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Digital Temperature Sensor Enables Multipoint Monitoring

Digital Temperature Sensor Enables Multipoint Monitoring

The DS28EA00 is a digital temperature sensor from Maxim Integrated Products’ Dallas Semiconductor. Its chain-mode feature determines the physical location of individual sensors linked in series through a common 1-Wire interface. Both communications and power are delivered through this interface, enabling accurate multipoint digital temperature measurements with minimal wiring complexity and cost.

Like all 1-Wire devices, the DS28EA00 has a unique 64-bit internal serial number that is used in a multi-drop environment to select a specific device for temperature results. A 1-Wire host controller uses the chain-mode command protocol to learn the 64-bit serial number of each part in the chain, starting with the first device on the line and proceeding sequentially (see the figure).

This sequence knowledge is directly linked to the relative physical location of each DS28EA00 in the chain. Additionally, the two chain-mode daisy-chain signal pins of the device are dual-purpose. They can be used to detect the physical location of a device in a network, or they can be used as a 5-V, 4-mA general-purpose I/O to control LED indicators or other signaling.

According to Scott Jones, Business Director for Dallas Semiconductor, the limitation on the physical length of the daisy chain is primarily based on capacitive loading of the1-Wire communication line. This is a function of the number of devices connected and the capacitive load introduced by the wire or traces used to connect parts. Based on analysis and testing, a system comprised of 100 parts or more can be reliably operated.

The DS28EA00 measures temperature over the –40°C to +85°C range. It is factory calibrated in a liquid bath to provide a worst-case conversion error of ±0.5°C within the ambient temperature range of -10°C to +85°C. Accuracy for a shifted ambient range of -40°C to -10°C is ±2.0°C, worst-case.

Jones states that the measured temperature is actually the temperature of the die. The temperature is respectively sensed and digitized from the differential base-emitter voltage output of a matched NPN-transistor pair and a first-order sigma-delta ADC. Conversion resolution is user programmable within a range of 9-bits to 12-bits.

Jones also states that temperature monitoring in rack- or chassis-based equipment was a key application that drove the development of the device. In such equipment, such as wireless base stations or enterprise servers, it is often necessary to monitor the temperature at multiple locations. For example, multipoint temperature monitoring is a critical capability in smart cooling for data centers.

The DS28EA00 is available in an 8-pin microSOP package. Prices start at $2.27 for 1000 pieces.

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