DC1589A: SuperCap Charger with Current-Limited Ideal Diode and V/I Monitor

The DC1589A is a constant-current/constant-voltage linear charger circuit 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 50mO 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 IC can be set to clamp the output voltage to 4.9V or 5.4V.

The Charge current (VOUT current limit) is programmed by connecting a resistor between PROG and GND. The voltage on the PROG pin represents the current flowing 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)