ADT7316(RevPrN) Ver la hoja de datos (PDF) - Analog Devices

Número de pieza

componentes Descripción

fabricante

ADT7316
(Rev.:RevPrN)

SPI/I2C® Compatible, 10-Bit Digital Temperature Sensor and Quad Voltage Output 12/10/8-Bit DAC

Analog Devices 

PRELIMINARY TECHNICAL DATA

ADT7316/7317/7318

V DD

I

Nx I

IB IAS

INTERNAL

S ENSE

TRA NSISTOR

BIAS

DIODE

V OUT +

TO A DC

VOU T-

Figure 11. Top Level Structure of Internal Temperature Sensor

LAYOUT CONSIDERATIONS

Digital boards can be electrically noisy environments, and

care must be taken to protect the analog inputs from

noise, particularly when measuring the very small voltages

from a remote diode sensor. The following precautions

should be taken:

1. Place the ADT7316/17/18 as close as possible to the

remote sensing diode. Provided that the worst noise

sources such as clock generators, data/address buses and

CRTs are avoided, this distance can be 4 to 8 inches.

2. Route the D+ and D- tracks close together, in parallel,

with grounded guard tracks on each side. Provide a

ground plane under the tracks if possible.

3. Use wide tracks to minimize inductance and reduce

noise pickup. 10 mil track minimum width and spacing

is recommended.

GND

D+

D-

GND

10 mil.

10 mil.

10 mil.

10 mil.

10 mil.

10 mil.

10 mil.

Figure 12. Arrangement of Signal Tracks

4. Try to minimize the number of copper/solder joints,

which can cause thermocouple effects. Where copper/

solder joints are used, make sure that they are in both

the D+ and D- path and at the same temperature.

Thermocouple effects should not be a major problem as

1oC corresponds to about 240µV, and thermocouple

voltages are about 3µV/oC of temperature difference.

Unless there are two thermocouples with a big tempera-

ture differential between them, thermocouple voltages

should be much less than 200mV.

5. Place 0.1µF bypass and 2200pF input filter capacitors

close to the ADT7316/17/18.

6. If the distance to the remote sensor is more than 8

inches, the use of twisted pair cable is recommended.

This will work up to about 6 to 12 feet.

7. For really long distances (up to 100 feet) use shielded

twisted pair such as Belden #8451 microphone cable.

Connect the twisted pair to D+ and D- and the shield

to GND close to the ADT7316/17/18. Leave the re-

mote end of the shield unconnected to avoid ground

loops.

Because the measurement technique uses switched current

sources, excessive cable and/or filter capacitance can affect

the measurement. When using long cables, the filter ca-

pacitor may be reduced or removed.

Cable resistance can also introduce errors. 1⍀ series resis-

tance introduces about 0.5oC error.

TEMPERATURE VALUE FORMAT

One LSB of the ADC corresponds to 0.25°C. The ADC

can theoretically measure a temperature span of 255 °C.

The internal temperature sensor is guaranteed to a low

value limit of -40 °C. It is possible to measure the full

temperature span using the external temperature sensor.

The temperature data format is shown in Tables 3.

The result of the internal or external temperature mea-

surements is stored in the temperature value registers, and

is compared with limits programmed into the Internal or

External High and Low Registers.

TABLE 3. Temperature Data Format (Internal and Ex-

ternal Temperature)

Temperature

-40 °C

Digital Output

DB9..........DB0

11 0110 0000

REV. PrN

–17–

Share Link: