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MC145053D 参数 Datasheet PDF下载

MC145053D图片预览
型号: MC145053D
PDF下载: 下载PDF文件 查看货源
内容描述: 10位A / D转换器的串行接口 [10-Bit A/D Converter a Serial Interface]
分类和应用: 转换器模数转换器光电二极管
文件页数/大小: 15 页 / 170 K
品牌: MOTOROLA [ MOTOROLA ]
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A reference circuit voltage of 5 volts is used for the applica-  
tion shown in Figure 15. However, the reference circuitry  
APPLICATIONS INFORMATION  
DESCRIPTION  
may be simplified by tying V  
the system’s positive supply. (See Figure 16.)  
to system ground and V to  
AG  
ref  
This example application of the MC145053 ADC interfaces  
four analog signals to a microprocessor.  
A bypass capacitor of approximately 0.22 µF across the  
V
and V pins is recommended. These pins are adjacent  
Figure 15 illustrates how the MC145053 is used as a cost-  
effective means to simplify this type of circuit design. Utilizing  
one ADC, four analog inputs are interfaced to a CMOS or  
NMOS microprocessor with a serial peripheral interface  
(SPI) port. Processors with National Semiconductor’s  
MICROWIRE serial port may also be used. Full duplex  
operation optimizes throughput for this system.  
ref  
AG  
on the ADC package which facilitates mounting the capacitor  
very close to the ADC.  
SOFTWARE CONSIDERATIONS  
The software flow for acquisition is straightforward. The  
four analog inputs, AN0 through AN3, are scanned by read-  
ing the analog value of the previously addressed channel  
into the MCU and sending the address of the next channel to  
be read to the ADC, simultaneously.  
The designer utilizing the MC145053 has the end-of-con-  
version signal (at pin 1) to define the conversion interval.  
EOC may be used to generate an interrupt, which is serviced  
by reading the serial data from the ADC. The software flow  
should then process and format the data.  
DIGITAL DESIGN CONSIDERATIONS  
Motorola’s MC68HC05C4 CMOS MCU may be chosen to  
reduce power supply size and cost. The NMOS MCUs may  
be used if power consumption is not critical. A V  
0.1 µF bypass capacitor should be closely mounted to the  
ADC.  
The MC145053 has the end-of-conversion (EOC) signal at  
output pin 1 to define when data is ready.  
or V  
DD  
SS  
When this ADC is used with a 16-bit (2-byte) transfer, there  
are two types of offsets involved. In the first type of offset, the  
channel information sent to the ADCs is offset by 12 bits.  
That is, in the 16-bit stream, only the first 4 bits (4 MSBs)  
contain the channel information. The balance of the bits are  
don’t cares. This results in 3 don’t-care nibbles, as shown in  
Table 2. The second type of offset is in the conversion result  
returned from the ADC; this is offset by 6 bits. In the 16-bit  
stream, the first 10 bits (10 MSBs) contain the conversion  
result. The last 6 bits are zeroes. The hexadecimal result is  
shown in the first column of Table 3. The second column  
shows the result after the offset is removed by a micro-  
processor routine. If the 16-bit format is used, the ADC can  
transfer one continuous 16-bit stream or two intermittent 8-bit  
streams.  
ANALOG DESIGN CONSIDERATIONS  
Analog signal sources with output impedances of less than  
1 kmay be directly interfaced to the ADC, eliminating the  
need for buffer amplifiers. Separate lines connect the V  
ref  
and V  
pins on the ADC with the controllers to provide  
AG  
isolation from system noise.  
Although not indicated in Figure 15, the V  
and sensor  
ref  
output lines may need to be shielded, depending on their  
length and electrical environment. This should be verified  
during prototyping with an oscilloscope. If shielding is  
required, a twisted pair or foil-shielded wire (not coax) is  
appropriate for this low frequency application. One wire of  
the pair or the shield must be V  
.
AG  
MC145053  
11  
MOTOROLA WIRELESS SEMICONDUCTOR  
SOLUTIONS DEVICE DATA