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参数资料
| 型号： | AD7859LASZ-REEL |
| 厂商： | Analog Devices Inc |
| 文件页数： | 5/28页 |
| 文件大小： | 0K |
| 描述： | IC ADC 12BIT 8CHAN LP 44-MQFP |
| 标准包装： | 800 |
| 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： | 44-QFP |
| 供应商设备封装： | 44-MQFP（10x10） |
| 包装： | 带卷 (TR) |
| 输入数目和类型： | 8 个单端，单极；8 个单端，双极；4 个伪差分，单极；4 个伪差分，双极 |
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AD7859/AD7859L
REV. A
–13–
FINISHED
LAST
REGISTER
WRITE
OPERATION
OR
ABORT
?
YES
NO
CAL REGISTER POINTER IS
AUTOMATICALLY INCREMENTED
READ CAL REGISTER
CAL REGISTER POINTER IS
AUTOMATICALLY RESET
WRITE TO CONTROL REGISTER SETTING STCAL = 0, RDSLT1 = 1,
RDSLT0 = 0, AND CALSLT1, CALSLT0 = 00, 01, 10, 11
START
Figure 7. Flowchart for Reading from the Calibration
Registers
Adjusting the Offset Calibration Register
The offset calibration register contains 16 bits. The two MSBs
are zero and the 14 LSBs contain offset data. By changing the
contents of the offset register, different amounts of offset on the
analog input signal can be compensated for. Decreasing the
number in the offset calibration register compensates for nega-
tive offset on the analog input signal, and increasing the number
in the offset calibration register compensates for positive offset
on the analog input signal. The default value of the offset cali-
bration register is 0010 0000 0000 0000 approximately. This is
not the exact value, but the value in the offset register should be
close to this value. Each of the 14 data bits in the offset register
is binary weighted; the MSB has a weighting of 5% of the refer-
ence voltage, the MSB-1 has a weighting of 2.5%, the MSB-2
has a weighting of 1.25%, and so on down to the LSB which has
a weighting of 0.0006%. This gives a resolution of
±0.0006% of
VREF approximately. The resolution can also be expressed as
±(0.05 × V
REF)/2
13 volts. This equals
±0.015 mV, with a 2.5 V
reference. The maximum offset that can be compensated for is
±5% of the reference voltage, which equates to ±125 mV with a
2.5 V reference and
±250 mV with a 5 V reference.
Q. If a +20 mV offset is present in the analog input signal and the
reference voltage is 2.5 V, what code needs to be written to the
offset register to compensate for the offset ?
A. 2.5 V reference implies that the resolution in the offset reg-
ister is 5%
× 2.5 V/213 = 0.015 mV. +20 mV/0.015 mV =
1310.72; rounding to the nearest number gives 1311. In
binary terms this is 00 0101 0001 1111, therefore increase
the offset register by 00 0101 0001 1111.
This method of compensating for offset in the analog input sig-
nal allows for fine tuning the offset compensation. If the offset
on the analog input signal is known, there is no need to apply
the offset voltage to the analog input pins and do a system cali-
bration. The offset compensation can take place in software.
Adjusting the Gain Calibration Register
The gain calibration register contains 16 bits. The two MSBs
are zero and the 14 LSBs contain gain data. As in the offset cali-
brating register the data bits in the gain calibration register are
binary weighted, with the MSB having a weighting of 2.5% of
the reference voltage. The gain register value is effectively multi-
plied by the analog input to scale the conversion result over the
full range. Increasing the gain register compensates for a
smaller analog input range and decreasing the gain register com-
pensates for a larger input range. The maximum analog input
range that the gain register can compensate for is 1.025 times
the reference voltage, and the minimum input range is 0.975
times the reference voltage.
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