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参数资料
| 型号： | MPC5604PEF0MLL6 |
| 厂商： | FREESCALE SEMICONDUCTOR INC |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 32-BIT, FLASH, 64 MHz, MICROCONTROLLER, PQFP100 |
| 封装： | 14 X 14 MM, 1.40 MM HEIGHT, 0.50 MM PITCH, ROHS COMPLIANT LQFP-100 |
| 文件页数： | 65/99页 |
| 文件大小： | 1130K |
| 代理商： | MPC5604PEF0MLL6 |
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MPC5604P Microcontroller Data Sheet, Rev. 7
Freescale Semiconductor
68
In this case, the time constant depends on the external circuit: in particular imposing that the transient is completed
well before the end of sampling time TS, a constraints on RL sizing is obtained:
Eqn. 9
Of course, RL shall be sized also according to the current limitation constraints, in combination with RS (source
impedance) and RF (filter resistance). Being CF definitively bigger than CP1, CP2 and CS, then the final voltage VA2
(at the end of the charge transfer transient) will be much higher than VA1. Equation 10 must be respected (charge
balance assuming now CS already charged at VA1):
Eqn. 10
The two transients above are not influenced by the voltage source that, due to the presence of the RFCF filter, is not able to
provide the extra charge to compensate the voltage drop on CS with respect to the ideal source VA; the time constant RFCF of
the filter is very high with respect to the sampling time (TS). The filter is typically designed to act as anti-aliasing.
Figure 17. Spectral representation of input signal
Calling f0 the bandwidth of the source signal (and as a consequence the cut-off frequency of the anti-aliasing filter, fF),
according to the Nyquist theorem the conversion rate fC must be at least 2f0; it means that the constant time of the filter is greater
than or at least equal to twice the conversion period (TC). Again the conversion period TC is longer than the sampling time TS,
which is just a portion of it, even when fixed channel continuous conversion mode is selected (fastest conversion rate at a
specific channel): in conclusion it is evident that the time constant of the filter RFCF is definitively much higher than the
sampling time TS, so the charge level on CS cannot be modified by the analog signal source during the time in which the
sampling switch is closed.
The considerations above lead to impose new constraints on the external circuit, to reduce the accuracy error due to the voltage
drop on CS; from the two charge balance equations above, it is simple to derive Equation 11 between the ideal and real sampled
voltage on CS:
10
2
10 RL CS CP1 CP2
++
=TS
VA2 CS CP1 CP2 CF
++
+
VA CF
VA1
+CP1 CP2
+CS
+
=
f0
f
Analog Source Bandwidth (VA)
f0
f
Sampled Signal Spectrum (fC = conversion Rate)
fC
f
Anti-Aliasing Filter (fF = RC Filter pole)
fF
2 f0 fC (Nyquist)
fF f0 (Anti-aliasing Filtering Condition)
TC 2 RFCF (Conversion Rate vs. Filter Pole)
Noise
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| MPC5604PEF0MLL7R | 制造商:FREESCALE 制造商全称:Freescale Semiconductor, Inc 功能描述:microcontroller units (MCUs) |
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