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參數(shù)資料
| 型號： | ADT7486ARMZ-REEL7 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | DIGITAL TEMP SENSOR-SERIAL, 16BIT(s), 1Cel, SQUARE, SURFACE MOUNT |
| 封裝： | LEAD FREE, PLASTIC, MO-187-BA, MSOP-10 |
| 文件頁數(shù)： | 3/16頁 |
| 文件大?。?/td> | 177K |
| 代理商： | ADT7486ARMZ-REEL7 |
Preliminary Technical Data
ADT7484/ADT7486
Rev. PrA | Page 11 of 16
TEMPERATURE MEASUREMENT
The ADT7484/ADT7486 each have two dedicated temperature
measurement channels: one for measuring the temperature of an
on-chip band gap temperature sensor, and one for measuring the
temperature of a remote diode, usually located in the CPU or GPU.
The ADT7484 monitors one local and one remote temperature
channel, whereas the ADT7486 monitors one local and two
remote temperature channels. Monitoring of each of the
channels is done in a round-robin sequence. The monitoring
sequence is in the order shown in Table 11.
Table 11. Temperature Monitoring Sequence
Channel
Number
Measurement
Conversion Time (ms)
0
Local temperature
52
1
Remote Temperature 1
52
2
Remote Temperature 2
(ADT7486 only)
52
TEMPERATURE MEASUREMENT METHOD
A simple method for measuring temperature is to exploit the
negative temperature coefficient of a diode by measuring the
base-emitter voltage (VBE) of a transistor operated at constant
current. Unfortunately, this technique requires calibration to
null the effect of the absolute value of VBE, which varies from
device to device.
The technique used in the ADT7484/ADT7486 measures the
change in VBE when the device is operated at three different
currents.
Figure 15 shows the input signal conditioning used to measure
the output of a remote temperature sensor. This figure shows
the remote sensor as a substrate transistor, which is provided for
temperature monitoring on some microprocessors, but it could
also be a discrete transistor. If a discrete transistor is used, the
collector is not grounded and should be linked to the base. To
prevent ground noise from interfering with the measurement,
the more negative terminal of the sensor is not referenced to
ground, but is biased above ground by an internal diode at the
D1 input. If the sensor is operating in an extremely noisy
environment, C1 can be added as a noise filter. Its value should
not exceed 1000 pF.
To measure ΔVBE, the operating current through the sensor is
switched between three related currents. Figure 15 shows N1 × I
and N2 × I as different multiples of the current I. The currents
through the temperature diode are switched between I and
N1 × I, giving ΔVBE1, and then between I and N2 × I, giving
ΔVBE2. The temperature can then be calculated using the two
ΔVBE measurements. This method can also cancel the effect of
series resistance on the temperature measurement. The
resulting ΔVBE 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 ΔVBE. 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.
C1*
D+
BIAS
DIODE
*CAPACITOR C1 IS OPTIONAL. IT SHOULD ONLY BE USED IN NOISY ENVIRONMENTS.
VDD
TO ADC
VOUT+
VOUT–
REMOTE
SENSING
TRANSISTOR
D–
I
N1 × I
N2 × I
IBIAS
LOW-PASS FILTER
fC =65kHz
0519
8-
00
4
Figure 15. Signal Conditioning for Remote Diode Temperature Sensors
READING TEMPERATURE MEASUREMENTS
The temperature measurement command codes are detailed in
Table 10. 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 0x04. The command codes and returned data are described
in Table 12.
Table 12. Temperature Channel Command Codes
Temp Channel
Command Code
Returned data
Internal
0x00
LSB, MSB
External 1
0x01
LSB, MSB
External 2
0x02
LSB, MSB
All Temps
0x00
Internal LSB, Internal MSB;
External 1 LSB, External 1
MSB; External 2 LSB,
External 2 MSB
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