herunterladen
Maxim > Design Support > Technical Documents > Application Notes > iButton
®
> APP 4255
Keywords: 1-wire power, EEPROM, temperature, SHA-1, Rpup, Vpup
APPLICATION NOTE 4255
How to Power the Extended Features of 1-Wire®
Devices
Jun 17, 2008
Abstract:
A 1
-Wire bus provides both communication and power between a host and slave devices on a single
line. Some 1-Wire devices offer extended features, which include EEPROM, temperature measurement, and a
SHA-1 engine. Operation of these special features can require additional power, so the 1-Wire device's pull-
up resistor (R
PUP
) must be sized accordingly.
Introduction
The 1-Wire bus is a simple signaling scheme that performs half-duplex bidirectional communications between
a master controller and one or more slaves, all sharing a common data line. Both power delivery and data
communication take place over this single line. Most 1-Wire devices use very little power, on the order of tens
of microamps, to operate and communicate. Some 1-Wire devices, however, need more power during specific
operations, such as an EEPROM write or a device-specific calculation or measurement. During these periods
of increased power demand, it is important that the voltage on the 1-Wire bus does not fall below the device's
minimum operating pullup voltage (V
PUP
). For most parasitic-powered 1-Wire devices, the minimum operating
voltage (V
PUP
) is 2.8V.
1-Wire Devices that Need Extra Power
Table 1 is a partial list of 1-Wire devices with special features that require extra power.
Page 1 of 6
