Thorsten , Look at the MAX038.PDF ( http://pdfserv.maxim-ic.com/arpdf/MAX038.pdf ) ... Fig. 3 ...page 12 and 13 ... pin 13 = PDI ... It's a phase detector input ... You don't think we can sync with that pin ??? I thought .... But i can be wrong ... I'm gonna try to Sync with ext. reference next week ... but i think it will work ! Best regards, Gilles