We used the crystal specs mentioned in the datasheet for the 920719.
| Parameter | Symbol | Conditions | Minimum | Typical | Maximum | Unit |
| Output frequency | Foscout | – | – | 32.768 | – | kHz |
| Frequency tolerance | – | Crystal-dependent | – | 100 | – | ppm |
| Start-up time | Tstartup | – | – | 500 | – | ms |
| XTAL drive level | Pdrv | For crystal selection | – | – | 0.5 | μW |
| XTAL series resistance | Rseries | For crystal selection | – | – | 70 | kΩ |
| XTAL shunt capacitance | Cshunt | For crystal selection | – | – | 2.2 | pF |
| External AC Input Amplitude | VIN (AC) | Ccouple = 100 pF;
Rbias= 10 Mohm | 400 | – | – | mVpp |
We actually used a 20 PPM industrial temp grade XTL and the frequency turned out 60ppm to the high side. By increasing the caps which didn't meet the XTL specs, I got it on frequency but now the startup time is about 1.5secs. I even tried removing the 10MΩ feedback resistor which sped it up some since this increased gain but this isn't right. I am sampling lower ESR XTLs now.
Can someone tell me what the part number is for the 32.768KHz XTL used on the EVB? The markings on the part don't help. The EVB came with a schematic but no BOM.
Thanks,
Rex
