LTC4059/LTC4059A

7

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OPERATIO

The LTC4059/LTC4059A are linear battery chargers de-

signed primarily for charging single cell lithium-ion bat-

teries. Featuring an internal P-channel power MOSFET,

the chargers use a constant-current/constant-voltage

charge algorithm with programmable current. Charge

current can be programmed up to 900mA with a final float

voltage accuracy of

±0.6%. No blocking diode or external

sense resistor is required; thus, the basic charger circuit

requires only two external components. The ACPR pin

(LTC4059A) monitors the status of the input voltage with

an open-drain output. The Li CC pin (LTC4059) disables

constant-voltage operation and turns the LTC4059 into a

precision current source capable of charging Nickel chem-

istry batteries. Furthermore, the LTC4059/LTC4059A are

designed to operate from a USB power source.

An internal thermal limit reduces the programmed charge

current if the die temperature attempts to rise above a

preset value of approximately 115

°C. This feature protects

the LTC4059/LTC4059A from excessive temperature, and

allows the user to push the limits of the power handling

capability of a given circuit board without risk of damaging

the LTC4059/LTC4059A or external components. Another

benefit of the thermal limit is that charge current can be set

according to typical, not worst-case, ambient tempera-

tures for a given application with the assurance that the

charger will automatically reduce the current in worst-

case conditions.

rises approximately 150mV above the BAT pin voltage, a

program resistor is connected from the PROG pin to

ground, and the EN pin is pulled below the shutdown

threshold (typically 0.92V).

If the BAT pin voltage is below 4.2V, or the Li CC pin is

charge the battery with the programmed current. This is

constant-current mode. When the BAT pin approaches the

final float voltage (4.2V), the LTC4059 enters constant-

voltage mode and the charge current begins to decrease.

To terminate the charge cycle the EN should be pulled

above the shutdown threshold. Alternatively, reducing the

input voltage below the BAT pin voltage will also terminate

the charge cycle.

APPLICATIO S I FOR ATIO

Programming Charge Current

The charge current is programmed using a single resistor

from the PROG pin to ground. The battery charge current

is 1000 times the current out of the PROG pin. The

program resistor and the charge current are calculated

using the following equations:

R

V

I

I

V

R

PROG

CHG

CHG

PROG

==

1000

121

1000

121

•

.

,•

.

For best stability over temperature and time, 1% metal-

film resistors are recommended.

The charge current out of the BAT pin can be determined

at any time by monitoring the PROG pin voltage and using

the following equation:

I

V

R

BAT

PROG

PROG

=

• 1000

Undervoltage Lockout (UVLO)

An internal undervoltage lockout circuit monitors the input

voltage and keeps the charger in undervoltage lockout until

The UVLO circuit has a built-in hysteresis of 115mV. If the

BAT pin voltage is below approximately 2.75V, then the

above approximately 3V. During undervoltage lockout

conditions, maximum battery drain current is 4

µA.

Power Supply Status Indicator

(ACPR, LTC4059A Only)

The power supply status output has two states: pull-down

and high impedance. The pull-down state indicates that

Undervoltage Lockout). When this condition is not met,

the ACPR pin is high impedance indicating that the

LTC4059A is unable to charge the battery.