BQ25886: powerpath managment at high temperatures

Andre,

JEITA has no influence on battery discharge through VSYS. Are you seeing switching action on SW?

Best Regards,

Ricardo

hi, i did not observe the SW-Pin while doing the climate test - i try to gather the information in an additional test run

Hi, i have performed a new test:

The Switch-Node wave form does changes significantly when the temperature is above ~43 °C (and does change back if temperature is low enought).

Additional i observe PG# and STAT:

• PG# is always 0
• STAT is 1 if Temperature is below ~43 °C and flashes while temperature is above ~43 °C

Hello Andre,

The charger can switch to PFM if it need to charge at lower currents due to thermal regulation, it looks like your bottom left picture is PFM operation.

You can refer to figure 12 in the datasheet for the die temperature and charge current reduction.

Sincerely,

Wyatt Keller

Hi,

i dont think this is the answer. Here is why i think so:

• The battery is at 100% RSOC at test begin -> no charging
• STAT Pin indicates 1 if temperature is lower than ~43 °C (=charge complete)
• The device was in a climate chamber with 40 °C ambiente temperatur -> its far to cold for thermal throttling based on the DIE temperature
• SW-Node wave form is different for charge/discharge/full

Charge (~ 7,5 V battery voltage):

Battery full (~ 8,4 V battery voltage):

Discharging (~ 8,4 V battery voltage):

Best regards

Andre

Hello Andre,

If your STAT pin is blinking you are in some kind of the follow fault condition: Charge suspend (Input over-voltage, TS fault, timer fault or battery over-voltage) OTG Buck Mode suspend (due to TS fault).

You may be able to narrow down the issue from these faults.

Sincerely,

Wyatt Keller

Hi,

the maximal charge temperatur is set to 45 °C - so with part tolerances and measurement inaccuracy i also think the charger has a "over temperature charge error" in my test (even if it is not charging at this moment).

So the blinking STAT pin is explainable (TS fault for charging temperature).

But why does the charger start to discharge the battery if external power is always available?

Note:

I have seen an mistake in my first post:

• incorrekt: RT1/RT2 values choosed based on datasheet (5.24 and 30.31 kR) = (charge temperatures: 0 ... 60 °C)
• correct: RT1/RT2 values choosed based on datasheet (5.24 and 30.31 kR) = (charge temperatures: 0 ... 45 °C)

Best regards

Andre

Hello,

the charger could not suspend the charge process because the battery is already full and the charger is not charging (STAT is 1 = HIGH indicates charge complete or charge disabled)

See my first picture from May 4, 2021 - the current is

• zero = device runs from externel power source

... or ...

• negativ = device runs from battery (with attached external power source)

but the current is never positive (= not charging). 

So the question is still:

• battery is full
• charger is not charging (STAT = 1)
• external power source is always available
• Why does the charger start to discharge the battery at high temperatures?

Best regards

Andre

Hello Andre,

It is possible for the charger to not supply power from VBUS even if it's good due to high temperature, over 150deg C it will not switch, 120deg C up to 150 it will reduce the duty cycle. Can you measure the die temperature? Is the IC getting very hot?

Sincerely,

Wyatt Keller

Hi,

i had monitored the temperature of the charger (not DIE but top case temperature) in my testcase from my first post:

So the max temperature of the charger was ~62 °C (You can even see when it is recharging the battery by the small spikes).

Because the charger has nothing to do (no or little current most of the time) the DIE temperature should be really close to the case temperature.

> Not thermal problem.

Best regards

Andre

Hello Andre,

Thanks for the additional info, it looks like thermal is not an issue. If you are also seeing the STAT pin blinking then a different fault may be preventing the charger from supplying VSYS from VBUS, the faults are outlined on page 23 of the datasheet (protections).

Sincerely,

Wyatt Keller

Hello,

I have made further tests:

Test A) 45°C Ambient:

parameters:

• batteries fully charged (8,4 V)
• ambient set to 45 °C (for the whole test)
• powersupply always available

testcase:

• run test as long as the discharge continues (=what is end-voltage for discharge-behavier?)

result:

• Discharge stops at 8,25 V

Test B) 45°C Ambient, RVSET=160kR

parameters:

• batteries fully charged (8,4 V)
• ambient set to 45 °C (for the whole test)
• powersupply always available
• RVSET changed from 470 kR to 160 kR (closer to datasheet min value for 8,4 V charge voltage)

testcase:

• run test as long as the discharge continues (what is end-voltage for discharge?)

result:

• same behavior as in test A (Discharge stops at 8,25 V)

Test C) 45°C Ambient, RVSET=15kR

parameters:

• RVSET changed to 15kR (= 8,2 V charge voltage)
• batteries fully charged (now 8,2 V)
• ambient set to 45 °C (for the whole test)
• powersupply always available

testcase:

• run test as long as the discharge continues (=what is end-voltage for discharge?)

result:

• no discharge observable

Test D) only heat up charger NTC

parameters:

• batteries fully charged (8,4 V)
• ambient set to 22 °C (room temperature for the whole test)
• powersupply always available
• RVSET= 470 kR 

testcase:

• only heat charger NTC to 50 °C (no other part) with hot air gun

result:

• if NTC is at 50 °C: discharging
• if NTC is at 22 °C: no discharging

At the moment this looks like the charger does fall back to the lowes possible charge voltage when the NTC temperature is above 45 °C and than discharges the battery as long as ~8,2V is not reached. (safety reason - batterie voltage to high!?)

I can't explain this behavior, but I can reliably reproduce it.

Hello Wyatt,

V_SYS is fine all the time from -20 up to 60 °C (no matter whether it comes from the battery or the power supply). 

Also the behavior itself was not a problem for me. But I needed to understand why it was happening to identify possible other effects.

Now that i have the explanation (JEITA) i am ok with it.

Best regards 

Andre