LTC4110
14
4110fb
for the battery chemistry selected. Specifi cally the TIMER
pin becomes active and used to detect faults conditions or
terminate the charge cycle itself as needed. Smart battery
SMBus charge control commands are still honored if any
are sent at any time. A smart battery can safely function
in a standard battery mode if identical in chemistry and
voltage confi guration as the standard battery. When the
TYPE pin selects a smart battery mode, this simply disables
the TIMER pin and its function in charge termination. The
smart battery is able to restart or terminate a charge cycle
at any time using charge commands over the SMBus. This
mode also enables smart battery wake-up and watchdog
functions based on t
TIMEOUT
per the smart battery stan-
dards. However it is not recommended to use a standard
battery with a LTC4110 confi gured for smart battery mode
operation. You can shorten battery life, damage or destroy
the battery. In the extreme case this can cause an explosion
since no charge termination mechanisms are active.
The following sections explain detailed operation for each
charge mode as selected by the TYPE pin.
STANDARD LI-ION/POLYMER BATTERY CHARGE MODE
The charger is programmed for standard Li-Ion batteries by
connecting the TYPE pin to GND. During Li-Ion charging,
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
OPERATION
current sense resistor (R
SNS(BAT)
) and CSP/CSN pin resis-
tors. 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. If adjusted, the
auto recharge threshold and overvoltage threshold will
track proportionally.
The charge cycle begins when the supply input is present
as sensed by the DCDIV pin and DCIN above UVLO, the
battery cell voltage is below the auto recharge threshold
(95% of the programmed fl oat voltage; see V
AR
), thermis-
tor temperature is within ideal limits, COLD, under range
(see SafetySignal Decoder section) or is optioned out and
the register bit CHARGE_INHIBIT is cleared (see Tables 6
and 7 for register details).
Soft-start ramps the charge current at a rate set by the
capacitor on the I
TH
pin. When charging begins, the pro-
grammable timer initiates timing and the CHGb (GPIO1
pin) status output is pulled LOW. An external capacitor
on the TIMER pin, along with the current set by the total
series resistance connected to the V
REF
pin, sets the total
charge time.
If the battery voltage is less than the 3.0V/cell bulk charge
threshold (V
BC
), the charger will begin with a precondition-
ing trickle charge current. The trickle current is programmed
by the resistor (R
PCC
) from the I
PCC
pin to ground. During
preconditioning trickle charging, if the battery voltage
stays below the bulk charge threshold (V
BC
) 25% of the
programmed bulk charge time, the battery may be defective
and the charge sequence will be terminated immediately.
To indicate this fault, the CHGb (GPIO1 pin) becomes high
impedance, the CHG_STATE_0 and CHG_STATE_1 register
bits will be set low and CHG_FLT register bit will be set
high. Charge is terminated and the timer reset until the
fault is cleared by the RESET_TO_ZERO or POR_RESET
SMBus write commands, SHDN pin toggle or the battery
removed and replaced. Removing the supply input will
not clear the fault if the battery is present.
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.
Figure 2. Charge Mode Operation
LTC4110
BACKUP LOAD
SYSTEM LOAD
BATTERY
OFF
OFF
ON
4110 F02
DCIN
CURRENT FLOW
INID
BATID
DCHFET
CHGFET
