LTC4010 Datasheet, PDF (8/20 Pages) Linear Integrated Systems – High Efficiency Standalone Nickel Battery Charger

LTC4010
U
OPERATIO (Refer to Figure 1)
NO DC ADAPTER
SHUTDOWN
DC ADAPTER PRESENT
NO BATTERY
OR
V_CC < 4.25V
TOP-OFF
CHARGE**
(C/10)
CHARGE
QUALIFICATION
V_CELL > 350mV, ADEQUATE V_CC,
CHARGER ENABLED AND
TEMPERATURE OK (OPTIONAL)
CHECK
BATTERY
V_CELL > 900mV
NiMH
∆T/∆t
FAST CHARGE**
(1C)
V_CELL < 900mV
VCELL ^{> 900mV}
PRECHARGE**
(C/5 FOR
t_MAX/12)
V_CELL < 900mV
V_CELL < 1.22V AT t_MAX*/12
OR TIME = t_MAX
FAULT
t_MAX/3
NiCd OR
NiMH – ∆V
AUTOMATIC
RECHARGE
V_CELL < 1.325V
V_CELL > 1.95V
OR PWM FAULTS
4010 F01
*t_MAX IS PROGRAMMED MAXIMUM FAST CHARGE DURATION
**OPTIONAL TEMPERATURE LIMITS APPLY
Figure 1. LTC4010 State Diagram
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 mi-
cropower 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 4.25V, 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 charg-
ing, 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
8
temperature is between 5°C and 45°C. If these tempera-
ture 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
4010p