BQ24773EVM-540: Charge current does not increase beyond a certain value

Hi Ved,

I just tested this on an EVM and was able to increase the charge current above 700 mA, so the issue is probably with your test setup and/or register settings. There are several reasons that your charge current might be clamped, so can you please answer the following questions to help narrow this down?

1) What is your battery voltage when you are testing this?
2) What is your maximum charge voltage register setting?
3) What is your minimum system voltage register setting?
4) Is your ILIM pin enabled or disabled?
5) What is your power supply's current limit, and what is your input current limit register setting?

Best regards,
Angelo

Hi Angelo, following are the register values for my setup:

(1) Battery Voltage = ~3.7-3.9 V

(2) Max Charge Voltage setting = 4192 mV

(3) Min System Voltage setting = 3328 mV

(4) The box next to EN_EXTLIM is checked, which I think means that it is enabled. The IBAT_SEL is set to Discharge current.

(5) My power supply current limit is 5A and Input Current limit register setting is 2944 mA.

* Also I'm disabling the watchdog timer for this setup.

Moreover, I tried charging the battery at the default BQ24773 settings but still this issue persists.

* I noticed in the BQ24773EVM User guide, there's a process for charging a battery using the charger at 3008 mA which requires an electronic load connected across the SYS-GND terminals. In my setup, there isn't any connection to SYS-GND terminals and both of them are left floating. Do I need to have a load connected across them to charge at higher currents?

* The value of this clamp current varies. When I tested today morning the clamp current was 960 mA.

Hi Ved,

Thanks for the info. Your register settings all seem fine, and you don't need a system load for this, so it's okay to leave SYS floating.

Can you try again using a capacitor connected to BAT instead of a real battery? I'm guessing the issue has something to do with your battery because almost everything else in our test setups match. You could also try disabling ILIM to see if that changes anything, but I doubt that's your issue.

Best regards,
Angelo

Hello Angelo!

The battery I'm testing doesn't have any protection IC installed, so I'm thinking it shouldn't be an issue. I'll try disabling the ILIM pin to see if it solves the problem. However, I'm suspecting that the power supply which I'm using to power the BQ24773EVM is not able to supply the required current. While the charger is charging the IC at ~950 mA, the power supply current displays as 0.25 A. I have never seen the power supply exceed this value of current. Does the power supply need to output a higher current than 0.25 A, if I want a higher current from my charger IC? I'm going to try changing the power supply.

Thanks!

Hi Ved,

You mentioned that your power supply's current limit is 5 A, and your input current limit register setting is 2944 mA, right? If that's the case, then your power supply shouldn't be the reason why only 0.25 A is being drawn. It makes sense for the input current to be relatively low compared to the charge current because your input voltage (19.5 V) is many times higher than your battery voltage (3.7-3.9 V).

It definitely wouldn't hurt to test the other possibilities (disabling the ILIM pin and trying a different power supply), but I'm still leaning toward the battery being the most likely culprit. If possible, please test this with a capacitor (regulated to 3.7 V by a sourcemeter or Kepco bipolar power supply) connected to BAT instead of a real battery. If the issue still exists when using a capacitor, then please send me a list of all your register values so I can try to duplicate the issue again on my own EVM.

Best regards,
Angelo

Hello Angelo, thanks for the info about the power supply.

I tried disabling the ILIM pin and using a different power supply, both of them did not work. I also tested with a different battery sample, but still the same results. I'll try connecting the capacitor and/or load tomorrow and let you know the results. In the meanwhile, here's a snapshot of the register settings for my current configuration. I've disabled the watchdog timer:

Hi Ved,

I just tried on an EVM with your register settings, VBUS = 19.5 V, VBAT = 3.8 V, and SYS floating, just like with your test setup (except with a 2200 µF capacitor instead of a real battery). I was able to increase ICHG above 700 mA, as shown in the waveform below, where I increased the ICHG register setting from 128 mA up to 1472 mA, then back down to 128 mA.

There's also another possibility that we haven't discussed yet. What are the states of the four switches on S1? If they aren't already, please have switches 1 and 2 open (in the down position) and switches 3 and 4 closed (in the up position), as described in the EVM User's Guide. I was able to suspend charging by playing around with those four switches, so they might be related to your issue.

Best regards,

Angelo

Thanks for the reply Angelo! I'll try changing the switch position as you mentioned and let you know the results. Also, the BQ24773 IC datasheet specifies that CMPIN needs to be grounded if its not in use. But, the BQ24773EVM-540 datasheet doesn't specify any connection for the CMPIN port. Shall I ground it also, along with changing the switch positions?

Thanks,

Ved Soni.

Hi Ved,

There's no need to ground the CMPIN port or make any sort of modifications to the EVM. Just try again with a capacitor instead of a real battery and with the four switches in the positions described in the User's Guide.

Best regards,
Angelo