Datasheet AD7314 (Analog Devices) - 6

AD7314 CE DATA-IN IS LOADED INTO CONTROL REGISTER ON THIS EDGE SCLK 1 2 3 4 11 12 15 16 t4 LEADING SDO ZERO DB9 DB8 DB0 t6 SDI DON'T DON'T POWER- CARE CARE DOWN
Figure 3. Serial Interface Diagram
Write Operation
pull-up resistor value for the ID pin. The recommended resistor Figure 3 also shows the interface diagram for a serial write to value in Figure 5 minimizes the additional power the AD7314 the AD7314. The write operation takes place at the same time has to dissipate, thus reducing any negative affects on the tem- as the read operation. Data is clocked into the control register perature sensor measurements. on the falling edge of SCLK. Only the third bit in the data stream provides a user-controlled function. This third bit is the power-
2.9V
down bit which, when set to a 1, puts the AD7314 into shutdown mode. The first two bits of the data stream are don’t cares while
100k AD7314* CONTROLLER*
all other bits in the data stream other than the power-down bit
ID
should be 0 to ensure correct operation of the AD7314. Data is loaded into the control register on the 15th rising SCLK edge. The data takes effect at this time, i.e., if the part is programmed
1k
to go into shutdown, it does so at this point. If the CE is brought low before this 15th SCLK edge, the control register will not be loaded and the power-down status of the part will not change.
*ADDITIONAL PINS OMITTED FOR CLARITY MICROCONTROLLER INTERFACING
Figure 5. Typical ID Pin Interface The AD7314 serial interface allows for easy interface to most microcontrollers and microprocessors. A typical interface circuit
MOUNTING THE AD7314
is shown in Figure 4. The AD7314 can be used for surface or air temperature sensing applications. If the device is cemented to a surface with thermally conductive adhesive, the die temperature will be within about
AD7314* CONTROLLER*
0.1∞C of the surface temperature, thanks to the device’s low
SCLK SCLK
power consumption. Care should be taken to insulate the back and leads of the device from the air, if the ambient air tempera-
SDI DOUT
ture is different from the surface temperature being measured.
SDO DIN
The ground pin provides the best thermal path to the die, so the
CE CE
temperature of the die will be close to that of the printed circuit ground track. Care should be taken to ensure that this is in good
*ADDITIONAL PINS OMITTED FOR CLARITY
thermal contact with the surface being measured. Figure 4. Typical Interface As with any IC, the AD7314 and its associated wiring and cir- cuits must be kept free from moisture to prevent leakage and The ID pin of the AD7314 can be used to distinguish the corrosion, particularly in cold conditions where condensation is device if used as a drop-in replacement temperature sensor. more likely to occur. Water-resistant varnishes and conformal Connected to Pin 7 (ID pin) is a 1 kW internal pull-down coatings can be used for protection. The small size of the AD7314 resistor. If a pull-up resistor is used on Pin 7 to aid in identify- package allows it to be mounted inside sealed metal probes that ing a device, then a pull-up value of 100 kW with VDD at 2.9 V provide a safe environment for the device. nominal is recommended. Figure 5 shows the recommended –6– REV. A 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