Analog Devices LTC4425

Description

The LTC4425 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 VIN in normal mode with a smart charge current profile to limit the inrush current until the VIN to VOUT 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 (VOUT current limit) is programmed by connecting a resistor between PROG and GND. The voltage on the PROG pin represents the current fl owing from VIN to VOUT 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.

Features

• 50mΩ Ideal Diode from VIN to VOUT
• Smart Charge Current Profi le Limits Inrush Current
• Internal Cell Balancer (No External Resistors)
• Programmable Output Voltage (LDO Mode)
• Programmable VIN to VOUT Current Limit
• Continuous Monitoring of VIN to VOUT Current viaPROG Pin
• Low Quiescent Current: 20μA
• VIN 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 DFNand 12-Lead MSOP Packages

Typical applications

• High Peak Power Battery/USB Powered Equipment
• PC Card/USB Modems
• Portable Instruments/Monitoring Equipment
• Industrial PDAs
• Power Meters, SuperCap Backup Circuits

More information

• Datasheet
• IC product information