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參數資料
| 型號： | EVAL-AD7291SDZ |
| 廠商： | Analog Devices Inc |
| 文件頁數： | 7/29頁 |
| 文件大?。?/td> | 0K |
| 描述： | BOARD EVAL FOR AD7291 |
| 標準包裝： | 1 |
| ADC 的數量： | 8 |
| 位數： | 12 |
| 采樣率（每秒）： | 22.22k |
| 數據接口： | I²C |
| 已用 IC / 零件： | AD7291 |
| 已供物品： | 板 |
| 相關產品： | AD7291BCPZ-RL7-ND - IC ADC I2C/SRL 22.22K 20LFCSP AD7291BCPZ-ND - IC ADC 12BIT SAR 8CH 20-LFCSP |
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AD7291
Data Sheet
Rev. B | Page 14 of 28
Temperature Value Format
VDRIVE
One LSB of the ADC corresponds to 0.25°C. The temperature
reading from the ADC is stored in a 12-bit twos complement
format, to accommodate both positive and negative tempera-
ture measurements. Sample temperature values are listed in
Table 7. The temperature conversion formulas are as follows:
VDRIVE controls the voltage at which the serial interface operates.
VDRIVE allows the ADC to easily interface to both 1.8 V and 3 V
processors. For example, if the AD7291 is operated with a VDD
of 3.3 V, the VDRIVE pin can be powered from a 1.8 V supply.
This enables the AD7291 to operate with a larger dynamic
range with a VDD of 3.3 V while still being able to interface to
1.8 V processors. Take care to ensure that VDRIVE does not
Ratings section).
Positive Temperature = ADC Code/4
Negative Temperature = (4096 ADC Code)/4
The previous formulae are for a VREF of 2.5 V only. If an
external reference is used, the temperature sensor requires an
external reference of between 2 V and 2.5 V for correct
operation. The temperature results (in Celsius) are calculated
using the following formula, where VEXT_REF is the value of the
external reference voltage.
THE INTERNAL OR EXTERNAL REFERENCE
The AD7291 can operate with either the internal 2.5 V on-chip
reference or an externally applied reference. The EXT_REF bit
in the command register is used to determine whether the
internal reference is used. If the EXT_REF bit is selected in the
command register, an external reference can be supplied
through the VREF pin. On power-up, the internal reference is
enabled. Suitable external reference sources for the AD7291
15
.
273
3
.
109
10
_
+
=
ADCCode
V
e
Temperatur
REF
EXT
Table 7. Temperature Data Format
Temperature (°C)
Digital Output
The internal reference circuitry consists of a 2.5 V band gap
reference and a reference buffer. When the AD7291 operates in
internal reference mode, the 2.5 V internal reference is available
at the VREF pin, which should be decoupled to GND1 using a
10 μF capacitor. It is recommended that the internal reference
be buffered before applying it elsewhere in the system.
40
1111 0110 0000
25
1111 1001 1100
10
1111 1101 1000
0.25
1111 1111 1111
0
0000 0000 0000
+0.25
0000 0000 0001
+10
0000 0010 1000
The internal reference is capable of sourcing up to 2 mA of
current when the converter is static. The reference buffer
requires 5.5 ms to power up and charge the 10 μF decoupling
capacitor during the power-up time.
+25
0000 0110 0100
+50
0000 1100 1000
+75
0001 0010 1100
+100
0001 1001 0000
RESET
+105
0001 1010 0100
The AD7291 includes a reset feature, which can be used to reset
the device and the content of all internal registers including the
command register to their default state. To activate the reset
operation, the PD/RST pin should be brought low for a
minimum of 1 ns and a maximum of 100 ns and be asynchronous
to the clock; therefore, it can be triggered at any time. If the PD/
RST pin is held low for greater than 100 ns, the part enters full
power-down mode. It is imperative that the PD/RST pin be held
at a stable logic level at all times to ensure normal operation.
+125
0001 1111 0100
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