BQ24045: Sometimes BQ24045 can't charge over discharge lithium battery

Hi Rock Su,

1. Yes, this is part of the battery detect routine, see figure 14 of d/s
2. The 125uA will only apply to TS low, this is a shutdown condition.  Battery detection current will be higher.
3. The current will be what was set with the PRE-TERM pin, but if a load is connected it could be drawing enough of the 5 mA pre-charge current to prevent voltage from rising and unit resetting. 
4. No, you do not need to sync the two voltages.  If the protector is open then precharge current will be enough to increase voltage.  Note if system load is connected to battery it will delay or prevent voltage from increasing.
5. It is possible that the load on the battery is preventing unit from charging due to the load pre-charge current. Have you tried charging with no load? In this condition check the current into device, is it equal to precharge?
6. This transition point should not be a problem.  We do not have higher voltage units.

Also, recommend testing with a R-PRE-TERM increased in value to provided more precharge current.

Best,

Hello Nick,

thank you for your reply. 

Now let me introduce my situation. We used BQ24230 + tps62742 as the power management of the system. This system can be used normally, and the charging and discharging of lithium battery are normal. But later, I want to increase the battery life of the product. I want to charge the battery voltage to 4.35v, so I later replaced it with bq24045 as the charging IC. 62742 remains unchanged, and 62742 is the load.

After I replaced the charging IC, the problems mentioned above appeared. After the battery is discharged to the protection state, 24045 can not charge the battery, while 24230 can.

I did the test again. I used the same lithium battery that was completely discharged to 0.5V (cell voltage, not the pack voltage) to test on 24045 and 24230 boards respectively.

Test #1, lithium battery + 24045 + 62742, it can be seen that the precharge current is 5.3mA, the current can be stable for about 30 seconds, and then it starts to slow down to 0, in this 30 seconds, the cell voltage will slowly rise to about 2V, and it will not change, you can see that 62742 has zero point output of several V, that is, load should be working.

Test  #2, lithium battery + 24230 + 62742, it can be seen that the precharge current is 4.3mA, the current can be continuously stable to charge the cell voltage to 3V, and then start to enter the fast charging stage, the current changes to 43.5ma, it can be seen that 62742 has a normal output of 3.3V. Everything is normal

So I want to know,

1. Why can't 24045 precharge current continuously and stably charge the battery to 2.5V (fast charging threshold), and why does the precharge current decrease slowly by 5.3mA?

2. Is the design difference between 24045 and 24230 the cause of this problem? If it is? What are the specific reasons?

Best Regards,

Peter

Hello Nick,

Continue with test #1 above:

I float the pre term pin. Under the same test conditions, the precharge current will change to 10mA, which can charge the battery to 2.0V, and then the battery voltage will remain unchanged. However, in this process, the current of 10mA will slowly decrease to 0.5ua, and the output of system load 62742 can reach 1.4V, and then remain unchanged.

I suspect that 24230 supports DPPM (dynamic power path

Management) function is not supported by 24045, which results in 24230 can be charged normally and 24045 can not be charged normally.

So, is the real reason DPPM?

Best Regards,

Peter

Hello Nick,

for your reply:

"Note if system load is connected to battery it will delay or prevent voltage from increasing."

Now I can basically confirm that the problem is caused by the system load.

thank you.

Best Regards,

Peter