
ADT7466
Temperature Data Format
The temperature data stored in the temperature data registers
consists of a high byte with an LSB size equal to 1°C. If higher
resolution is required, two additional bits are stored in the
extended temperature registers, giving a resolution of 0.25°C.
The temperature measurement range for both local and remote
measurements is, by default, 0°C to 127°C (binary), so the ADC
output code equals the temperature in degrees Celsius, and half
the range of the ADC is not actually used.
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The ADT7466 can also be operated by using an extended
temperature range from 64°C to +191°C. In this case, the
whole range of the ADC is used, but the ADC code is offset by
+64°C, so it does not correspond directly to the temperature.
(0°C = 0100000) .
The user can switch between these two temperature ranges by
setting or clearing Bit 7 in Configuration Register 1. The
measurement range should be switched only once after power-
up, and the user should wait for two monitoring cycles
(approximately 68 ms) before expecting a valid result. Both
ranges have different data formats, as shown in Table 11.
Table 11. Temperature Data Format
Temperature
Binary
1
64°C
0 000 0000
0°C
0 000 0000
1°C
0 000 0001
10°C
0 000 1010
25°C
0 001 1001
50°C
0 011 0010
75°C
0 100 1011
100°C
0 110 0100
125°C
0 111 1101
127°C
0 111 1111
191°C
0 111 1111
1
Binary scale temperature measurement returns 0 for all temperatures ≤0°C.
2
Offset binary scale temperature values are offset by +64.
While the temperature measurement range can be set to 64°C
to +191°C for both local and remote temperature monitoring,
the ADT7466 itself should not be exposed to temperatures
greater than those specified in the Absolute Maximum Ratings
table. Furthermore, the device is guaranteed to only operate at
ambient temperatures from 40°C to +125°C. In practice, the
device itself should not be exposed to extreme temperatures,
and may need to be shielded in extreme environments to
comply with these requirements. Only the remote temperature
monitoring diode should be exposed to temperatures above
+120°C and below 40°C. Care should be taken in choosing a
remote temperature diode to ensure that it can function over
the required temperature range.
Offset Binary
2
0 000 0000
0 100 0000
0 100 0001
0 100 1010
0 101 1001
0 111 0010
1 000 1011
1 010 0100
1 011 1101
1 011 1111
1 111 1111
Nulling Out Temperature Errors
The ADT7466 automatically nulls out temperature
measurement errors due to series resistance, but systematic
errors in the temperature measurement can arise from a
number of sources, and the ADT7466 can reduce these errors.
As CPUs run faster, it is more difficult to avoid high frequency
clocks when routing the D+, D tracks around a system board.
Even when recommended layout guidelines are followed, there
may still be temperature errors attributed to noise being
coupled onto the D+/D lines. High frequency noise generally
has the effect of giving temperature measurements that are too
high by a constant amount. The ADT7466 has temperature
offset registers at addresses 0x26 and 0x27 for the remote and
local temperature channels. A one time calibration of the
system can determine the offset caused by system board noise
and null it out using the offset registers. The offset registers
automatically add a twos complement 8-bit reading to every
temperature measurement. The LSB adds 1°C offset to the
temperature reading so the 8-bit register effectively allows
temperature offsets of up to ±128°C with a resolution of 1°C.
This ensures that the readings in the temperature measurement
registers are as accurate as possible.
Table 12. Temperature Offset Registers
Register
Description
0x24
Thermistor 1/Remote 2 offset
0x25
Thermistor 2 offset
0x26
Remote1 temperature offset
0x27
Local temperature offset
Table 13. Temperature Measurement Registers
Register
Description
0x0D
Remote temperature
0x0E
Local temperature
0x08
Extended Resolution 1
Bits 1:0 remote temperature LSBs
0x09
Extended Resolution 2
Bits 1:0 local temperature LSBs
Associated with each temperature measurement channel are
high and low limit registers. Exceeding the programmed high or
low limit causes the appropriate status bit to be set. Exceeding
either limit can also generate ALERT interrupts.
Default
0x00 (0°C)
0x00 (0°C)
0x00 (0°C)
0x00 (0°C)
Default
0x00
0x00
0x00
0x00
Table 14. Temperature Measurement Limit Registers
Register
Description
0x1A
Remote1 temperature low limit
0x1B
Remote1 temperature high limit
0x1C
Local temperature low limit
0x1D
Local temperature high limit
0x14
Thermistor 1/Remote 2 low limit
0x15
Thermistor 1/Remote 2 high limit
0x16
Thermistor 2 low limit
0x17
Thermistor 2 high limit
Default
0x00
0x7F
0x00
0x7F
0x00
0xFF
0x00
0xFF