BQ24040_16 Datasheet, PDF (19/38 Pages) Texas Instruments – Single Cell Li-Ion and Li-Pol Battery Charger With Auto Start

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bq24040, bq24041, bq24045
SLUS941F – SEPTEMBER 2009 – REVISED MARCH 2015
8.4.9 Termination and Timer Disable Mode (TTDM) - TS Terminal High
The battery charger is in TTDM when the TS terminal goes high from removing the thermistor (removing battery
pack/floating the TS terminal) or by pulling the TS terminal up to the TTDM threshold.
When entering TTDM, the 10 hour safety timer is held in reset and termination is disabled. A battery detect
routine is run to see if the battery was removed or not. If the battery was removed then the CHG terminal will go
to its high impedance state if not already there. If a battery is detected the CHG terminal does not change states
until the current tapers to the termination threshold, where the CHG terminal goes to its high impedance state if
not already there (the regulated output will remain on).
The charging profile does not change (still has pre-charge, fast-charge constant current and constant voltage
modes). This implies the battery is still charged safely and the current is allowed to taper to zero.
When coming out of TTDM, the battery detect routine is run and if a battery is detected, then a new charge cycle
begins and the CHG LED turns on.
If TTDM is not desired upon removing the battery with the thermistor, one can add a 237k resistor between TS
and V_SS to disable TTDM. This keeps the current source from driving the TS terminal into TTDM. This creates
≉0.1°C error at hot and a ≉3°C error at cold.
8.4.10 Timers, bq24040 and bq24045 only
The pre-charge timer is set to 30 minutes. The pre-charge current, can be programmed to off-set any system
load, making sure that the 30 minutes is adequate. The bq24041 does not have a safety timer.
The fast charge timer is fixed at 10 hours and can be increased real time by going into thermal regulation, IN-
DPM or if in USB current limit. The timer clock slows by a factor of 2, resulting in a clock than counts half as fast
when in these modes. If either the 30 minute or ten hour timer times out, the charging is terminated and the CHG
terminal goes high impedance if not already in that state. The timer is reset by disabling the IC, cycling power or
going into and out of TTDM.
8.4.11 Termination
Once the OUT terminal goes above VRCH, (reaches voltage regulation) and the current tapers down to the
termination threshold, the CHG terminal goes high impedance and a battery detect route is run to determine if
the battery was removed or the battery is full. If the battery is present, the charge current will terminate. If the
battery was removed along with the thermistor, then the TS terminal is driven high and the charge enters TTDM.
If the battery was removed and the TS terminal is held in the active region, then the battery detect routine will
continue until a battery is inserted.
8.4.12 Battery Detect Routine
The battery detect routine should check for a missing battery while keeping the OUT terminal at a useable
voltage. Whenever the battery is missing the CHG terminal should be high impedance.
The battery detect routine is run when entering and exiting TTDM to verify if battery is present, or run all the time
if battery is missing and not in TTDM. On power-up, if battery voltage is greater than V_RCH threshold, a battery
detect routine is run to determine if a battery is present.
The battery detect routine is disabled while the IC is in TTDM, or has a TS fault. See Figure 14 for the Battery
Detect Flow Diagram.
8.4.13 Refresh Threshold
After termination, if the OUT terminal voltage drops to V_RCH (100mV below regulation) then a new charge is
initiated, but the CHG terminal remains at a high impedance (off).
8.4.14 Starting a Charge on a Full Battery
The termination threshold is raised by ≉14%, for the first minute of a charge cycle so if a full battery is removed
and reinserted or a new charge cycle is initiated, that the new charge terminates (less than 1 minute). Batteries
that have relaxed many hours may take several minutes to taper to the termination threshold and terminate
charge.
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