LTC4110
22
4110fb
system load not be adequate to absorb the current. The
primary protection is accomplished with an external current
sense resistor (R
CL
), connected between the CLP and CLN
pins, through which the system load current fl ows. When
the voltage across the resistor reaches 10mV (I
BDT
) or
less, representing a low forward current, calibration mode
is terminated. The current protection can be completely
disabled by connecting both CLP and CLN pins to GND.
As an alternative where R
CL
sensing is not an option for
the application, a secondary method is accomplished by
monitoring the supply voltage through the DCDIV pin.
Once the DCDIV pin voltage goes above V
OVP
, calibration
mode is terminated. In either case, the CAL_FLT register is
set high and the charge mode is automatically entered to
begin recharging the battery. Both of these protections are
automatically disabled when not in calibration. However,
in calibration,
one or the other
of these two protective
methods
should
be used. You can optionally do both.
Failure to implement any form of protection can result in
destructive voltages being generated in the application.
If the calibration cycle fails due to loss of the main power
source a fault condition results that sets the CAL_FLT
register bit and backup mode is entered.
An optional external thermistor network is sampled at
regular intervals to monitor battery temperature and to
detect battery presence. If the thermistor value indicates
a temperature outside of ideal limits (hot or over-range)
the calibration current is halted and the CAL_FLT bit will
be set high. When the thermistor value returns to an ac-
ceptable value (under-range, cold or ideal), charge mode
is automatically entered to begin recharging the battery.
Calibration can be restarted by clearing the CAL_FLT bit
and sending another CAL_START command.
An open thermistor (over-range) indicates absence of a
battery. To defeat the temperature monitoring function, re-
place the thermistor with a resistor to indicate ideal battery
temperature. When a thermistor is not used, the resistor
circuit must be routed through the battery connector if
battery presence detection is required. If the battery should
be removed during calibration, calibration will terminate
and the CAL_FLT read bit will be set high.
The CAL_FLT bit can be cleared by writing a one to the
CAL_RESET or POR_RESET registers, or by forcing the
SHDN pin high. The CAL_FLT bit is not cleared by remov-
ing and reapplying the supply input if the battery has
maintained suffi cient voltage (V
BAT
≥ 2.7V).
Calibration can start only if the CAL_FLT bit in the
BBuStatus() register is clear. Once the LTC4110 is in cali-
bration state, the following events will stop calibration:
• BKDRV is sensed. The CAL_FLT bit is set.
• A HOT thermistor is sensed. The CAL_FLT bit is set.
• Loss of battery presence is sensed. The CAL_FLT bit is
set.
• The calibration cutoff threshold has been reached.
The CAL_COMPLETE bit is set. The LTC4110 will start
charging based upon the TYPE and SELA pins.
• An OVER_TEMP_ALARM, RESERVED_ALARM, or
TERMINATE_DISCHARGE_ALARM bit in the Alarm-
Warning() register is set. The CAL_FLT bit is set. The
LTC4110 will start charging.
• Loss of AC presence. The CAL_FLT bit is set.
SHUTDOWN MODE
The LTC4110 can be forced into either a micropower
shutdown state or an all logic register reset state with
the SHDN pin.
OPERATION
Figure 6. Calibration Mode Operation
LTC4110
BATTERY
OFF
OFF
ON
4110 F06
BACKUP LOAD
CURRENT FLOW
INID
BATID
DCHFET
CHGFET
SYSTEM LOAD
DCIN
