参数资料
型号: AD7472BRZ
厂商: Analog Devices Inc
文件页数: 3/21页
文件大小: 0K
描述: IC ADC 12BIT PARALLEL 24SOIC
标准包装: 31
位数: 12
采样率(每秒): 1.5M
数据接口: 并联
转换器数目: 1
功率耗散(最大): 12mW
电压电源: 模拟和数字
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 24-SOIC(0.295",7.50mm 宽)
供应商设备封装: 24-SOIC W
包装: 管件
输入数目和类型: 1 个单端,单极
REV. B
AD7470/AD7472
–10–
CIRCUIT DESCRIPTION
CONVERTER OPERATION
The AD7470/AD7472 are 10-bit/12-bit successive approxima-
tion analog-to-digital converters based around a capacitive
DAC. The AD7470/AD7472 can convert analog input signals in
the range 0 V to VREF. Figure 2 shows a very simplified sche-
matic of the ADC. The control logic, SAR, and the capacitive
DAC are used to add and subtract fixed amounts of charge
from the sampling capacitor to bring the comparator back into a
balanced condition.
CAPACITIVE
DAC
SWITCHES
SAR
CONTROL LOGIC
COMPARATOR
OUTPUT DATA
10-/12-BIT PARALLEL
VIN
VREF
CONTROL
INPUTS
Figure 2. Simplified Block Diagram of AD7470/AD7472
Figure 3 shows the ADC during its acquisition phase. SW2 is
closed and SW1 is in Position A. The comparator is held in a
balanced condition and the sampling capacitor acquires the
signal on VIN.
COMPARATOR
VIN
CONTROL LOGIC
CAPACITIVE
DAC
AGND
2k
SW2
SW1
A
B
Figure 3. ADC Acquisition Phase
Figure 4 shows the ADC during conversion. When conversion
starts, SW2 will open and SW1 will move to position B, causing
the comparator to become unbalanced. The ADC then runs
through its successive approximation routine and brings the
comparator back into a balanced condition. When the compara-
tor is rebalanced, the conversion result is available in the SAR
register.
COMPARATOR
VIN
CONTROL LOGIC
CAPACITIVE
DAC
AGND
2k
SW2
SW1
A
B
Figure 4. ADC Conversion Phase
TYPICAL CONNECTION DIAGRAM
Figure 5 shows a typical connection diagram for the AD7470/
AD7472. Conversion is initiated by a falling edge on
CONVST.
Once
CONVST goes low, the BUSY signal goes high, and at
the end of conversion, the falling edge of BUSY is used to acti-
vate an interrupt service routine. The
CS and RD lines are then
activated in parallel to read the 10- or 12-data bits. The recom-
mended REF IN voltage is 2.5 V providing an analog input
range of 0 V to 2.5 V, making the AD7470/AD7472 a unipolar
ADC. It is recommended to perform a dummy conversion after
power-up as the first conversion result could be incorrect. This
also ensures that the part is in the correct mode of operation.
The
CONVST pin should not be floating when power is applied
as a rising edge on
CONVST might not wake up the part.
In Figure 5 the VDRIVE pin is tied to DVDD, which results in logic
output voltage values being either 0 V or DVDD. The voltage
applied to VDRIVE controls the voltage value of the output logic
signals. For example, if DVDD is supplied by a 5 V supply and
VDRIVE by a 3 V supply, the logic output voltage levels would be
either 0 V or 3 V. This feature allows the AD7470/AD7472 to
interface to 3 V parts while still enabling the ADC to process
signals at 5 V supply.
10 F
0.1 F
PARALLED
INTERFACE
2.5V*
*RECOMMENDED REF IN VOLTAGE
0V TO
REF IN
1nF
10 F
0.1 F
47 F
AD7470/
AD7472
AVDD
VDRIVE
DVDD
REF IN
DB0–
DB9 (DB11)
CS
BUSY
CONVST
RD
VIN
C/ P
ANALOG
SUPPLY
2.7V–5.25V
++
Figure 5. Typical Connection Diagram
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