ADT7488A(2012) Ver la hoja de datos (PDF) - ON Semiconductor
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ADT7488A Datasheet PDF : 13 Pages
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ADT7488A
current I. The currents through the temperature diode are
switched between I and N1 I, giving DVBE1, and then
between I and N2 I, giving DVBE2. The temperature can
then be calculated using the two DVBE measurements. This
method can also cancel the effect of series resistance on the
temperature measurement. The resulting DVBE waveforms
are passed through a 65 kHz low-pass filter to remove noise
and then through a chopper-stabilized amplifier to amplify
and rectify the waveform, producing a dc voltage
proportional to DVBE. The ADC digitizes this voltage, and
a temperature measurement is produced. To reduce the
effects of noise, digital filtering is performed by averaging
the results of 16 measurement cycles for low conversion
rates. Signal conditioning and measurement of the internal
temperature sensor is performed in the same manner.
VCC
I
N1 I N2 I IBIAS
REMOTE
SENSING
TRANSISTOR
D1+
C1*
D1−
BIAS
DIODE
LOW-PASS FILTER
fC = 65 kHz
*CAPACITOR C1 IS OPTIONAL. IT SHOULD ONLY BE USED IN NOISY ENVIRONMENTS.
Figure 15. Signal Conditioning for Remote Diode Temperature Sensors
VOUT+
To ADC
VOUT−
Reading Temperature Measurements
The temperature data returned is two bytes in little endian
format, that is, LSB before MSB. All temperatures can be
read together by using Command Code 0x00 with a read
length of 0x06. The command codes and returned data are
described in Table 14.
Table 14. TEMPERATURE CHANNEL COMMAND
CODES
Temp
Channel
Internal
External 1
External 2
All Temps
Command
Code
0x00
0x01
0x02
0x00
Returned Data
LSB, MSB
LSB, MSB
LSB, MSB
Internal LSB, Internal MSB;
External 1 LSB, External 1 MSB,
External 2 LSB, External 2 MSB
SST Temperature Sensor Data Format
The data for temperature is structured to allow values in
the range of 512C to be reported. Thus, the temperature
sensor format uses a twos complement, 16-bit binary value
to represent values in this range. This format allows
temperatures to be represented with approximately a
0.016C resolution.
Table 15. SST TEMPERATURE DATA FORMAT
Twos Complement
Temperature (5C)
−125
−80
−40
−20
−5
−1
0
+1
+5
+20
+40
+80
+125
LSB
1110 0000
1110 1100
1111 0110
1111 1011
1111 1110
1111 1111
0000 0000
0000 0000
0000 0001
0000 0100
0000 1010
0001 0100
0001 1111
MSB
1100 0000
0000 0000
0000 0000
0011 1110
1100 0000
1100 0000
0000 0000
0100 0000
0100 0000
1100 0010
0000 0000
0000 0000
0100 0000
Using Discrete Transistors
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 is
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