LTC4121/LTC4121-4.2
1
4121fc
For more information www.linear.com/LTC4121
TYPICAL APPLICATION
FEATURES DESCRIPTION
40V 400mA Synchronous
Step-Down Battery Charger
The LT C
®
4121 is a 400mA constant-current/constant-
voltage (CC/CV) synchronous step-down battery charger.
In addition to CC/CV operation, the LTC4121 regulates its
input voltage to a programmable percentage of the input
open-circuit voltage. This technique maintains maximum
power transfer with high impedance input sources such
as solar panels.
An external resistor programs the charge current up to
400mA. The LTC4121-4.2 is suitable for charging Li-Ion/
Polymer batteries, while the programmable float voltage
of the LTC4121 is suitable for several battery chemistries.
The LTC4121 and LTC4121-4.2 include an accurate RUN
pin threshold, low voltage battery preconditioning and bad
battery fault detection, timer termination, auto-recharge,
and NTC temperature qualified charging. The FAULT pin
provides an indication of bad battery or temperature faults.
Once charging is terminated, the LTC4121 signals end-of-
charge via the CHRG pin, and enters a low current SLEEP
mode. An auto-restart feature starts a new charging cycle
if the battery voltage drops by 2.2%.
LTC4121 Efficiency vs V
IN
at V
FLOAT
= 8.4V
APPLICATIONS
n
Wide Input Voltage Range: 4.4V to 40V
n
Temperature Compensated Input Voltage
Regulation for Maximum Power Point Tracking
(MPPT)
n
Adjustable Float Voltage 3.5V to 18V (LTC4121)
n
Fixed 4.2V Float Voltage Option (LTC4121-4.2)
n
High Efficiency: Up to 95%
n
50mA to 400mA Programmable Charge Current
n
±1% Feedback Voltage Accuracy
n
Programmable 5% Accurate Charge Current
n
Thermally Enhanced, Low Profile (0.75mm)
16-Lead (3mm × 3mm) QFN Package
n
Handheld Instruments
n
Solar Powered Devices
n
Industrial/Military Sensors and Devices
L, LT , LT C , LT M , Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
INTV
CC
BOOST
SW
CHGSNS
BAT
FB
FBG
IN
RUN
MPPT
PROG
LTC4121
GND
10k
10µF
R
PROG
V
IN
V
BAT
+ 200mV
TO 40V
22nF
SLF6025T-470MR48
2.2µF
FREQ
+
22µF
1.96M
787k
4121 TA01a
Li-Ion
High Efficiency, Wide Input Voltage Range Charging with LTC4121
V
IN
(V)
5
87
EFFICIENCY (%)
89
91
93
95
97
10 15 20
4121 TA01b
25 30 35 40
200mA, R
PROG
= 6.04k
400mA, R
PROG
= 3.01k
V
BAT
= 8.3V