LTC4110
16
4110fb
When the battery voltage exceeds the bulk charge threshold
(V
BC
), the charger begins the bulk charge portion of the
charge cycle. As the battery accepts charge, the voltage
increases. Constant-current charge continues until the
battery approaches the constant voltage. At this time, the
charge current will begin to drop, signaling the beginning
of the constant-voltage portion of the charge cycle.
The charger will maintain the constant voltage across the bat-
tery until either C/x is reached or 100% of the programmed
bulk charge time has elapsed during bulk charge. When
the current drops to approximately 20% of the full-scale
charge current, an internal C/x comparator will initiate the
start of the top-off stage. The top-off stage charges for
25% of the total programmed bulk charge time. When the
time elapses, charge is terminated and CHGb (GPIO1 pin)
is forced to a high impedance state and CHG_STATE_0 and
CHG_STATE_1 register bits will be set low. Should the total
bulk charge time elapse before C/x is reached, charge is
terminated and a CHG_FLT fault is indicated until cleared
by the RESET_TO_ZERO or POR_RESET SMBus write
commands, SHDN pin toggle or the battery removed and
replaced. Fault conditions are not cleared when the supply
input is removed if the battery has suffi cient voltage.
An optional external thermistor network is sampled at
regular intervals to monitor battery temperature and to
detect battery presence. If the thermistor temperature is
hot (see the SafetySignal Decoder section), the charge
timer is paused, charge current is halted, CHG_FLTb (GPIO3
pin) is forced low and the CHG_FLT bit will be set high.
CHGb (GPIO1 pin) , CHG_STATE_0 and CHG_STATE_1
register bits will not be affected. When the thermistor
value returns to an acceptable value, charging resumes,
CHG_FLTb (GPIO3 pin) returns to high impedance and the
CHG_FLT bit will be reset low. An open thermistor indicates
absence of a battery. To defeat the temperature monitoring
function, replace 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.
After a charge cycle has ended without fault, the charge
cycle is automatically restarted if the average battery cell
voltage falls below the auto recharge threshold. At any
time charging can be forced to stop by pulling the SHDN
pin high or setting the CHARGE_INHIBIT bit high through
the SMBus.
SMART BATTERY CHARGE MODE
This section explains operation for smart batteries with a
SMBus interface. Smart Li-Ion is selected by connecting
the TYPE pin to the V
DD
pin and smart Nickel (NiMH/NiCd)
is selected by connecting the TYPE pin to the V
REF
pin.
The LTC4110 only implements a subset of smart battery
charger commands; the actual charging algorithm is
determined by LTC4110 through external resistors even
if the battery is “smart.”
The LTC4110 operates as a high effi ciency, synchronous,
PWM fl yback battery charger with constant current and
constant fl oat voltage regions of operation. The constant-
charge current is programmed by the combination of a
resistor (R
CHG
) from the I
CHG
pin to ground, a battery
current sense resistor (R
SNS(BAT)
) and CSP/CSN pin
resistors. For Li-Ion the constant voltage (fl oat voltage)
is programmed to one of four values (4.2V, 8.4V, 12.6V,
16.8V) depending on the number of series cells using the
SELC pin and can be adjusted ±0.3V/cell with the V
CHG
pin. For nickel batteries the constant-voltage function is
not used, however, a non-zero value is still required to be
written to the ChargingVoltage() register. The internal auto
recharge function is inhibited for smart batteries.
If the battery voltage exceeds 107.5% (V
BOV
) of the
programmed fl oat voltage during any stage of charge,
the charger pauses until the voltage drops below the
hysteresis (V
BOVH
). The timer is not stopped and no fault
is indicated. This function is disabled when nickel based
smart batteries are used.
There are four states associated with smart battery charge
mode, namely:
• SMBus Wake-Up Charge State
• SMBus Preconditioning Charge State
• SMBus Bulk Charge State
• SMBus OFF State
These states are explained in the following four sections.
OPERATION
