BQ34Z100-R2: Managing chip temperature during charging

Hi Vojtech,

Is the chip itself heating up or is the temperature reading from the chip heating up? Ideally you should use an external thermistor and place it on the battery pack to get an accurate temperature reading of the pack.

Regards,

Evan

Hi Evan,

thank you very much for the response. I am talking about the  internal chip temperature readings that are going that high. The chip is also warm when touching it.
The external thermistor reads temperature around 25degC, corresponding the ambient temperature, and the battery itself does not heat during charging.

Thanks!

Vojtech

Hi Vojtech,

Thanks for the clarification, its strange that the gauge is heating up to 60 degC but at least this is still inside the operating temperature range so it should not cause any damage to the part.

Can you share your schematic? I can review it for any potential errors.

Thanks,

Evan

Hi Evan,

thank you for the assistance. In the attached pdf you can find the circuit used for sensing the SOC in our prototype.
A little explanation to the circuit and used parts:

* The sensed battery is a 12.8 V, 100 Ah LiFePO4 battery with 4 cells.
* In the scheme, GND references to negative pole of the battery, I often call this BAT -, it might happen that I will be changing these two terms.
* The sense resistor R22 is 10 mOhm, 5W, but in the next version will be replaced with 10 W.
* Our system is connected between BATT + and PACK - such that the BQ34Z100 senses all currents flowing through.
* Negative pole of the charger is also connected to PACK-
* Connections to the board is done using fixed terminal blocks rated up to 32 A
* The Ground and PACK - are distributed across the PCB using copper planes with dimension 110x61 mm (separate layers)
* BQ34Z100 chip is powered through voltage regulator converting 12 V to 3.3 V

If you have any questions I will be happy to answer. If you can give an advice how to improve the design or if you spot a mistake, I would appreciate your help.

Best

Vojtech
SOC_Circuit.pdf

Hi Vojtech,

Thanks for the explanations/clarifications.

You Schematic looks good! I don't see any obvious errors.

Is this rise in temperature seen on multiple boards or just 1 in particular?

Regards,

Evan

Hi Evan,

this heating affects all our PCBs in the current design, therefore I am wondering if I am not making any mistake in the circuit or if there is any good practise for reducing the heating.
For now the temperatures are not limiting us, however for further development it would be nice to get the temperature a bit lower if we decide to go for higher charging currents.

Thanks!

Best,

Vojtech

Hi Vojtech,

I also assume a mistake in the design, please allow me sometime to pass the schematic on to my colleagues for a second review.

I would also verify the voltages and currents are what you expect around the gauge, particularly BAT.

Regards,

Evan

Hi Evan,

thanks for the support. I would appreciate further review of the circuit. We have verified that the gauge readings and the current and voltages during charging are correct. At the same time the readings are correct also during discharging (15 A charging, 0.5 - 1.2 A discharging, up to 15 W load). As I keep exploring, it seems to me that the heat might be propagating from the terminal block where the battery is connected to the PCB, towards the BQ34Z100 chip which is placed not far from the terminal.

Best,

Vojtech

Hello Vojtech,

I will look into this and get back to you as soon as possible.

Regards,

Siddharth

Hi Siddharth,

thank you very much for that.

Best,

Vojtech

Hello Vojtech,

The schematic looks alright upon further inspection. Would you be able to send us the board layout files as well?

Regards,

Siddharth

Hi Siddharth,

I can share the gerber files with you. Can I do it via a private message?

Best,

Vojtech

Hello Siddharth,

I have sent you the files via PM.

Best,

Vojtech