Features

• 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

Typical Application

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 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 fl owing 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.