10

LTC4065/LTC4065A

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OPERATIO

typical, not worst-case, ambient temperatures for a given

application with the assurance that the charger will auto-

matically reduce the current in worst-case conditions.

The charge cycle begins when the following conditions are

mately 80mV above the BAT pin voltage, a program

resistor is present from the PROG pin to ground and the EN

pin (LTC4065 only) is pulled below the shutdown thresh-

old (typically 0.82V).

If the BAT pin voltage is below 2.9V, the charger goes into

trickle charge mode, charging the battery at one-tenth the

programmed charge current to bring the cell voltage up to

a safe level for charging. If the BAT pin voltage is above

4.1V, the charger will not charge the battery as the cell is

near full capacity. Otherwise, the charger goes into the fast

charge constant-current mode.

When the BAT pin approaches the final float voltage

(4.2V), the LTC4065 enters constant-voltage mode and

the charge current begins to decrease. When the current

drops to 10% of the full-scale charge current, an internal

comparator turns off the N-channel MOSFET on the CHRG

pin and the pin assumes a high impedance state.

cally 4.5 hours). When this time elapses, the charge cycle

terminates and the CHRG pin assumes a high impedance

state. To restart the charge cycle, remove the input voltage

(typically 0.82V) for LTC4065, or momentarily float the

PROG pin and reconnect it (LTC4065A). The charge cycle

will automatically restart if the BAT pin voltage falls below

When the input voltage is not present, the battery drain

current is reduced to less than 4

µA. The LTC4065 can also

be shut down by pulling the EN pin above the shutdown

threshold voltage. To put LTC4065A in shutdown mode,

float the PROG pin. This reduces input quiescent current

to less than 20

µAandbatterydraincurrenttolessthan1µA.

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

1

1000

•,

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

the BAT pin voltage. The 3.6V UVLO circuit has a built-in

hysteresis of approximately 0.6V and the automatic shut-

down threshold has a built-in hysteresis of approximately

50mV. During undervoltage lockout conditions, maxi-

mum battery drain current is 4

µA and maximum supply

current is 11

µA.

Shutdown Mode

The LTC4065 can be disabled by pulling the EN pin above

the shutdown threshold (approximately 0.82V). The

LTC4065A can be disabled by floating the PROG pin. In

shutdown mode, the battery drain current is reduced to

less than 1

µA and the supply current to about 20µA.

Timer and Recharge

The LTC4065 has an internal termination timer that starts

when an input voltage greater than the undervoltage

shutdown the battery voltage is less than the recharge

threshold.

At power-up or when exiting shutdown, if the battery

voltage is less than the recharge threshold, the charge

time is set to 4.5 hours. If the battery voltage is greater than

the recharge threshold at power-up or when exiting shut-

down, the timer will not start and charging is prevented

since the battery is at or near full capacity.