Datasheet

LTC3559/LTC3559-1
11
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OPERATION
The LTC3559/LTC3559-1 are linear battery chargers with
dual monolithic synchronous buck regulators. The buck
regulators are internally compensated and need no external
compensation components.
The battery charger employs a constant- current/constant-
voltage charging algorithm and is capable of charging a
single Li-Ion battery at charging currents up to 950mA. The
user can program the maximum charging current available
at the BAT pin via a single PROG resistor. The actual BAT
pin current is set by the status of the HPWR pin.
For proper operation, the BAT and PV
IN
pins must be tied
together. If a buck regulator is also enabled during the
battery charging operation, the net current charging the
battery may be lower than the actual programmed value.
Refer to Figure 1 for an explanation.
Figure 1. Current Being Delivered at the BAT Pin Is 500mA. Both Buck Regulators Are Enabled. The Sum of the
Average Input Currents Drawn by Both Buck Regulators Is 200mA. This Makes the Effective Battery Charging Current
Only 300mA. If the HPWR Pin Were Tied LO, the BAT Pin Current Would Be 100mA. With the Buck Regulator
Conditions Unchanged, This Would Cause the Battery to Discharge at 100mA
V
CC
PROG
R
PROG
1.62k
SUSP
HPWR
EN1
2.2μF
500mA
LTC3559/
LTC3559-1
EN2
MODE
HIGH
HIGH
HIGH
LOW (PULSE SKIP MODE)
BAT
USB (5V)
PV
IN
SW1
V
OUT1
SINGLE Li-lon
CELL 3.6V
SW2
V
OUT2
200mA
300mA
3559 F01
+
+
APPLICATIONS INFORMATION
Battery Charger Introduction
The LTC3559/LTC3559-1 have a linear battery charger
designed to charge single-cell lithium-ion batteries. The
charger uses a constant-current/constant-voltage charge
algorithm with a charge current programmable up to
950mA. Additional features include automatic recharge,
an internal termination timer, low-battery trickle charge
conditioning, bad-battery detection, and a thermistor
sensor input for out of temperature charge pausing.
Furthermore, the battery charger is capable of operating
from a USB power source. In this application, charge
current can be programmed to a maximum of 100mA or
500mA per USB power specifi cations.
Input Current vs Charge Current
The battery charger regulates the total current delivered
to the BAT pin; this is the charge current. To calculate the
total input current (i.e., the total current drawn from the
V
CC
pin), it is necessary to sum the battery charge current,
charger quiescent current and PROG pin current.
Undervoltage Lockout (UVLO)
The undervoltage lockout circuit monitors the input volt-
age (V
CC
) and disables the battery charger until V
CC
rises
above V
UVLO
(typically 4V). 200mV of hysteresis prevents
oscillations around the trip point. In addition, a differential
undervoltage lockout circuit disables the battery charger
when V
CC
falls to within V
DUVLO
(typically 50mV) of the
BAT voltage.