LTC6903CMS8 Linear Technology, LTC6903CMS8 Datasheet - Page 6

• Manufacturer Part Number: LTC6903CMS8
• Description: IC OSC PROGRAM SPI SERIAL 8-MSOP
• Manufacturer: Linear Technology
• Type: Oscillator, Siliconr

Specifications of LTC6903CMS8

• Frequency: 68MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Current - Supply: 7mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Count: -
• Lead Free Status / Rohs Status: Not Compliant

LTC6903/LTC6904
block Diagram
Theory oF operaTion
applicaTions inFormaTion
The LTC6903/LTC6904 contain an internal feedback loop
which controls a high frequency square wave VCO oper-
ating between 34MHz and 68MHz. The internal feedback
loop frequency is set over an octave by a 10-bit resistor
DAC. The VCO tracks the internal feedback loop frequency
and the output frequency of the VCO is divided by one of
sixteen possible powers of two.
Higher VCO frequencies and lower output divider settings
can result in higher output jitter. Random jitter at the lower
Frequency Setting Information
The frequency output of the LTC6903/LTC6904 is deter-
mined by the following equation:
where DAC is the integer value from 0-1023 represented
by the serial port register bits DAC[9:0] and OCT is the
integer value from 0-15 represented by the serial port
register bits OCT [3:0].

f
=
2
OCT
•



2078
2
–
1024
DAC
( )
Hz



+
–
V
8
+
DAC
I
SET
+
–
V
A1
SET
GND
1
SDI
f
MO
2
= 68MHz • k
SERIAL PORT
OSCILLATOR
frequency ranges is very low because of the high output
divisor.
The higher frequency settings will display some deter-
ministic jitter from coupling between the control loop
and the output. This shows up in the frequency spectrum
as spurs separated from the fundamental frequency by
1MHz to 2MHz.
Use the following two steps to choose binary numbers
“OCT” and “DAC” in order to set frequency “f”:
1) Use Table 1 to Choose “OCT” or use the following
formula, rounding down to the integer value less than or
equal to the result.
2) Choose “DAC” by the following formula, rounding DAC
to the nearest integer:
MASTER
SCK
OE
OCT
DAC
7
3
V
+
=
=
I
– V
SET
SEN (LTC6903)
ADR (LTC6904)
3 322
2048
SET
4
.
–
log
2078



PROGRAMMABLE
CLK
OCT
1039
6
DIVIDER
f
( ) •
Hz



CLK
f
5
2
6903 BD
(
10
+
OCT
)
69034fc