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| 型号： | MIC281-7YM6 TR |
| 厂商： | Micrel Inc |
| 文件页数： | 11/14页 |
| 文件大小： | 657K |
| 描述： | IC SUPERVISOR THERMAL SOT23-6 |
| 标准包装： | 3,000 |
| 系列： | IttyBitty® |
| 功能： | 温度监控系统（传感器） |
| 传感器类型： | 外部 |
| 感应温度： | 外部传感器 |
| 精确度： | ±3°C（最小值） |
| 拓扑： | ADC，寄存器库 |
| 输出类型： | I²C?/SMBus? |
| 输出警报： | 无 |
| 输出风扇： | 无 |
| 电源电压： | 3 V ~ 3.6 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | SOT-23-6 |
| 供应商设备封装： | SOT-23-6 |
| 包装： | 带卷 (TR) |
| 其它名称： | MIC281-7YM6TR MIC281-7YM6TR-ND |
icrel, Inc.
MIC281
pril 23, 2014
11
Revision 2.0
Application Information
Remote Diode Section
Most small-signal PNP transistors with characteristics
similar to the JEDEC 2N3906 will perform well as remote
temperature sensors. Table 4 lists several examples of
such parts that Micrel has tested for use with the MIC281.
Other transistors equivalent to these should also work well.
Table 4. Transistors suitable for use as remote diodes
Vendor
Part
Number
Package
Fairchild Semiconductor
MMBT3906
SOT-23
On Semiconductor
MMBT3906L
SOT-23
Philips Semiconductor
SMBT3906
SOT-23
Samsung Semiconductor
KST3906-TF
SOT-23
Minimizing Errors
Self-Heating
One concern when using a part with the temperature
accuracy and resolution of the MIC281 is to avoid errors
induced by self-heating (V
DD
?I
DD
) + (V
OL
?I
OL
). In order to
understand what level of error this might represent, and
how to reduce that error, the dissipation in the MIC281
must be calculated and its effects reduced to a
temperature offset. The worst-case operating condition for
the MIC281 is when V
DD
= 3.6V.The maximum power
dissipated in the part is given in the following equation:
P
D
= [(I
DD
?V
DD
)+(I
OL(DATA)
?V
OL(DATA)
)]
P
D
= [(0.4mA?3.6V)+(6mA?0.5V)]
P
D
= 4.44mW
R
?J-A)
of SOT23-6 package is 230癈/W, therefore the
theoretical maximum self-heating is:
4.44mW ?230癈/W = 1.02癈
In most applications, the DATA pin will have a duty cycle
of substantially below 25% in the low state. These
considerations, combined with more typical device and
application parameters, give a better system-level view of
device self-heating. This is illustrated by the next equation.
In any application, the best approach is to verify
performance against calculation in the nal application
environment. This is especially true when dealing with
systems for which some temperature data may be poorly
dened or unobtainable except by empirical means.
P
D
= [(I
DD
?V
DD
)+(I
OL(DATA)
?V
OL(DATA)
)]
P
D
= [(0.23mA? 3.3V)+(25% ? 1.5mA? 0.15V)] PD =
0.815mW
R
?J-A)
of SOT23-6 package is 230癈/W, therefore the
typical self-heating is:
0.815mW ?230癈/W = 0.188癈
Series Resistance
The operation of the MIC281 depends upon sensing the
V
CB-E
of a diode-connected PNP transistor (diode) at two
different current levels. For remote temperature
measurements, this is done using an external diode
connected between T1 and ground. Because this
technique relies upon measuring the relatively small
voltage difference resulting from two levels of current
through the external diode, any resistance in series with
the external diode will cause an error in the temperature
reading from the MIC281. A good rule of thumb is that for
each ohm in series with the external transistor, there will
be a 0.9癈 error in the MIC281s temperature
measurement. It is not difcult to keep the series
resistance well below an ohm (typically <0.1&), so this will
rarely be an issue.
Filter Capacitor Selection
It is usually desirable to employ a lter capacitor between
the T1 and GND pins of the MIC281. The use of this
capacitor is recommended in environments with a lot of
high frequency noise (such as digital switching noise), or if
long traces or wires are used to connect to the remote
diode. The recommended total capacitance from the T1
pin to GND is 2200pF. If the remote diode is to be at a
distance of more than six-to-twelve inches from the
MIC281, using twisted pair wiring or shielded microphone
cable for the connections to the diode can signicantly
reduce noise pickup. If using a long run of shielded cable,
remember to subtract the cables conductor-to-shield
capacitance from the 2200pF total capacitance.
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