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LTC4425EDD

Description
Linear SuperCap Charger with Current-Limited Ideal Diode and V/I Monitor
File Size239KB,20 Pages
ManufacturerLinear ( ADI )
Websitehttp://www.analog.com/cn/index.html
Download Datasheet View All

LTC4425EDD Overview

Linear SuperCap Charger with Current-Limited Ideal Diode and V/I Monitor

Electrical Specifications Subject to Change
FEATURES
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LTC4425
Linear SuperCap Charger
with Current-Limited Ideal
Diode and V/I Monitor
DESCRIPTION
The LTC
®
4425 is a constant-current/constant-voltage linear
charger designed to charge a 2-cell supercap stack from
either a Li-Ion/Polymer battery, a USB port, or a 2.7V to
5.5V current-limited supply. The part operates as an ideal
diode with an extremely low 50mΩ on-resistance making it
suitable for high peak-power/low average power applications.
The LTC4425 charges the output capacitors to an externally
programmed output voltage in LDO mode at a constant
charge current, or to V
IN
in normal mode with a smart charge
current profile to limit the inrush current until the V
IN
to V
OUT
differential is less than 250mV. In addition the LTC4425 can
be set to clamp the output voltage to 4.9V or 5.4V.
Charge current (V
OUT
current limit) is programmed by
connecting a resistor between PROG and GND. The
voltage on the PROG pin represents the current flowing
from V
IN
to V
OUT
for current monitoring. An internal active
balancing circuit maintains equal voltages across each
supercapacitor and clamps the peak voltage across each
cell to a pin-selectable maximum value. The LTC4425
operates at a very low 20μA quiescent current (shutdown
current <3μA) and is available in a low profile 12-pin
3mm
×
3mm DFN or a 12-lead MSOP package.
50mΩ Ideal Diode from V
IN
to V
OUT
Smart Charge Current Profile Limits Inrush Current
Internal Cell Balancer (No External Resistors)
Programmable Output Voltage (LDO Mode)
Programmable V
IN
to V
OUT
Current Limit
Continuous Monitoring of V
IN
to V
OUT
Current via
PROG Pin
Low Quiescent Current: 20μA
V
IN
Power Fail, PGOOD Indicator
2.45V/2.7V Cell Protection Shunts
(4.9V/5.4V SuperCap Max Top-Off Voltage)
3A Peak Current Limit, Thermal Limiting
Tiny Application Circuit, 3mm
×
3mm
×
0.75mm DFN
and 12-Lead MSOP Packages
APPLICATIONS
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High Peak Power Battery/USB Powered Equipment
Industrial PDAs
Portable Instruments/Monitoring Equipment
Power Meters, SuperCap Backup Circuits
PC Card/USB Modems
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Charging 2-Cell Series Supercapacitor from Li-Ion Source
0.6
V
IN
Li-Ion
1.5M
PFI
1F
V
MID
1F
V
OUT
V
IN
TO HIGH PEAK
POWER LOAD
CHARGE CURRENT (A)
0.5
0.4
0.3
0.2
0.1
I
MONITOR
2k
GND
4425 TA01
Charge Current vs V
IN
to V
OUT
FULL CHARGE CURRENT
V
FB
= V
IN
+
1.2M
FB
V
IN
CURRENT LIMITED
BY PMOS RDSON
1/10 CHARGE
CURRENT
IDEAL DIODE
FORWARD VOLTAGE = 15mV
PFI_RET
SEL
EN
LTC4425
PFO
PROG
470k
2.45V/2.7V
0
0
0.2
0.4
0.6
V
IN
– V
OUT
(V)
0.8
1
4425 TA02
4425p
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