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Maxim > Design Support > Technical Documents > Reference Designs > Battery Management > APP 960
Keywords: usb power, lithium ion, li+ battery, usb powered, portable devices, digital cameras, PDAs,
pdas, MP3 players, USB, 5V, 3.3V, 100mA, 500mA
REFERENCE DESIGN 960 INCLUDES: Tested Circuit Schematic Description
Portable Supply Derives +5V and +3.3V Power
from USB Port
Sep 05, 2002
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 MAX1797 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
(V
BATT
) to 5V, and IC3 bucks that 5V output down to 3.3V.
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