Analog Devices is offering a high accuracy digital temperature sensor that covers a wide industrial range. The tiny package also incorporates a humidity sensor. There is no necessity of adding a separate analog to digital converter to this sensor, as the device has one built into it, and provides a high-resolution digital output of 16 bits. With a wide operating voltage range, the device is suitable for industrial, domestic, and commercial use.
The ADT7420UCPZ-R2 from Analog Devices measures temperatures from -40°C to +150°C, while operating from a voltage range of 2.7 to 5.5 V. The device is available in a 4 mm x 4 mm package commonly known as Lead Frame Chip Scale Package (LFCSP). This wire bond plastic encapsulated near chip scale package has a substrate of copper lead frame within a leadless package format. Input/output copper pads are positioned on the perimeter edges of the package.
This allows the user to solder the perimeter pads and the exposed paddle available on the bottom surface of the package to the PCB. The exposed thermal pad on the bottom of the package conducts heat away from the package when it is soldered to the copper layer on the PCB. The thermal and perimeter pads are tin plated to provide good soldering.
Within the ADT7420 is an internal band gap reference, along with a temperature sensor. The 16-bit ADC within the device monitors the temperature and digitizes it to a resolution of 0.0078°C. By default, the ADC resolution is set to 13 bits or 0.0625°C, which should be adequate for most users. However, the user can change the ADC resolution via a programmable mode, to 16 bits. The programmable mode is accessible to the user through an I2C serial interface.
Analog Devices guarantees the ADT7420 will operate reliably when supplied from 2.7 V to 5.5 V. Typical current consumption by the device id 210 µA when operating from a supply voltage of 3.3 V. The user can optionally power down the device to make it enter a shutdown mode where the current consumption is typically 2.0 µA at 3.3 V. There is an additional power saving mode, where the user programs the device to read one sample per second. The temperature drift for ADT7420 is merely 0.0073°C.
The ADT7420 exhibits very high temperature accuracy of ±0.20°C between -10°C and +85°C, when working from a 3.0 V supply. When working from a wider supply voltage of 2.7 to 3.3V, the temperature accuracy of the device is ±0.25°C between -20°C and +105°C. As soon as the device powers up, the first temperature reading is available within 6 ms.
Implementing the ADT7420 is very easy, as it does not need any temperature calibration or correction by the user. The user also does not require any linearity correction for the usable temperature range. The user can program the device to produce an interrupt when it senses the temperature crossing a preset critical temperature.
Applications for the ADT7420 include replacement for RTD and thermistor, and compensation for thermocouple cold junction. Typically, the device is usable in medical equipment, and for industrial control and test, food transport and storage, environmental monitoring and HVAC, and Laser diode temperature control applications.
