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參數(shù)資料
| 型號： | ADM1021A |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Low-Cost Microprocessor System Temperature Monitor |
| 中文描述： | 低成本的微處理器系統(tǒng)溫度監(jiān)控 |
| 文件頁數(shù)： | 6/12頁 |
| 文件大小： | 163K |
| 代理商： | ADM1021A |
ADM1021A
–6–
REV. A
C1*
D+
D
–
REMOTE
SENSING
TRANSISTOR
I
N I
I
BIAS
V
DD
V
OUT+
TO ADC
V
OUT
–
BIAS
DIODE
LOWPASS FILTER
f
C
= 65kHz
CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS.
C1 = 2.2nF TYPICAL, 3nF MAX.
*
Figure 12. Input Signal Conditioning
The technique used in the ADM1021A is to measure the
change in V
BE
when the device is operated at two different
currents.
This is given by:
V
BE
=
KT
/
q
×
ln
(
N
)
where:
K
is Boltzmann’s constant,
q
is charge on the electron (1.6
×
10
–19
Coulombs),
T
is absolute temperature in Kelvins,
N
is ratio of the two currents.
Figure 12 shows the input signal conditioning used to measure
the output of an external temperature sensor. This figure shows
the external sensor as a substrate transistor, provided for tem-
perature monitoring on some microprocessors, but it could
equally well be a discrete transistor. If a discrete transistor is
used, the collector will not be grounded and should be linked to
the base. To prevent ground noise interfering with the measure-
ment, the more negative terminal of the sensor is not referenced
to ground, but is biased above ground by an internal diode at
the D– input. If the sensor is operating in a noisy environment,
C1 may optionally be added as a noise filter. Its value is typically
2200 pF, but should be no more than 3000 pF. See the section
on layout considerations for more information on C1.
To measure
V
BE
, the sensor is switched between operating
currents of I and N
×
I. The resulting waveform is passed through a
65 kHz low-pass filter to remove noise, then to a chopper-
stabilized amplifier that performs the functions of amplification
and rectification of the waveform to produce a dc voltage propor-
tional to
V
BE
. This voltage is measured by the ADC to give a
temperature output in 8-bit two's complement format. To fur-
ther reduce the effects of noise, digital filtering is performed by
averaging the results of 16 measurement cycles.
Signal conditioning and measurement of the internal temperature
sensor is performed in a similar manner.
DIFFERENCES BETWEEN THE ADM1021 AND THE
ADM1021A
Although the ADM1021A is pin-for-pin compatible with the
ADM1021, there are some differences between the two devices.
Below is a summary of these differences and reasons for the changes.
1. The ADM1021A forces a larger current through the remote
temperature sensing diode, typically 205
μ
A versus 90
μ
A
for the ADM1021. The main reason for this is to improve
the noise immunity of the part.
2. As a result of the greater Remote Sensor Source Current the
operating current of the ADM1021A is higher than that of
the ADM1021, typically 205 mA versus 160 mA.
3. The temperature measurement range of the ADM1021A is
0
°
C to 127
°
C, compared with –128
°
C to +127
°
C for the
ADM1021. As a result, the ADM1021 should be used if
negative temperature measurement is required.
4
The power-on-reset values of the remote and local tempera-
ture values are –128
°
C in the ADM1021A as compared with
0
°
C in the ADM1021. As the part is powered up converting
(except when the part is in standby mode, i.e., Pin 15 is
pulled low) the part will measure the actual values of remote
and local temperature and write these to the registers.
5. The four MSBs of the Revision Register may be used to
identify the part. The ADM1021 Revision Register reads
0xh and the ADM1021A reads 3xh.
6. The power-on default value of the Address Pointer Register
is undefined in the ADM1021A and is equal to 00h in the
ADM1021. As a result, a value must be written to the Address
Pointer Register before a read is done in the ADM1021A.
The ADM1021 is capable of reading back local temperature
without writing to the Address Pointer Register as it defaulted
to the local temperature measurement register at power-up.
7. Setting the mask bit (Bit 7 Config Reg) on the ADM1021A
will mask current and future ALERTs. On the ADM1021
the mask bit will only mask future ALERTs. Any current
ALERT will have to be cleared using an ARA.
TEMPERATURE DATA FORMAT
One LSB of the ADC corresponds to 1
°
C, so the ADC can
theoretically measure from –128
°
C to +127
°
C, although the
device does not measure temperatures below 0
°
C so the
actual
range is 0
°
C to 127
°
C.
The temperature data format is shown in
Table I.
The results of the local and remote temperature measurements
are stored in the local and remote temperature value registers,
and are compared with limits programmed into the local and
remote high and low limit registers.
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| ADM1021AARQ-REEL | 功能描述:IC SENSOR TEMP DUAL3/5.5V 16QSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 熱管理 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 功能:溫度監(jiān)控系統(tǒng)（傳感器） 傳感器類型:內(nèi)部和外部 感應(yīng)溫度:-40°C ~ 125°C，外部傳感器 精確度:±2.5°C 本地（最大值），±5°C 遠(yuǎn)程（最大值） 拓?fù)?ADC，比較器，寄存器庫 輸出類型:2 線 SMBus? 輸出警報(bào):無 輸出風(fēng)扇:無 電源電壓:2.7 V ~ 5.5 V 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:SOT-23-8 供應(yīng)商設(shè)備封裝:SOT-23-8 包裝:Digi-Reel® 其它名稱:296-22675-6 |
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