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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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on the first four rising edges of SCLK, and the previous 10-bit  
conversion result is shifted out on the first nine falling edges  
of SCLK. After the fourth rising edge of SCLK, the new mux  
address is available; therefore, on the next edge of SCLK  
(the fourth falling edge), the analog input voltage on the  
selected mux input begins charging the RC DAC and con-  
tinues to do so until the tenth falling edge of SCLK. After this  
tenth SCLK edge, the analog input voltage is disabled from  
the RC DAC and the RC DAC begins the “hold” portion of the  
A/D conversion sequence. Also upon this tenth SCLK edge,  
control of the internal circuitry is transferred to the internal  
clock oscillator which drives the successive approximation  
logic to complete the conversion. If 16 SCLK cycles are used  
during each transfer, then there is a constraint on the mini-  
mum SCLK frequency. Specifically, there must be at least  
one rising edge on SCLK before the A/D conversion is com-  
plete. If the SCLK frequency is too low and a rising edge  
does not occur during the conversion, the chip is thrown out  
of sync with the processor and CS needs to be toggled in or-  
der to restore proper operation. If 10 SCLKs are used per  
transfer, then there is no lower frequency limit on SCLK. Also  
note that if the ADC is operated such that CS is inactive high  
between transfers, then the number of SCLK cycles per  
transfer can be anything between 10 and 16 cycles, but the  
“rising edge” constraint is still in effect if more than 10 SCLKs  
are used. (If CS stays active low for multiple transfers, the  
number of SCLK cycles must be either 10 or 16.)  
and leakage currents through the ESD protection diodes on  
the selected channel occur. These leakage currents cause  
an offset voltage to appear across any series source resis-  
tance on the selected channel. Therefore, any source resis-  
tance greater than 1 k(Motorola test condition) may induce  
errors in excess of guaranteed specifications.  
There are three tests available that verify the functionality  
of all the control logic as well as the successive approxima-  
tion comparator. These tests are performed by addressing  
$B, $C, or $D and they convert a voltage of (V + V )/2,  
ref AG  
V
, or V , respectively. The voltages are obtained internal-  
ref  
AG  
ly by sampling V or V  
ref AG  
onto the appropriate elements of  
the RC DAC during the sample phase. Addressing $B, $C, or  
$D produces an output of $200 (half scale), $000, or $3FF  
(full scale), respectively, if the converter is functioning prop-  
erly. However, deviation from these values occurs in the  
presence of sufficient system noise (external to the chip) on  
V
, V , V , or V .  
DD SS ref AG  
POWER AND REFERENCE PINS  
V
and V  
DD  
SS  
Device Supply Pins (Pins 7 and 14)  
V
is normally connected to digital ground; V  
is con-  
DD  
SS  
nected to a positive digital supply voltage. Low frequency  
(V – V ) variations over the range of 4.5 to 5.5 volts do  
DD  
SS  
not affect the A/D accuracy. (See the Operations Ranges  
Table for restrictions on V and V relative to V and  
EOC  
ref AG  
DD  
lines, as on  
End-of-Conversion Output (Pin 1)  
V
.) Excessive inductance in the V  
or V  
DD SS  
SS  
EOC goes low on the tenth falling edge of SCLK. A low-to-  
high transition on EOC occurs when the A/D conversion is  
complete and the data is ready for transfer.  
automatic test equipment, may cause A/D offsets > ± 1 LSB.  
Use of a 0.1 µF bypass capacitor across these pins is recom-  
mended.  
ANALOG INPUTS AND TEST MODES  
V
AG  
and V  
ref  
Analog Reference Voltage Pins (Pins 8 and 9)  
AN0 through AN4  
Analog Multiplexer Inputs (Pins 2 – 6)  
Analog reference voltage pins which determine the lower  
and upper boundary of the A/D conversion. Analog input volt-  
The input AN0 is addressed by loading $0 into the mux  
address register. AN1 is addressed by $1, AN2 by $2, AN3  
by $3, and AN4 by $4. Table 2 shows the input format for a  
16-bit stream. The mux features a break-before-make  
switching structure to minimize noise injection into the ana-  
log inputs. The source resistance driving these inputs must  
ages V  
produce a full scale output and input voltages  
ref  
produce an output of zero. CAUTION: The analog  
V  
AG  
input voltage must be V  
and V  
. The A/D conversion  
and V must be as  
AG  
SS  
DD  
result is ratiometric to V – V . V  
noise-free as possible to avoid degradation of the A/D  
conversion. Ideally, V and V should be single-point con-  
nected to the voltage supply driving the system’s transduc-  
ers. Use of a 0.22 µF bypass capacitor across these pins is  
strongly urged.  
ref AG ref  
ref AG  
be  
1 k.  
During normal operation, leakage currents through the  
analog mux from unselected channels to a selected channel  
MC145053  
7
MOTOROLA WIRELESS SEMICONDUCTOR  
SOLUTIONS DEVICE DATA