• State
  • Locked Locked
  • Replies 7 replies
  • Subscribers 64 subscribers
  • Views 2509 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

bq25504 for lithium ion battery charging

Pratap NNV
Prodigy 110 points
Other Parts Discussed in Thread: BQ25504, LM3658

Hi, I would like to know the following about bq25504 as they are not available in the datasheet. Please help at the earliest.

1. Does it implement CC/CV charging?

2. Are there any safety timers to stop charging the battery if it's voltage is not raising (like the ones in LM3658)?

3. The battery charging current is rated as 100mA. Should this be taken as the limit for CC mode for charging ?

4. Can the charging current be programmed or is it fixed always at 100mA?

5. As a safety precaution, we would like to monitor the thermistor pin of battery while charging to discard charging at high battery temperatures. Will it be possible with bq25504? The existing temperature sensor on the chip will not accurately indicate battery temperature as I understand it is intended to monitor ambient temperature. We are intending to charge less than 1ah li ion batteries. Can you suggest if this chip is good enough for that as it doesn't sense the thermistor pin resistance of battery?

  • 0
    TI__Guru**** 166106 points
    Regarding 1, no. It only implements CV charging because the charge current is typically delivered in pulses/bursts from a high impedance source due to the bq25504's MPP feature.
    Regarding 2, no. The expectation is that the input source (for example, solar panel) will not always be providing power so no timer needed.
    Regarding 3 and 4, the average input current to the boost converter is 100mA assuming a low impedance source. With a high impedance source, the output current, delivered in pulses/bursts, will be less. The maximum pulse/burst current can be estimated using a power balance: efficiency = VSTOR*ISTOR/(VMPP*IINAVG). IINAVG is difficult to determine.
    Regarding 5, the chip does not have thermistor sense. You would need to add two external comparators with reference and resistors to monitor the thermistor.

    What is your input source type, voltage (e.g., open circuit for solar panel) and current (e.g. short circuit for solar panel)?
  • 0 in reply to Jeff F
    Prodigy 110 points
    Thanks Jeff, few more doubts:

    6. What is the voltage at CV mode charging?

    7. I do not plan to connect any system load to VSTOR pin, so how do I determine the battery charging current?

    Approximate panel specs: Voc 2.3V and Isc 80mA.
  • 0 in reply to Pratap NNV
    TI__Guru**** 166106 points

    Regarding 6, CV is the VBAT_OV set by the external resistors.

    Regarding 7, with no load on VSTOR, the battery charging current is output current of the boost converter.  As with any boost converter, you have to estimate output current using an efficiency power balance:  eff=(VBAT*IBAT) / (VIN*IIN) where VIN~=80%*2.3V.  IIN is difficult to determine without very careful (averaging over a long time period) measurement because it will be pulsing with some dead time.  You can see inductor current measurements in the scope plots toward the end of the datasheet.

  • 0 in reply to Jeff F
    Prodigy 110 points
    8. Is there an inherent limit to battery charging current. Say my battery is discharged down to 2V and CV voltage is 4.2V , how much charging current can I expect?

    9. If I connect battery is reverse polarity, is there any safety feature that will prevent charging ?

    10. Say the protection circuit inside my battery is not functional and the load deeply discharges it or say battery self discharges itself. What is the lowest battery voltage which will enable charging?
  • 0 in reply to Pratap NNV
    TI__Guru**** 166106 points
    Regarding 8, the maximum charge current is limited by the input power available.
    Regarding 9, there is no integrated reverse polarity protection. You will need to add that externally.
    Regarding 10, the main boost charger continues to operate as long as VSTOR > VSTOR_CHGEN ~=1.8V.
  • 0 in reply to Jeff F
    Prodigy 110 points
    11. Regd the calculation for CEQ, my battery mah is 300 and charged voltage is 4.2. I am getting CEQ as 1714285. What should the additional cap value be for this battery and can it be electrolytic?

    12. How will the device function in the following scenario: Pin = 0. Will my load connected to VSTOR be disconnected to prevent battery discharging below VBATT_UV?
  • 0 in reply to Jeff F
    Prodigy 180 points
    Hi Jeff,
    Im planning to use BQ25504 to charge a 18650 li-ion battery 3.7V from a solar cell with Vin=4.5V and Iin=2.2mA.
    Is it able to charge the battery cause i think Iin=2.2mA is too low for charging.

    best regard,