参数资料
型号: AD7854LARSZ
厂商: Analog Devices Inc
文件页数: 7/28页
文件大小: 0K
描述: IC ADC 12BIT PARALLEL LP 28SSOP
标准包装: 47
位数: 12
采样率(每秒): 100k
数据接口: 并联
转换器数目: 2
功率耗散(最大): 30mW
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: 28-SSOP(0.209",5.30mm 宽)
供应商设备封装: 28-SSOP
包装: 管件
输入数目和类型: 1 个伪差分,单极;1 个伪差分,双极
AD7854/AD7854L
REV. B
–15–
Transfer Functions
For the unipolar range the designed code transitions occur
midway between successive integer LSB values (i.e., 1/2 LSB,
3/2 LSBs, 5/2 LSBs . . . FS – 3/2 LSBs). The output coding is
straight binary for the unipolar range with 1 LSB = FS/4096 =
3.3 V/4096 = 0.8 mV when VREF = 3.3 V. The ideal input/
output transfer characteristic for the unipolar range is shown in
Figure 14.
OUTPUT
CODE
111...111
111...110
111...101
111...100
000...011
000...010
000...001
000...000
0V 1LSB
+FS –1LSB
VIN = (AIN(+) – AIN(–)), INPUT VOLTAGE
1LSB =
FS
4096
Figure 14. AD7854/AD7854L Unipolar Transfer
Characteristic
Figure 13 shows the AD7854/AD7854L’s
±VREF/2 bipolar ana-
log input configuration. AIN(+) cannot go below 0 V, so for the
full bipolar range, AIN(–) should be biased to at least +VREF/2.
Once again the designed code transitions occur midway between
successive integer LSB values. The output coding is twos
complement with 1 LSB = 4096 = 3.3 V/4096 = 0.8 mV. The
ideal input/output transfer characteristic is shown in Figure 15.
OUTPUT
CODE
011...111
011...110
000...001
111...111
000...000
000...010
000...001
000...000
VIN = (AIN(+) – AIN(–)), INPUT VOLTAGE
1LSB =
FS
4096
0V
(VREF/2) – 1LSB
(VREF/2) + 1 LSB
VREF/2
+ FS – 1LSB
FS = VREFV
Figure 15. AD7854/AD7854L Bipolar Transfer Characteristic
Input Ranges
The analog input range for the AD7854/AD7854L is 0 V to
VREF in both the unipolar and bipolar ranges.
The only difference between the unipolar range and the bipolar
range is that in the bipolar range the AIN(–) should be biased
up to at least +VREF/2 and the output coding is twos comple-
ment (see Table V and Figures 14 and 15).
Table V. Analog Input Connections
Analog Input
Input Connections
Connection
Range
AIN(+)
AIN(–)
Diagram
0 V to VREF
1
VIN
AGND
Figure 12
±VREF/22
VIN
VREF/2
Figure 13
NOTES
1Output code format is straight binary.
2Range is
±V
REF/2 biased about VREF/2. Output code format is twos complement.
Note that the AIN(–) pin on the AD7854/AD7854L can be
biased up above AGND in the unipolar mode, or above VREF/2
in bipolar mode if required. The advantage of biasing the lower
end of the analog input range away from AGND is that the analog
input does not have to swing all the way down to AGND. Thus,
in single supply applications the input amplifier does not have to
swing all the way down to AGND. The upper end of the analog
input range is shifted up by the same amount. Care must be
taken so that the bias applied does not shift the upper end of the
analog input above the AVDD supply. In the case where the ref-
erence is the supply, AVDD, the AIN(–) should be tied to AGND
in unipolar mode or to AVDD/2 in bipolar mode.
. . .
AIN(+)
AIN(–)
VIN = 0 TO VREF
TRACK AND HOLD
AMPLIFIER
DB0
DB11
STRAIGHT
BINARY
FORMAT
AD7854/AD7854L
Figure 12. 0 to VREF Unipolar Input Configuration
2’S
COMPLEMENT
FORMAT
VREF/2
. . .
AIN(+)
AIN(–)
VIN = 0 TO VREF
TRACK AND HOLD
AMPLIFIER
DB0
DB11
AD7854/AD7854L
Figure 13.
±VREF/2 about VREF/2 Bipolar Input Configuration
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