LTC4059_15 Datasheet, PDF (7/12 Pages) Linear Technology – 900mA Linear Li-Ion Battery Chargers with Thermal Regulation in 2 2 DFN

U
OPERATIO
The LTC4059/LTC4059A are linear battery chargers de-
signed primarily for charging single cell lithium-ion bat-
teries. Featuring an internal P-channel power MOSFET,
the chargers use a constant-current/constant-voltage
charge algorithm with programmable current. Charge
current can be programmed up to 900mA with a final float
voltage accuracy of ±0.6%. No blocking diode or external
sense resistor is required; thus, the basic charger circuit
requires only two external components. The ACPR pin
(LTC4059A) monitors the status of the input voltage with
an open-drain output. The Li CC pin (LTC4059) disables
constant-voltage operation and turns the LTC4059 into a
precision current source capable of charging Nickel chem-
istry batteries. Furthermore, the LTC4059/LTC4059A are
designed to operate from a USB power source.
An internal thermal limit reduces the programmed charge
current if the die temperature attempts to rise above a
preset value of approximately 115°C. This feature protects
the LTC4059/LTC4059A from excessive temperature, and
allows the user to push the limits of the power handling
capability of a given circuit board without risk of damaging
the LTC4059/LTC4059A or external components. Another
LTC4059/LTC4059A
benefit of the thermal limit is that charge current can be set
according to typical, not worst-case, ambient tempera-
tures 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 V_CC pin
rises approximately 150mV above the BAT pin voltage, a
program resistor is connected from the PROG pin to
ground, and the EN pin is pulled below the shutdown
threshold (typically 0.92V).
If the BAT pin voltage is below 4.2V, or the Li CC pin is
pulled above V_{Li CC} (LTC4059 only), the LTC4059 will
charge the battery with the programmed current. This is
constant-current mode. When the BAT pin approaches the
final float voltage (4.2V), the LTC4059 enters constant-
voltage mode and the charge current begins to decrease.
To terminate the charge cycle the EN should be pulled
above the shutdown threshold. Alternatively, reducing the
input voltage below the BAT pin voltage will also terminate
the charge cycle.
APPLICATIO S I FOR ATIO
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_PROG
=
1000
•
1.21V _,
I_CHG
I_CHG
=
1000
•
1.21V
R_PROG
For best stability over temperature and time, 1% metal-
film resistors are recommended.
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_BAT
=
V_PROG
R_PROG
•
1000
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in undervoltage lockout until
V_CC rises approximately 150mV above the BAT pin voltage.
The UVLO circuit has a built-in hysteresis of 115mV. If the
BAT pin voltage is below approximately 2.75V, then the
charger will remain in undervoltage lockout until V_CC rises
above approximately 3V. During undervoltage lockout
conditions, maximum battery drain current is 4µA.
Power Supply Status Indicator
(ACPR, LTC4059A Only)
The power supply status output has two states: pull-down
and high impedance. The pull-down state indicates that
V_CC is above the undervoltage lockout threshold (see
Undervoltage Lockout). When this condition is not met,
the ACPR pin is high impedance indicating that the
LTC4059A is unable to charge the battery.
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