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Programmable 2A 2-Cell Supercap Charger with Automatic Cell Balancing in a Compact 9mm2 Package

Mar 4 2010 - MILPITAS, CA
  • Linear Technology Corporation introduces the LTC4425, the latest in a family of 2-cell supercapacitor chargers for addressing high peak power, data backup and “dying gasp” needs in portable and data storage applications. The device employs a linear CC-CV architecture with thermal limiting to charge two supercapacitors in series to a programmable output voltage from a Li-Ion/Polymer battery, a USB port, or other 2.7V to 5.5V current-limited supply.

    LTC4425 PR Image

    The LTC4425 features two operating modes: charge current profile (normal) mode and LDO mode. The device's charge current profile mode charges the top of the supercap stack to the input voltage VIN with a charge current that varies inversely with the input-to-output voltage differential in order to present excessive heating. The LDO mode charges the stack to an externally programmed output voltage with a fixed charge current that is also externally programmable. Charge current is resistor programmable up to 2A (3A peak), and each capacitor is protected against overvoltage by internal shunts (2.45V/2.7V selectable). The LTC4425's on-board current-limited ideal diode features extremely low 50mΩ on resistance to prevent back-driving of VIN, making it suitable for a wide variety of high peak power battery and USB-powered equipment, industrial PDAs, portable instruments and monitoring equipment, power meters, supercap backup circuits and PC card/USB modems.

    The LTC4425's automatic cell balancing feature maintains equal voltages across both cells, eliminating the need for balancing resistors while protecting each supercapacitor from overvoltage damage while minimizing current drain on the capacitors. The IC operates with a very low 20µA quiescent current when the output voltage is in regulation and draws only 2µA in shutdown from either VIN or VOUT, whichever is higher. The basic charging circuit requires only six external components and is highly compact, offered in a tiny 9mm2 package footprint as well as a leaded package. Other key features include a VIN power fail indicator and continuous monitoring of VIN to VOUT current via the PROG pin. Additional protection features include current and thermal limiting that reduces charge current in cases of excessive temperature.

    The LTC4425 is available in two compact, thermally enhanced packages; a 12-lead, low-profile (0.75mm) 3mm × 3mm DFN package and a 12-lead MSOP package. Operation from –40ºC to 85ºC operating junction temperature is guaranteed. The LTC4425 is in stock, priced starting at $2.25 each in 1,000-piece quantities. For more information, visit

    Summary Features LTC4425

    • Linear Constant-Current, Constant-Voltage, (CC-CV) Charging of Two Series Supercapacitors
    • 50m Ideal Diode from VIN to VOUT
    • Smart Charge Current Profile Limits Inrush Current
    • Automatic Cell Balancing Prevents Capacitor Overvoltage During Charging
    • Programmable Output Voltage (LDO Mode)
    • Programmable VIN to VOUT Current Limit
    • Continuous Monitoring of VOUT Current via PROG Pin
    • Low Quiescent Current: 20µA
    • VIN Power Fail Indicator
    • Programmable Charging Current (Up to 2A Continuous), 3A Peak Current Limit
    • Selectable 2.45V or 2.7V Max Voltage per Cell (4.9V/5.4V Supercap Max Top-Off Voltage)
    • Tiny Application Circuit, All Components <1mm High
    • Compact, Low-Profile (0.75mm) 3mm × 3mm 12-Lead DFN Package & MSOP-12 Package

    2A 2-Cell Linear Supercap Charger with Auto Cell Balancing

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