BQ25713: How to increase VSYS with respect to VBAT

Hi Sudha,

What is CELL_BATPRESZ pin voltage set up to?

After battery insertion, can you re-check that MinSystemVoltage() register value is not reset?

Best Regards,

Linhong

Hi Linhong,

In our design, we are using MYIR  and carrier card which has Bq25713. Bq25713 REGN pin is set to 6V and CELL_BATPRESZ voltage is set to 3.7V (3S ie 55%), when we set Reg 0X05/04 to 11V (0X2B) and Reg 0x0D/0C is to 11.26V, we observed CELL_BATPRESZ reduced to 2.2V  and VSYS is set to 11.2V  when main power supply is connected , However when we set Reg 0X05/04 to 12.6V and Reg 0x0D/0C is set to 11.26V, we observed CELL_BATPRESZ reduced to 1.6V  and VSYS is set to 0. If we connect  battery we are observing VSYS as 10.5V same as battery voltage.

Ever if we revert back the settings (Reg 0X05/04 to 11V  and Reg 0x0D/0C is set to 11.26V) we are observing VSYS value as 0 with Main power supply. If we change MYIR board then only we are getting VSYS when Main is connected

I request your guidance on this VSYS behavior.

If we insert battery, MinSystemVoltage() is not resetting.

Thanks and Regards,

Sudha Nayak

Hi Sudha,

Do you have EN_LDO turn on in Reg0x01/02? In order to regulate VSYS above battery voltage, BATFET operates in LDO mode.

Also, it is very critical to ensure a fixed value on CELL_BATPRESZ, as it sets a few important default charging parameters. You might have multiple sources connected to power up CELL_BATPRESZ, but they are fighting against each other. We need to sort them out, which one is dominate and why.

To simplify the debug, I suggest have battery always connected, before you set up registers. And please let me if you can achieve what you want under such condition.

Best Regards,

Linhong

Hi Linhong,

EN_LDO is turned on.

Could you please give us some more information on important charging parameters which may get affected by CELL_BATPRESZ. Because we tried to change reg 0x05/04 values, however it is not helping us to improve CELL_BATPRESZ voltage.

Thanks and Regards,

Sudha Nayak

Hi Sudha,

Please refer to Datasheet 9.3.3.3. CELL_BATPRESZ is an input, variation might come from external. But make sure REGN is also stable though.

Also watch for faults in Reg20/21, and 22/23 . It will give us addition clues what might be wrong.

Best Regards,

Linhong

Hi Linhong,

When only battery is connected, reg value of 0x21 is 00 and 0x20 is 10 (SYSOVP_STAT is set high) . We tried to clear latch-off by either writing 0 to the SYSOVP bit, however this is is continuously setting as 1.

In document it is mentioned that, upon battery removal (CELL_BATPRESZ pin goes LOW) , however in our case it is not happening. Is it causing any issue?

Thanks and Regards,

Sudha Nayak

Hi Linhong,

As per some design modification now we are able to set CELL_BATPRESZ  to 3.6V which is above 55% of 10.7V (3S battery voltage). Now SYSOVP_STAT is low.

Our Main supply voltage supply is 12V and after changing  Reg values of 0x05/04 and 0x0D/0x0C to 12V ie(0x32) we are receiving VSYS  as12V. However if we try to increase register values to 14V , we are receiving VSYS  as12V only.

We wanted to know whether we can boost the VSYS voltage above the Main supply voltage . If yes, which register settings we need to modify?

We are able to reduce VSYS to different voltage levels when main supply is connected.

If we change Reg values of 0x05/04 and 0x0D/0x0C to 12V and connect  only battery, we are receiving battery voltage as VSYS ie 10.7V. We are not able to do buck or boost when only battery is connected to the system.

We wanted to know how we can increase or decrease voltage levels at VSYS  ,when only battery is connected?

Thanks and Regards,

Sudha Nayak

Hi Sudha,

I am not sure if I have misunderstood your application: if you have only battery connected, no adapter, you cannot boost VSYS above battery. you can use OTG mode if it helps.

In order to boost VSYS, you have to have adapter connected, where battery is optional in this case.

Best Regards,

Linhong

Dear Linhong,

Since Sudha in on leave for a few days, I am pitching in here on her behalf. 

Thank you for your reply. 

Could you please confirm if my below understanding is correct about BQ25713?

1. BQ25713 can support higher battery voltage compared to Main voltage in boost mode. Is this true?

2. BQ25713 with adapter connected can support boost mechanism and can support higher Vsys than adapter input. 

3. With just Battery and no adapter, max Vsys is what Battery output voltage will be. 

4. With just battery and no adapter, can we control Vsys lower than Battery voltage? If so, what registers should be set to enable this? 

Thanks and warm regards

Dharin

Hi Dharin,

You are welcome! Here are my comment:

1. Yes

2. Yes.

3. Yes.

4. Very limited control. There is no voltage regulation for it, but you can reduce discharge current Reg0x38/39 to manipulate the voltage difference, but only to some extent.

Please keep in mind, buck/boost convert is between adapter and SYS/BAT. There is only a power FET between SYS and BAT, therefore not much you can do to control SYS from BAT.

Regards,

Linhong

Dear Linhong,

Thank you for answering to my queries. We understand it completely and we will design our system accordingly. 

Thanks and warm regards

Dharin

Hi Linhong,

Thank you for your support on understanding and solving this issue.

Best Regards,

Sudha Nayak

Hi Sudha,

Thanks for using TI parts. We're glad we can help!

To better track the thread, please click "This resolved my issue" button if your question got answered.

Best Regards,

Linhong