Post Go back to editing

LTC6906 Rset selection and output frequency accuracy/stability

Category: Hardware
Product Number: LTC6906

Hi,

The datasheet of LTC6906 mentioned that the leakage current near Rset could affect output frequency accuracy of the device and recommends using a guard ring connecting to pin 5 to mitigate the issue. Can I also avoid this issue by using a smaller Rset and a higher divider ratio so that leakage current becomes less significant? The datasheet seems to suggest an Rset range between 100 k and 1 M. Will an Rset below 100 k affect reliability or output frequency accuracy/stability of the device? If power consumption is not a concern for my design, can I get better accuracy by using a small Rset (e.g 10 k) and a high divider ratio? Are there other factors that impacts output frequency (e.g. 5 V vs. 3.3 V input)?

Thank you

  • The LTC6906 was optimized for low power consumption operation and the minimum Rset is 100k.  Using a lower value resistor for Rset may work, but is certainly not guaranteed over temperature or part-to-part variation and is not recommended. If you want to use a lower Rset resistor value, consider the LTC6990 or LTC6900.

  • LTC6990 or LTC6900 appears to have higher error (1.5% vs 0.65% according to datasheet). If power consumption is not a concern for me, are there other parts that offer better frequency accuracy and stability while being resistor programmable? Or LTC6906 is my best choice?

  • Yes, the LTC6906 is the most accurate resistor set part that we have. The only part that we have that is more accurate is the LTC6930=X.XX family but these are fixed frequency parts. If your desired frequency happens to be supported by this family, then it would provide a more accurate solution. But it not, then the LTC6906 is the most accurate part that we have.