LM3622AM-8.2 NSC [National Semiconductor], LM3622AM-8.2 Datasheet - Page 7

• Manufacturer Part Number: LM3622AM-8.2
• Description: Lithium-Ion Battery Charger Controller
• Manufacturer: NSC [National Semiconductor]

Typical Application
The low dropout linear charger shown in Figure 2 provides
constant current and constant voltage charging of 1-cell
lithium-ion battery packs. J1 and J2 are used for selecting
the operation of the low-voltage detection. The LM3622 ini-
tializes the charge cycle based on the battery voltage and
the enable status of the low-voltage detection.
When the low-voltage detection is disabled, the LM3622
starts the charge cycle constant current mode if the battery
voltage is below the controller’s regulation level. In constant
current mode, the LM3622 modulates the base drive of Q2 to
regulate a constant 100mV across the current sense resistor
R1, thus generating charge current of
which is equal to 0.5A in this case.
Once the battery voltage reaches the target regulation level
set by the LM3622, Q2 is controlled to regulate the voltage
across the battery, and the constant voltage mode of the
charging cycle starts. Once the charger is in the constant
voltage mode, the charger maintains a regulated voltage
across the battery and the charging current is dependent on
the state of the charge of the battery. As the cell approaches
a fully charged condition, the charge current falls to a very
low value.
When the low-voltage detection is enabled and the initial bat-
tery voltage is below the low-voltage threshold, the LM3622
turns Q2 off and forces the LV pin low to drive Q1 on to start
a wake up charge phase. Q1 in conjunction with R2 provides
a low current source to recondition the battery. During the
wake up charge mode, Q1 is driven into saturation and the
wake up charge current is programmed by R2,
where V
collector-emitter on state voltage of Q1, V
ward voltage of D1, and LVth is the low-voltage threshold
level set by switch J2.
I-charge (wake) = (V
IN
is the input supply voltage, V
FIGURE 2. Low Dropout, Constant Current/Constant Voltage Li-ion Battery Charger
I-charge = 0.1V/R1
IN
– V
CE
1 – V
D
D
1 – LVth)/R2
1 is the diode for-
CE
1 is the
7
Once the battery voltage reaches the low-voltage threshold,
the LV pin transitions to a high-impedance state to end the
wake up charge phase, and the EXT pin resumes the base
drive of Q2 to start the constant current mode. The charging
cycle is completed in constant voltage mode when the bat-
tery is fully charged. Figure 3 shows the timing diagram of
the charge cycle with the low-voltage detection enabled.
D1 is a general-purpose silicon diode used for isolating the
battery from the charger circuitry that could discharge the
battery when the input source is removed. Changing D1 to a
Schottky diode will reduce the overall dropout voltage of the
circuit, but the penalty is higher leakage current associated
with Schottky diodes.
DS100974-13
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