AD7291 查看數據表（PDF） - Analog Devices
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AD7291 Datasheet PDF : 28 Pages
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AD7291
Data Sheet
Table 12. Channel Selection Bits for Command Register
D15 D14 D13 D12 D11 D10 D9 D8
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
Selected Analog Input Channel
No channel selected
Convert on Channel 7 (VIN7)
Convert on Channel 6 (VIN6)
Convert on Channel 5 (VIN5)
Convert on Channel 4 (VIN4)
Convert on Channel 3 (VIN3)
Convert on Channel 2 (VIN2)
Convert on Channel 1 (VIN1)
Convert on Channel 0 (VIN0)
Comments
If more than one channel is
selected, the AD7291 converts the
selected channels starting with the
lowest channel in the sequence.
Table 13. TSENSE Data Format
Input
D11 (MSB)
D10
D9
D8 D7 D6 D5 D4 D3 D2 D1
D0 (LSB)
Value (°C)
−512
+256 +128 +64 +32 +16 +8 +4 +2 +1 +0.5 +0.25
Sample Delay and Bit Trial Delay
Ideally, no I2C bus activity must occur while an ADC conversion is
taking place. However, this cannot be possible, for example, when
operating in autocycle mode. It is therefore recommended to
enable the noise delayed bit trial and sampling function by writing
a 1 to Bit D5 in the command register. This mechanism delays
critical sample intervals and bit trials while there is activity on
the I2C bus. This results in a quiet period for each bit decision,
and conversion results are less susceptible to interference from
external noise.
On power-up, the bit trial and sample interval delay mechanism
is not enabled. It is recommended that this feature must be
enabled for normal operation. When enabled, the AD7291
delays the bit trials, mitigating against the effect of activity on
the I2C bus. In cases where there is excessive activity on the
interface lines, enabling these bits can cause the overall
conversion time to increase.
The AD7291 also incorporates functionality that allows it to
reject glitches shorter than 50 ns. This feature improves the
noise susceptibility of the device.
VOLTAGE CONVERSION RESULT REGISTER (0x01)
The voltage conversion result register is a 16-bit read-only
register that stores the conversion result from the ADC in
straight binary format. A 2-byte read is necessary to read data
from this register. Table 14 and Table 15 show the contents of
the first and second bytes of data to be read from the AD7291.
Each AD7291 conversion result consists of four channel address
bits (see Table 14 and Table 15) and the 12-bit data result.
Bit D15 to Bit D12 are the channel address bits that identify
the ADC channel that corresponds to the subsequent result.
Bit D11 to Bit D0 contain the most recent ADC result.
Table 14. Conversion Value Register (First Read)
MSB
D15 D14 D13 D12 D11 D10 D9 D8
ADD3 ADD2 ADD1 ADD0 B11 B10 B9 B8
Table 15. Conversion Value Register (Second Read)
LSB
D7 D6 D5 D4 D3 D2 D1 D0
B7 B6 B5 B4 B3 B2 B1 B0
Table 16. Channel Address Bits for the Result Register
ADD2 ADD2 ADD1 ADD0 Analog Input Channel
0
0
0
0
VIN0
0
0
0
1
VIN1
0
0
1
0
VIN2
0
0
1
1
VIN3
0
1
0
0
VIN4
0
1
0
1
VIN5
0
1
1
0
VIN6
0
1
1
1
VIN7
1
0
0
0
TSENSE
1
0
0
1
TSENSE average result
Temperature Value Format
The temperature reading from the ADC is stored in an 11-bit
twos complement format, D11 to D0, to accommodate both
positive and negative temperature measurements. The tem-
perature data format is provided in Table 13.
TSENSE CONVERSION RESULT REGISTER (0x02)
The TSENSE result register is a 16-bit read-only register used to
store the ADC data generated from the internal temperature
sensor. This register stores the temperature readings from the
ADC in a 12-bit twos complement format, D11 to D0, and
uses Bit D15 to Bit D12 to store the channel address bits.
Conversions take place approximately every 5 ms. Table 13
details the temperature data format that applies to the internal
temperature sensor.
Rev. C | Page 18 of 28
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