LTC4071
operaTion
Low Battery Disconnect/Connect: LBD/LBC
The low battery disconnect (V
LBD
) and connect (V
LBC
) volt-
age levels are programmed by the LBSEL pin. As shown
in the Block Diagram the battery disconnects from V
CC
by
shutting off MP1 when the BAT voltage falls below V
LBD
.
This disconnect function protects Li-Ion batteries from
permanent damage due to deep discharge. If the voltage
of a Li-Ion cell drops below a certain level, the cell may be
permanently damaged. Disconnecting the battery from V
CC
prevents the load at V
CC
as well as the LTC4071 quiescent
current from further discharging the battery.
Once disconnected the V
CC
voltage collapses towards
ground. When an input supply is reconnected the bat-
tery charges through the internal body diode of MP1.
The input supply voltage should be larger than V
LBC_VCC
to ensure that MP1 is turned on. When the V
CC
voltage
reaches V
LBC_VCC
, MP1 turns on and connects V
CC
and
BAT. While disconnected, the BAT pin voltage is indirectly
sensed through MP1’s body diode. Therefore V
LBC
varies
with charge current and junction temperature. Please see
the Typical Performance Characteristics section for more
information.
Low Battery Select: LBSEL
The low battery discharge cutoff voltage level is pro-
grammed by the LBSEL pin.
The LBSEL pin allows the user to trade-off battery run-
time and maximum shelf life. A lower battery disconnect
threshold maximizes run time by allowing the battery to
fully discharge before the disconnect event. Conversely,
by increasing the low battery disconnect threshold more
capacity remains following the disconnect event which
extends the shelf life of the battery. For maximum run
time, tie LBSEL to V
CC
so that the battery disconnects at
V
CC
= 2.7V. For extended shelf life, tie LBSEL to GND so
that the battery disconnects at V
CC
= 3.2V. If a high peak
current event is expected, users may temporarily select
the lower disconnect threshold. This avoids disconnect-
ing the battery too early when the load works against the
battery series resistance and temporarily reduces V
CC
.
4071fc
9
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
