LTC4010
10
4010fb
Shutdown State
The LTC4010 remains in micropower shutdown until V
CC
(Pin 15) is driven above BAT (Pin 10). In shutdown all
status and PWM outputs and internally generated supply
voltages are inactive. Current consumption from V
CC
and
BAT is reduced to a very low level.
Charge Qualification State
Once V
CC
is greater than BAT, the LTC4010 exits micropower
shutdown, enables its own internal supplies 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 4.2V,
V
CC
is 510mV above BAT and V
CELL
is between 350mV and
1.95V. If V
CELL
is below 350mV, no charging will occur, and
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
LTC4010 is paused. If V
TEMP
is above 200mV but below
2.85V, the LTC4010 verifies that the sensed temperature
is between 5°C and 45°C. If these temperature limits
are not met or if its own die temperature is too high, the
LTC4010 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 LTC4010 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 LTC4010 continues to monitor important voltage and
temperature parameters during all charging states. If V
CC
drops to the BAT voltage or lower, 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 LTC4010
returns to the charge qualification state. If V
CELL
exceeds
1.95V, charging 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 a resonable value, charging is suspended, the
charge timer is paused and the LTC4010 indicates a fault
condition. 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 LTC4010
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 LTC4010
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, voltage-based termination
processing begins immediately. Otherwise –∆V termination
is disabled for a stabilization period of t
MAX
/12. In that
case, the LTC4010 makes another fault check at t
MAX
/12,
requiring the average 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.
operaTion
(Refer to Figure 1)
