ADT7316ARQ 데이터 시트보기 (PDF) - Analog Devices

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ADT7316ARQ

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

Analog Devices 

ADT7316/ADT7317/ADT7318

Table 8. VDD Data Format, VREF = 2.28 V

Digital Output

VDD Value (V)

Binary

Hex

2.5

01 0110 1110

16E

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 1100

2DC

5.5

11 0010 0101

325

6.0

11 0110 1110

36E

6.5

11 1011 0111

3B7

7.0

11 1111 1111

3FF

ON-CHIP REFERENCE

The ADT7316/ADT7317/ADT7318 have an on-chip 1.2 V band

gap reference that is gained up by a switched capacitor amplifier

to give an output of 2.28 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 consump-

tion. The internal reference is used as the reference for the

ADC. The ADC is used for measuring VDD and the internal

and external temperature sensors. The internal reference is

always used when measuring VDD, and the internal and exter-

nal temperature sensors. The external reference is the default

power-up reference for the DACs.

ROUND ROBIN MEASUREMENT

On power-up, the ADT7316/ADT7317/ADT7318 go into round

robin mode, but monitoring is disabled. Setting Bit C0 of the

Configuration 1 Register (Address 0x18) to 1 enables conversions.

It sequences through the three channels of VDD, the internal

temperature sensor, and the external temperature sensor and

takes a measurement from each. Once the conversion is completed

on the external temperature sensor, the device loops around for

another measurement cycle on all three channels. (This method

of taking a measurement on all three channels in one cycle is

called round robin.) Setting Bit 4 of the Control Configura-

tion 2 register (Address 0x19) 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 tem-

perature sensor) is measured in each conversion cycle.

The time taken to monitor all channels is typically not of

interest, because 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 the Specifications section.

VDD

I

N×I

IBIAS

INTERNAL

SENSE

TRANSISTOR

BIAS

DIODE

VOUT+

TO ADC

VOUT–

Figure 44. Top Level Structure of Internal Temperature Sensors

SINGLE-CHANNEL MEASUREMENT

Setting C4 of the Control Configuration 2 register (Address

0x19) enables the single-channel mode and allows the ADT7316/

ADT7317/ ADT7318 to focus on one channel only. A channel

is selected by writing to Bit C0 and Bit C1 in the Control Con-

figuration 2 register. For example, to select the VDD channel for

monitoring, write to the Control Configuration 2 register and

set C4 = 1 (if this has not been done), then write all 0s to Bit C0

to Bit C1. All subsequent conversions are done on the VDD channel

only. To change the channel selection to the internal tempera-

ture 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 ADT7316/ADT7317/ ADT7318 stops

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

operation is completed.

TEMPERATURE MEASUREMENT METHOD

Internal Temperature Measurement

The ADT7316/ADT7317/ADT7318 contain an on-chip, band

gap temperature sensor whose output is digitized by the on-chip

ADC. The temperature data is stored in the internal temperature

value register. As both positive and negative temperatures can

be measured, the temperature data is stored in twos comple-

ment format, as shown in Table 9. The thermal characteristics

of the measurement sensor can change, and therefore an offset

is added to the measured value to enable the transfer function

to match the thermal characteristics. This offset is added before

the temperature data is stored. The offset value used is stored in

the internal temperature offset register.

External Temperature Measurement

The ADT7316/ADT7317/ADT7318 can measure the tempera-

ture of one external diode sensor or diode-connected transistor.

The forward voltage of a diode or diode-connected transistor,

operated at a constant current, exhibits a negative temperature

coefficient of about –2 mV/°C. Unfortunately, the absolute value

of VBE varies from device to device, and individual calibration is

required to null this out, so the technique is unsuitable for mass

production.

Rev. B | Page 24 of 44

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