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參數(shù)資料
| 型號： | LM74A |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | SPI/MICROWIRE 12-Bit Plus Sign Temperature Sensor (LM74 in Die Form) |
| 中文描述： | 的SPI / MICROWIRE的12位帶符號溫度傳感器（LM74在模具中） |
| 文件頁數(shù)： | 8/12頁 |
| 文件大?。?/td> | 605K |
| 代理商： | LM74A |
1.0 Functional Description
The LM74A temperature sensor incorporates a band-gap
type temperature sensor and 12-bit plus sign
Σ
ADC (Delta-
Sigma Analog-to-Digital Converter). Compatibility of the
LM74’s three wire serial interface with SPI and MICROWIRE
allows simple communications with common microcontrol-
lers and processors. Shutdown mode can be used to opti-
mize current drain for different applications.AManufacture’s/
Device ID register identifies the LM74A as National
Semiconductor product.
1.1 POWER UP AND POWER DOWN
The LM74A always powers up in a known state. The power
up default condition is continuous conversion mode. Imme-
diatly after power up the LM74A will output an erroneous
code until the first temperature conversion has completed.
When the supply voltage is less than about 1.6V (typical),
the LM74A is considered powered down. As the supply
voltage rises above the nominal 1.6V power up threshold,
the internal registers are reset to the power up default state
described above.
1.2 SERIAL BUS INTERFACE
The LM74A operates as a slave and is compatible with SPI
or MICROWIRE bus specifications. Data is clocked out on
the falling edge of the serial clock (SC), while data is clocked
in on the rising edge of SC. A complete transmit/receive
communication will consist of 32 serial clocks. The first 16
clocks comprise the transmit phase of communication, while
the second 16 clocks are the receive phase.
When CS is high SI/O will be in TRI-STATE
. Communica-
tion should be initiated by taking chip select (CS) low. This
should not be done when SC is changing from a low to high
state. Once CS is low the serial I/O pin (SI/O) will transmit
the first bit of data. The master can then read this bit with the
rising edge of SC. The remainder of the data will be clocked
out by the falling edge of SC. Once the 14 bits of data (one
sign bit, twelve temperature bits and 1 high bit) are transmit-
ted the SI/O line will go into TRI-STATE. CS can be taken
high at any time during the transmit phase. If CS is brought
low in the middle of a conversion the LM74A will complete
the conversion and the output shift register will be updated
after CS is brought back high.
The receive phase of a communication starts after 16 SC
periods. CS can remain low for 32 SC cycles. The LM74A
will read the data available on the SI/O line on the rising
edge of the serial clock. Input data is to an 8-bit shift register.
The part will detect the last eight bits shifted into the register.
The receive phase can last up to 16 SC periods. All ones
must be shifted in order to place the part into shutdown. A
zero in any location will take the LM74A out of shutdown.
The following codes should only be transmitted to the
LM74A:
00 hex
01 hex
03 hex
07 hex
0F hex
1F hex
any others may place the part into a Test Mode. Test Modes
are used by National Semiconductor to thoroughly test the
function of the LM74A during production testing. Only eight
bits have been defined above since only the last eight trans-
mitted are detected by the LM74A, before CS is taken HIGH.
The following communication can be used to determine the
Manufacturer’s/Device ID and then immediately place the
part into continuous conversion mode. With CS continuously
low:
Read 16 bits of temperature data
Write 16 bits of data commanding shutdown
Read 16 bits of Manufacture’s/Device ID data
Write 8 to 16 bits of data commanding Conversion Mode
Take CS HIGH.
Note that 250 ms will have to pass for a conversion to
complete before the LM74A actually transmits temperature
data.
3F hex
7F hex
FF hex
1.3 TEMPERATURE DATA FORMAT
Temperature data is represented by a 13-bit, two’s comple-
ment word with an LSB (Least Significant Bit) equal to
0.0625C:
Temperature
Digital Output
Binary
0100 1011 0000 0111
0011 1110 1000 0111
0000 1100 1000 0111
0000 0000 0000 1111
0000 0000 0000 0111
1111 1111 1111 1111
1111 0011 1000 0111
1110 0100 1000 0111
Hex
4B 07h
3E 87h
0B 87h
00 0Fh
00 07h
FF FFh
F3 87h
E4 87h
+150C
+125C
+25C
+0.0625C
0C
0.0625C
25C
55C
Note: The last two bits are TRI-STATE and depicted as one
in the table.
The first data byte is the most significant byte with most
significant bit first, permitting only as much data as neces-
sary to be read to determine temperature condition. For
instance, if the first four bits of the temperature data indicate
an overtemperature condition, the host processor could im-
mediately take action to remedy the excessive tempera-
tures.
1.4 SHUTDOWN MODE/MANUFACTURER’S ID
Shutdown mode is enabled by writing XX FF to the LM74A
as shown in
Figure 7
c. The serial bus is still active when the
LM74A is in shutdown. Current draw drops to less than 10
μA between serial communications. When in shutdown
mode the LM74A always will output 1000 0000 0000 0XX.
This is the manufacturer’s/Device ID information. The first
5-bits of the field (1000 0XXX) are reserved for manufactur-
er’s ID.
L
www.national.com
8
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相關(guān)代理商/技術(shù)參數(shù) |
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| LM74A-3MDA | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:SPI/MICROWIRE 12-Bit Plus Sign Temperature Sensor (LM74 in Die Form) |
| LM74A-5MDA | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:SPI/MICROWIRE 12-Bit Plus Sign Temperature Sensor (LM74 in Die Form) |
| LM74BX-0500 WAF | 制造商:Texas Instruments 功能描述: |
| LM74CIBP-3 | 功能描述:IC TEMP SENSOR DGTL 5-MICROSMD 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 |
| LM74CIBP-5 | 功能描述:IC TEMP SENSOR DGTL 5-MICROSMD 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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