BQ25895: BQ25895 cannot be charged with 7V input

Hello Frank,

Couple questions:

• Can you please share the test setup (VBAT, IBAT, ISYS, input current limit, VINDPM settings)?
• Can you please share the register contents during the 7V VBUS test? Looking for any faults triggering during the test.
• Is the VINDPM threshold being modified as well when increasing VBUS?
• I'm assuming the VSOLAR is the 7V input, what is the current rating for this input? The device might be entering INDPM and having to reduce the charge current to keep the system running.

Thanks. 

Hi,

Please kindly check the register below:

register for 5.4v input. It works well.

register for 7.7v input. Cannot be charged.

I have checked the register, the 7.4v input cannot charge the battery.

I have checked the informaction of the register. The register setting seems not have big problems. Could you please help me check it and give me some suggestions? Thank you.

BR

Frank

Hello Frank,

According to the register values when the 7V source is connected, the internal BATFET (Q4) is off; please refer to register 0x09[5]. If Q4 is off there is no path to charge or discharge the battery. If Q4 wasn't turned off via I2C, something is causing Q4 to turn off, possible an OCP condition during testing, please verify this.

On both sets of register values the status of VBUS is "No input", REG0x0B[7:5]. Can you verify if this is an error on the I2C read or the test setup?

Also, the customer is trying to charge at 5A with a 15W input. This is making the device go into VINDPM. I recommend lowering the charge current when using the 5V source.

Thanks.

Hi Fernando,

I have let the customer write 0x09 register value->0x44 too when 7v input. But when read the value, it become to 0x64 again.

What do you mean about the OCP condition during testing? How can i solve it?

Thank you.

BR

Frank

Hello Frank,

By OCP, I mean the system over current protection.

Is the 7V input an input from a solar panel? If so, what is the current it can provide and what's the system current?

I'm thinking if the device is going into DPM and there is a high transient current going through the BATFET from the battery, forcing it to turn off.

Do you have any waveforms of the start up sequence including the system load and input voltage/current?

Hi,

The input 7V isn't a solar panel. It can provide the system current.

I don't know why the device go to DPM. it shouldn't have high transient current here, if yes, the 5V condition will not work well too.

Will send you the waveforms later.

Thank you.

BR

Frank

Hi,

The customer removes the battery and the BQ converter can be started. Then plug in the battery, the system can work well. but the converter cannot start with the battery when 7V input. But can be started when 5v input. Could you please help me check why?

Thank you.
BR
Frank

Hello Frank,

We need to isolate what's causing the BATFET to turn off. Are both sources plugged in at the same time or just the 7V? What is the system current?

Can you verify the following when plugging in the 7V source only.

• voltage of REGN
• voltage at PMID
• voltage and current at SYS
• voltage and current of BAT
• status of STAT (blinking, etc.)

Please share the waveform of the SYS startup when plugging in the 7V source. Look for any high transients coming from the battery as well.

Frank Xiao said:

I don't know why the device go to DPM. it shouldn't have high transient current here, if yes, the 5V condition will not work well too.

During 5V operation, the device was in VINDPM according to the register contents provided.

When changing the VBUS voltage, the VINDPM threshold should also be changed. Are they writing "FORCE_VINDPM" bit and modifying the threshold before plugging in the 7V source?

Thanks.