LTC6930-X.XX

10

6930fa

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

calculation 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 oscil-

lator 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.