BQ24075T: About Timer

Hello Ryu,

Thanks for reaching out. This is a very good question. I believe that you are referring to the safety timer. The T_maxch is a timer that is set by the customer, using the resistor and timer factor calculation on the datasheet, the value to use is dependent on the battery manufacturer. This timer changes proportionally to the amount of charge current that is going to the battery.

In section 9.3.9, "For example, if the charging current is reduced by half for two minutes, the timer clock is reduced to half the frequency and the counter counts half as fast resulting in only one minute of "counting" time." 

V/R

Rafael Camarillo

Hello Ryu,

Rafael Camarillo said:

In section 9.3.9, "For example, if the charging current is reduced by half for two minutes, the timer clock is reduced to half the frequency and the counter counts half as fast resulting in only one minute of "counting" time." 

This means that whatever reduction in charge current from the set charge current (ISET), will be reflected on the timer by also reducing the timer proportional to the amount of charge current reduction.

If charge current is reduced by 0.5 then the timer will count 0.5 times as fast to compensate for the reduction in charge current. If charge current is reduced by 0.25 then the clock timer will be reduced to 0.25 of the frequency, which means for the timer counter to increment 1 time it will have to clk 4 times to compensate for the charge current. 

V/R

Rafael Camarillo