LTC4011 Linear Technology, LTC4011 Datasheet - Page 10

• Manufacturer Part Number: LTC4011
• Description: High Efficiency Standalone Nickel Battery Charger
• Manufacturer: Linear Technology

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OPERATIO
LTC4011
Shutdown State
The LTC4011 remains in micropower shutdown until
DCIN (Pin 1) is driven above V
status and PWM outputs and internally generated termi-
nations or supply voltages are inactive. Current consump-
tion from V
Charge Qualification State
Once DCIN is greater than V
cropower shutdown, enables its own internal supplies,
provides V
V
cell voltage. The IC also verifies that V
4.25V, V
350mV and 1.95V. If V
is entered, which is described in more detail below. Once
adequate voltage conditions exist for charging, READY is
asserted.
If the voltage between V
the LTC4011 is paused. If V
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
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
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
below 350mV, charging stops and the LTC4011 returns to
the charge qualification state. If V
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
10
CDIV
4
to GND to allow measurement of the average single-
CC
TEMP
RT
CC
is 500mV above BAT and V
voltage for temperature sensing, and switches
and BAT is reduced to a very low level.
is greater than 2.85V, battery temperature
U
CC
(Refer to Figure 1)
CELL
drops below 4.25V or V
TEMP
is above 1.95V, the fault state
CC
TEMP
and GND is below 200mV,
CC
CELL
, the LTC4011 exits mi-
(Pin 8). In shutdown all
is above 200mV but
exceeds 1.95V, charg-
CC
CELL
is at or above
TEMP
is between
CELL
drops
pin is
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
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
period programmed with the TIMER pin. If sufficient V
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
is initially above 1.325V, cell voltage processing begins
immediately. Otherwise –∆V termination is disabled for a
stabilization period of t
makes another fault check at t
age cell voltage to be above 1.22V. This ensures the
battery pack is accepting a fast charge. If V
above this voltage threshold, the fault state is entered. Fast
charge state duration is limited to t
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.
MAX
/12 minutes, where t
MAX
CELL
MAX
/12. In that case, the LTC4011
is below 900mV, the LTC4011
is the maximum fast charge
MAX
/12, requiring the aver-
MAX
and the fault state
CELL
is not
CELL
CELL
4011p