LTC4064 datasheet(10/16 Pages) LINER

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LTC4064

4064f

Programming The Timer

The programmable timer is used to terminate the charge

cycle. The timer duration is programmed by an external

capacitor at the TIMER pin. The total charge time is:

Time (Hours) = (3 Hours) • (CTIMER/0.1µF) or

CTIMER = 0.1µF • Time (Hours)/3 (Hours)

The timer starts when an input voltage greater than the

undervoltage lockout threshold level is applied and the

SHDN pin is greater than the manual shutdown threshold

voltage level. After a time-out occurs, the charge current

stops, and the CHRG output assumes a high impedance

state to indicate that the charging has stopped. Connect-

ing the TIMER pin to ground disables the timer function.

Recharge

After a charge cycle has terminated, if the battery voltage

drops below the recharge threshold of 3.90V a new charge

cycle will begin. The recharge circuit integrates the BAT

pin voltage for a few milliseconds to prevent a transient

from restarting the charge cycle.

If the battery voltage remains below 2.48V during trickle

charge for 1/4 of the programmed time, the battery may be

defective and the charge cycle will end. In addition, the

recharge comparator is disabled and a new charge cycle

will not begin unless the input voltage is toggled off-then-

on, the SHDN pin is momentarily pulled to ground, or the

BAT pin is pulled above the 2.48V trickle charge threshold.

Open-Drain Status Outputs

The LTC4064 has three open-drain status outputs: ACPR,

CHRG and FAULT. The ACPR pin pulls low when an input

voltage greater than the undervoltage lockout threshold is

applied and becomes high impedance when power (VIN <

VUV) is removed. CHRG and FAULT work together to

indicate the status of the charge cycle. Table 1 describes

the status of the charge cycle based on the CHRG and

FAULT outputs.

APPLICATIO S I FOR ATIO

Table 1.

FAULT

CHRG

Description

High

Low

Charge cycle has started, C/10 has not been

reached and charging is proceeding normally.

Low

Charge cycle has started, C/10 has not been

reached, but the charge current and timer

have been paused due to an NTC out-of-

temperature condition.

High

µA

C/10 has been reached and charging is

pull-down

proceeding normally.

Low

µA

C/10 has been reached but the charge current

pull-down

and timer have paused due to an NTC out-of-

temperature condition.

High

Normal timeout (charging has terminated).

Low

High

If FAULT goes low and CHRG goes high

impedance simultaneously, then the LTC4064

has timed out due to a bad cell (VBAT <2.48V

after one-quarter the programmed charge time).

If CHRG goes high impedance first, then

the LTC4053 has timed out normally (charging

has terminated), but NTC is indicating an out-

of-temperature condition.

CHRG Status Output Pin

When the charge cycle starts, the CHRG pin is pulled to

ground by an internal N-channel MOSFET capable of

driving an LED. When the charge current drops to 10% of

the full-scale current (C/10), the N-channel MOSFET is

latched off and a weak 30

µA current source to ground is

connected to the CHRG pin. After a time-out occurs,

the pin assumes a high impedance state. By using two

different value pull-up resistors a microprocessor can

detect three states from this pin (charging, C/10 and time-

out). See Figure 3.

When the LTC4064 is in charge mode, the CHRG pin is

pulled low by the internal N-channel MOSFET. To detect

this mode, force the digital output pin, OUT, high and

measure the voltage at the CHRG pin. The N-channel

MOSFET will pull the pin low even with the 2k pull-up

resistor. Once the charge current drops to 10% of the

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