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LTC4089/LTC4089-5

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then no external components are necessary. However,

if more conductance is needed, an external P-channel

MOSFET can be added from BAT to OUT. The GATE pin

of the LTC4089/LTC4089-5 drives the gate of the PFET for

automatic ideal diode control. The source of the external

MOSFET should be connected to OUT and the drain should

be connected to BAT. In order to help protect the external

MOSFET in over-current situations, it should be placed in

close thermal contact to the LTC4089/LTC4089-5.

Battery Charger

The battery charger circuits of the LTC4089/LTC4089-5

are designed for charging single cell lithium-ion batter-

ies. Featuring an internal P-channel power MOSFET, the

charger uses a constant-current/constant-voltage charge

algorithm with programmable current and a program-

mable timer for charge termination. Charge current can be

programmed up to 1.2A. The ﬁnal ﬂoat voltage accuracy

is ±0.8% typical. No blocking diode or sense resistor is

required when powering either the IN or the HVIN pins.

The CHRG open-drain status output provides information

regarding the charging status of the LTC4089/LTC4089-5

at all times. An NTC input provides the option of charge

qualiﬁcation using battery temperature.

An internal thermal limit reduces the programmed charge

current if the die temperature attempts to rise above a

preset value of approximately 105°C. This feature protects

the LTC4089/LTC4089-5 from excessive temperature, and

allows the user to push the limits of the power handling

capability of a given circuit board without risk of dam-

aging the LTC4089/LTC4089-5. Another beneﬁt of the

LTC4089/LTC4089-5 thermal limit is that charge current

can be set according to typical, not worst-case, ambient

temperatures for a given application with the assurance

that the charger will automatically reduce the current in

worst-case conditions.

The charge cycle begins when the voltage at the OUT

pin rises above the battery voltage and the battery volt-

age is below the recharge threshold. No charge current

actually ﬂows until the OUT voltage is 100mV above

the BAT voltage. At the beginning of the charge cycle, if

the battery voltage is below 2.8V, the charger goes into

trickle charge mode to bring the cell voltage up to a safe

level for charging. The charger goes into the fast charge

constant-current mode once the voltage on the BAT pin

rises above 2.8V. In constant current mode, the charge

current is set by RPROG. When the battery approaches the

ﬁnal ﬂoat voltage, the charge current begins to decrease

as the LTC4089/LTC4089-5 switches to constant-voltage

mode. When the charge current drops below 10% of the

programmed charge current while in constant-voltage

mode the CHRG pin assumes a high impedance state.

An external capacitor on the TIMER pin sets the total

minimum charge time. When this time elapses the

charge cycle terminates and the CHRG pin assumes a

high impedance state, if it has not already done so. While

charging in constant current mode, if the charge current

is decreased by thermal regulation or in order to maintain

the programmed input current limit the charge time is

automatically increased. In other words, the charge time is

extended inversely proportional to the actual charge current

delivered to the battery. For Li-Ion and similar batteries that

require accurate ﬁnal ﬂoat potential, the internal bandgap

reference, voltage ampliﬁer and the resistor divider provide

regulation with ±0.8% accuracy.

Trickle Charge and Defective Battery Detection

At the beginning of a charge cycle, if the battery volt-

age is low (below 2.8V) the charger goes into trickle

charge reducing the charge current to 10% of the full-

scale current. If the low battery voltage persists for one

quarter of the total charge time, the battery is assumed

to be defective, the charge cycle is terminated and the

CHRG pin output assumes a high impedance state. If

for any reason the battery voltage rises above ~2.8V the

charge cycle will be restarted. To restart the charge cycle

(i.e., when the dead battery is replaced with a discharged

battery), simply remove the input voltage and reapply it

or cycle the TIMER pin to 0V.

Programming Charge Current

The formula for the battery charge current is:

CHG

PROG

•,

50 000

where VPROG is the PROG pin voltage and RPROG is the total

resistance from the PROG pin to ground. Keep in mind that

OPERATIO

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