10
LTC4011
4011p
OPERATIO
U
Shutdown State
The LTC4011 remains in micropower shutdown until
DCIN (Pin 1) is driven above V
CC
(Pin 8). In shutdown all
status and PWM outputs and internally generated termi-
nations or supply voltages are inactive. Current consump-
tion from V
CC
and BAT is reduced to a very low level.
Charge Qualification State
Once DCIN is greater than V
CC
, the LTC4011 exits mi-
cropower shutdown, enables its own internal supplies,
provides V
RT
voltage for temperature sensing, and switches
V
CDIV
to GND to allow measurement of the average single-
cell voltage. The IC also verifies that V
CC
is at or above
4.25V, V
CC
is 500mV above BAT and V
CELL
is between
350mV and 1.95V. If V
CELL
is above 1.95V, the fault state
is entered, which is described in more detail below. Once
adequate voltage conditions exist for charging, READY is
asserted.
If the voltage between V
TEMP
and GND is below 200mV,
the LTC4011 is paused. If V
TEMP
is above 200mV but
below 2.85V, the LTC4011 verifies that the sensed tem-
perature is between 5°C and 45°C. If these temperature
limits are not met or if its own die temperature is too high,
the LTC4011 will indicate a fault and not allow charging to
begin. If V
TEMP
is greater than 2.85V, battery temperature
related charge qualification, monitoring and termination
are disabled.
Once charging is fully qualified, precharge begins (unless
the LTC4011 is paused). In that case, the V
TEMP
pin is
monitored for further control. The charge status indicators
and PWM outputs remain inactive until charging begins.
Charge Monitoring
The LTC4011 continues to monitor important voltage and
temperature parameters during all charging states. If the
DC input is removed, charging stops and the shutdown
state is entered. If V
CC
drops below 4.25V or V
CELL
drops
below 350mV, charging stops and the LTC4011 returns to
the charge qualification state. If V
CELL
exceeds 1.95V, charg-
ing stops and the IC enters the fault state. If an external
thermistor indicates sensed temperature is beyond a range
of 5°C to 60°C, or the internal die temperature exceeds an
internal thermal limit, charging is suspended, the charge
timer is paused and the LTC4011 indicates a fault condi-
tion. Normal charging resumes from the previous state
when the sensed temperature returns to a satisfactory
range. In addition, other battery faults are detected during
specific charging states as described below.
Precharge State
If the initial voltage on V
CELL
is below 900mV, the LTC4011
enters the precharge state and enables the PWM current
source to trickle charge using one-fifth the programmed
charge current. The CHRG status output is active during
precharge. The precharge state duration is limited to
t
MAX
/12 minutes, where t
MAX
is the maximum fast charge
period programmed with the TIMER pin. If sufficient V
CELL
voltage cannot be developed in this length of time, the fault
state is entered, otherwise fast charge begins.
Fast Charge State
If adequate average single-cell voltage exists, the LTC4011
enters the fast charge state and begins charging at the
programmed current set by the external current sense
resistor connected between the SENSE and BAT pins. The
CHRG status output is active during fast charge. If V
CELL
is initially above 1.325V, cell voltage processing begins
immediately. Otherwise –∆V termination is disabled for a
stabilization period of t
MAX
/12. In that case, the LTC4011
makes another fault check at t
MAX
/12, requiring the aver-
age cell voltage to be above 1.22V. This ensures the
battery pack is accepting a fast charge. If V
CELL
is not
above this voltage threshold, the fault state is entered. Fast
charge state duration is limited to t
MAX
and the fault state
is entered if this limit is exceeded.
Charge Termination
Fast charge termination parameters are dependent upon
the battery chemistry selected with the CHEM pin. Volt-
age-based termination (–∆V) is always active after the
initial voltage stabilization period. If an external thermistor
network is present, chemistry-specific limits for ∆T/∆t
(rate of temperature rise) are also used in the termination
algorithm. Temperature-based termination, if enabled,
becomes active as soon as the fast charge state is entered.
(Refer to Figure 1)