LTC4069(RevB) Просмотр технического описания (PDF) - Linear Technology

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LTC4069
(Rev.:RevB)

Standalone 750mA Li-Ion Battery Charger in 2 × 2 DFN with NTC Thermistor Input

Linear Technology 

LTC4069

OPERATION

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 VCC pin

rises above 3.5V and approximately 80mV above the BAT

pin voltage, a 1% program resistor is connected from the

PROG pin to ground and the NTC pin voltage stays between

0.76 • VCC and 0.35 • VCC or below 0.016 • VCC.

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 LTC4069 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.

An internal timer sets the total charge time, tTIMER (typically

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

terminates and the CHRG pin assumes a high impedance

state. The charge cycle will automatically restart if the

BAT pin voltage falls below VRECHRG (typically 4.1V).

To manually restart the charge cycle, remove the input

voltage and reapply it, or momentarily float the PROG pin

and reconnect it.

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:

RPROG

=

1000

•

1V

ICHG

,

ICHG

=

1000V

RPROG

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:

8

IBAT

=

VPROG

RPROG

•

1000

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 hysteresis 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 LTC4069 can be disabled by floating the PROG pin. In

shutdown mode, the battery drain current is reduced to

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

Timer and Recharge

The LTC4069 has an internal termination timer that starts

when an input voltage greater than the undervoltage lockout

threshold is applied to VCC, or when leaving shutdown and

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 temperature is either too high

or too low, the timer will pause until the battery returns

to normal temperature. If the battery 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 LTC4069 continuously

monitors the BAT pin voltage using a comparator with a

2ms filter time. When the battery voltage falls below 4.1V

(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. Also, if the battery voltage does

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