LM3621 National Semiconductor, LM3621 Datasheet - Page 10

• Manufacturer Part Number: LM3621
• Description: Single Cell Lithium-Ion Battery Charger Controller
• Manufacturer: National Semiconductor

www.national.com
Application Information
Battery Charger Operation Information
Figure 4 shows a general battery charger configuration using
LM3621. The LM3621 provides all the necessary control
functions for charging Lithium-Ion batteries precisely and
safely. It features constant voltage and constant current
mode operation. The on chip timer provides all critical timing
functions to properly initialize the charging cycle, avoid over
charging the battery above its maximum capacity level, and
cut off charging to a defective battery. The LM3621 also pro-
vides the high accuracy of output voltage regulation without
requiring a trim pot or precision resistors. A built-in power
down switch prevents the battery from discharging through
the LM3621.
Input Supply Voltage
The voltage supply to LM3621 must never exceed 6.0V or
catastrophic damage may occur to the IC. When power is
first applied to the battery charger, the LM3621 will remain in
a reset state until the voltage on the V
for at least one second. This ensures that the power source
is stable before a charge cycle is initiated. Figure 2 shows
the state diagram for the charge cycle operation. Once the
LM3621 emerges from the reset state after power up, it will
not go into the reset state again until the voltage on the V
pin drops below approximately 2.2V. When the LM3621 is in
DD
pin exceeds 3.4V
FIGURE 4. General Application Circuit
DD
10
the reset state, the PFD (Pass FET Drive) pin is pulled low
so that current is not allowed to flow into the load (e.g., Li+
battery). The LM3621 transitions from the reset state to
standby mode when the conditions for a stable power source
are met.
Digital Control Inputs
The LM3621 has four digital input control pins: Enable,
Boost, V
allow unused digital input pins to be left open circuited. En-
able is used to initiate a charge cycle, Boost is used to in-
crease the maximum regulation current output, V
trols the maximum output voltage, and ChgInt is used to
instantaneously interrupt (and resume) a charge cycle in
progress.
Current Boost Mode
This mode is activated when the “Boost” pin is pulled high.
The charger increases the maximum output current equal to
a V
a charge interrupt signal.
Charge Interrupt Control
Charging is interrupted with the digital input “ChgInt” pulled
low. The PFD pin is pulled to ground turning off the series
low pass FET. This is useful to prevent charging a battery if,
for example, the ambient temperature is excessively high.
CSR
level of 0.9V. This mode of operation is overridden by
SET
and ChgInt. To ensure proper operation, never
DS100107-4
SET
con-