Super capacitor charger IC with embedded power loop

Typically designers use a smart switch or MOSFET with a whole host of additional circuitry to create this function. By combining a P-channel MOSFET current switch with two independent current limits, a power loop, reverse blocking and a system ready pin in a tiny 12-pin TSOPJW package, the AAT4620 ensures the super capacitor is charged as quickly as possible without violating the host power specification, while reducing component count and board space requirements.



The AAT4620 offers two independent, programmable current limits to control current during host/card negotiation. As long as thermal dissipation is low, the integrated current limiting will allow the capacitor to charge until it reaches 98 percent of its final value. Set by two external resistors, the current limits support 10 percent +/- accuracy over the normal operating temperature range.



An integrated digital power loop automatically monitors and reduces the charging current to a safe level when high levels of charge result in excessive temperature and threaten to send the chip into thermal shutdown. By regulating charge current and therefore die temperature, this circuit ensures the super capacitor charges continuously and as quickly as possible.



Integrated reverse blocking protection prevents discharge of the super capacitor to the power supply. A system-ready output pin with externally programmable hysteresis alerts the system when the super capacitor is fully charged and ready for use.



The AAT4620 also features a quiescent current of only 40µA typical. In shutdown mode, the supply current drops to 1µA.



The device is available in a Pb-free, 12-pin TSOPJW package and specified across the -40 to to +85 degrees C temperature range.