ADT7516 datasheet(22/44 Pages) AD

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ADT7516/ADT7517/ADT7519

Rev. B | Page 22 of 44

BIAS

DIODE

INTERNAL

SENSE

TRANSISTOR

VDD

TO ADC

VOUT+

VOUT–

N × I

IBIAS

Figure 46. Top Level Structure of Internal Temperature Sensor

Table 7. Thermal Voltage Output (0 V to 2 VREF)

O/P Voltage (V)

Default °C

Max °C

Sample °C

–40

–128

0.25

–26

–114

+14

0.5

+12

–100

+28

0.75

–85

+43

+17

–71

+57

1.12

+23

–65

+63

1.47

+43

–45

+83

1.5

+45

–43

+85

+73

–15

+113

2.25

+88

+127

2.5

+102

+14

UDB1

2.75

+116

+28

UDB1

+42

UDB1

3.25

UDB1

+56

UDB1

3.5

UDB1

+70

UDB1

3.75

UDB1

+85

UDB1

+99

UDB1

4.25

UDB1

+113

UDB1

4.5

UDB1

+127

UDB1

1 Upper deadband has been reached. DAC output is not capable of increasing.

See Figure 41.

For negative temperatures,

Offset Register Code (d) = (0 V Temp) + 128

(1)

where D7 of Offset Register Code is set to 1 for negative

temperatures.

For example,

Offset Register Code (d) = −40 + 128 = 88d = 0x58

Since a negative temperature has been inserted into the

equation, DB7 (MSB) of the offset register code is set to 1.

Therefore, 0x58 becomes 0xD8.

0x58 + DB7(1) = 0xD8

For positive temperatures,

Offset Register Code (d) = 0 V Temp

(2)

For example,

Offset Register Code (d) = 10d = 0x0A

The following equation is used to work out the various

temperatures for the corresponding 8-bit DAC output:

8-Bit Temp = (DAC O/P)/1 LSB + (0 V Temp)

(3)

For example, if the output is 1.5 V, VREF-IN = 2.25 V, 8-bit DAC

has an LSB size = 2.25 V/256 = 8.79 × 10–3, and 0 V temp is at

−128°C, then the resultant temperature is

1.5/(8.79 × 10−3) + (−128) = +43°C

The following equation is used to work out the various

temperatures for the corresponding 10-bit DAC output:

10-Bit Temp = [(DAC O/P)/1 LSB] × 0.25 + (0 V Temp)

(4)

For example, if the output is 0.4991 V, VREF-IN = 2.25 V, 10-bit

DAC has an LSB size = 2.25 V/1024 = 2.197 × 10–3, and 0 V

temperature is at −40°C, then the resulting temperature is

[0.4991/(2.197 × 10–3)] × 0.25 + (–40) = +16.75°C

Figure 47 shows a graph of the DAC output vs. temperature for

a VREF-IN = 2.25 V.

TEMPERATURE (°C)

0.15

–128 –110 –90 –70 –50 –30 –10 10

90 110 127

0.30

0.45

0.60

0.75

0.90

1.05

1.20

1.35

1.50

1.65

1.80

1.95

2.10

2.25

0V = –128°C

0V = –40°C

0V = 0°C

Figure 47. DAC Output vs. Temperature VREF-IN = 2.25 V

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