LTC4065L View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC4065L

Standalone 250mA Li-Ion Battery Charger in 2 ×2 DFN

Linear Technology 

LTC4065L/

LTC4065LX/LTC4065L-4.1

OPERATION

Undervoltage Lockout (UVLO)

An internal undervoltage lockout circuit monitors the input

voltage and keeps the charger in undervoltage lockout until

VCC rises above 3.6V and approximately 80mV above the

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

teresis of approximately 0.6V and the automatic shutdown

threshold has a built-in hysteresis of approximately 50mV.

During undervoltage lockout conditions, maximum battery

drain current is 4μA and maximum supply current is 11μA.

Shutdown Mode

The LTC4065L can be disabled by pulling the EN pin

above the shutdown threshold (approximately 0.82V).

In shutdown mode, the battery drain current is reduced

to less than 1μA and the supply current to about 20μA.

Timer and Recharge

The LTC4065L has an internal termination timer that

starts when an input voltage greater than the undervolt-

age lockout threshold is applied to VCC, or when leaving

shutdown the battery voltage is less than the recharge

threshold.

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

age 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 shutdown,

the timer will not start and charging is prevented since the

battery is at or near full capacity.

Once the charge cycle terminates, the LTC4065L continu-

ously monitors the BAT pin voltage using a comparator

with a 2ms filter time. When the average battery voltage

falls 100mV below the float voltage (which corresponds

to 80% to 90% battery capacity), a new charge cycle is

initiated and a 2.25 hour timer begins. This ensures that

the battery is kept at, or near, a fully charged condition and

eliminates the need for periodic charge cycle initiations.

The CHRG output assumes a strong pull-down state during

recharge cycles until C/10 is reached when it transitions

to a high impendance state.

Trickle Charge and Defective Battery Detection

At the beginning of a charge cycle, if the battery voltage

is low (below 2.9V), the charger goes into trickle charge,

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

rent (Note: The LTC4065LX has full charge current at

low-battery voltage). If the low-battery voltage persists

for one quarter of the total time (1.125 hour), the battery

is assumed to be defective, the charge cycle is terminated

and the CHRG pin output pulses at a frequency of 2Hz with

a 75% duty cycle. If for any reason the battery voltage

rises above 2.9V, the charge cycle will be restarted. To

restart the charge cycle (i.e., when the defective battery

is replaced with a discharged battery), simply remove the

input voltage and reapply it or temporarily pull the EN pin

above the shutdown threshold.

CHRG Status Output Pin

The charge status indicator pin has three states: pull-

down, pulse at 2Hz (see Trickle Charge and Defective

Battery Detection) and high impedance. The pull-down

state indicates that the LTC4065L is in a charge cycle. A

high impedance state indicates that the charge current

has dropped below 10% of the full-scale current or the

LTC4065L is disabled. Figure 2 shows the CHRG status

under various conditions.

4065lfb

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