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CS5317-KS 数据表(PDF) 11 Page - Cirrus Logic |
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CS5317-KS 数据表(HTML) 11 Page - Cirrus Logic |
11 / 32 page Data Output Characteristics & Coding Format As shown in Figure 4, the CS5317 outputs its 16- bit data word in a serial burst. The data appears at the DATA pin on the rising edge of the same CLKOUT cycle in which DOUT falls. Data changes on the rising edge of CLKOUT, and can be latched on the falling edge. The CLKOUT rate is set by the CLKIN input (fclkin/2 in the CLKOR mode; fclkin*128 in the CLKG1 mode; and fclkin*256 in the CLKG2 mode). DOUT returns high after the last bit is transmitted. After trans- mitting the sixteen data bits, DATA will remain high until DOUT falls again, initiating the next data output cycle. A 3-state capability is available for bus-oriented applications. The 3-state control input is termed Data Output Enable, DOE, and is asynchronous with respect to the rest of the CS5317. If DOE is taken high at any time, even during a data burst, the DATA, DOUT and CLKOUT pins go to a high impedance state. Any data which would be output while DOE is high is lost. Power Supplies Since the A/D converter’s output is digitally fil- tered in the CS5317, the device is more forgiving and requires less attention than conventional 16- bit A/D converters to grounding and layout arrangements. Still, care must be taken at the de- sign and layout stages to apply the device properly. The CS5317 provides separate analog and digital power supply connections to isolate digital noise from its analog circuitry. Each sup- ply pin should be decoupled to its respective ground, AGND or DGND. Decoupling should be accomplished with 0.1 µF ceramic capacitors. If significant low frequency noise is present in the supplies, 10 µF tantalum capacitors are recom- mended in parallel with the 0.1 µF capacitors. The positive digital power supply of the CS5317 must never exceed the positive analog supply by more than a diode drop or the chip could be per- manently damaged. If the two supplies are de- rived from separate sources, care must be taken that the analog supply comes up first at power-up. Figure 1 shows a decoupling scheme which al- lows the CS5317 to be powered from a single set of ± 5V rails. The digital supplies are derived from the analog supplies through 10 Ω resistors to prevent the analog supply from dropping be- low the digital supply. PLL Characteristics A phase-locked loop is included on the CS5317 and is used to generate the requisite high fre- quency A/D sampling clock. A functional diagram of the PLL is shown in Figure 5. The PLL consists of a phase detector, a filter, a VCO (voltage-controlled oscillator), and a counter/di- vider. The phase detector inputs are CLKIN ( θ1) and a sub-multiple of the VCO output signal ( θ2). The inputs to the phase detector are positive-edge triggered and therefore the duty cycle of the CLKIN signal is not significant. With this type of phase detector, the lock range of the PLL is equal to the capture range and is independent of the low pass filter. The output of the phase detector is in- put to an external low pass filter. The filter characteristics are used to determine the transient response of the loop. The output voltage from the filter functions as the input control voltage to the VCO. The output of the VCO is then divided in frequency to provide an input to the phase detec- tor. The clock divider ratio is a function of the PLL mode which has been selected. Phase Detector Gain (Kd) A properly designed and operating phase-locked loop can be described using steady state linear analysis. Once in frequency lock, any phase dif- ference between the two inputs to the phase detector cause a current output from the detector during the phase error. While either the +50 µA or the -50 µA current source may be turned on, the average current flow is: CS5317 DS27F4 11 |
类似零件编号 - CS5317-KS |
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类似说明 - CS5317-KS |
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