Product category:
Power Supply ICs and Controllers
News Release from: Advanced Analogic Technologies | Subject: AAT4620
Edited by the Electronicstalk Editorial
Team on 18 May 2007
Switch integrates safe charging
circuitry
Power switch for high-side load-switching applications enables safe and speedy charging of supercapacitors in PC modem cards.
AnalogicTech has introduced a P-channel current-limited MOSFET power switch for high-side load-switching applications in PC modem cards Integrating all the circuitry required to limit current, protect the PC card connector, continuously charge the capacitor, and notify the system when it is ready for use, the AAT4620 ensures that a supercapacitor - typically used to average out high pulse currents - can be quickly charged without exceeding the host power supply specifications
This article was originally published on Electronicstalk on 16 Jun 2004 at 8.00am (UK)
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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 supercapacitor 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% of its final value.
Set by two external resistors, the current limits support +/-10% 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 supercapacitor 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 typical quiescent current of only 40uA.
In shutdown mode, the supply current drops to 1uA.
The device is available in a Pb-free, 12-pin TSOPJW package and specified across the -40 to +85C temperature range.
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