ADT7473_11 ONSEMI [ON Semiconductor], ADT7473_11 Datasheet - Page 15

• Manufacturer Part Number: ADT7473_11
• Description: dbCOOL Remote Thermal Monitor and Fan Control
• Manufacturer: ONSEMI [ON Semiconductor]

Local Temperature Measurement
gap temperature sensor whose output is digitized by the
on−chip 10−bit ADC. The 8−bit MSB temperature data is
stored in the local temperature register (0x26). Because both
positive and negative temperatures can be measured, the
temperature data is stored in Offset 64 format or twos
complement format, as shown in Table 10 and Table 11.
Theoretically, the temperature sensor and ADC can measure
temperatures from −63°C to +127°C (or −63°C to +191°C in
the extended temperature range) with a resolution of
+0.25°C. However, this exceeds the operating temperature
range of the device, so local temperature measurements
outside the ADT7473/ADT7473−1 operating temperature
range are not possible.
Table 6. Twos Complement Temperature Data Format
1. Bold numbers denote 2 LSBs of measurement in the Extended
Table 7. Extended Range, Temperature Data Format
1. Bold numbers denote 2 LSBs of measurement in the Extended
The ADT7473/ADT7473−1 contains an on−chip band
Resolution Register 2 (Register 0x77) with 0.25°C resolution.
Resolution Register 2 (Register 0x77) with 0.25°C resolution.
Temperature
Temperature
10.25°C
50.75°C
–128°C
25.5°C
–63°C
–50°C
–25°C
–10°C
100°C
125°C
127°C
–64°C
–63°C
100°C
125°C
191°C
75°C
–1°C
10°C
25°C
50°C
75°C
0°C
0°C
1°C
Digital Output (10−Bit) (Note 1)
Digital Output (10−Bit) (Note 1)
1000 0000 00 (diode fault)
1100 0001 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
0000 0000 00 (diode fault)
0000 0001 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
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15
Remote Temperature Measurement
of two remote diode sensors or diode−connected transistors
connected to Pin 10 and Pin 11 or to Pin 12 and Pin 13.
transistor operated at a constant current exhibits a negative
temperature coefficient of about −2 mV/°C. Unfortunately,
the absolute value of V
individual calibration is required to null this out, so the
technique is unsuitable for mass production. The technique
used in the ADT7473/ADT7473−1 is to measure the change
in V
currents. This is given by:
where:
k is Boltzmann’s constant.
T is the absolute temperature in Kelvin.
q is the charge on the carrier.
N is the ratio of the two currents.
measure the output of a remote temperature sensor. This
figure shows the external sensor as a substrate transistor,
provided for temperature monitoring on some micro−
processors. It could also be a discrete transistor such as a
2N3904/2N3906.
The ADT7473/ADT7473−1 can measure the temperature
The forward voltage of a diode or diode−connected
Figure 24 shows the input signal conditioning used to
DV
BE
BE
when the device is operated at three different
= kT/q x ln(N)
BE
varies from device to device and