Introduction
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1
Introduction
The bq2404x series of devices are highly integrated Li-ion linear charger devices targeted at space-limited
portable applications. The devices operate from either a USB port or AC adapter.
The bq2404x has a single power output that charges the battery. A system load can be placed in parallel
with the battery as long as the average system load does not keep the battery from charging fully during
the 10 hour safety timer.
The battery is charged in three phases: conditioning, constant current, and constant voltage. In all charge
phases, an internal control loop monitors the IC junction temperature and reduces the charge current if an
internal temperature threshold is exceeded.
The charger power stage and charge current sense functions are fully integrated. The charger function
has high-accuracy current and voltage regulation loops, charge status display, and charge termination.
The pre-charge current and termination current threshold are programmed via an external resistor on the
bq24040 and bq24045. The fast charge current value is also programmable via an external resistor.
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Considerations With Evaluating the bq2404x
Refer to the data sheet for specific details on the charger ICs. The main differences between the bq24040
and the bq24041 are that the Pre-Term pin is replaced with an Auto Start (I/O) (ASI/ASO) feature, a
different Over-Voltage Protection Threshold, and a Temperature Sense Pin (TS) versus a BAT_EN pin.
The main difference between the bq24040 and bq24045 is in the regulation voltage. The bq24040 is 4.2-V
and bq24045 is 4.35-V regulation voltage.
The ISET current control loop sets the maximum charge current. This maximum programmed current level
can be further reduced by entering a USB mode, selected by the ISET2 pin.
The ASO output is dependent on the OUT pin to power the internal OR gate along with at least one high
signal on the input (bq24041).
A system load may be connected to the OUT pin, which takes away some of the charge current. Normally
it is not recommended to operate the device in pre-charge since the system load keeps the battery from
recovering; but, since the PRE_TERM pin can program a higher pre-charge current this restriction is not
necessary.
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Performance Specification Summary
Specification
Test Conditions
MIN
TYP
MAX
UNIT
Input DC voltage, V
IN
Recommended input voltage range
4.45
6.45
V
Reduced Performance,
IN
(1)
Will not charge with Over Voltage input condition. Limited
3.5
28
V
charging with under voltage input.
Power Dissipation
(2)
P
DISS
= (V
IN
– V
OUT
) × I
OUT
1.5
W
I
OUT
(3)
RISET = 1 k
Ω
0.54
0.8
A
(1)
Input voltage range is specified for normal operation. Input voltage between UVLO and 4.75 V has limited functionality, but does
not damage the IC nor present any safety issue with the battery. Input voltage above OVP and less than 30 Vdc has no
operation and will not damage the IC. Lower input voltage (closer to dropout operation) produces less heat dissipation and
potentially better performance.
(2)
The junction temperature rise above ambient is proportional to the power dissipation. Once the junction temperature reaches
~125°C, thermal regulations reduces the programmed charge current.
(3)
The EVM is set for 800 mA, by changing R1 to lower values, it can support up to 1000 mA.
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1-A Single-Input, Single-Cell Li-Ion Battery Charger
SLUUA77 – January 2013
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