:

Input voltage (VIN) is at minimum (4.38V).

EN1=LOW, EN2=HIGH, using Ilim=1.5A (1.1K) and Iset=1.4A (620R)

CE = GND and SYSOFF = GND

No load at OUT, and voltage measured at this point is 4.25V

With battery connected charge current is only 200mA (0.42V) (measured at Iset pin using this equation VISET = ICHARGE / 400 × RISET). If I turns cjharge on without battery connected I expect CHG pin to be high-Z, but it blinks. With battery connected CHG goes LOW and led turns on, but only with 200mA.

Questions, with EN1, EN2 configured to use Ilim and Iset, why the output current is too low? Vin is at minimum but inside the operational range and I have no load at OUT.

For reference battery voltage at this situation is 3.6V.

  • 0
    TI__Mastermind 23170 points

    Hi Leonardo,

    It seems like your device is either going into DPPM because your voltage at OUT is 4.25 (DPPM threshold is 4.3 V). What is the measured voltage at the input? It could be that you're using a power source that is not able to handle the charge current.

    Another possibility is that your device is entering thermal regulation. Without a good thermal design, the max programmed charge current may not be reached. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 50 points

    Anthony, thanks for your answer, input voltage is 4.38V provided by LM5088 with 7A capacitiy (this power supply was tested, no drop voltage). When I apply the Vin BQ24075 starts charge the battery with 200mA and remains at this all time, then BQ24075 doesn't get hot. I have tested increase the input voltage and as far as I increase the voltage the current gets higher and higher and when it arrives at 5.5V the current is near to configured current.

    Is DPPM mode applied to non USB mode (EN2=H, EN1=L) too? Doesn't make sense this input voltage range starts at 4.35V if it needs 5.5V (value that I can't use at my design) to charge at configured current, I chose this IC only because this low voltage input specification. 

    Another problem is if apply Vin without a battery connected the CHG pin starts blink immediately and this situation based on datasheet information is only for timers errors, I was expecting high-Z. 

    Leonardo

  • 0 in reply to Leonardo Prates
    TI__Mastermind 23170 points

    Hi Leonardo,

    This does look like DPPM if you are increasing the input voltage and you are seeing more charge current. 

    In USB Mode, you will be affected by VINDPM which reduces the input current limit reaches the VIN-DPM threshold (4.5 V) as well. This threshold is to maintain USB compliance. 

    Leonardo Prates said:
    Doesn't make sense this input voltage range starts at 4.35V if it needs 5.5V (value that I can't use at my design) to charge at configured current, I chose this IC only because this low voltage input specification. 

    I understand. This design is due to the BQ24075 being a linear charger with power path that is intended to regulate the output voltage at 5.5 V (pass through if VIN is lower). With it being a linear charger, we require voltage at OUT and IN to have sufficient headroom otherwise the device begins to operate in undesirable ways. 

    Leonardo Prates said:
    Another problem is if apply Vin without a battery connected the CHG pin starts blink immediately and this situation based on datasheet information is only for timers errors, I was expecting high-Z. 

    This is due to the battery detection routine. If you monitor the BAT pin voltage, you'll notice the voltage puling due to the device checking if there is a battery. This is the charging toggling that you see that is reflected in the CHG pin blinking. 

    Let me know if there are any additional questions. 

    Best Regards,

    Anthony Pham