ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 19

• Manufacturer Part Number: ADT7467
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

Table 7. Temperature Data Format
Temperature
–128°C
–125°C
–100°C
–75°C
–50°C
–25°C
–10°C
0°C
10.25°C
25.5°C
50.75°C
75°C
100°C
125°C
127°C
1
Table 8. Extended Range, Temperature Data Format
Temperature
–64°C
–1°C
0°C
1°C
10°C
25°C
50°C
75°C
100°C
125°C
191°C
1
Bold numbers denote 2 LSB of measurement in Extended Resolution
Register 2 (Reg. 0x77) with 0.25°C resolution.
Bold numbers denote 2 LSB of measurement in Extended Resolution
Register 2 (Reg. 0x77) with 0.25°C resolution.
Figure 25. Measuring Temperature Using an NPN Transistor
Figure 26. Measuring Temperature Using a PNP Transistor
2N3904
2N3906
NPN
PNP
1000 0000 00
1000 0011 00
1001 1100 00
1011 0101 00
1100 1110 00
1110 0111 00
1111 0110 00
0000 0000 00
0000 1010 01
0001 1001 10
0011 0010 11
0100 1011 00
0110 0100 00
0111 1101 00
0111 1111 00
0000 0000 00
0011 1111 00
0100 0000 00
0100 0001 00
0100 1010 00
0101 1001 00
0111 0010 00
1000 1001 00
1010 0100 00
1011 1101 00
1111 1111 00
Digital Output (10-Bit)
Digital Output (10-Bit)
D+
D–
D+
D–
ADT7467
ADT7467
1
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Rev. A| Page 19 of 80
Nulling Temperature Errors
As CPUs run faster, it is more difficult to avoid high frequency
clocks when routing the D+/D– traces around a system board.
Even when recommended layout guidelines are followed, some
temperature errors may still be attributed to noise coupled onto
the D+/D– lines. Constant high frequency noise usually
attenuates or increases temperature measurements by a linear,
constant value.
The ADT7467 has temperature offset registers at Addresses
0x70 and 0x72 for the Remote 1 and Remote 2 temperature
channels. By performing a one-time calibration of the system,
the user can determine the offset caused by system board noise
and null it using the offset registers. The offset registers auto-
matically add an Offset 64/twos complement 8-bit reading to
every temperature measurement. The LSBs add 0.5°C offset to
the temperature reading; therefore, the 8-bit register effectively
allows temperature offsets of up to ±64°C with a resolution of
0.5°C. This ensures that the readings in the temperature
measurement registers are as accurate as possible.
Temperature Offset Registers
Reg. 0x70 Remote 1 temperature offset = 0x00 (0°C default)
Reg. 0x71 local temperature offset = 0x00 (0°C default)
Reg. 0x72 Remote 2 temperature offset = 0x00 (0°C default)
ADT7460/ADT7467 Backwards-Compatible Mode
By setting Bit 1 of Configuration Register 5 (Reg. 0x7C), all
temperature measurements are stored in the Zone Temp value
registers (Registers 0x25, 0x26, and 0x27) in twos complement
format in the range −64°C to +127°C. (The ADT7468 makes
calculations based on the Offset 64 extended range and clamps
the results if necessary.) The temperature limits must be
reprogrammed in twos complement format. If a twos
complement temperature below −63°C is entered, the
temperature is clamped to −63°C. In this mode, the diode fault
condition remains −128°C = 1000 0000, whereas the fault
condition is represented by −64°C = 0000 0000 in the extended
temperature range (−64°C to +191°C).
Temperature Measurement Registers
Reg. 0x25 Remote 1 temperature
Reg. 0x26 local temperature
Reg. 0x27 Remote 2 temperature
Reg. 0x77 Extended Resolution 2 = 0x00 default
<7:6> TDM2, Remote 2 temperature LSBs
<5:4> LTMP, local temperature LSBs
<3:2> TDM1, Remote 1 temperature LSBs
ADT7467