Datasheet

LTC6930-X.XX

6930fd

APPLICATIONS INFORMATION

Table 1. Frequency Setting and Available Frequencies

÷1 ÷2 ÷4 ÷8 ÷16 ÷32 ÷64 ÷128

DIV Pin Settings

[DIVC][DIVB][DIVA] 000 001 010 011 100 101 110 111

LTC6930-4.19 4.194304MHz 2.097152MHz 1.048576MHz 524.288kHz 262.144kHz 131.072kHz 65.536kHz 32.768kHz

LTC6930-5.00 5.000MHz 2.500MHz 1.250MHz 625.0kHz 312.5kHz 156.25kHz 78.125kHz 39.0625kHz

LTC6930-7.37 7.3728MHz 3.6864MHz 1.8432MHz 921.6kHz 460.8kHz 230.4kHz 115.2kHz 57.6kHz

LTC6930-8.00 8.000MHz 4.000MHz 2.000MHz 1000kHz 500.0kHz 250.0kHz 125.0kHz 62.5kHz

LTC6930-8.19 8.192MHz 4.096MHz 2.048MHz 1024kHz 512.0kHz 256.0kHz 128.0kHz 64.0kHz

5 years is not 5 times the drift for one year. A sample cal-

culation for drift over 5 years at 30ppm/√kHr is as follows:

5 years • 365.25 days/year • 24 hours/day = 43,830

hours = 43.830kHr

√43.830kHr = 6.62√kHr

6.62√kHr • 30ppm/√kHr = 0.0198% over 5 years.

Drift calculations assume that the part is in continuous

operation during the entire time period of the calculation.

The movement of ions which results in drift is usually aided

by electric fields in the operating parts, and the typical drift

spec applies while the part is powered up. Conservative

calculations would use a tenth of the drift specification for

time when power is not applied to the part.

Setting the Frequency

The output frequency of the LTC6930 is chosen from the

values in Table 1 and set using the DIV pins, as noted

in the table. Master oscillator frequency is preset in the

factory, and the DIV pins select an internal binary divider

of up to 128.

For example, if the desired oscillator output frequency

is 2.5MHz, finding 2.5MHz in Table 1 shows that the

LTC6930-5.00 should be ordered, having a master

oscillator frequency of 5MHz, and a DIV value of [001]

should be used. This would equate to grounding DIVC

and DIVB, while connecting DIVA to the positive supply.

Frequencies other than those shown in Table 1 may

be requested.