BQ2406X Datasheet, PDF (17/31 Pages) Texas Instruments – 1A SINGLE-CHIP Li-Ion/Li-Pol CHARGE MANAGEMENT IC WITH THERMAL REGULATION

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800
175
700
IBAT
150
600
125
500
T_J Junction Temperature
400
100
300
75
200
50
100
0
25
4
6
8
10
12
14
16
18
V_I - Input Voltage - V
Figure 6. Thermal Regulation Loop Performance
bq2406x
SLUS689 – JUNE 2006
DYNAMIC TIMER FUNCTION
The charge and pre-charge safety timers are programmed by the user to detect a fault condition if the charge
cycle duration exceeds the total time expected under normal conditions. The expected charge time is usually
calculated based on the fast charge current rate.
When the thermal loop is activated the charge current is reduced, and a false safety timer fault can be observed
if the thermal loop is active for a long period of time. To avoid this undesirable fault condition the bq2406x
activates the dynamic timer control, an internal circuit that slows down the safety timer's clock. The dynamic
timer control circuit effectively adds an extra time to the programmed timeout value. The dynamic timer control
circuit is enabled under the following conditions:
1. If battery voltage is below the pre-charge threshold: the pre-charge timer value is modified while the Thermal
regulation loop is active
2. If the battery voltage is above the pre-charge threshold: the safety timer value is modified if the Thermal
regulation loop is active.
The bq2406x dynamic timer control (DTC) monitors the voltage at pin ISET during pre-charge and fast charge,
and increases the safety timers effective timeout value when the charge current is out of regulation and the
thermal loop is active. Under normal current regulation operation, the voltage at pin ISET is set by the control
loops to either V_(SET) or V_(PRECHG). If the thermal loop is active, the voltage at pin ISET is lower than the
regulation voltage, and 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 the following graph.
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