BQ51050B: LiPo 3.7V charging

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.

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

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.

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

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

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

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