7411(2017) 데이터 시트보기 (PDF) - Analog Devices

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7411
(Rev.:2017)

SPI-/I2C-Compatible, 10-Bit Digital Temperature Sensor and 8-Channel ADC

Analog Devices 

Data Sheet

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

close to the ADT7411.

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

the use of twisted-pair cable is recommended. This works

up to about 6 feet to 12 feet.

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

pair cable, such as Belden #8451 microphone cable.

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

GND close to the ADT7411. Leave the remote 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 capacitor can

be reduced or removed.

Cable resistance can also introduce errors. A series resistance of

1 Ω introduces about 0.5°C 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 Table 6.

The result of the internal or external temperature measurements is

stored as twos complement format in the temperature value

registers and is compared with limits programmed into the

internal or external high and low registers.

Table 6. Temperature Data Format (Internal and External

Temperature)

Temperature (°C)

Digital Output

−40

11 0110 0000

−25

11 1001 1100

−10

11 1101 1000

−0.25

11 1111 1111

0

00 0000 0000

+0.25

00 0000 0001

+10

00 0010 1000

+25

00 0110 0100

+50

00 1100 1000

+75

01 0010 1100

+100

01 1001 0000

+105

01 1010 0100

+125

01 1111 0100

Temperature Conversion Formula:

Positive Temperature = ADC Code/4

Negative Temperature = (ADC Code1 − 512)/4

1 DB9 is removed from the ADC Code.

ADT7411

Interrupts

The measured results from the internal temperature sensor,

external temperature sensor, VDD pin, and AIN inputs are

compared with their THIGH/VHIGH (greater than comparison)

and TLOW/VLOW (less than or equal to comparison) limits. An

interrupt occurs if the measurement exceeds or equals the limit

registers. These limits are stored in on-chip registers. Note that

the limit registers are eight bits long while the conversion results

are 10 bits long. If the limits are not masked out, then any out-

of-limit comparisons generate flags that are stored in the

Interrupt Status 1 register (Address 00h) and the Interrupt

Status 2 register (Address 01h). One or more out-of limit results

causes the INT/INT output to pull either high or low depending

on the output polarity setting. It is good design practice to mask

out interrupts for channels that are of no concern to the

application.

Figure 27 shows the interrupt structure for the ADT7411.

It gives a block diagram representation of how the various

measurement channels affect the INT/INT pin.

ADT7411 REGISTERS

The ADT7411 contains registers that are used to store the

results of external and internal temperature measurements, VDD

value measurements, analog input measurements, high and low

temperature limits, supply voltage and analog input limits,

configure multipurpose pins, and generally control the device.

See Table 7 for a detailed description of these registers.

The register map is divided into registers of 8 bits. Each register

has its own individual address but some consist of data that is

linked with other registers. These registers hold the 10-bit

conversion results of measurements taken on the temperature,

VDD, and AIN channels. For example, the MSBs of the VDD

measurement are stored in Register Address 06h while the two

LSBs are stored in Register Address 03h. The link involved

between these types of registers is that when the LSB register is

read first, the MSB registers associated with that LSB register

are locked out to prevent any updates. To unlock these MSB

registers the user has only to read any one of them, which has

the effect of unlocking all previously locked out MSB registers.

Therefore, for the example given above, if Register 03h is read

first, MSB Register 06h and Register 07h would be locked out to

prevent any updates to them. If Register 06h is read this register,

then Register 07h would be subsequently unlocked.

FIRST READ

COMMAND

LSB

REGISTER

OUTPUT

DATA

LOCK ASSOCIATED

MSB REGISTERS

Figure 29. Phase 1 of 10-Bit Read

Rev. C | Page 19 of 36

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