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| 型号： | NCT75DR2G |
| 厂商： | ON Semiconductor |
| 文件页数： | 5/15页 |
| 文件大小： | 181K |
| 描述： | IC SENSOR TEMP DGTL 8SOIC |
| 标准包装： | 1 |
| 功能： | 温度监控系统（传感器） |
| 传感器类型： | 内部 |
| 感应温度： | -55°C ~ 125°C |
| 精确度： | ±3°C |
| 拓扑： | ADC（三角积分型），控制逻辑，寄存器库 |
| 输出类型： | 2 线串行，I²C?/SMBUS? |
| 输出警报： | 是 |
| 输出风扇： | 无 |
| 电源电压： | 3 V ~ 5.5 V |
| 工作温度： | -55°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SOICN |
| 包装： | 标准包装 |
| 其它名称： | NCT75DR2GOSDKR |
NCT75
http://onsemi.com
5
APPLICATION INFORMATION
Functional Description
The NCT75 temperature sensor converts an analog
temperature measurement to a digital representation by
using an on-chip measurement transistor and a 12 bit
Delta-Sigma ADC.
The device includes an open drain ALERT
output which
can be used to signal that the programmed temperature limit
has been exceeded.
The two main modes of operation are normal and
shutdown mode. In normal mode the NCT75 performs
a new temperature conversion every 80 ms. This new value
is then updated to the temperature value register
(address 0x00) and also compared to the T
OS
register limit
(default = 80癈). If the temperature value register is read
during the conversion sequence the value returned is the
previously stored value. A bus read does not affect the
conversion that is in progress.
In shutdown mode temperature conversion is disabled and
the temperature value register holds the last valid
temperature reading. The NCT75 can still be communicated
with in this mode as the interface is still active. The device
mode is controlled via bit 0 of the configuration register.
While in shutdown mode a conversion can be initiated by
writing an arbitrary value to the one-shot register (0x04).
This has the effect of powering up the NCT75, performing
a conversion, comparing the new temperature with the
programmed limit and then going back into shutdown mode.
The OS
/ALERT
pin can be configured in many ways to
allow it to be used in many different system configurations.
The overtemperature output can be configured to operate
as a comparator type output (which is self clearing once the
temperature has returned below the hysteresis value) or an
interrupt type output (which requires the master to read an
internal register AND the temperature to return below the
hysteresis value before going into an inactive state). The
ALERT
pin can also be configured as an active high or active
low output.
Temperature Measurement Results
The results of the on chip temperature measurements are
stored in the temperature value register and compared with
the T
OS
and T
HYST
limit register.
The temperature value, T
OS
and T
HYST
registers are
16 bits wide and have a resolution of 0.0625癈. The data is
stored as a 12 bit 2s complement word. The data is left
justified, D15 is the MSB and is the sign bit. The four LSBs
(D3 to D0) are always 0 as they are not part of the result.
While the ADC of the NCT75 can theoretically measure
temperatures in the range of 128癈 to 127癈, the NCT75
is guaranteed to measure from 55癈 to +125癈.
Table 6 shows the relevant temperature bits for a 12 bit
temperature reading. A 2-byte read is required to obtain the
full 12 bit temperature reading. If an 8 bit (1癈 resolution)
reading is required then a single byte read is sufficient.
Table 6. 12-BIT TEMPERATURE DATA FORMAT
Temperature
Binary Value
D15 to D4
Hex Value
55癈
1100 1001 0000
0xC90
25癈
1110 0111 0000
0xE70
0.0625癈
1111 1111 1111
0xFFF
0癈
0000 0000 0000
0x000
+0.0625癈
0000 0000 0001
0x001
+25癈
0001 1001 0000
0x190
+75.25癈
0100 1011 0100
0x4B4
+100癈
0110 0100 0000
0x640
+125癈
0111 1101 0000
0x7D0
Temperature Data Conversion
12-bit Temperature Data Format
Positive Temperature = ADC Code (decimal)/16
Example 190h = 400d/16 = +25?/SPAN>C
Negative Temperature = (ADC Code(decimal) 4096)/16
Example E70h = (3696d 4096)/16 = 25?/SPAN>C
One-shot Mode
One of the features of the NCT75 is a One-shot
Temperature Measurement Mode. This mode is useful if
reduced power consumption is a design requirement.
To enable one-shot mode bit 5 of the configuration
register needs to be set. Once, enabled, the NCT75 goes
immediately into shutdown mode. Here, the current
consumption is reduced to a typical value of 3 mA. Writing
address 0x04 to the address pointer register initiates a
one-shot temperature measurement. This powers up the
NCT75, carries out a temperature measurement, and then
powers down again. The data written to this register is
irrelevant and is not stored. It is the write operation that
causes the one-shot conversion.
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