LTC4110_15 Datasheet, PDF (18/52 Pages) Linear Technology – Battery Backup System Manager

LTC4110
OPERATION
SMBUS WAKE-UP CHARGE STATE
The battery will be charged with a fixed “wake-up” current
regardless of previous ChargingCurrent() and Charging-
Voltage() register values during wake-up charging. The cur-
rent is identical to the preconditioning charge current which
is programmed with an external resistor through the I_PCC
pin. The wake-up timer has the same period as t_TIMEOUT,
typically 175sec (see t_TIMEOUT).
The following conditions must be met to allow wake-up
charge of the battery:
• The SafetySignal must be RES_COLD, RES_IDEAL, or
RES_UR.
• AC must be present. This is qualified by DCDIV > V_AC
+ V_ACH and DCIN above UVLO.
• Wake-up charge initiates if a battery does not write
non-zero values to ChargingCurrent() and Chargin-
Voltage() registers when AC power is applied and a
battery is present or when AC is present and a battery
is subsequently connected.
The following conditions will terminate the wake-up charge
state and end charge attempts, unless otherwise noted.
• The t_TIMEOUT period is reached (see t_TIMEOUT) when
the SafetySignal is RES_COLD or RES_UR. The state
machine will go to the SMBus OFF state. The CHG_FLT
bit is not set.
• The SafetySignal is registering RES_HOT. The state
machine will go to the SMBus OFF state.
• The SafetySignal is registering RES_OR. The state
machine will go to the reset state.
• The LTC4110 will leave the wake-up charge state and
go into the SMBus preconditioning charge state if the
ChargingCurrent() AND ChargingVoltage() registers
have been written to non-zero values.
• The AC power is no longer present (DCDIV < V_AC or
DCIN below UVLO). The state machine will go to the
reset state.
• The ALARM_INHIBITED becomes set in the
ChargerStatus() register. The state machine will go to
the SMBus OFF state.
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• CHARGE_INHIBIT is set in the BBuControl() register.
Charge is stopped, however, the wake-up timer is not
paused. Clearing CHARGE_INHIBIT will enable the
LTC4110 to resume charging.
• There is insufficient DCIN voltage to charge the battery
as determined by the internal UVLO. This causes the
state machine to enter the reset state and stop all charge
activity. The LTC4110 will resume wake-up charging when
there is sufficient DCIN voltage to charge the battery.
• The CAL_START bit in the BBuControl() register is set.
Charge is stopped and the LTC4110 enters the calibra-
tion state.
• Writing a zero value to either the ChargingVoltage() or
ChargingCurrent() register. The state machine will go
to the SMBus OFF state.
• RESET_TO_ZERO is set in the BBuControl() register.
Charge is stopped; the SMBus OFF State is entered.
SMBUS PRECONDITIONING CHARGE STATE
During the SMBus preconditioning charge state, the charger
will be operating in the preconditioning charge current
limit. The following conditions must be met in order to
allow SMBus preconditioning charge to start:
• The ChargingVoltage() AND ChargingCurrent() registers
must be written to non-zero values. The LTC4110 will
not directly report the status of these registers. The
battery needs only write one pair of ChargingVoltage()
and ChargingCurrent() registers to stay in this state. The
t_TIMEOUT timer is not operational in SMBus precondition-
ing charge state.
• The SafetySignal must be RES_COLD, RES_IDEAL, or
RES_UR.
• AC must be present and sufficient. This is qualified by
DCDIV > V_AC + V_ACH and DCIN > UVLO.
The following conditions will affect the SMBus precondi-
tioning charge state as specified below:
• The SafetySignal is registering RES_HOT. Charge is
stopped; the SMBus OFF state is entered.
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