BQ24298: Not seeing Constant Current charging

Hi,

Can you share the VIN voltages at the different charge currents as measured close to the charger pin?

Best Regards,

Juan Ospina

i just ran a test with a battery discharged to 3.5V, when plugged in, the charging started at 2A, but dropped to 1.8A within 5 or so minutes. The Battery charge voltage held steady at ~4V.

Hello,

Can you please share register values while charging. Preferably all register values, but particularly register REG02, REG04, REG08, and REG09.

Best Regards,

Juan Ospina 

Input Source control Reg00: 00110111

Charge Current control Reg02: 10011100

Precharge/Termination control Reg03: 00010000

Charge Voltage control Reg04: 10110010

Charge Termination Reg05: 11011100

System Status Reg08: 10101100

New Faults Reg09: 00000000

Hi Christopher,

Thank you for the register values. Based on your REG08 register value, it looks like DPM_STAT is high indicating that the device might be in VINDPM or IINDPM. Is there a load currently connected to your charger? If not then what is the VBUS voltage as measured closed to the charger VBUS pin?

Best Regards,
Juan Ospina

Our charger just feeds into VBUS with no additional load (aside from the load on VSYS). Our VBUS voltage is at 4.2V during charging.

Actually, Im not quite sure what we changed, but it looks like we do see CC charging until we hit 3.7-3.75 V now. Is that where we would expect to see the charging switch from CV to CC? What drives where that switch occurs?

Also, we are seeing a watchdog timer fault, that resets our register values to default. Does that have anything to do with our DPM issue?

Hi Christopher,

The watchdog fault can certainly have an impact as it will reset register configurations. I would recommend resetting the watchdog timer periodically, or disabling the watchdog timer.

With regards to the DPM, it is difficult to say exactly what causes it. Since no load is applied and charge current is not increased then I would suspect that it is related to VINDPM. I recommend testing with a lower VINDPM setting or a higher VBUS setting to see if that resolves the DPM status register.

One additional question would be, where is the battery voltage measured? Is it measured using the ADC, or measured using a DMM? If using a DMM, is it measured at the battery cell voltage or at the IC pin voltage? These have an impact on understanding the charger's behavior while charging.

Best Regards,

Juan Ospina

We are using a Max17260 Fuel Gauge to collect the battery OCV. 

Sorry I am a bit confused on the VBUS/VINDPM setting. While charging, isnt the battery on VBAT ultimately part of the load on VBUS? Is VINDPM supposed to be set to lower than 4.2V, because that is the VBUS voltage we see when charging a depleted battery?

Hi Christopher,

Christopher Verdegan said:

While charging, isnt the battery on VBAT ultimately part of the load on VBUS? Is VINDPM supposed to be set to lower than 4.2V, because that is the VBUS voltage we see when charging a depleted battery?

I'm not really sure of what your current VINDPM setting is, if it is already at your battery regulation voltage then it shouldn't be lowered further.

Christopher Verdegan said:

Our VBUS voltage is at 4.2V during charging.

Given that your VBUS setting is equal to your VINDPM setting, you are likely to see current limitations due to VINDPM. Are you able to test charging with a higher VBUS voltage?

Christopher Verdegan said:

We are using a Max17260 Fuel Gauge to collect the battery OCV.

This might be measuring battery voltage closer to the Cell in that case.  If there is a large resistance between the pin and the cell of the battery its possible your device can enter CV mode much earlier since the current * resistance will raise the VBAT Pin voltage up to regulation. Are you able to run a charge cycle while measuring voltage close to the VBAT pin of the charger? The VBAT pin should reach approximately 4.2V at the transition point from CC to CV.

Best Regards,

Juan Ospina

Juan Ospina said:

I'm not really sure of what your current VINDPM setting is, if it is already at your battery regulation voltage then it shouldn't be lowered further.

We have VINDPM at default 4.36V and VREG (charge voltage control Reg04) is set to default 4.208V. Would you recommend we lower our VINDPM to 4.216V?

Juan Ospina said:

Given that your VBUS setting is equal to your VINDPM setting, you are likely to see current limitations due to VINDPM. Are you able to test charging with a higher VBUS voltage?

We are using a 5V USB-C charger input for VBUS, which is what we would like to use for our system. We can try testing a higher voltage input, but ultimately we will need it to work with the 5V.

Hi Christopher,

Christopher Verdegan said:

We have VINDPM at default 4.36V and VREG (charge voltage control Reg04) is set to default 4.208V. Would you recommend we lower our VINDPM to 4.216V?

4.36V would be a safer bet.

Christopher Verdegan said:

We are using a 5V USB-C charger input for VBUS, which is what we would like to use for our system. We can try testing a higher voltage input, but ultimately we will need it to work with the 5V.

It sounds like the 5V USB-C may not be able to source as much current as required for the application since you are measuring VBUS at 4.2V. Can you try using a stronger source such that VBUS is measured at a higher voltage at the input pin? Preferably higher than the 4.36V VINDPM setting.

Best Regards,

Juan Ospina