BQ24072T: Battery charging stopped at 4.1 V and not fully charged

Hi Sowmiya,

Is this the same issue as this thread: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1032565/bq24072t-bq24072trgtt

This appears to be the same schematic.

Can you verify that removing the resistors on the BAT pin and test again? It'd also be helpful to know the state of the /CHG and /PG pins when we see the charging stop at 4.1V Can you also verify that this is a BQ24072T and not a BQ24079T? 

Best Regards,

Anthony Pham

HI Anthony ,

Thankyou. We are using BQ24072T. Here exactly what we are facing is , battery can charge from 0 to 4.1V without any issues. We have kept charging in Hardware control and when battery reaches 4.1 V , the battery stops charging and we get battery full indication .

Can you suggest why is this so ?
Where as when we charge the same battery with BQ24072 ,battery could charge upto 4.2V and only after that we get full charge indication .
Please help me on this

Hi Sowmiya,

Can you provide the voltage of the /CHG, /PG, and TS pin? 

Best Regards,

Anthony Pham

Anthony,

During charging  , PG is low and CHG is also low ,TS is not used and so we have used 200K Ohm and 49K Ohm in the divider.

Can you suggest us the default setting for ISET,ILIM ,TMR .Bcz we are using ISET value --7.6 K Ohm for 150 mA , ILIM --1.1K Ohm , TMR --47K Ohm
Can this be the reason for battery not charging above 4.1 V.

Hi Sowmiya,

Do the /PG and /CHG pins remain low when the battery is at 4.1V? If the voltage for TS is between 12.5% and 25% of your VIN, the resistors should be fine. As you are not using the TS functionality, 200k and 49k should be fine. Can you measure the TS voltage?

Does this occur if you increase the fast charge current to 300 mA? The concern is that if you are using a protector on the battery, the termination current set with 150mA may not be enough. 

Can you provde the current measurement out as the battery voltage approaches 4.1V?

Best Regards,

Anthony Pham

Anthony ,

Thanks.I will provide you the data soon .FYI , 

#1.What should be the default state of TD pin ?Does keeping TD pin low or high affects the battery charging from 4.1 V to 4.2 V  ?
#2.  Do input applied to divider circuit of TS pin should be same as the input to IC or can this vary ?

Hi Sowmiya,

Sowmiya R1 said:

What should be the default state of TD pin ?Does keeping TD pin low or high affects the battery charging from 4.1 V to 4.2 V  ?

Ahhhh I see, it looks like the schematic has mislabeled the TD pin. To ensure that the device does terminate, which it appears it is not, the TD pin should be low. 

Sowmiya R1 said:

Do input applied to divider circuit of TS pin should be same as the input to IC or can this vary ?

No, it can vary but the reference voltage used for the voltage based battery monitoring system is based on VIN. 

Best Regards,

Anthony Pham

Hi Anthony,

We have  one more query .
What should be the default state of CE pin and in rare case we found battery not charging .We could find the reason why it is happening. Do you suspect anything  in this.
Since we are not using TS Pin , we  have kept default values as 200 K Ohm and 49 .9 K Ohm. Do we need to change any of these ?