LTC3552 Datasheet, PDF (1/24 Pages) Linear Technology – Standalone Linear Li-Ion Battery Charger and Dual Synchronous Buck Converter

LTC3552
FEATURES
Standalone Linear Li-Ion
Battery Charger and Dual
Synchronous Buck Converter
DESCRIPTIO
■ _{Programmable Charge Current Up to 950mA}
■ _{Complete Linear Charger and Dual DC/DC}
Regulator
■ _{Buck Converter Output Voltage from 0.6V to 5V}
■ _{No MOSFET, Sense Resistor or Blocking Diode}
Required
■ _{Thermal Regulation Maximizes Charge Rate}
Without Risk of Overheating*
■ _{Charges Directly from a USB Port}
■ _{Programmable Charge Current Termination}
■ _{Preset 4.2V Charge Voltage with ±1% Accuracy}
■ _{Charge Current Monitor Output for Gas Gauging*}
■ _{Automatic Recharge}
■ _{Charge Status Output}
■ _{“Power Present” Output}
■ _{2.9V Trickle Charge Threshold}
■ _{Soft-Start Limits Inrush Current}
■ _{Low Quiescent Current Buck Converter (40µA)}
■ _{Current Mode Operation, Constant Frequency (2.25MHz)}
■ _{Low Profile (5mm × 3mm × 0.75mm) DFN Package}
U
APPLICATIO S
■ _{Cellular Telephones, PDAs, MP3 Players}
■ _{Bluetooth Applications}
The LTC^®3552 is a complete constant-current/constant-
voltage linear charger with a dual DC/DC converter for
single cell lithium-ion batteries. Its DFN package and low
external component count make the LTC3552 ideally suited
for portable applications. Furthermore, the LTC3552 is
designed to work within USB power specifications.
No external sense resistor or external blocking diode is
required due to the internal MOSFET architecture. The
charge voltage is fixed at 4.2V and the charge current is
programmed with a resistor. The charge cycle terminates
when the charge current drops below the programmed
termination threshold after the final float voltage is reached.
When the input supply (wall adapter or USB supply) is
removed, the LTC3552 enters a low current state dropping
the battery drain current to less than 2µA. Thermal regula-
tion maximizes charge rate without risk of overheating.
The synchronous step-down switching regulators gen-
erate adjustable output voltages from 5V down to 0.6V.
The switching frequency is set at 2.25MHz, allowing the
use of small surface mount inductors and capacitors.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by U.S. patents, including 6522118, 6700364, 5481178, 6580258, 6304066,
6127815, 6498466, 6611131.
TYPICAL APPLICATIO
Single Cell Li-Ion Battery Charger with
C/5 Termination and Dual DC/DC Converter
V_IN
4.5V TO
6.5V
V_OUT2
2.5V/
400mA
1µF
C_OUT2
4.7µF
CER
619Ω
1.24k
4.7µH
LTC3552
V_IN
RUN1
ITERM
RUN2
PROG
BAT
CHRG
PWR
EN
SW2
V_CC
POR
MODE/SYNC
SW1
C_FF2
68pF
R4
887k
V_FB2
R3
280k
GND ^VFB1
800mA
+
10µF
2.2µH
R2
604k
C_FF1
33pF
R1
301k
4.2V
1-CELL
Li-Ion
BATTERY
V_OUT1
1.8V/
800mA
C_OUT1
10µF
CER
3552 TA01
Efficiency Curve/
Power Loss of Regulators
100
1000
95
90
EFFICIENCY
100
85
80
10
POWER LOSS
75
70
1
65
60
0.1
1
10
100
1000
LOAD CURRENT (mA)
V_CC = 3.3V, V_OUT = 1.8V
Burst Mode OPERATION
3552 TA01b
REGULATOR 1, NO LOAD ON REGULATOR 2
3552f
1