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LTC4110

4110fa

for the battery chemistry selected. Speciﬁcally 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 conﬁguration 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 tTIMEOUT per the smart battery stan-

dards. However it is not recommended to use a standard

battery with a LTC4110 conﬁgured 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 efﬁciency, synchronous,

PWM ﬂyback battery charger with constant-current and

constant ﬂoat voltage regions of operation. The constant-

charge current is programmed by the combination of a

resistor (RCHG) from the ICHG pin to ground, a battery

OPERATION

current sense resistor (RSNS(BAT)) and CSP/CSN pin resis-

tors. The constant voltage (ﬂoat 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 VCHG 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 ﬂoat voltage; see VAR), 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 ITH 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 VREF pin, sets the total

charge time.

If the battery voltage is less than the 3.0V/cell bulk charge

threshold (VBC), the charger will begin with a precondition-

ing trickle charge current. The trickle current is programmed

by the resistor (RPCC) from the IPCC pin to ground. During

preconditioning trickle charging, if the battery voltage

stays below the bulk charge threshold (VBC) 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% (VBOV) of the

programmed ﬂoat voltage during any stage of charge,

the charger pauses until the voltage drops below the

hysteresis (VBOVH). The timer is not stopped and no fault

is indicated.

Figure 2. Charge Mode Operation

LTC4110

BACKUP LOAD

SYSTEM LOAD

BATTERY

OFF

4110 F02

DCIN

CURRENT FLOW

INID

BATID

DCHFET

CHGFET

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