Datasheet

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BATTERY CHARGING: CONSTANT CURRENT PHASE
I(OUT) + I
O(OUT)
+
V
(SET)
K
SET)
R
ISET
(3)
I(OUT) + I
(PRECHG)
+
V
(PRECHG)
K
SET)
R
ISET
X
I
O(OUT)
10
(4)
CHARGE CURRENT TRANSLATOR
V(ISET) + I(OUT)
R
ISET
K
(SET)
(5)
BATTERY VOLTAGE REGULATION
bq2406x
SLUS689A – JUNE 2006 – REVISED OCTOBER 2006
Table 3. Charge Status
(1)
Charge State STAT1 STAT2
Precharge in progress ON ON
Fast charge in progress ON OFF
Done (termination enabled only) OFF ON
Charge Suspend (temperature)
Timer Fault
Charger off
OFF OFF
Selected Input power overvoltage detected
Battery absent
Batteryshort
(1) Pulse loading on the OUT pin may cause the IC to cycle between Done and charging states (LEDs
Flashing)
The bq2406x 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):
Where K
(SET)
is the output current set factor and V
(SET)
is the output current set voltage.
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.
Where K
(SET)
is the output current set factor and V
(PRECHG)
is the precharge set voltage.
At low constant current charge currents, less than 350 mA, it is recommended that a 0.47- µ F capacitor be
placed between the ISET and BAT pins to insure stability, see Figure 16 .
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.
The battery pack voltage is sensed through the BAT pin, which is tied directly to the positive side of the battery
pack. The bq2406x monitors the battery pack voltage between the BAT and VSS pins. When the battery voltage
rises to V
O(REG)
threshold the voltage regulation phase begins and the charging current begins to taper down.
The voltage regulation threshold V
O(REG)
is fixed by an internal IC voltage reference.
17
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