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Using a generic 0 to 1V analog multiplier to ensure accurate power management in battery-powered applications

Posted: 25 Feb 2008 ?? ?Print Version ?Bookmark and Share

Keywords:Li-ion battery? power management? analog multiplier?

Measuring load power can be important in applications such as notebook computers in which the entire circuit (load) is powered by either a Li-ion battery pack or the AC adapter that is used to charge the battery itself. Because the supply voltage is different for each voltage source, the current in the load is also different. In a typical case, the AC adapter can supply 16V, while the battery pack can be composed of three Li-ion batteries that provide a supply voltage of about 12.6V when fully charged, and about 9V when close to end-of-life.

In order to accurately manage the power of the circuit, it is not sufficient to just measure the current in the load because that does not provide information about what type of voltage source is being supplied. Furthermore, some portable applications can be constrained in terms of available pins at the MCU and, therefore, need to get the power measurement directly, rather than measuring current and voltage separately and then multiplying the two in firmware.

In some applications, measuring the power (voltage and current) delivered to a load is more important than simply measuring the current with a conventional current-sense amplifier. In particular, load power measurement enables accurate power management in applications, such as battery-powered devices, that can be powered by either a battery or AC adapter. This application note shows how to create a simple analog multiplier (from the MAX4210D/E/F) that is capable of multiplying two input signals ranging from 0 to 1V, thus ensuring accurate load-power measurement.

View the PDF document for more information.

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