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參數(shù)資料
| 型號： | NCT210RQR2G |
| 廠商： | ON Semiconductor |
| 文件頁數(shù)： | 7/15頁 |
| 文件大?。?/td> | 184K |
| 描述： | IC TEMP SENSOR LOC/REM 16QSOP |
| 標(biāo)準(zhǔn)包裝： | 2,500 |
| 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： | -65°C ~ 127°C |
| 精確度： | ±3°C 本地（最大），±5°C 遠(yuǎn)程（最大） |
| 拓?fù)洌?/td> | ADC（三角積分型），比較器，寄存器庫 |
| 輸出類型： | 2 線 SMBus? |
| 輸出警報： | 是 |
| 輸出風(fēng)扇： | 無 |
| 電源電壓： | 3 V ~ 5.5 V |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 16-SSOP（0.154"，3.90mm 寬） |
| 供應(yīng)商設(shè)備封裝： | 16-QSOP |
| 包裝： | 帶卷 (TR) |
NCT210
http://onsemi.com
7
Functional Description
The NCT210 contains a two-channel A-to-D converter
with special input-signal conditioning to enable operation
with remote and on-chip diode temperature sensors. When
the NCT210 is operating normally, the A-to-D converter
operates in free-running mode. The analog input multiplexer
alternately selects either the on-chip temperature sensor to
measure its local temperature or the remote temperature
sensor. These signals are digitized by the ADC and the
results stored in the local and remote temperature value
registers as 8-bit, twos complement words.
The measurement results are compared with local and
remote, high and low temperature limits, stored in four
on-chip registers. Out-of-limit comparisons generate flags
that are stored in the status register, and one or more
out-of-limit results will cause the ALERT
output to pull low.
The limit registers can be programmed and the device
controlled and configured via the serial System
Management Bus (SMBus). The contents of any register can
also be read back via the SMBus.
Control and configuration functions consist of:
" Switching the Device between Normal Operation and
Standby Mode
" Masking or Enabling the ALERT
Output
" Selecting the Conversion Rate
On initial powerup, the remote and local temperature
values default to 128癈. Since the device normally powers
up converting, a measurement of local and remote
temperature is made, and these values are then stored before
a comparison with the stored limits is made. However, if the
part is powered up in standby mode (STBY
pin pulled low),
no new values are written to the register before a comparison
is made. As a result, both RLOW and LLOW are tripped in
the status register, thus generating an ALERT
output. This
can be cleared in one of two ways.
1. Change both the local and remote lower limits to
128癈 and read the status register (which in turn
clears the ALERT
output).
2. Take the part out of standby and read the status
register (which in turn clears the ALERT
output).
This works only if the measured values are within
the limit values.
Measurement Method
A simple method of measuring temperature is to exploit
the negative temperature coefficient of a diode, or the
base-emitter voltage of a transistor, operated at constant
current. Unfortunately, this technique requires calibration to
null the effect of the absolute value of V
BE,
which varies
from device to device.
The technique used in the NCT210 is to measure the
change in V
BE
when the device is operated at two different
currents. This is given by:
(eq. 1)
DV
BE
+ kTq 1n (N)
where:
k is Boltzmanns constant.
q is the charge on the electron (1.6 ?10
19
Coulombs).
T is the absolute temperature in Kelvins.
N is the 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 temperature monitoring on some
microprocessors, but it could 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 measurement, 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, one can
optionally be added as a noise filter. Its value is typically
2,200 pF, but it should be no more than 3,000 pF. See the
Layout Considerations section for more information.
To measure DV
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, and
then to a chopper-stabilized amplifier that performs the
functions of amplification and rectification of the waveform
to produce a dc voltage proportional to DV
BE
. This voltage
is measured by the ADC to give a temperature output in
8-bit, twos complement format. To reduce the effects of
noise further, 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.
Figure 12. Input Signal Conditioning
LOW-PASS FILTER
f
C
= 65 kHz
REMOTE
SENSING
TRANSISTOR
BIAS
DIODE
D+
D
V
DD
I
BIAS
I
N ?I
V
OUT+
V
OUT
To ADC
C1*
*CAPACITOR C1 IS OPTIONAL. IT IS ONLY
NECESSARY IN NOISY ENVIRONMENTS.
C1 = 2.2 nF TYP, 3 nF MAX
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