参数资料
型号: AD7877ACPZ-REEL7
厂商: Analog Devices Inc
文件页数: 21/45页
文件大小: 0K
描述: IC ADC 12BIT TOUCHSCREEN 32LFCSP
标准包装: 1,500
类型: 电阻
触摸面板接口: 4 线
输入数/键: 1 TSC
分辨率(位): 12 b
评估套件: 可供
数据接口: 串行,SPI?
数据速率/采样率 (SPS,BPS): 125k
电压基准: 外部,内部
电源电压: 2.7 V ~ 5.25 V
电流 - 电源: 1µA
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 32-VFQFN 裸露焊盘,CSP
供应商设备封装: 32-LFCSP-VQ
包装: 带卷 (TR)
配用: EVAL-AD7877EBZ-ND - BOARD EVALUATION FOR AD7877
Data Sheet
AD7877
Rev. D | Page 27 of 44
When the DAC output voltage is zero, it sinks the maximum
current through R1. The feedback current and, therefore, VOUT
are at their maximum. As the DAC output voltage increases, the
sink current and, thus, the feedback current decrease, and VOUT
falls. If the DAC output exceeds VREF, it starts to source current,
and VOUT has to further decrease to compensate. When the
DAC output is at full scale, VOUT is at its minimum.
Note that the effect of the DAC on VOUT is opposite in voltage
mode to that in current mode. In current mode, increasing
DAC code increases the sink current, so VOUT increases with
increasing DAC code. In voltage mode, increasing DAC code
increases the DAC output voltage, reducing the sink current.
Calculate the resistor values as follows:
1. Decide on the feedback current as before.
2. Calculate the parallel combination of R1 and R3 when the
DAC output is zero
RP = VREF/IFB
3. Calculate R2 as before, but use RP and VOUT(MAX)
R2 = RP(VOUT(MAX) VREF)/VREF
4. Calculate the change in feedback current between
minimum and maximum output voltages as before using
I = VR2(MAX)/R2 VR2(MIN)/R2
This is equal to the change in current through R1 between
zero output and full scale, which is also given by
I = current at zero current at full scale
= V/R1 (VREF V)/R1
= V/R1
5. R1 = VFS/.
6. Calculate R3 from R1 and R using
R3 = (R1 × RP)/(R1 RP)
Example:
1. VCC = 5 V and VFS = VCC. VOUT(MIN) is 20 V and VOUT(MAX) is
25 V. VREF is 1.25 V. Allow 100 A around the feedback loop.
2. RP = 1.25 V/100 A = 12.5 k.
3. R2 = 12.5 k × (25 1.25 )/1.25 = 237 k.
Use the nearest preferred value of 240 k.
4. I = 25 V/240 k 20 V/240 k = 21 A.
5. R1 = 5 V/21 A = 238 k.
Use the nearest preferred value of 250 k.
6. R3 = (180 k × 12.5 k)/(180 k 12.5 k) = 13.4 k.
Use nearest preferred value of 13 k.
The actual adjustment range using these values is 21 V to 26 V.
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