Analog Devices dBCool ADT7467 Manual page 18

ADT7467
Table 6. Temperature Data Format
Temperature Digital Output (10-Bit)
–128°C 1000 0000 00
–125°C 1000 0011 00
–100°C
1001 1100 00
–75°C 1011 0101 00
–50°C 1100 1110 00
–25°C 1110 0111 00
–10°C 1111 0110 00
0°C
0000 0000 00
10.25°C 0000 1010 01
25.5°C 0001 1001 10
50.75°C 0011 0010 11
75°C 0100 1011 00
100°C
0110 0100 00
125°C 0111 1101 00
127°C 0111 1111 00
1
Bold numbers denote 2 LSB of measurement in Extended Resolution
Register 2 (Reg. 0x77) with 0.25°C resolution.
Table 7. Extended Range, Temperature Data Format
Temperature Digital Output (10-Bit)
–64°C
0000 0000 00
–1°C
0011 1111 00
0°C 0100 0000 00
1°C 0100 0001 00
10°C 0100 1010 00
25°C
0101 1001 00
50°C 0111 0010 00
75°C 1000 1001 00
100°C 1010 0100 00
125°C 1011 1101 00
191°C
1111 1111 00
1 Bold numbers denote 2 LSB of measurement in Extended Resolution
Register 2 (Reg. 0x77) with 0.25°C resolution.
2N3904
NPN
Figure 25. Measuring Temperature Using an NPN Transistor
2N3906
PNP
Figure 26. Measuring Temperature Using a PNP Transistor
1
1
ADT7467
D+
D–
ADT7467
D+
D–
Rev. 0 | Page 18 of 80
Nulling Out Temperature Errors
As CPUs run faster, it is getting 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 attributable 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, 0x72 for the Remote 1 and Remote 2 temperature
channels. By doing a one-time calibration of the system, the
user can determine the offset caused by system board noise and
null it out 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 so 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 (0x7C), all tempera-
ture measurements are stored in the Zone Temp value registers
(0x25, 0x26, and 0x27) in twos complement in the range −64°C
to +127°C. (The ADT7468 still makes calculations based on the
Offset64 extended range and clamps the results, if necessary.)
The temperature limits must be reprogrammed in twos comple-
ment. 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, while in the
extended temperature range (−64°C to +191°C), the fault
condition is represented by −64°C = 0000 0000.
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.