Datasheet AD7314 (Analog Devices) - 5

AD7314 CIRCUIT INFORMATION Table I. Temperature Data Format
The AD7314 is a 10-bit digital temperature sensor. The part houses an on-chip temperature sensor, a 10-bit A/D converter,
Digital Output
and reference and serial interface logic functions in an MSOP
Temperature ( C) DB9 . DB0
package. The A/D converter section consists of a conventional –128 10 0000 0000 successive approximation converter based around a capacitor –125 10 0000 1100 DAC. The parts are capable of running on a 2.65 V to 5.5 V –100 10 0111 0000 power supply. –75 10 1101 0100 The on-chip temperature sensor allows an accurate measurement –50 11 0011 1000 of the ambient device temperature to be made. The working –25 11 1001 1100 measurement range of the AD7314 is –35∞C to +85∞C. –0.25 11 1111 1111 0 00 0000 0000
CONVERTER DETAILS
0.25 00 0000 0001 The conversion clock for the part is internally generated so no 10 00 0010 1000 external clock is required except when reading from and writing 25 00 0110 0100 to the serial port. In normal mode, an internal clock oscillator 50 00 1100 1000 runs the automatic conversion sequence. A conversion is initi- 75 01 0010 1100 ated every 400 ms. At this time, the part wakes up and performs 100 01 1001 0000 a temperature conversion. This temperature conversion typically 125 01 1111 0100 takes 25 ms, at which time the part automatically shuts down. 127 01 1111 1100 The result of the most recent temperature conversion is avail- able in the serial output register at any time. The AD7314 can
Serial Interface
be placed in a shutdown mode, via the control register, in The serial interface on the AD7314 consists of four wires, CE, which case the on-chip oscillator is shut down and no further SCLK, SDI, and SDO. The interface can be operated in 3-wire conversions are initiated until the AD7314 is taken out of shut- mode with SDI tied to ground, in which case the interface has down mode. The conversion result from the last conversion prior read-only capability, with data being read from the data register to shutdown can still be read from the AD7314 even when it is via the SDO line. The SDI line is used to write the part into in shutdown mode. standby mode, if required. The CE line is used to select the device when more than one device is connected to the serial In the automatic conversion mode, every time a read or write clock and data lines. To ensure that the serial port is reset prop- operation takes place, the internal clock oscillator is restarted at erly after power-up, the CE must be at a logic low before the the end of the read or write operation. The result of the conver- first serial port access. The serial clock is active only when CE is sion is available, typically 25 ms later. Similarly, when the part is high. For correct data synchronization, it is important that the taken out of shutdown mode, the internal clock oscillator is CE be low when the serial port is not being accessed. restarted and the conversion result is available, typically 25 ms later. Reading from the device again before conversion is com- The part operates in a slave mode and requires an externally plete will provide the same set of data. applied serial clock to the SCLK input to access data from the data register. The serial interface on the AD7314 is designed to
Temperature Value Register
allow the part to be interfaced to systems that provide a serial The temperature value register is a read-only register that stores clock that is synchronized to the serial data, such as the 80C51, the temperature reading from the ADC in 10-bit twos comple- 87C51, 68HC11, 68HC05, and PIC16Cxx microcontrollers as ment format. The temperature data format is shown in Table I. well as DSP processors. This shows the full theoretical range of the ADC from –128∞C to +127∞C, but in practice the temperature measurement range A read operation from the AD7314 accesses data from the is limited to the operating temperature range of the device (–35∞C temperature value register while a write operation to the part to +85∞C). writes data to the control register. Input data is not loaded into the control register until the rising edge of the 15th SCLK cycle. Data on the SDI line is latched in on the falling edge of the serial clock while data is updated on the SDO line on the rising edge of the serial clock.
Read Operation
Figure 3 shows the interface diagram for a serial read from the AD7314. The CE line enables the SCLK input. A leading zero and 10 bits of data are transferred during a read operation. Read operations occur during streams of 16 clock pulses. Output data is updated on the rising edge of SCLK. The serial data is accessed in a number of bytes if 10 bits of data are being read. At the end of the read operation, the SDO line remains in the state of the last bit of data clocked out of the AD7314 until CE returns low, at which time the SDO line goes into three-state. REV. A –5– Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION PRODUCT HIGHLIGHTS SPECIFICATIONS TIMING CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS ORDERING GUIDE PIN CONFIGURATION PIN FUNCTION DESCRIPTIONS CIRCUIT INFORMATION CONVERTER DETAILS Temperature Value Register Serial Interface Read Operation Write Operation MICROCONTROLLER INTERFACING MOUNTING THE AD7314 SUPPLY DECOUPLING TYPICAL TEMPERATURE ERROR GRAPHS OUTLINE DIMENSIONS Revision History