BQ27427: schematic review

Hello Comi

I've attached the mark up down below of the schematics, also I can only do the battery gauge portion. The highlighted green portion is good and the blue is of concerns, " If an external thermistor is used for temperature input, the thermistor should be connected between this pin and VSS." Also wanted to validate the you have it as Batt(+) >> BAT >> SRX >> Load (+). As for the excel I agreed on point 3 about the comment but if you it is really needed you could possibility share the thermistor but it is better to communicate via i2c, lastly point 4 the biggest information that the battery gauge will give you is State of Charge (SOC), Full charge capacity (FFC), chemical capacity (Qmax), temperature and etc. You would need to read the Technical reference manual to better understand all the information you can get from battery gauge.

Thank you,
Alan

Hi Alan,

Thanks for your reply.

The highlighted green portion is good and the blue is of concerns, " If an external thermistor is used for temperature input, the thermistor should be connected between this pin and VSS."

Alan Frias said:

The highlighted green portion is good and the blue is of concerns, " If an external thermistor is used for temperature input, the thermistor should be connected between this pin and VSS." Also wanted to validate the you have it as Batt(+) >> BAT >> SRX >> Load (+).

--- I reserve battery NTC connection to both charger IC TS pin and fuel gauge BIN pin,  TS pin expects a pull up resistor to NTC and have a desent voltage on TS pin.  While BIN pin expects a low ( close to 0V?) voltage. Our fuel guage is on phone board, so we need to get battery temperature via NTC and it should be read from charger IC TS, not BIN?

My question is that TS requires decent voltage while BIN require low voltage, how to handle this conflict? Or am I wrong on that?

---please help to check the following charging flow, is it correct?

BR,

Comi

Hello Comi,

Comi Li said:

My question is that TS requires decent voltage while BIN require low voltage, how to handle this conflict? Or am I wrong on that?

- The battery gauge does have an internal temperatures sensor that can be used if the battery gauge is place closely to the battery cell. However if you are sharing a thermistor with a charger than it would be up to the user to test to see it this is workable. 

Comi Li said:

---please help to check the following charging flow, is it correct?

- Yes the charging flow is correct for the battery gauge.

Thank you,
Alan

Hi Alan,

Could you help review the schematic of our BQ27427?

28-103590-01_01_20250519.zip

BR,

Comi

Hi Alan,

Please find as attached.

28-103590-01_01_20250520.pdf

BR,

Comi

Hello Comi,

Sorry for the confusion but it seems you sent me some kind of layer stack up pdf and not the schematics. Could you send me your schematics to review them.

Thank you,
Alan

Hi Alan,

Sorry make you confused.

Actually, we have already reviewed the schematic diagram. Now, CIsco engineers need us to review the layout. I apologize for the typo above.

Can you help review the layout of BQ27427?

BR，

Comi

HI Alan,

Engineer has some question about gauge config,Please kinldy help for the below questions:

1.what if fuel gauge report 95%, but the battery voltage already reach 4.35V(maximum)?

2.how can we know if fuel gauge report an accurate battery capacity? 

3.do we need fuel gauge calibration?

4.can we use full charging capacity reported by fuel gauge to estimate battery health?

BR,

Comi

Hi Alan,

Thanks for your comments! i have few furth more questions to be answered:

Please find my feedback about your questions as below:

1. what if fuel gauge report 95%, but the battery voltage already reach 4.35V(maximum)?

Alan: There can be multiple factors that can cause this, a .log from bqstudio would help within the investigation. The most likely reason is that the cell is going through the "taper current" process where it reaches the maximum voltage but is still taking in current that is gradually decreasing with time as it reaches 100%.

[Comi]:is there a register setting to set the maximum and minimum battery voltage for fuel gauge (e.g. 3.5v min/4.3v max), so that fuel gauge always report 100% at 4.3v and 0% at 3.5v?

1. how can we know if fuel gauge report an accurate battery capacity? 

Alan: If the fuel gauge is setup properly with a custom chemID, the soc% accuracy should be within 1%. Validation of the system could be done with a external system.

[Comi]:Is chemID a setting in register? I attached our cell datasheet, it is not a standard cell, I am not sure if the chemID has been existed in your system

1. do we need fuel gauge calibration?

Alan: Yes there is a calibration tab for this process that would need to be done with a high precision power supply/load and is one of the first steps you would need to perform.

[Comi]:we have battery simulator in our LAB, is there a guide to help us make the first step you mentioned, do we need to prepare couple of batteries and send to you for calibration?

1. can we use full charging capacity reported by fuel gauge to estimate battery health?

Alan: It is possible however outside of age there are other factors that could influence this such as last pervious discharge/charge cycle, temperature and etc.

[Comi]: so battery health can not be assessed by single full charging capacity, if we report couple average full charging capacity like what we have in Iphone,  Iphone can tell the current battery capacity, can we say the battery is not in good condition if the capacity reaches certain thresholds(80% e.g.)?

BR,

Comi