BQ24090: how to trigger BQ24090 for 10-hour safety timer.

Hi KPK, 

There are multiple scenarios which could be causing the 10 hour safety timer to not trigger. First there is TTDM (termination and timer disable mode), this feature disables the safety timer when the TS pin is pulled high or floated. If your TS connection is accidently floating the 10 hour timer will never trigger.

The timer can also be increased in real time if the device goes into thermal regulation, IN-DPM (i.e. input voltage fold back), or in usb current limit. For any of these three conditions the timer clock slows by a factor of 2 while in these modes. 

Regards,

Garrett 

 Hi Garrett, I've  connected TS to battery NTC(10k ohms),the voltage of TS is fixed to about 0.5V in room temperature and keep on charging battery parallel with system load more than 12.5 hours, the system load will avoid charging termination, but still cannot trigger 10-hour safety timer.

Best reggards

Li Wansheng

hi Garrett,

Do think think this portion of the circle circuit connection is correct?

The Charger_OFF pin is controlled by external MCU to pull HIGH/LOW on the TS pin to enable/disable the charging. 

Best Regards,
KPK

Hello Poh,

Pulling TS low is ok for disabling the charger, but pulling TS above VTTDM(TS) will disable the safety timer. The MCU should only be able to pull this pin low if you do not want to go into TTDM. 

Can you confirm that charge does not terminate after >20 hours to rule out whether timer is being slowed?

Best regards,

Nick

hi Nick,

The charging never stop even after >20 hrs. I measured the TS is still 0.5V, this should considered disable charging am I right? 

Can I clarify on the definition of the fixed 10hrs safety timer? does it means under any condition, any charging sequence should stop in 10 hrs?  [Assume without enter TTDM (termination and timer disable mode), this feature disables the safety timer when the TS pin is pulled high or floated. If your TS connection is accidently floating the 10 hour timer will never trigger]. 

TS connects to battery NTC via 10kohm to GND and MCU Charger_OFF port.

MCU port has three conditions:

1.High-Z : normal
2.Low:disable charging
3.High:TTDM mode.

Best regards,
KPK

Hi KPK,

V-TS=0.5V is in the voltage range for normal operation. Figure 9-4 from the BQ24090 data sheet shows device behavior across the whole V-TS range.

The device has two safety timers one for the precharge phase which is set for 30 minutes, then once the battery voltage crosses the LOWV threshold (2.5 V) the fast charge phase begins and the 10 hour safety timer is started. During charging the timer may be slowed down as mentioned in the thread above or be reset three ways. These are disabling the IC, cycling input power, or going in and out of TTDM.

Yes, if your TS connection is accidently floating or constantly pulled high (above 1.6V) the 10 hour safety timer is held in reset and will never trigger.

Also your battery's NTC should be connected to TS and directly to ground without the additional 10k resistor you mention.

Best regards,

Garrett

I've used EVM and TS pin connected 10kohms to GND,OUT pin connected to DC electronic Load to simulate defected-battery.

Precharge safety-timer is triggered after 2.0V/70mA continuously charging around 30 minutes.

But fast charge safety-timer is not triggered after 3.0V/360mA continuously charging more than 15 hours.

Hello Li,

It is possible the timer is being reset when input power cycled. You may also try with MCU disconnected entirely to make sure it is not interfering. How many units are you seeing this issue on?

Thanks,

Nick

Hi,Nick,

Tested in 1 set of EVM only without MCU connection, but unsuccessful to trigger 10-hour timer.

BTW, have you triggered 10-hour safety timer successfully ?

Best regards

Li Wansheng

Hello Li,

May I know the jumper configuration you have set on the EVM? The safety timer has been verified to work on this device as per the datasheet specification. 

Best regards,

Nick