BQ24600: BQ24600 Slow Battery Charging Issues

Jessynia Filgueira

Part Number: BQ24600

Tool/software:

Hello,

I am trying to use the BQ2600RVAR chip for battery charging on one of our projects and am having issues with the charging speed of the chip. Currently the batteries only draw 100-120 mA of current during the charging process and this current seems to remain fairly consistent until charging completes.

I am trying to charge a 7.2V battery with the charging circuit attached utilizing the chip. BAT_CHG is the connection to the battery and DC_PRESENT is connected to a 12V power supply. In order to charge the battery, we have added a 10 KOhm resistor across BAT_THERM and ground, and additionally have removed the C182 capacitor and stacked it on top of the R209 resistor so that it is parallel with only that resistor. This configuration allowed the chip to enter a charging state and the status LED begins to display solid while charging.

Once the batteries are finished charging, the status LED then begins to blink to indicate so. Some of the charging voltage readings I am reading at the pins are below:

Vcc = 11.1 V

VFB = 1.91 V

PG = 83 mV

Iset = 130 mV

TS = 1.68 V

SRP - SRN = 1 mV

Status = ON

To test, two batteries were ran dead and then set to charge, which took over a full day to reach complete charge. The first battery finished charging at 7.4V and the second one at 7.38V capacity. The Iset pin reads at 130 mV which should give up to .65 A. Is there anyway to increase the charging speed of this chip and reach a current closer to what is set?

Thank You

27 days ago

0 Aaron Bagger 27 days ago

TI__Prodigy 720 points

Hi Jessynia,

Does this issue still persist when charging the battery without the charging circuit?

Best Regards,

Aaron

0 Jessynia Filgueira 27 days ago in reply to Aaron Bagger

Prodigy 10 points

Hi Aaron,

No, the battery wants to consume more current when plugged into the power supply. This issue exists when the charging chip is used.

0 Nicholas Smith1 26 days ago

Prodigy 210 points

Aaron,

the battery also notably stopped charging at 7.4V not the expected 8.4V regulation voltage.

0 Aaron Bagger 26 days ago in reply to Jessynia Filgueira

TI__Prodigy 720 points

Hi Jessynia and Nicholas,

I will be looking more into this and will follow up with updates.

Best Regards,

Aaron

0 Aaron Bagger 25 days ago in reply to Aaron Bagger

TI__Prodigy 720 points

Hi Nicholas,

Your chosen resistor values for the VFB pin seem fairly large. I would try reducing the VFB resistor ladder resistances proportionally to see if that helps the issue.

Best Regards,

Aaron

0 Nicholas Smith1 25 days ago in reply to Aaron Bagger

Prodigy 210 points

Are you sure? The Vfb in the datasheet has a similarly high 900k and 100k resistor stack. We can check, but was there anything else that we could test on the circuit?

0 Nicholas Smith1 24 days ago in reply to Nicholas Smith1

Prodigy 210 points

Aaron, we tried with a 301k and 100k and the issue still persists. Vfb is sitting around 1.5-1.6V so it SHOULD be fast charging, but the slow charge seems to be still in effect.

0 Christian Moyer 24 days ago in reply to Nicholas Smith1

TI__Mastermind 31701 points

Hello Nicholas,

Nicholas Smith1 said:
Aaron, we tried with a 301k and 100k and the issue still persists.

Which issue still persists: The issue of charging stopping at 7.4V, the slow charge speed, or both?

Nicholas Smith1 said:
Vfb is sitting around 1.5-1.6V

We have a min/max value of the transision voltage from precharge to fastcharge. Do you ever see it go into fastcharge? What is the expected fastcharge current? What current are you seeing?

Can you upload another image of the schematic?, it's not very clear.

Best Regards,

christian.

0 Nicholas Smith1 24 days ago in reply to Christian Moyer

Prodigy 210 points

There were two issues with the current setup:

One is the slow charge (125mA) never transitioned to fast charge. We changed the resistor divider to shift it out of Vlowv with a 1Meg/380k ohm resistor setup with no change in performance. Once we changed it to 301k/100k, the fastcharge transition still did not occur.

Two, the regulation voltage stopped at 7.4V, but that may have been because of the earlier 1Meg/380k ohm resistor setup.

I've also attached a clearer picture of the schematic. We expect the battery to charge up to 8.4V at 0.67 A, but have not seen it go above the 0.125A precharge current if anything.

0 Christian Moyer 21 days ago in reply to Nicholas Smith1

TI__Mastermind 31701 points

Hello Nicholas,

Nicholas Smith1 said:
Two, the regulation voltage stopped at 7.4V, but that may have been because of the earlier 1Meg/380k ohm resistor setup.

Please re-test this behavior to see if the issue was resolved.

Can you measure Vref?

Best Regards,

Christian.

0 Jessynia Filgueira 21 days ago in reply to Christian Moyer

Prodigy 10 points

Hi Christian,

It looks like the voltage regulation issue is solved. Vref measures at 3.29 V.

The device is still maintaining a slow charge state.

0 Christian Moyer 20 days ago in reply to Jessynia Filgueira

TI__Mastermind 31701 points

Hello Jessynia,

Jessynia Filgueira said:
It looks like the voltage regulation issue is solved

That is good to hear.

Jessynia Filgueira said:
The device is still maintaining a slow charge state.

This slow current lasts until it reaches 8.4V?
Do you see any changes if you increase the current using the resistor divder?
Is there any system load?
Is the 12V adapter capable of supplying the full charge current?

Best regards,

Christian.

0 Jessynia Filgueira 20 days ago in reply to Christian Moyer

Prodigy 10 points

Hi Christian,

To answer a few of those questions:

I have not been able to reach the full 8.4V yet since the charging is so slow. I would need faster charging to verify
Yes, I did see an increase in voltage across R208 from 1 mV to 2 mV
Yes, there is a system load
The 12V adapter gets power via benchtop power supply so power shouldn't be an issue

Additionally, here are some scope captures of the high drive(first photo) and low drive(second photo) signals incase it may be useful:

0 Christian Moyer 19 days ago in reply to Jessynia Filgueira

TI__Mastermind 31701 points

Hello Jessynia,

Do you still see this behavior without a system load?

Best Regards,

Christian

0 Jessynia Filgueira 18 days ago in reply to Christian Moyer

Prodigy 10 points

Hi Christian,

I removed the system load and retested the battery charging circuit. The behavior remained the same with voltage across R208 at 2 mV and Vfb at 1.89V.

As an additional note, I have been able to verify the battery will charge up to 8.35V now.

0 Christian Moyer 17 days ago in reply to Jessynia Filgueira

TI__Mastermind 31701 points

Hello Jessynia,

Can you measure the ISET pin?

0 Jessynia Filgueira 17 days ago in reply to Christian Moyer

Prodigy 10 points

Hi Christian,

The Iset measurement is at .203 V. This measurement was done with a 51.1K resistor on R195.

0 Christian Moyer 14 days ago in reply to Jessynia Filgueira

TI__Mastermind 31701 points

Hello Jessynia,

Can you provide your PCB layout file?

Best Regards,

Christian

0 Nicholas Smith1 14 days ago in reply to Christian Moyer

Prodigy 210 points

Christian,

Not publicly, no. Will need a secure link to exchange that info.

0 Christian Moyer 13 days ago in reply to Nicholas Smith1

TI__Mastermind 31701 points

Hello Nicholas.

I sent you a friendship, Please provide PCB layout in private chat.

Best Regards,

Christian

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BQ24600: BQ24600 Slow Battery Charging Issues