ADM1034 datasheet(16/40 Pages) AD

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ADM1034

Rev. 0 | Page 16 of 40

TEMPERATURE MEASUREMENT SYSTEM

INTERNAL TEMPERATURE MEASUREMENT

The ADM1034 contains an on-chip band gap temperature

sensor. The on-chip ADC performs conversions on the sensor’s

output, outputting the data in 13-bit format. The resolution of

the local temperature sensor is 0.03125°C.

Table 7 shows the format of the temperature data MSBs. Table 8

shows the same for the LSBs. To ensure accurate readings, read

the LSBs first. This locks the current LSBs and MSBs until the

MSBs are read. They then start to update again. (Reading only

the MSBs does not lock the registers.) Temperature updates to

the look-up table take place in parallel; so fan speeds may be

updated even if the MSBs are locked.

Table 7. Temperature Data Format

(Local Temperature and Remote Temperature High Bytes)

Temperature (°C)

Digital Output

−64°C

0000 0000

−40°C

0001 1000

−32°C

0010 0000

−2°C

0011 1110

−1°C

0011 1111

0°C

0100 0000

1°C

0100 0001

2°C

0100 0010

10°C

0100 1010

20°C

0101 0100

50°C

0111 0010

75°C

1000 1011

100°C

1010 0100

125°C

1011 1101

150°C

1101 0110

191°C

1111 1111

Table 8. Local and Remote Sensor Extended Resolution

Extended Resolution (°C)

Temperature Low Bits

0.0000

00000

0.03125

00001

0.0625

00010

0.125

00100

0.250

01000

0.375

01100

0.500

10000

0.625

10100

0.750

11000

0.875

11100

Temperature (°C) = (MSB − 64°C) + (LSB × 0.03125)

Example: MSB = 0101 0100 = 84d

LSB = 11100 = 28

Temperature °C = (84 – 64) + (28 × 0.03125) = 20.875

REMOTE TEMPERATURE MEASUREMENT

The ADM1034 can measure the temperature of two external

diode sensors or diode-connected transistors, which are

connected to Pins 9 and 10 and Pins 11 and 12. These pins are

dedicated temperature input channels. The series resistance

cancellation (SRC) feature can automatically cancel out the

effect of up to 1 kΩ of resistance in series with the remote

thermal diode.

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. Therefore, the technique

is unsuitable for mass production.

ADM1034

2N3904

D+

D–

ADM1034

2N3906

D+

D–

Figure 27. Measuring Temperature by Using Discreet Transistors

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