欢迎访问ic37.com |
会员登录 免费注册
发布采购

ML2281CCS 参数 Datasheet PDF下载

ML2281CCS图片预览
型号: ML2281CCS
PDF下载: 下载PDF文件 查看货源
内容描述: 与多路复用器选项串行I / O 8位A / D转换器 [Serial I/O 8-Bit A/D Converters with Multiplexer Options]
分类和应用: 转换器复用器光电二极管
文件页数/大小: 26 页 / 411 K
品牌: MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
 浏览型号ML2281CCS的Datasheet PDF文件第10页浏览型号ML2281CCS的Datasheet PDF文件第11页浏览型号ML2281CCS的Datasheet PDF文件第12页浏览型号ML2281CCS的Datasheet PDF文件第13页浏览型号ML2281CCS的Datasheet PDF文件第15页浏览型号ML2281CCS的Datasheet PDF文件第16页浏览型号ML2281CCS的Datasheet PDF文件第17页浏览型号ML2281CCS的Datasheet PDF文件第18页  
ML2281, ML2282, ML2284, ML2288  
REFERENCE  
The signal at the analog input is sampled during the interval  
when the sampling switch is closed prior to conversion  
start. The sampling window (S/H acquisition time) is 1/2  
CLK period wide and occurs 1/2 CLK period before DO  
goes from high impedance to active low state. When the  
sampling switch closes at the start of the S/H acquisition  
time, 8pF of capacitance is thrown onto the analog input.  
1/2 CLK period later, the sampling switch is opened and the  
signal present at the analog input is stored. Any error on the  
analog input at the end of the S/H acquisition time will  
cause additional conversion error. Care should be taken to  
allow adequate charging or settling time from the source.  
If more charging or settling time is needed to reduce these  
analog input errors, a longer CLK period can be used.  
The voltage applied to the reference input to these  
converters defines the voltage span of the analog input  
(the difference between V  
and V ) over which  
IN MIN  
IN MAX  
the 256 possible output codes apply. The devices can be  
used in either ratiometric applications or in systems  
requiring absolute accuracy. The reference pin must be  
connected  
to a voltage source capable of driving the reference input  
resistance, typically 10k. This pin is the top of a resistor  
divider string used for the successive approximation  
conversion.  
In a ratiometric system, the analog input voltage is  
proportional to the voltage used for the A/D reference.  
This voltage is typically the system power supply, so the  
The ML2281X family has improved latchup immunity.  
Each analog input has dual diodes to the supply rails, and  
a minimum of ±25mA (±100mA typically) can be injected  
into each analog input without causing latchup.  
V
pin can be tied to V . This technique relaxes the  
REF  
CC  
stability requirements of the system reference as the analog  
input and A/D reference move together maintaining the  
same output code for a given input condition.  
DYNAMIC PERFORMANCE  
Signal-to-Noise-Ratio  
For absolute accuracy, where the analog input varies  
between specific voltage limits, the reference pin can be  
biased with a time and temperature stable voltage source.  
Signal-to-noise ration (SNR) is the measured signal-to-noise  
at the output of the converter. The signal is the RMS  
magnitude of the fundamental. Noise is the RMS sum of all  
the nonfundamental signals up to half the sampling  
frequency. SNR is dependent on the number of quantization  
levels used in the digitization process; the more levels, the  
smaller the quantization noise. The theoretical SNR for a  
sine wave is given by  
The maximum value of the reference is limited to the V  
CC  
supply voltage. The minimum value, however, can be quire  
small to allow direct conversion of inputs with less than 5V  
of voltage span. Particular care must be taken with regard to  
noise pickup, circuit layout and system error voltage sources  
when operating with a reduced span due to the increased  
sensitivity of the converter.  
SNR = (6.02N + 1.76)dB  
ANALOG INPUTS AND SAMPLE/HOLD  
where N is the number of bits. Thus for ideal 8-bit converter,  
SNR = 49.92dB.  
An important feature of the ML2281 family of devices is that  
they can be located at the source of the analog signal and  
then communicate with a controlling µP with just a few  
wires. This avoids bussing the analog inputs long distances  
and thus reduces noise pickup on these analog lines.  
However, in some cases, the analog inputs have a large  
common mode voltage or even some noise present along  
with the valid analog signal.  
Harmonic Distortion  
Harmonic distortion is the ratio of the RMS sum of  
harmonics to the fundamental. Total harmonic distortion  
(THD) of the ML2281 Series is defined as  
2
2
2
2
V
+ V + V + V  
3 4 5  
The differential input of these converters reduces the effects  
of common mode input noise. Thus, if a common mode  
voltage is present on both “+” and “–” inputs, such as 60Hz,  
the converter will reject this common mode voltage since it  
only converts the difference between “+” and “–” inputs.  
2
THD = 20log  
V
1
where V is the RMS amplitude of the fundamental and V ,  
V , V , V are the RMS amplitudes of the individual  
1
5
2
3
4
harmonics.  
The ML2281 family have a true sample and hold circuit  
which samples both “+” and “–” inputs simultaneously. This  
simultaneous sampling with a true S/H will give common  
mode rejection and AC linearity performance that is superior  
to devices where the two input terminals are not sampled at  
the same instant and where true sample and hold capability  
does not exist. Thus, the ML2281 family of devices can  
reject AC common mode signals from DC-50kHz as well as  
maintain linearity for signals from DC-50kHz.  
Intermodulation Distortion  
With inputs consisting of sine waves at two frequencies, f  
and f , any active device with nonlinearities will create  
distortion products, of order (m + n), at sum and difference  
frequencies of mf + nf , where m, n = 0, 1, 2, 3… .  
Intermodulation terms are those for which m or n is not  
equal to zero. The (IMD) intermodulation distortion  
specification includes the second order terms (f + f ) and  
(f – f ) and the third order terms (2f + f ), (2f – f ),  
A
B
A
B
A
A
B
A
A
B
A
B
B
(f + 2f ) and (f – 2f ) only.  
B
A
B
14