REV. E

–7–

AD7814

AD7814*

SCLK

DOUT

DIN

CS

8051*

P3.1

P3.0

P1.2

P1.3

*ADDITIONAL PINS OMITTED FOR CLARITY

Figure 4. AD7814 to 8051 Interface

AD7814 to PIC16C6x/7x Interface

Figure 5 shows an interface circuit between the AD7814 and the

PIC16C6x/7x microcontroller. The PIC16C6x/7x synchronous

serial port (SSP) is configured as an SPI master with the clock

polarity bit set to a logic one. In this mode, the serial clock line

of the PIC16C6x/7x idles high between data transfers. Data is

transferred to and from the AD7814 in two 8-bit serial data

operations. In the example shown, port line RA1 is being used

to generate the

CS for the AD7814.

AD7814*

SCLK

DOUT

DIN

CS

PIC16C6x/7x*

SCK

SDO

SDI

RA1

*ADDITIONAL PINS OMITTED FOR CLARITY

Figure 5. AD7814 to PIC16C6x/7x Interface

AD7814 to ADSP-21xx Interface

Figure 6 shows an interface between the AD7814 and the

ADSP-21xx DSP processor. To ensure correct operation of the

interface, the SPORT control register should be set up as follows:

TFSW = RFSW = 1, Alternate Framing

INVRFS = INVTFS = 1, Active Low Framing Signal

DTYPE = 00, Right Justify Data

SLEN = 1111, 16-Bit Data Words

ISCLK = 1, Internal Serial Clock

TFSR = RFS = 1, Frame Every Word

IRFS = 0, RFS Configured As Input

ITFS = 1, TFS Configured As Output

The interface requires an inverter between the SCLK line of the

ADSP-21xx and the SCLK input of the AD7814. The ADSP-

21xx has the TFS and RFS of the SPORT tied together with

TFS set as an output and RFS set as an input. The DSP operates

in alternate framing mode and the SPORT control register is set

up as described earlier.

AD7814*

SCLK

DOUT

DIN

CS

ADSP-21xx*

SCK

DR

DT

RFS

*ADDITIONAL PINS OMITTED FOR CLARITY

TFS

Figure 6. AD7814 to ADSP-21xx Interface

MOUNTING THE AD7814

The AD7814 can be used for surface or air temperature sensing

applications. If the device is cemented to a surface with ther-

mally conductive adhesive, the die temperature will be within

about 0.1

°C of the surface temperature, thanks to the device’s

low power consumption. Care should be taken to insulate the

back and leads of the device from the air, if the ambient air

temperature is different from the surface temperature being

measured.

The ground pin provides the best thermal path to the die, so the

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

thermal contact with the surface being measured.

As with any IC, the AD7814 and its associated wiring and cir-

cuits must be kept free from moisture to prevent leakage and

corrosion, particularly in cold conditions where condensation is

more likely to occur. Water-resistant varnishes and conformal

coatings can be used for protection. The small size of the

AD7814 package allows it to be mounted inside sealed metal

probes, which provide a safe environment for the device.

SUPPLY DECOUPLING

The AD7814 should be decoupled with a 0.1

µF ceramic

if the AD7814 is mounted remotely from the power supply.

TEMPERATURE – C

–0.4

–55

–0.2

0

0.2

0.4

0.6

0.8

1.0

–40

0

25

40

85

100

120

Figure 7. Typical Temperature Error