ltc4069edc-trpbf Linear Technology Corporation, ltc4069edc-trpbf Datasheet - Page 8

• Manufacturer Part Number: ltc4069edc-trpbf
• Description: Standalone 750ma Li-ion Battery Charger In 2 X 2 Dfn With Ntc Thermistor Input
• Manufacturer: Linear Technology Corporation

OPERATIO
LTC4069
application with the assurance that the charger will auto-
matically reduce the current in worst-case conditions.
The charge cycle begins when the voltage at the V
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 • V
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, t
cally 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 V
ally restart the charge cycle, remove the input voltage and
reapply it, or momentarily float the PROG pin and recon-
nect 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:
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
R
PROG
=
1000
CC
U
•
I
and 0.35 • V
CHG
1
V
RECHRG
,
I
CHG
=
(typically 4.1V). To manu-
CC
1000
R
PROG
or below 0.016 • V
V
TIMER
CC
(typi-
pin
CC
.
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in undervoltage lockout
until V
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 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 V
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 pre-
vented since the battery is at or near full capacity.
Once the charge cycle terminates, the LTC4069 continu-
ously 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 capac-
ity), 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 peri-
odic charge cycle initiations. Also, if the battery voltage
I
BAT
CC
=
rises above 3.6V and approximately 80mV above
R
V
PROG
PROG
• 1000
CC
, or when leaving
4069fa