LM3622 Datasheet, PDF (6/9 Pages) National Semiconductor (TI) – Lithium-Ion Battery Charger Controller

Functional Description
FIGURE 1. LM3622 Simplified Block Diagram
DS100974-11
The simplified LM3622 block diagram in Figure 1 gives a
general idea of the circuit operation. The controller integrates
the reference, feedback and drive functions on-chip to con-
trol a linear, lithium-ion battery charger in constant voltage
and constant current (CVCC) charge operation. The regu-
lated output voltage is sensed between CEL and CS, and the
battery charge current is sensed across a current-sense re-
sistor between CS and GND. The EXT pin is designed for
driving a series pass element, which can be a PNP transistor
or a P-MOSFET.
Tying the LV_ENB pin to ground enables the controller’s
low-voltage detection circuit. When the low-voltage detection
circuit is enabled and a battery voltage below a preset
threshold is detected, the LM3622 will drive the LV pin low
and shut off the current flowing into the EXT pin to suspend
the CVCC charge process. The low-voltage threshold is user
selectable to be either 2.15V/cell or 2.7V/cell by pulling the
LV_SEL pin to GND or V_CC respectively. The LV pin is a NPN
open collector output that can be used to turn on a low cur-
rent source to wake up charge a deeply depleted battery.
When the low-voltage detection is disabled (LV_ENB pulled up
to V_CC), the LM3622 always starts the charge cycle in con-
stant current mode at any battery voltage below the control-
ler’s regulation level, and maintains the LV pin at a
high-impedance state.
Application Information
CEL Pin Current Drain
The LM3622 has an internal power down switch in series
with the on-chip resistor divider that is used for sensing the
battery voltage. In the event that the V_CC supply is removed,
the power down switch will disconnect the resistor divider
from the CS pin, preventing the battery from discharging
through the CEL pin.
EXT Pin
The EXT pin is internally pulled up to V_CC via a 20µA current
source making it possible to eliminate the external
base-emitter resistor when driving a PNP transistor, or the
gate-source resistor when driving a P-MOSFET. However,
the voltage applied to EXT is not allowed to be higher than
(V_CC + 0.3V), otherwise the reverse current from EXT pin to
V_CC pin may cause damage to the device.
LV Pin Current Rating
The LV pin is a low power, NPN open collector output that is
rated to sink 10mA maximum. Therefore, the value of the pull
up resistor should be chosen high enough to limit the current
to be less than 10mA.
CS Pin
In normal operation, the current limit threshold voltage for
the CS pin is 100mV typical. In case of a fault condition, the
voltage to this pin should be limited to below 5V.
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