ADT7460ARQZ-RL7 ONSEMI [ON Semiconductor], ADT7460ARQZ-RL7 Datasheet - Page 16

• Manufacturer Part Number: ADT7460ARQZ-RL7
• Description: dBCOOL Remote Thermal Monitor and Fan Controller
• Manufacturer: ONSEMI [ON Semiconductor]

twos complement format. To further reduce the effects of
noise, digital filtering is performed by averaging the results
of 16 measurement cycles. A remote temperature
measurement takes nominally 25.5 ms. The results of
remote temperature measurements are stored in 10−bit, twos
complement format, as illustrated in Table 9. The extra
resolution for the temperature measurements is held in the
Extended Resolution Register 2 (Reg. 0x77). This gives
temperature readings with a resolution of 0.25°C.
Table 9. Temperature Data Format
1. Bold numbers denote 2 LSBs of measurement in the Extended
Table 10. Temperature Measurement Registers
Register
Resolution Register 2 (0x77) with 0.25°C resolution.
0x25
0x26
0x27
0x77
Figure 25. Measuring Temperature Using an
Temperature
Figure 26. Measuring Temperature Using a
+10.25°C
+50.75°C
+25.5°C
+100°C
+125°C
+127°C
−128°C
−125°C
−100°C
−75°C
−50°C
−25°C
−10°C
+75°C
0°C
2N3904
2N3906
NPN
PNP
Extended Resolution 2
Remote 1 temperature
Remote 2 temperature
NPN Transistor
PNP Transistor
Local temperature
Description
Digital Output (10−Bit) (Note 1)
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
D+
D–
D+
D–
ADT7460
ADT7460
Default
0x80
0x80
0x80
0x00
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ADT7460
16
Reading Temperature from the ADT7460
the ADT7460 as an 8−bit value (with 1°C resolution) or as
a 10−bit value (with 0.25°C resolution). If only 1°C
resolution is required, the temperature readings can be read
back at any time and in no particular order.
2−register read for each measurement. The extended
resolution register (Reg. 0x77) should be read first. This
causes all temperature reading registers to be frozen until all
temperature reading registers have been read from. This
prevents an MSB reading from being updated while its two
LSBs are being read, and vice versa.
Nulling Out Temperature Errors
high frequency clocks when routing the D+, D− traces
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 ADT7460 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, one 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
0.25°C offset to the temperature reading so the 8−bit register
effectively allows temperature offsets of up to ±32°C with
a resolution of 0.25°C. This ensures that the readings in the
temperature measurement registers are as accurate as
possible.
Temperature Measurement Limit Registers
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 SMBALERT
interrupts.
Table 11. Extended Resolution Temperature
Measurement Register Bits (Addr = 0x77)
Table 12. Temperature Offset Registers
<7:6>
<5:4>
<3:2>
It is important to note that temperature can be read from
If the 10−bit measurement is required, this involves a
As CPUs run faster, it becomes more difficult to avoid
Associated with each temperature measurement channel
Register
Bit
0x70
0x71
0x72
Mnemonic
TDM2
TDM1
LTMP
Remote 1 temperature offset
Remote 2 temperature offset
Local temperature offset
Description
Remote 2 temperature LSBs
Remote 1 temperature LSBs
Local temperature LSBs
Description
0x00 (0°C)
0x00 (0°C)
0x00 (0°C)
Default