BQ24085_17 Datasheet, PDF (18/42 Pages) Texas Instruments – 750-mA Single-Chip Li-Ion and Li-Pol Charge Management IC With Thermal Regulation

bq24085, bq24086, bq24087, bq24088
SLUS784E – DECEMBER 2007 – REVISED DECEMBER 2015
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The bq24085/6/7/8 dynamic timer control (DTC) monitors the voltage on pin ISET during pre-charge and fast
charge, and if in thermal regulation slows the clock frequency proportionately to the change in charge current.
The time duration is based on a 2²⁴ ripple counter, so slowing the clock frequency is a real time correction. The
DTC circuit changes the safety timers clock period based on the V_(SET)/V_(ISET) ratio (fast charge) or
V_(PRECHG)/V_(SET) ratio (pre-charge). Typical safety timer multiplier values relative to the V_(SET)/V_(ISET) ratio is shown
in Figure 12 and Figure 13.
The device deglitch timers are set by the same oscillators as the safety and precharge timers. In thermal
regulation, the timers are scaled appropriately, see Figure 2.
5
4
3
2
1
0
0
1
2
3
4
5
V_(SET)/V_(ISET) - V
Figure 12. Safety Timer Linearity
Internal Clock Period Multiplication Factor
45
R_TMR = 70 kW
40
35
30
R_TMR = 50 kW
25
20
R_TMR = 30 kW
15
10
5
0
0
1
2
3
4
5
6
V_SET/V_ISET - V
Figure 13. bq24085/6/78 Safety Timer Linearity for R_TMR Values
18
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