BQ24040 Datasheet, PDF (21/31 Pages) Texas Instruments – 800mA Single-Input Single Cell Li-Ion Battery Charger With Auto Start

bq24040
bq24041
www.ti.com.................................................................................................................................... SLUS941A – SEPTEMBER 2009 – REVISED SEPTEMBER 2009
TS (bq24040)
The TS pin is designed to follow the new JEITA temperature standard for Li-Ion batteries. There are now four
thresholds, 60°C, 45°C, 10°C, and 0°C. Normal operation occurs between 10°C and 45°C. If between 0°C and
10°C the charge current level is cut in half and if between 45°C and 60°C the regulation voltage is reduced to
4.1Vmax, see Figure 26. The TS feature is implemented using an internal 50μA current source to bias the
thermistor (designed for use with a 10k NTC β = 3370 (SEMITEC 103AT-2 or Mitsubishi TH05-3H103F)
connected from the TS pin to V_SS. If this feature is not needed, a fixed 10k can be placed between TS and V_SS to
allow normal operation. This may be done if the host is monitoring the thermistor and then the host would
determine when to pull the TS pin low to disable charge.
The TS pin has two additional features, when the TS pin is pulled low or floated/driven high. A low disables
charge (similar to a high on the BAT_EN feature) and a high puts the charger in TTDM.
Above 60°C or below 0°C the charge is disable. Once the thermistor reaches –10°C the TS current folds back
to keep a cold thermistor (between –10°C and –50°C) from placing the IC in the TTDM mode. If the TS pin is
pulled low into disable mode, the current is reduce to 30μA, see Figure 24. Since the I_TS curent is fixed along
with the temperature thresholds, it is not possible to use thermistor values other than the 10k NTC (at 25°C).
Termination and Timer Disable Mode (TTDM) -TS pin high
The battery charger is in TTDM when the TS pin goes high from removing the thermistor (removing battery
pack/floating the TS pin) or by pulling the TS pin 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 pin will go to its
high impedance state if not already there. If a battery is detected the CHG pin does not change states until the
current tapers to the termination threshold, where the CHG pin 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 pin into TTDM. This creates 0.1°C
error at hot and a 3°C error at cold.
Timers
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 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 pin 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.
Termination
Once the OUT pin goes above VRCH, (reaches voltage regulation) and the current tapers down to the
termination threshold, the CHG pin 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 pin is driven high and the charge enters TTDM. If the battery
was removed and the TS pin is held in the active region, then the battery detect routine will continue until a
battery is inserted.
Copyright © 2009, Texas Instruments Incorporated
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