ADT7316ARQ-REEL 데이터 시트보기 (PDF) - Analog Devices

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ADT7316ARQ-REEL

±0.5°C Accurate Digital Temperature Sensor and Quad Voltage Output 12-/10-/8-Bit DACs

Analog Devices 

The technique used in the ADT7316/ADT7317/ADT7318 is to

measure the change in VBE when the device is operated at two

different currents. This is given by

ΔVBE = KT/q × ln (N)

where:

K is Boltzmann’s constant.

q is the charge on the carrier.

T is the absolute temperature in Kelvin.

N is the ratio of the two currents.

Figure 41 shows the input signal conditioning used to measure

the output of an external temperature sensor. This figure shows

the external sensor as a discrete substrate transistor. If a PNP

transistor is used, the base is connected to the D− input and the

emitter to the D+ input. If an NPN transistor is used, the emitter is

connected to the D− input and the base to the D+ input.

A 2N3906 is recommended to be used as the external transistor.

To prevent ground noise interfering with the measurement, the

more negative terminal of the sensor is not referenced to ground,

but is biased above ground by an internal diode at the D− input.

As the sensor is operating in a noisy environment, C1 is pro-

vided as a noise filter. See the Layout Considerations section on

for more information on C1.

To measure ΔVBE, the sensor is switched between operating

currents of I and N × I. The resulting waveform is passed

through a low-pass filter to remove noise, then to a chopper

stabilized amplifier that performs the functions of amplification

and rectification of the waveform to produce a dc voltage pro-

portional to ΔVBE. This voltage is measured by the ADC to give

a temperature output in 10-bit twos complement format. To

further reduce the effects of noise, digital filtering is performed

by averaging the results of 16 measurement cycles.

ADT7316/ADT7317/ADT7318

TEMPERATURE VALUE FORMAT

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

retically 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 Table 9. The result of the internal or external tempera-

ture measurements is stored in the temperature value registers

and is compared with limits programmed into the internal or

external high and low registers.

Table 9. Temperature Data Format (Internal and External

Temperature)

Temperature

Digital Output

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

−40°C

11 0110 0000

−25°C

11 1001 1100

−10°C

11 1101 1000

−0.25°C

11 1111 1111

0°C

00 0000 0000

0.25°C

00 0000 0001

10°C

00 0010 1000

25°C

00 0110 0100

50°C

00 1100 1000

75°C

01 0010 1100

100°C

01 1001 0000

105°C

01 1010 0100

125°C

01 1111 0100

Temperature Conversion Formula

Positive Temperature = ADC Code/4

Negative Temperature = (ADC Code − 512)/4

where DB9 is removed from the ADC code in the Negative

Temperature equation.

Rev. B | Page 25 of 44

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