LTC1799CS5 Linear Technology, LTC1799CS5 Datasheet - Page 8

• Manufacturer Part Number: LTC1799CS5
• Manufacturer: Linear Technology
• Type: Silicon Oscillatorr

Specifications of LTC1799CS5

• Mounting Style: Surface Mount
• Screening Level: Commercial
• 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
LTC1799
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
LTC1799 has a conservative guaranteed voltage coeffi-
cient of 0.1%/V but, as Figure 5 shows, the typical supply
sensitivity is lower.
High Frequency Power Supply Rejection
The accuracy of the LTC1799 may be affected when its
power supply generates significant noise with frequency
contents in the vicinity of the programmed value of f
If a switching power supply is used to power up the
LTC1799, and if the ripple of the power supply is more than
a few tens of millivolts, make sure the switching frequency
and its harmonics are not related to the output frequency
of the LTC1799. Otherwise, the oscillator may show an
additional 0.1% to 0.2% of frequency error.
If the LTC1799 is powered by a switching regulator and the
switching frequency or its harmonics coincide with the
output frequency of the LTC1799, 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
0.10
0.15
0.05
0
2.5
R
PIN 4 = FLOATING (÷10)
SET
Figure 5. Supply Sensitivity
3.0
= 31.6k
U
SUPPLY VOLTAGE (V)
3.5
U
4.0
4.5
–40°C
25°C
W
5.0
85°C
1799 F05
5.5
U
OSC
.
START-UP TIME
The start-up time and settling time to within 1% of the final
value can be estimated by t
20µs. Note the start-up time depends on R
independent from the setting of the divider pin. For in-
stance with R
its 200kHz final value (N = 10) in approximately 160µs.
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 LTC1799 depends on the value of the resistor R
When switch S1 is closed, the output frequency of the
LTC1799 depends on the value of the parallel combination
of R
The start-up time and settling time of the LTC1799 with
switch S1 open (or closed) is described by t
above. Once the LTC1799 starts and settles, and switch S1
closes (or opens), the LTC1799 will settle to its new output
frequency within approximately 25µs.
SET2
S1
R
R
SET2
SET1
SET1
3V OR 5V
is connected in parallel with set resistor R
and R
–10
60
50
40
30
20
10
0
0
SET
1
2
3
SET2
V
GND
SET
= 50k, the LTC1799 will settle with 1% of
100
TIME AFTER POWER APPLIED (µs)
+
LTC1799
31.6k
Figure 6. Start-Up Time
.
10k
OUT
DIV
200k
200
5
4
Figure 7
÷100
300
÷1
START
V
+
÷10
400
1799 F07
f
OR
f
OSC
OSC
≅ R
T
V
A
500
+
= 10MHz •
= 10MHz •
= 25°C
= 5V
1799 F06
SET
600
(2.8µs/kΩ) +
SET
START
SET
(
(
N • R
N • R
10k
resistors.
sn1799 1799fbs
SET1
SET1
and it is
SET1
10k
shown
)
//R
SET1
SET2
via
)
.