![]() Figure 2 graphs this calculation based on a V PUP of 5V with a device that has a minimum V PUP of 2.8V. The available current can be calculated by dividing the potential voltage drop from nominal V PUP to the minimum V PUP by the pullup resistor (R PUP). If the available current is not sufficient for the application, then a lower pullup resistor or a low-impedance bypass to the pullup resistor will be necessary. So for this example, there are 1.1mA available before the 1-Wire voltage drops below the minimum V PUP. V PUPmin = 2.8V, resulting in I AVAIL = 1.1mA The available current can be calculated as I AVAIL = (V PUP - V PUPmin)/R PUP. Available Powerįor a given V PUP and R PUP, the voltage difference between V PUP and the 1-Wire device's V PUPmin determines the current available for special functions. ![]() Example of the EC table for the DS28EA00. EC Table Parameters Specifying Extra Power Demand Parameter DescriptionĭS1961S, DS1972, DS2431, DS28E01, DS28E04, DS28E00įigure 1. The pullup resistor's specification (R PUP) in the EC table is for 1-Wire communication only and does not include additional power requirements for the special operations. How to Identify Extra Power Requirements in the EC TableĪny additional power requirements for a device are listed in the data sheet's electrical characteristics (EC) table under a variety of terms (Table 2). For most parasitic-powered 1-Wire devices, the minimum operating voltage (V PUP) is 2.8V.ġ-Wire Devices that Need Extra Power Table 1. 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). Some 1-Wire devices, however, need more power during specific operations, such as an EEPROM write or a device-specific calculation or measurement. ![]() Most 1-Wire devices use very little power, on the order of tens of microamps, to operate and communicate. Both power delivery and data communication take place over this single line. 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. Operation of these special features can require additional power, so the 1-Wire device's pull-up resistor (R PUP) must be sized accordingly. Some 1-Wire devices offer extended features, which include EEPROM, temperature measurement, and a SHA-1 engine. The DS28E18EVKIT# evaluation kit is available for $89.A 1-Wire bus provides both communication and power between a host and slave devices on a single line. The DS28E18 is available at Maxim Integrated’s website for $0.64 (1000-up, FOB USA) also available from authorized distributors.
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