LTC3558_15 Datasheet, PDF (13/32 Pages) Linear Technology – Linear USB Battery Charger with Buck and Buck-Boost Regulators

LTC3558
OPERATION
The LTC3558 is a linear battery charger with a monolithic
synchronous buck regulator and a monolithic synchro-
nous buck-boost regulator. The buck regulator is inter-
nally compensated and needs 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, PV_IN1 and PV_IN2 pins
must be tied together, as shown in Figure 1. Cur-
rent being delivered at the BAT pin is 500mA. Both
switching regulators are enabled. The sum of the
average input currents drawn by both switching regulators
is 200mA. This makes the effective battery charging cur-
rent only 300mA. If the HPWR pin were tied LO, the BAT
pin current would be 100mA. With the switching regulator
conditions unchanged, this would cause the battery to
discharge at 100mA.
USB (5V)
R_PROG
HIGH
HIGH
HIGH
LOW
V_CC
PROG
LTC3558
BAT
PV_IN1
PV_IN2
SUSP
SWAB2
HPWR
EN1
EN2
MODE
SWCD2
V_OUT2
SW1
3558 F01
500mA
300mA
200mA
+
+
10μF
SINGLE Li-lon
CELL 3.6V
2.2μH
V_OUT1
Figure 1. For Proper Operation, the BAT, PV_IN1 and PV_IN2 Pins Must Be Tied Together
APPLICATIONS INFORMATION
Battery Charger Introduction
The LTC3558 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.
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 specifications.
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
3558f
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