LTC6930 LINER [Linear Technology], LTC6930 Datasheet - Page 9

• Manufacturer Part Number: LTC6930
• Description: 32.768kHz to 8.192MHz Precision ?Power Oscillators
• Manufacturer: LINER [Linear Technology]

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:
where t
spikes are generated by driving 5.5V into a 5pF load.
Power is supplied to the output driver of the LTC6930
from the V
(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
capacitor connected between V
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.
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.
0.1μF
I
C1
PEAK
GND
rf
is the rise/fall time of the signal. In this case, 14mA
=
C
+
LOAD
and GND pins on each side of the output pin
Figure 1. Recommended Layout
•
V
SWING
•
t
1
rf
+
and GND (Pins 6 and 8)
GND
6930 F01
V
OUT
+
C2
0.1μF
Startup Time
The startup time of the LTC6930 is typically 50μs from the
time that valid power is applied to the fi rst output pulse.
The output is held low for the fi rst 50μs to prevent any
glitches, runt pulses, or invalid frequency output during
startup.
Long-Term Drift
Long-term stability of silicon oscillators is specifi ed in
ppm/√kHr, which is typical of other silicon devices such
as operational amplifi ers 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 specifi ed with drift measured in ppm/year be-
cause their drift mechanism is different. A comparison of
various drift rates over a fi ve 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
0.045
0.040
0.035
0.030
0.025
0.020
0.015
0.010
0.005
Figure 2. 5 Year Drift at Various Rates
0
0
20
MONTHS
40
LTC6930-X.XX
60ppm/√kHr
30ppm/√kHr
10ppm/√kHr
60
6930 F02
80
6930fa
9