LTC3559 Linear Technology, LTC3559 Datasheet - Page 11

• Manufacturer Part Number: LTC3559
• Description: Linear USB Battery Charger
• Manufacturer: Linear Technology

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OPERATION
APPLICATIONS INFORMATION
The LTC3559 is a linear battery charger with dual monolithic
synchronous buck regulators. The buck regulators are
internally compensated and need no external compensa-
tion 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
Battery Charger Introduction
The LTC3559 has 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. Ad-
ditional 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.
Futhermore, 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.
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
LOW (PULSE SKIP MODE)
R
1.62k
PROG
USB (5V)
HIGH
HIGH
HIGH
V
PROG
SUSP
HPWR
EN1
EN2
MODE
CC
LTC3559
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
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.
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
charger quiescent current and PROG pin current.
Undervoltage Lockout (UVLO)
The undervoltage lockout circuit monitors the input volt-
age (V
above V
oscillations around the trip point. In addition, a differential
undervoltage lockout circuit disables the battery charger
when V
BAT voltage.
CC
SW1
SW2
PV
BAT
pin), it is necessary to sum the battery charge current,
IN
CC
CC
3559 F01
UVLO
500mA
200mA
) and disables the battery charger until V
falls to within V
+
(typically 4V). 200mV of hysteresis prevents
300mA
2.2 F
V
V
OUT1
OUT2
+
SINGLE Li-lon
CELL 3.6V
DUVLO
(typically 50mV) of the
IN
LTC3559
pins must be tied
CC
11
rises
3559f