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.

  • Resolved

BQ51050B: LiPo 3.7V charging

Part Number: BQ51050B

I want to charge a small LiPo battery of 3,7V. Can it be charged with the BQ51050B component? 

As I can see, the output voltage options are around 4,2V.

1 - How the component can notice that the battery is completely charged at 3,7V?

2 - How the component will stop charging the battery?

3 - How the charging ending can be notified? I see that CHG can do that, but as long as I have test it, CHG is always high (both charging or not)

I am measuring the currents with an INA219 between the battery and the BQ51050B. Using the 3,7V battery, I checked that it was charged to 4,096V. Afterwards, it started decreasing the voltage in a constant negative current of -70mA (consuming from the battery). Which could be the reason for that?

Thank you so much in advance,

Gerardo

  • Hello
    1 - How the component can notice that the battery is completely charged at 3,7V?---If you have a LiPo battery it it will probably be charged to 4.2V, check battery manufactures recommendations. Charge is terminated based on charge termination current, see date sheet section 8.3.3

    2 - How the component will stop charging the battery?--During the Taper phase of charging current will decrease to termination current.

    3 - How the charging ending can be notified? I see that CHG can do that, but as long as I have test it, CHG is always high (both charging or not)---Use the CHG pin, it will indicated charge complete.

    Adding resistance between charger and battery will cause sense voltage at BAT to change can cause problems, current sense resistor for INA219 may be an issue.
    Charging current can be monitored at the ILIM pin, this voltage is proportional to charge current.

    Best Regards,

    Bill Johns,  Applications Engineer

    Texas Instruments Inc

    Dallas, Texas

    Please click "This resolved my issue" button if this post answers your question.

  • In reply to Bill Johns:

    Hi Bil,

    1 - I have been monitoring the charge of the 3,7V battery, and I could check it was charged to 4,242V. But then, without taking away from the Qi transmitter, it started discharging continously. Which could be the reason for that?

    At 4,1V I was seeing voltage in ILIM, but from 4,2V and in the discharge, there is no voltage there.That showed that the charge was finished, didn't it?

    3 - I attach two images. The first one is CHG when the battery is charging. The second one is obtained in CHG when it is not charging. Should that be the correct performance?

    Thank you so much in advance,

    Gerardo

  • In reply to Gerardo L:

    Hi Gerardo

    1.) I have been monitoring the charge of the 3,7V battery, and I could check it was charged to 4,242V. But then, without taking away from the Qi transmitter, it started discharging continously. Which could be the reason for that?---Bill J--This does not sound right. It stop charging at 4.2V (4.242V is close enought), but should not discharge. Is a system load connected to battery? Can you tell where the battery current is going?

    2.) At 4,1V I was seeing voltage in ILIM, but from 4,2V and in the discharge, there is no voltage there.That showed that the charge was finished, didn't it?---Bill J--Yes, in constant current charge (4.1V) the voltage on ILIM will be higher. At about 4.2V unit is in constant voltage mode and current is decreasing, ILIM voltage decreasing. At charge complete the voltage should be 0V.

    3 - I attach two images. The first one is CHG when the battery is charging. The second one is obtained in CHG when it is not charging. Should that be the correct performance?----Bill J--the CHG pin is open drain, what do you have it pulled up to? Does look odd.

    Best Regards,

    Bill Johns,  Applications Engineer

    Texas Instruments Inc

    Dallas, Texas

    Please click "This resolved my issue" button if this post answers your question.

  • In reply to Bill Johns:

    Hi Bill,

    Thank you so much for your information.

    1 - Please, find attached the schematic used below. Vcc is the V of our system. However, the battery is discharging faster than the usual discharge in a normal operation. Therefore, I suppose it is related with Qi.

    In addition, our coil is not completely tuned with C14, C15, C16, C17 and C18 to the Qi frequencies. Could that be a reason for the discharge?

    2 - Is there a way to calculate the exact current charge from the voltage in ILIM? Is it proportional to VIlim?

    3 - I do not have it pulled up. It goes to a GPIO port in a microcontroller, with the purpose of notifying when the system is being charged and when the charge is finished. Is it necessary to be pulled up?

    Best regards,

    Gerardo

  • In reply to Gerardo L:

    1.) Please, find attached the schematic used below---Bill J -- Schematic look OK.
    Vcc is the V of our system.---Bill J. If you disable the LDO using EN is battery discharge OK.
    Therefore, I suppose it is related with Qi.---Bill J. The typical standby current into BAT pin is 12uA, battery charged condition or not on a
    charger.

    In addition, our coil is not completely tuned with C14, C15, C16, C17 and C18 to the Qi frequencies. Could that be a reason for the discharge?---Bill J. No, this would show up as a communications, trouble starting or efficiency problem. But not battery drain.

    2.) Is there a way to calculate the exact current charge from the voltage in ILIM? Is it proportional to VIlim? --- Bill J. the ILIM pin is a current source that is I-OUT / 262 and voltage is developed across the resistor. (Vilim/Rilim) * 262

    3 - I do not have it pulled up. It goes to a GPIO port in a microcontroller, with the purpose of notifying when the system is being charged and when the charge is finished. Is it necessary to be pulled up?---Bill J-- Yes

    Best Regards,

    Bill Johns,  Applications Engineer

    Texas Instruments Inc

    Dallas, Texas

    Please click "This resolved my issue" button if this post answers your question.

  • In reply to Bill Johns:

    Hi Bill,

    Again, thank you so much.

    What value of resistor should I use for the pull up of CHG?

    I have been trying with 1,2KOhm, and the result is the same of not pulling up (3V not charging, and 2.5V charging in CHG), and keeps discharging once fully charged. And also with 8KOhm resistor (0,008V not charging, 0V charging in CHG), but in this case, there is no further discharge once fully charged. Which could be the reason for that?

    Thank you so much in advance,
    Gerardo
  • In reply to Gerardo L:

    Hi Bill,

    It works using a 4,7KOhm resistor to pull-up. CHG started to work perfectly then.

    However, I see in the datasheet that the minimum charging current is 500mA. For the batteries I am using, the maximum charging current is 85mA.

    1 - Is there any way to charge at 85mA? Can I modify Rilim to get such current?

    2 - How that overcurrent can affect the batteries?

    3 - If the batteries have a Protection Circuit, does the overcurrent affect them? Or does it protect them from such problem?

    Thank you so much,

    Gerardo

  • In reply to Gerardo L:

    Hi Gerardo

    1 - Is there any way to charge at 85mA? Can I modify Rilim to get such current? -- Bill J -- The current sense input ILIM losses accuracy at low currents. Termination at low current ( below 30mA) is difficult. Regulation accuracy at 85mA could be an issue.

    2 - How that overcurrent can affect the batteries?---Bill J -- This will depend on the battery, consult battery manufacture.

    3 - If the batteries have a Protection Circuit, does the overcurrent affect them? Or does it protect them from such problem?---Bill J -- The Protection Circuit will typically prevent over charge from voltage and over current discharge. It would be best to consult maker of protection circuit and battery manufacture.

    Best Regards,

    Bill Johns,  Applications Engineer

    Texas Instruments Inc

    Dallas, Texas

    Please click "This resolved my issue" button if this post answers your question.

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.