LTC6905IS5 Linear Technology, LTC6905IS5 Datasheet - Page 7

• Manufacturer Part Number: LTC6905IS5
• Manufacturer: Linear Technology
• Type: Silicon Oscillatorr

Specifications of LTC6905IS5

• 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

THEORY OF OPERATION
As shown in the Block Diagram, the LTC6905’s master
oscillator is controlled by the ratio of the voltage between
the V
(I
mately 1V below V
bias voltage.
A resistor R
“locks together” the voltage (V
variation. This provides the LTC6905’s high precision. The
master oscillation frequency reduces to:
To extend the output frequency range, the master oscillator
signal is divided by 1, 2 or 4 before driving OUT (Pin 5).
The LTC6905 is optimized for use with resistors between
10k and 25k, corresponding to oscillator frequencies
between 17.225MHz and 170MHz. The divide-by value is
determined by the state of the DIV input (Pin 4). Tie DIV to
V
+
RES
or drive it to within 0.4V of V
f
MO
). The voltage on the SET pin is forced to approxi-
+
and SET pins and the current entering the SET pin
=
168 5
SET
.
, connected between the V
MHz
R
SET
+
by the PMOS transistor and its gate
•
10
k
Ω
+
+
1 5
– V
+
.
to select ÷1. This is the
SET
MHz
) and current, I
+
and SET pins,
RES
,
highest frequency range, with the master output frequency
passed directly to OUT. The DIV pin may be fl oated or driven
to midsupply to select ÷2, the intermediate frequency
range. The lowest frequency range, ÷4, is selected by
tying DIV to GND or driving it below 0.5V. Figure 1 shows
the relationship between R
frequency, including the overlapping frequencies.
30
25
20
15
10
5
10
Figure 1. R
÷4 ÷2
OUTPUT FREQUENCY (MHz)
60
SET
÷1
vs Output Frequency
SET
110
, divider setting and output
160
6905 F01
LTC6905
6905fd
7