bq20z75 V1.81 - Control of DSG in Battery Status during UN Thermal testing

Dear all,

I might have made my question to complicated - to make it more simple....

• If during UN Thermal testing the SOT Chg temperature is exceeded with more than 10 deg C but no chg current is flowing - will this create any PF ?

Appreciate any comments 

Best regards

Kjell Ramberg  

Hi Kjell,

If there is no chg current flowing, and the sense resistor actually detects likewise, the pF bit SOTC will not get set becuase current >0 is a requirement for SOTC to get set. Refer to table. 2-6, pg 20 of the TRM of the device.

thanks

Onyx

Hi Onyx

Thanks again for your support.

That is what I have expected - no FP exceeding the SOT Chg temperature when current = 0. The reason for my question is that I thought that this also applies for SOT Dsg, - no PF exceeding SOT Dsg temperature when current = 0.

When I have done tests in a climate chamber I got PF when exceeding the SOT Dsg temperature, but not when exceeding SOT Chg temperature - bot cases - current reports 0.

I will do a second run (checking both ba20z75 V 1.60 and bz20z75 V 1.81) to verify and report back.

Best regards

Kjell

Hi Onyx,

I have now made a second test with two batteries in a climate chamber and achieved some interesting results for both bq20z75 V1.60 and bq2075 V.181. Both modules are calibrated and checked thoroughly. Both voltage, current and temperature measurements are very accurate.

The reason for my consern is that all Lithium Ion batteries we are using needs to be UN approved and certified. One of the UN test is a thermal test going from minus 40deg C to + 75deg C. The requirements to pass this test is the voltage level measured at the output when the battery has stabilised at + 20deg C after the thermal test.

During the thermal test there is no load or charging current flowing except for the current consumption from the bq.

• SOT Chg is set to +65deg C. When doing the temperature cycling passing the SOT Chg temperature nothing happen - as expected because current is reported to be 0. Since both OTC and OTD temperature is exceeded both flags are set, XDSG in Operation status is also set. Everything seems to work as expected.
• SOT Dsg is set to +75 deg C. Compared to SOT Chg - no conditions are changed but once the SOT Dsg temp is exceeded SOTD in PF Status is set even when current is reported to 0.

If this situation happen during the UN testing we would not pass the test because it is not possible to measure the battery voltage because SOT Dsg created a PF.

The "cure" is to increase the SOT Dsg temperature well above the max testing temperature - we would rather prefer to use the default +75deg C but we do not dear to take the risk missing an UN approval. 

I have checked this many times and for different PCB's - but they alle behave the same.

I think that this topic might be of interest for others in the community since UN approval is a must for anybody wanting to ship their batteries.

Is there a reasonable explenation why SOT Chg do not set any PF but SOT Dsg does when current is 0 for both situations ?

Best regards

Kjell   

Hi Kjell,

I believe that the device polls the DSG bit in the battery status when checking for SOT chg or SOT Dsg. Unfortunately, this bit being clear (i.e 0) corresponds to a charging status while it being set corresponds to both discharge mode (current < 0) and relaxation mode (current =0). This means that even when current=0, the battery status DSG bit will be set. This explains why SOTC bit doesn't get set since the DSG bit is set,while the SOTD bit gets set in the PF in the other case.

thanks

Onyx