LTC4425 Datasheet, PDF (1/20 Pages) Linear Technology – Linear SuperCap Charger with Current-Limited Ideal Diode and V/I Monitor

FEATURES
n _{50mΩ Ideal Diode from VIN to VOUT}
n _{Smart Charge Current Profile Limits Inrush Current}
n _{Internal Cell Balancer (No External Resistors)}
n _{Programmable Output Voltage (LDO Mode)}
n _{Programmable VIN to VOUT Current Limit}
n _{Continuous Monitoring of VIN to VOUT Current via}
PROG Pin
n _{Low Quiescent Current: 20μA}
n _{VIN Power Fail, PGOOD Indicator}
n _{2.45V/2.7V Cell Protection Shunts}
(4.9V/5.4V SuperCap Max Top-Off Voltage)
n _{3A Peak Current Limit, Thermal Limiting}
n _{Tiny Application Circuit, 3mm × 3mm × 0.75mm DFN}
and 12-Lead MSOP Packages
APPLICATIONS
n _{High Peak Power Battery/USB Powered Equipment}
n _{Industrial PDAs}
n _{Portable Instruments/Monitoring Equipment}
n _{Power Meters, SuperCap Backup Circuits}
n _{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.
Electrical Specifications Subject to Change
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.
TYPICAL APPLICATION
Charging 2-Cell Series Supercapacitor from Li-Ion Source
V_IN
Li-Ion
1.5M
PFI
1.2M
PFI_RET
SEL
EN
+–
V_OUT V_IN
TO HIGH PEAK
POWER LOAD
1F
V_MID
1F
V_IN
FB
LTC4425
2.45V/2.7V
GND
470k
PFO
PROG
I_MONITOR
2k
4425 TA01
Charge Current vs V_IN to V_OUT
0.6
FULL CHARGE CURRENT
V_FB = V_IN
0.5
0.4
0.3 ^{CURRENT LIMITED}
BY PMOS RDSON
0.2
0.1
0
0
1/10 CHARGE
CURRENT
IDEAL DIODE
FORWARD VOLTAGE = 15mV
0.2 0.4 0.6 0.8
1
V_IN – V_OUT (V)
4425 TA02
4425p
1