AN960| Application Note
Maxim > App Notes > BATTERY MANAGEMENT Keywords: usb power, lithium ion, li+ battery, usb powered, portable devices, digital cameras, PDAs, pdas, MP3 players, USB, 5V, 3.3V, 100mA, 500mA
Feb 11, 2002
APPLICATION NOTE 960
Portable Supply Derives +5V and +3.3V Power from USB Port
Abstract: A portable device using the circuit of Figure 1 derives power from the USB bus. The MAX1811 uses USB power charges a lithium-ion (Li+) battery at, USB compatible, 100mA or 500mA rates. Battery power is then stepped up with the MAX1747 to create the 5V supply rail. The 5V supply rail is then stepped down with the MAX1837 to create the 3.3V supply rail. The circuit includes a low battery shutdown to protect the Li+ battery and offers a convenient charging LED. The Figure 1 circuit is powered by a universal serial bus (USB) port. It produces +5V and +3.3V to power portable devices such as digital cameras, MP3 players, and PDAs. It allows the port to maintain communications while supplying power, e.g., to charge a Li+ battery. IC2 boosts the battery voltage (VBATT) to 5V, and IC3 bucks that 5V output down to 3.3V.
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