ADM1034ARQZ-REEL View Datasheet(PDF) - ON Semiconductor
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ADM1034ARQZ-REEL Datasheet PDF : 39 Pages
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ADM1034
Table 4. Temperature Data Format − (Local
Temperature and Remote Temperature High Bytes)
Temperature (5C)
Digital Output
−64°C
−40°C
−32°C
−2°C
−1°C
0°C
1°C
2°C
10°C
20°C
50°C
75°C
100°C
125°C
150°C
191°C
0000 0000
0001 1000
0010 0000
0011 1110
0011 1111
0100 0000
0100 0001
0100 0010
0100 1010
0101 0100
0111 0010
1000 1011
1010 0100
1011 1101
1101 0110
1111 1111
Table 5. Local and Remote Sensor Extended
Resolution
Extended Resolution (5C)
Temperature Low Bits
0.0000
0.03125
0.0625
0.125
0.250
0.375
0.500
0.625
0.750
0.875
00000
00001
00010
00100
01000
01100
10000
10100
11000
11100
Temperature (°C) = (MSB − 64°C) + (LSB x 0.03125)
Example: MSB = 0101 0100 = 84d
LSB = 11100 = 28
Temperature °C = (84 – 64) + (28 x 0.03125) = 20.875
Remote Temperature Measurement
The ADM1034 can measure the temperature of two
external diode sensors or diode−connected transistors, which
are connected to Pins 9 and 10 and Pins 11 and 12. These pins
are dedicated temperature input channels. The series
resistance cancellation (SRC) feature can automatically
cancel out the effect of up to 1 kW of resistance in series with
the remote thermal diode.
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. Therefore,
the technique is unsuitable for mass production.
2N3906
ADM1034
D+
2N3904
D–
ADM1034
D+
D–
Figure 26. Measuring Temperature by Using Discreet
Transistors
The ADM1034 operates at three different currents to
measure the change in Vbe. Figure 27 shows the input signal
conditioning used to measure the output of an external
temperature sensor. It also shows the external sensor as a
substrate transistor, provided for temperature monitoring on
some microprocessors. The external sensor could work
equally well as a discrete transistor.
If a discrete transistor is used, the collector is not grounded,
and should be linked to the base. If a PNP transistor is used,
the base is connected to the D− input and the emitter to the D+
input. If an NPN transistor is used, the emitter is connected to
the D− input and the base to the D+ input.
If the sensor is used in a very noisy environment, a
capacitor value up to 1000 pF may be placed between the D+
and D− inputs to filter the noise. However, additional
parasitic capacitance on the lines between D+, D−, and the
thermal diode should also be considered. The total
capacitance should never be greater than 1000 pF.
To measure each DVbe, the sensor is switched between
operating currents of I, (N1 x I), and (N2 x I). The resulting
waveform is passed through a 65 kHz low−pass filter to
remove noise, then to a chopper−stabilized amplifier that
amplifies and rectifies the waveform. This produces a dc
voltage proportional to DVbe. These voltage measurements
determine the temperature of the thermal diode, while
automatically compensating for any series resistance on the
D+ and/or D− lines. The temperature is stored in two
registers as a 13−bit word.
To further reduce the effects of noise, digital filtering is
performed by averaging the results of 16 measurement cycles
at conversion rates of less than or equal to 8 Hz. An external
temperature measurement takes nominally 32 ms when
averaging is enabled and 6 ms when averaging is disabled.
One LSB of the ADC corresponds to 0.03125°C. The
ADM1034 can theoretically measure temperatures from
−64°C to +191.96875°C, although these are outside its
operating range. The extended temperature resolution data
format is shown in Table 5. The data for the local and remote
channels is stored in the extended temperature resolution
registers (Reg. 0x40 = Local, Reg. 0x42 = Remote 1, and
Reg. 0x44 = Remote 2).
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