ADT7467ARQZ-R7 datasheet(16/77 Pages) ONSEMI

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ADT7467

Rev. 3 | Page 16 of 77 | www.onsemi.com

Table 6. 10-Bit Analog-to-Digital Output Code vs. VIN

Input Voltage

A/D Output

VCC (5 VIN)

VCC (3.3 VIN)

VCCP

Decimal

Binary (10 Bits)

<0.0065

<0.0042

<0.00293

00000000 00

0.0065 to 0.0130

0.0042 to 0.0085

0.0293 to 0.0058

00000000 01

0.0130 to 0.0195

0.0085 to 0.0128

0.0058 to 0.0087

00000000 10

0.0195 to 0.0260

0.0128 to 0.0171

0.0087 to 0.0117

00000000 11

0.0260 to 0.0325

0.0171 to 0.0214

0.0117 to 0.0146

00000001 00

0.0325 to 0.0390

0.0214 to 0.0257

0.0146 to 0.0175

00000001 01

0.0390 to 0.0455

0.0257 to 0.0300

0.0175 to 0.0205

00000001 10

0.0455 to 0.0521

0.0300 to 0.0343

0.0205 to 0.0234

00000001 11

0.0521 to 0.0586

0.0343 to 0.0386

0.0234 to 0.0263

00000010 00

…

1.6675 to 1.6740

1.100 to 1.1042

0.7500 to 0.7529

256 (1/4 scale)

01000000 00

…

3.330 to 3.3415

2.200 to 2.2042

1.5000 to 1.5029

512 (1/2 scale)

10000000 00

…

5.0025 to 5.0090

3.300 to 3.3042

2.2500 to 2.2529

768 (3/4 scale)

11000000 00

…

6.5983 to 6.6048

4.3527 to 4.3570

2.9677 to 2.9707

1013

11111101 01

6.6048 to 6.6113

4.3570 to 4.3613

2.9707 to 2.9736

1014

11111101 10

6.6113 to 6.6178

4.3613 to 4.3656

2.9736 to 2.9765

1015

11111101 11

6.6178 to 6.6244

4.3656 to 4.3699

2.9765 to 2.9794

1016

11111110 00

6.6244 to 6.6309

4.3699 to 4.3742

2.9794 to 2.9824

1017

11111110 01

6.6309 to 6.6374

4.3742 to 4.3785

2.9824 to 2.9853

1018

11111110 10

6.6374 to 6.4390

4.3785 to 4.3828

2.9853 to 2.9882

1019

11111110 11

6.6439 to 6.6504

4.3828 to 4.3871

2.9882 to 2.9912

1020

11111111 00

6.6504 to 6.6569

4.3871 to 4.3914

2.9912 to 2.9941

1021

11111111 01

6.6569 to 6.6634

4.3914 to 4.3957

2.9941 to 2.9970

1022

11111111 10

>6.6634

>4.3957

>2.9970

1023

11111111 11

TEMPERATURE MEASUREMENT

A simple method of measuring temperature is to exploit the

negative temperature coefficient of a diode, measuring the base-

emitter voltage (VBE) of a transistor operated at constant

current. Unfortunately, this technique requires calibration to

null the effect of the absolute value of VBE, which varies from

each device.

The technique used in the ADT7467 is to measure the change

in VBE when the device is operated at three currents. Previous

devices have used only two operating currents, but the use of a

third current allows automatic cancellation of resistances in

series with the external temperature sensor.

Figure 24 shows the input signal conditioning used to measure

the output of an external temperature sensor. This figure shows

the external sensor as a substrate transistor, but it could equally

be a discrete transistor. If a discrete transistor is used, the

collector is not grounded and should be linked to the base. To

prevent ground noise from 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. C1 can optionally be added as a noise filter (the

recommended maximum value is 1000 pF). However, a better

option in noisy environments is to add a filter as described in

the Noise Filtering section.

Local Temperature Measurement

The ADT7467 contains an on-chip band gap temperature

sensor whose output is digitized by the on-chip 10-bit ADC.

The 8-bit MSB temperature data is stored in the local tempera-

ture register (Address 0x26). Because both positive and negative

temperatures can be measured, the temperature data is stored in

Offset 64 format or twos complement format, as shown in

Table 7 and Table 8. Theoretically, the temperature sensor and

ADC can measure temperatures from −128°C to +127°C (or

−64°C to +191°C in the extended temperature range) with a

resolution of 0.25°C. However, this exceeds the operating

temperature range of the device, preventing local temperature

measurements outside the ADT7467 operating temperature range.

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