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SMD Crystal-Adapter

Posted by Circuit Labs on Sunday, November 23, 2008

064003ukThe idea for this adapter was really born out of necessity. The 24.576-MHz crystal oscillator that is used in the Audio ADC 2000, (24 bit/96 kHz, March 2001) is not (easily) available any more. A colleague who was interested in the circuit and was keen to try out the prototype realised that a 25 MHz oscillator was used at the time. In order to create useful recording material it is of course necessary to use the correct sampling frequency, 48 kHz, that is. This requires 512 times 48000 Hz, or 24.576 MHz. Fortunately this frequency is available as part of a series of oscillators from Citizen, the CSX-750FC series, to be more specific.

These oscillators are housed in a very small SMD package. We originally used the SG531P-series from Seiko Epson in the design for the A/D-converter. This comes in a kind of 8-pin DIL package. So, to nevertheless enable us to use the Citizen version, we designed a very small circuit board that adapts the SMD device with 4 pins to the footprint for the 8-pin DIP version. The connection pin order is the same. In addition, we have made the PCB also suitable for the 14-pin version (SG531P series). This requires two additional pins. These are located at pins 7 and 8 of the 14-pin package and are connected to pins 4 and 5 respectively of the 8-pin package.064003uk[3]

Pin 1 is in both cases the enable pin and pin 8 (8-pin) and 14 (14-pin) are +5 V. Pay close attention when ordering the oscillator. It so happens that there are also 3.3-V versions (CSX-750FB and FJ). You need a 5-V version for the Audio-DAC. There is also a third letter after the type number, which indicates the accuracy: C or F for 100 ppm and B for 50 ppm.

064003uk[5]If the PCB is to be used in place of an 8-pin oscillator then you can trim the board along the line that is clearly visible on the solder side of the board. The solder side (copper side) is the top side. Just to be clear: the dot on the package of the CSX750FCC is pin 1 of the oscillator. We used thin pin headers for the connections so that the small adaptor can be fitted into an IC-socket or soldered directly onto a PCB. The IC is available from Digi-Key.

Author: Ton Giesberts

(Elektor Electronics Magazine – 2006)



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