LTC6930-X.XX

9

6930fa

MONTHS

0

40

0.045

0.040

0.035

0.030

0.025

0.020

0.015

0.010

0.005

0

6930 F02

20

80

60

10ppm/√kHr

30ppm/√kHr

60ppm/√kHr

APPLICATIONS INFORMATION

state. The 2ns rise and fall times of the LTC6930 mean that

the instantaneous power supply current required during

the rise and fall portions of the waveform is much greater

than the average.

The instantaneous power supply current may be calculated

by a similar formula:

IC

V

t

PEAK

LOAD

SWING

rf

=

••

1

spikes are generated by driving 5.5V into a 5pF load.

Power is supplied to the output driver of the LTC6930

(Pins 6 and 8). Allowances must be made in the design

to provide for output load related supply current spikes,

especially in high accuracy applications. A 0.1μF ceramic

as close as possible to the device will decouple the rest

of the circuit from spikes caused by powering a capacitive

output load of up to 50pF. See Figure 1.

Startup Time

The startup time of the LTC6930 is typically 50μs from the

time that valid power is applied to the first output pulse.

The output is held low for the first 50μs to prevent any

glitches, runt pulses, or invalid frequency output during

startup.

Long-Term Drift

Long-term stability of silicon oscillators is specified in

ppm/√kHr, which is typical of other silicon devices such

as operational amplifiers and voltage references. Because

drift in silicon-based oscillators is generated primarily by

movement of ions in the silicon, most of the drift is ac-

complished early in the life of the device and the drift can

be expected to level off in the long term. The ppm/√kHr

unit models this time variant decay. Crystal oscillators

are often specified with drift measured in ppm/year be-

cause their drift mechanism is different. A comparison of

various drift rates over a five year time period is shown

in Figure 2.

When calculating the amount of drift to be expected, it is

important to consider the entire time in the calculation,

because the relationship to time is not linear. The drift

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

Figure 2. 5 Year Drift at Various Rates

Switching the DIV Pins

The LTC6930 is designed to quickly and cleanly respond

to the digital inputs. The output will respond to the DIV

pins within a single clock cycle without introducing any

sliver or runt pulses.

6930 F01

OUT

C2

0.1μF

C1

0.1μF

GND

GND

Figure 1. Recommended Layout