参数资料
型号: XE8801AMI000WP
厂商: Semtech
文件页数: 18/135页
文件大小: 0K
描述: SENSING MACHINE WITH 16 + 10 BIT
标准包装: 558
系列: XE880x
应用: 感测机
核心处理器: Coolrisc816?
程序存储器类型: 闪存(22 kB)
控制器系列: XE8000
RAM 容量: 512 x 8
接口: UART,USRT
输入/输出数: 24
电源电压: 2.4 V ~ 5.5 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 模具
包装: 托盘
配用: XE8000MP-ND - PROG BOARD AND PROSTART2 CARD
其它名称: Q2722595
Semtech 2005
www.semtech.com
16-29
XE8801A – SX8801R
Supply
GAIN = 1
GAIN =5
GAIN = 10
GAIN = 20
GAIN =100
Unit
VDD = 5V
79
78
100
99
97
dB
VDD = 3V
72
79
90
86
dB
Table 16-29 PSRR (n = 16 bits, VIN = VREF = 2.5V, fS = 500kHz)
16.9
Application Hints
16.9.1
Input Impedance
The PGAs of the acquisition chain employ switched-capacitor techniques. For this reason, while a conversion is
done, the input impedance on the selected channel of the PGAs is inversely proportional to the sampling frequency
fS and to stage gain as given in equation 22.
gain
f
Hz
Z
s
in
9
10
768
(Eq. 22)
The input impedance observed is the input impedance of the first PGA stage that is enabled or the input impedance
of the ADC if all three stages are disabled.
PGA1 (with a gain of 10), PGA2 (with a gain of 10) and PGA3 (with a gain of 10) each have a minimum input
impedance of 150k
at f
S = 512kHz (see Specification Table). Larger input impedance can be obtained by reducing
the gain and/or by reducing the sampling frequency. Therefor, with a gain of 1 and a sampling frequency of 100kHz,
Zin > 7.6M.
The input impedance on channels that are not selected is very high (>100M
).
16.9.2
PGA Settling or Input Channel Modifications
PGAs are reset after each writing operation to registers RegAcCfg1-5. Similarly, input channels are switched after
modifications of AMUX[4:0] or VMUX. To ensure precise conversion, the ADC must be started after a PGA or inputs
common-mode stabilization delay. This is done by writing bit START several cycles after PGA settings modification or
channel switching. Delay between PGA start or input channel switching and ADC start should be equivalent to OSR
(between 8 and 1024) number of cycles. This delay does not apply to conversions made without the PGAs.
If the ADC is not settled within the specified period, there is most probably an input impedance problem (see
previous section).
16.9.3
PGA Gain & Offset, Linearity and Noise
Hereafter are a few design guidelines that should be taken into account when using the ZoomingADC
:
1)
Keep in mind that increasing the overall PGA gain, or "zooming" coefficient, improves linearity but degrades
noise performance.
2)
Use the minimum number of PGA stages necessary to produce the desired gain ("zooming") and offset.
Bypass unnecessary PGAs.
3)
For high gains (>50), use PGA stage 1. For low gains (<50) use stages 2 and 3.
4)
For the lowest noise, set the highest possible gain on the first (front) PGA stage used in the chain. For
example, in an application where a gain of 20 is needed, set the gain of PGA2 to 10, set the gain of PGA3
to 2.
Not
Recommended
for
New
Designs
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