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

VDD Monitoring

The ADT7411 also has the capability of monitoring its own

power supply. The part measures the voltage on its VDD pin to a

resolution of 10 bits. The resulting value is stored in two 8-bit

registers, with the 2 LSBs stored in register Address 03h and the

8 MSBs stored in register Address 06h. This allows the user to

have the option of just doing a 1-byte read if 10-bit resolution is

not important. The measured result is compared with the VHIGH

and VLOW limits. If the VDD interrupt is not masked out then any

out-of-limit comparison generates a flag in the Interrupt Status 2

register, and one or more out-of-limit results causes the

INT/INT output to pull either high or low, depending on the

output polarity setting.

Measuring the voltage on the VDD pin is regarded as monitoring

a channel along with the internal, external, and AIN channels.

The user can select the VDD channel for single-channel

measurement by setting Bit C4 = 1 and by setting Bit C0 to

Bit C2 to all 0s in the Control Configuration 2 register.

When measuring the VDD value, the reference for the ADC is

sourced from the internal reference. Table 5 shows the data

format. As the maximum VDD voltage measurable is 7 V,

internal scaling is performed on the VDD voltage to match the

2.25 V internal reference value. The following is an example of

how the transfer function works.

ADC Reference = 2.25 V

1 LSB = ADC Reference/210 = 2.25/1024 = 2.197 mV

Scale Factor = Full Scale VCC/ADC Reference = 7/2.25 = 3.11

Conversion Result = VDD/(Scale Factor × LSB Size)

= 5/(3.11 × 2.197 mV)

= 2DBh

Table 5. VDD Data Format, VREF = 2.25 V

Digital Output

VDD Value (V)

Binary

Hex

2.5

01 0110 1110

16E

2.7

01 1000 1011

18B

3.0

01 1011 0111

1B7

3.5

10 0000 0000

200

4.0

10 0100 1001

249

4.5

10 1001 0010

292

5.0

10 1101 1011

2DB

5.5

11 0010 0100

324

6.0

11 0110 1101

36D

6.5

11 1011 0110

3B6

7.0

11 1111 1111

3FF

ADT7411

On-Chip Reference

The ADT7411 has an on-chip 1.125 V band gap reference that

is gained up by a switched capacitor amplifier to give an output

of 2.25 V. The amplifier is powered up for the duration of the

device monitoring phase and is powered down once monitoring

is disabled. This saves on current consumption. The internal

reference is used as the reference for the ADC.

Round Robin Measurement

Upon power-up, the ADT7411 goes into round robin mode but

monitoring is disabled. Setting Bit C0 of the Configuration 1

register to 1 enables conversions. It sequences through all

available channels, taking a measurement from each in the

following order: VDD, internal temperature sensor, external

temperature sensor/(AIN1 and AIN2), AIN3, AIN4, AIN5,

AIN6, AIN7, and AIN8. Pin 7 and Pin 8 can be configured as

either external temperature sensor pins or standalone analog

input pins. Once conversion is completed on the AIN8 channel,

the device loops around for another measurement cycle.

This method of taking a measurement on all the channels in

one cycle is called round robin. Setting Bit 4 of the Control

Configuration 2 register (Address 19h) disables the round robin

mode and in turn sets up the single-channel mode. The single-

channel mode is where only one channel, for example, the

internal temperature sensor, is measured in each conversion cycle.

The time taken to monitor all channels will normally not be of

interest, as the most recently measured value can be read at any

time. For applications where the round robin time is important,

typical times at 25°C are given in Table 1.

Single-Channel Measurement

Setting Bit C4 of the Control Configuration 2 register enables

the single-channel mode and allows the ADT7411 to focus on

one channel only. A channel is selected by writing to Bit C0 to

Bit C3 in the Control Configuration 2 register. For example,

to select the VDD channel for monitoring, write to the Control

Configuration 2 register and set C4 to 1 (if not done so already),

then write all 0s to Bit C0 to Bit C3. All subsequent conversions

are done on the VDD channel only. To change the channel selection

to the internal temperature channel, write to the Control

Configuration 2 register and set C0 = 1. When measuring in

single-channel mode, conversions on the channel selected occur

directly after each other. Any communication to the ADT7411

stops the conversions, but they are restarted once the read or

write operation is completed.

Rev. C | Page 17 of 36

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