ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 20

• Manufacturer Part Number: ADT7468
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7468
Transistors, such as 2N3904, 2N3906, or equivalents in SOT-23
packages, are suitable devices to use.
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
Digital Output (10-Bit)
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
Digital Output (10-Bit)
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
D+
D–
D+
D–
ADT7468
ADT7468
1
1
Rev. A | Page 20 of 84
Nulling Temperature Errors
As CPUs are developed that 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 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 ADT7468 has temperature offset registers at Addresses 0x70
and 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
using the offset registers. The offset registers automatically 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 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)
ADT7463/ADT7468 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 of −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. 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 at −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