BQ25820: Unable to charge battery and REGN always 0V.

For context, after cross-referencing with the EVK schematic, the main difference is that we opted to remove the power path option by disconnecting VSYS from the AC input path. Instead, VSYS is now permanently connected to the battery.

I might have missed it, but I didn’t see any special notes regarding VSYS apart from the SYS_OVP check in the buck controller, which led me to believe that connecting it directly to the battery would be a reasonable solution.

My question is: Do you think disconnecting VSYS from ACIN could prevent the battery charging and buck controller from functioning correctly?

Hi Christian,

Thank you for your reply. I have connect VSYS to ACIN and the charger appears to be working (both STAT1/2 pin are now LOW when 12Vin applied) but it is still not charging. 

In the plot above, the yellow line represents the battery path, while the green line corresponds to my raw battery input before the battery protector. I can see that the charger cycles up to 4.2V.

However, the issue arises when a fault is detected—at 4.2V, it appears to trigger a battery overvoltage protection (OVP) event, which is reflected in my fault register (0x24).

Below, I have attached a plot where the yellow line represents the signal probed at the FB pin, while the green line remains my raw battery input.

I have also shared a snapshot of my register readout in the following format: Reg[Address]:[Data]

00> Reg[0x21]: 0x 8
00> Reg[0x22]: 0x80
00> Reg[0x23]: 0x 2
00> Reg[0x24]: 0x10
00> Reg[0x25]: 0x 1
00> Reg[0x26]: 0x 0
00> Reg[0x27]: 0x10
00> Reg[0x28]: 0x 0
00> Reg[0x29]: 0x 0
00> Reg[0x2A]: 0x 0

I have attached my schematic for your review too. The only differnce here is that I have removed R16 and populated R15.

Hi Christian,

I did more troubeshooting and found that the charger was able to charge under the following settings:

1. Set VBAT_LOWV to 0x01 = 55% of VFB_REG
2. Set REGHG to 0x00 = 93% of VFB_REG
3. And bypass the battery protector IC: BQ298006RUGT

Here is a plot I captured during the charging phase—green represents the battery voltage, while blue shows the battery current. Meanwhile, my register at 0x21 fluctuates between 0x0C (CV mode) and 0x0F (Termination Done). Does this behavior seem correct to you?

And I have two follow up questions:

1. Can this charger works with BQ298006RUGT?
2. And using the BQ298006RUGT, if my battery is in shutdown mode, can this charger wakes it up? 

Thank you for your help.

Hello Kenneth,

Kenneth Er said:

Meanwhile, my register at 0x21 fluctuates between 0x0C (CV mode) and 0x0F (Termination Done). Does this behavior seem correct to you?

Is the battery connected in this case?

Do you have a system load?

Can you provide a register dump?

Kenneth Er said:

• Can this charger works with BQ298006RUGT?
• And using the BQ298006RUGT, if my battery is in shutdown mode, can this charger wakes it up? 

I do not support the BQ298006RUGT, I recommend posting a new question related to this device.

Best Regards,

Christian.

Hi Christian,

I truly appreciate your quick responses.

The battery is connected and there is no system load. Please see the register dump with nPG, STAT1 and STAT2 pin status together with my probe measurements. (Yellow = FB pin, Green = battery voltage, Blue = current measurement at battery). 

The STAT1 and STAT2 pins are internally pulled up. If 0 = ON, 1 = OFF.

Questions

1. From the result, it appears to charge my battery and prematurely entires fully charge state. Did I messed up the resistors value or my register?
   1. I haved managed to notice a CC mode once that's only when my battery is at arounbd 2.1V - 2.4V.  
2. From the oscilloscope snapshots below, I am also rather concerned that BQ25820 could cycle up to 4.2V when it reached the full charge mode. Is this correct too? 
3. Noted on the BQ298006RUGT support. But could I check if my battery is 0V (at shutdown mode), could BQ25820 apply voltage to the battery nonetheless? I just need an external voltage applied to wake up the battery protector.

Before charging

From here, you can see the battery is not at full capacity at around 2.8V.

During charging

Charge completed but my battery is still not at full capacity.

The follow plot is a zoomed in view.

Hello Kenneth,

Kenneth Er said:

From the result, it appears to charge my battery and prematurely entires fully charge state. Did I messed up the resistors value or my register?

1. I haved managed to notice a CC mode once that's only when my battery is at arounbd 2.1V - 2.4V.  

What is the charge voltage that you are trying to program? Based on the resistor setting the charge voltage is 3.6V is this correct?

Kenneth Er said:

Noted on the BQ298006RUGT support. But could I check if my battery is 0V (at shutdown mode), could BQ25820 apply voltage to the battery nonetheless? I just need an external voltage applied to wake up the battery protector.

Yes, the BQ25820 should be able to apply a voltage when battery is 0V

Best Regards,

Christian.

Hi Christian,

It turns out that the SYS pin was the actual fix needed for the board. The other issue preventing the battery from charging was due to the PMOS reverse protection. The clamping diode was sized incorrect because it did not allow the PMOS to turn on when the battery voltage is 0V (Shutdown mode). Currently, I'm able to see the battery being charged in CC mode. I will do more testing and raise another question if new problem occured. 

Thank you.

Hello Kenneth,

That is good to hear, i will close this thread for now.

Best Regards,

Christian.