LTC6900IS5 Linear Technology, LTC6900IS5 Datasheet - Page 8

• Manufacturer Part Number: LTC6900IS5
• Manufacturer: Linear Technology
• Type: Silicon Oscillatorr

Specifications of LTC6900IS5

• Mounting Style: Surface Mount
• Screening Level: Industrial
• Product Length (mm): 2.9mm
• Product Depth (mm): 1.75mm
• Product Height (mm): 0.9mm
• Package / Case: TSOT-23
• Lead Free Status / RoHS Status: Not Compliant

APPLICATIO S I FOR ATIO
LTC6900
POWER SUPPLY REJECTION
Low Frequency Supply Rejection (Voltage Coefficient)
Figure 5 shows the output frequency sensitivity to power
supply voltage at several different temperatures. The
LTC6900 has a guaranteed voltage coefficient of 0.1%/V
but, as Figure 5 shows, the typical supply sensitivity is
twice as low.
High Frequency Power Supply Rejection
The accuracy of the LTC6900 may be affected when its
power supply generates significant noise with a frequency
content in the vicinity of the programmed value of f
a switching power supply is used to power the LTC6900,
and if the ripple of the power supply is more than 20mV,
make sure the switching frequency and its harmonics are
not related to the output frequency of the LTC6900.
Otherwise, the oscillator may show additional frequency
error.
If the LTC6900 is powered by a switching regulator and the
switching frequency or its harmonics coincide with the
output frequency of the LTC6900, the jitter of the oscillator
output may be affected. This phenomenon will become
noticeable if the switching regulator exhibits ripples be-
yond 30mV.
8
–0.05
0.15
0.10
0.05
0
2.5
R
PIN 4 = FLOATING ( 10)
SET
Figure 5. Supply Sensitivity
3.0
= 63.2k
U
SUPPLY VOLTAGE (V)
3.5
U
4.0
4.5
–40 C
25 C
W
5.0
85 C
6900 F05
5.5
U
OSC
. If
START-UP TIME
The start-up time and settling time to within 1% of the final
value can be estimated by t
10 s. Note the start-up time depends on R
independent from the setting of the divider pin. For in-
stance with R
of its 200kHz final value (N = 10) in approximately 380 s.
Figure 6 shows start-up times for various R
Figure 7 shows an application where a second set resistor
R
switch S1. When switch S1 is open, the output frequency
of the LTC6900 depends on the value of the resistor R
When switch S1 is closed, the output frequency of the
LTC6900 depends on the value of the parallel combination
of R
The start-up time and settling time of the LTC6900 with
switch S1 open (or closed) is described by t
above. Once the LTC6900 starts and settles, and switch S1
closes (or opens), the LTC6900 will settle to its new output
frequency within approximately 70 s.
Jitter
The Peak-to-Peak Jitter vs Output Frequency graph, in the
Typical Performance Characteristics section, shows the
typical clock jitter as a function of oscillator frequency and
power supply voltage. The capacitance from the SET pin,
(Pin 3), to ground must be less than 10pF. If this require-
ment is not met, the jitter will increase.
SET2
SET1
is connected in parallel with set resistor R
and R
–10
30
10
70
60
50
40
20
0
0
SET
20k
SET2
TIME AFTER POWER APPLIED ( s)
= 100k, the LTC6900 will settle with 1%
63.2k
200
Figure 6. Start-Up Time
.
400
400k
START
600
T
V
800
A
+
= 25 C
= 5V
R
6900 F06
SET
1000
(3.7 s/k ) +
SET
START
SET
resistors.
and it is
SET1
shown
SET1
6900f
via
.