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Table 6. Twos Complement Temperature Data Format
Temperature
Digital Output (10-Bit)
–128°C
1000 0000 00 (diode fault)
–63°C
1100 0001 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 (diode fault)
–63°C
0000 0001 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 23. Measuring Temperature Using an NPN Transistor
2N3906
PNP
Figure 24. Measuring Temperature Using a PNP Transistor
1
1
ADT7473
D+
D–
ADT7473
D+
D–
Rev. 0 | Page 17 of 76
Nulling Out Temperature Errors
As CPUs run faster, it becomes 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 ADT7473 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 out using the offset registers. The offset registers automati-
cally add a 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/ADT7473 Backwards-Compatible Mode
By setting Bit 1 of Configuration Register 5 (0x7C), all tempera-
ture measurements are stored in the zone temperature value
registers (0x25, 0x26, and 0x27) in twos complement in the
range −63°C to +127°C. (The ADT7473 still makes calculations
based on the Offset 64 extended range and clamps the results, if
necessary.) The temperature limits must be reprogrammed in
twos complement. 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.
ADT7473
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