ADT7473 查看數據表（PDF） - ON Semiconductor
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ADT7473 Datasheet PDF : 74 Pages
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ADT7473
Local Temperature Measurement
The ADT7473/ADT7473−1 contains an on−chip band
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
Temperature
Digital Output (10−Bit) (Note 1)
–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 LSBs of measurement in the Extended
Resolution Register 2 (Register 0x77) with 0.25°C resolution.
Table 7. Extended Range, Temperature Data Format
Temperature
Digital Output (10−Bit) (Note 1)
–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 LSBs of measurement in the Extended
Resolution Register 2 (Register 0x77) with 0.25°C resolution.
Remote Temperature Measurement
The ADT7473/ADT7473−1 can measure the temperature
of two remote diode sensors or diode−connected transistors
connected to Pin 10 and Pin 11 or to Pin 12 and Pin 13.
The forward voltage of a diode or diode−connected
transistor operated at a constant current exhibits a negative
temperature coefficient of about −2 mV/°C. Unfortunately,
the absolute value of VBE varies from device to device and
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 VBE when the device is operated at three different
currents. This is given by:
DVBE = kT/q x ln(N)
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.
Figure 24 shows the input signal conditioning used to
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.
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