BQ24085_17 Datasheet, PDF (16/42 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
www.ti.com
Table 3. Charge Status⁽¹⁾
Charge State
Precharge in progress
Fast charge in progress
Done (termination enabled only)
Charge Suspend (temperature)
Timer Fault
Charger off
Selected Input power overvoltage detected
Battery absent
Batteryshort
STAT1
ON
ON
OFF
OFF
STAT2
ON
OFF
ON
OFF
(1) Pulse loading on the OUT pin may cause the IC to cycle between Done and charging states (LEDs
Flashing)
8.3.5 Battery Charging: Constant Current Phase
The bq24085/6/7/8 family offers on-chip current regulation. The current regulation is defined by the value of the
resistor connected to ISET pin.
During a charge cycle the fast charge current I_O(OUT) is applied to the battery if the battery voltage is above the
V_(LOWV) threshold (2.95 V typical):
I(OUT) =
I_{O(OUT )}
=
V_(SET) ´ K_(SET)
R_ISET
where
• K_(SET) is the output current set factor and V_(SET) is the output current set voltage.
(3)
During a charge cycle if the battery voltage is below the V_(LOWV) threshold a pre-charge current I_(PRECHG) is
applied to the battery. This feature revives deeply discharged cells.
( ) I OUT
=
I_(PRECHG)
=
V_(PRECHG) ´K_(SET)
R_ISET
:
I_{O(OUT )}
10
where
• K_(SET) is the output current set factor and V_(PRECHG) is the precharge set voltage.
(4)
At low constant current charge currents, less than 200 mA, TI recommends that a 0.1-μF capacitor be placed
between the ISET and BAT pins to insure stability.
8.3.6 Charge Current Translator
When the charge function is enabled, internal circuits generate a current proportional to the charge current at the
ISET pin. This current, when applied to the external charge current programming resistor R_ISET generates an
analog voltage that can be monitored by an external host to calculate the current sourced from the OUT pin.
V (ISET) = I(OUT)´ ^RISET
K_(SET)
(5)
8.3.7 Battery Voltage Regulation
The battery pack voltage is sensed through the BAT pin, which is tied directly to the positive side of the battery
pack. The bq24085/6/7/8 monitors the battery pack voltage between the BAT and VSS pins. When the battery
voltage rises to V_O(REG) threshold, the battery charging enters the voltage regulation phase, and charging current
begins to taper down. The voltage regulation threshold V_O(REG) is fixed by an internal IC voltage reference.
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