LTC6907CS6 Linear Technology, LTC6907CS6 Datasheet - Page 10

• Manufacturer Part Number: LTC6907CS6
• Manufacturer: Linear Technology
• Type: Silicon Oscillatorr

Specifications of LTC6907CS6

• 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
LTC6907
10
Alternative Methods for Setting the Output Frequency
Any means of sinking current from the SET pin will control
the output frequency of the LTC6907. Equation 2 (re-
peated below) gives the fundamental relationship between
frequency and the SET pin voltage and current:
This equation shows that the LTC6907 converts conduc-
tance (I
resistance (R
V
it is given approximately by:
where
V
response of V
Performance graphs. V
°C. At room temperature V
60mV/decade of increase in I
If the SET pin is driven with a current source generating
I
SET
SET
SET
V
I
(I
t
V
ƒ
S
OSC
, the oscillator output frequency will be:
T
S
SET
OSC
varies with temperature and the SET pin current. The
is the voltage across an internal diode, and as such
≅ 82 • 10
= kT/q = 25.9mV at T = 300°K (27°C)
is also temperature dependent)
SET
=
≅
≅
≅
25 9
ƒ
V
/V
25 9
T
OSC
1
SET
SET
.
.
•
SET
–18
Log
mV Log
mV
) to frequency or, equivalently, converts
=
= V
to temperature is shown in the Typical
Amps
e
V
•
U
I
•
SET
SET
SET
Log
I
SET
I
SET
S
/I
e
•
SET
e
changes approximately –2.3mV/
U
⎛
⎜
⎝
5
SET
⎛
⎝ ⎜
82 10
pF
) to period.
82 10
SET
•
increases 18mV/octave or
I
5
I
SET
•
SET
pF
.
I
SET
–
W
18
–
18
A
A
⎞
⎟
⎠
⎞
⎠ ⎟
– .
–
2 3
2 2 3 .
U
mV C
mV C °
/
°
/
(2)
Jitter and Divide Ratio
At a given output frequency, a higher master oscillator
frequency and a higher divide ratio will result in lower jitter
and higher power supply dissipation. Indeterminate jitter
percentage will decrease by a factor of slightly less than
the square root of the divider ratio, while determinate jitter
will not be similarly attenuated. Please consult the speci-
fication tables for typical jitter at various divider ratios.
Figure 12 and Figure 13 show a current controlled oscilla-
tor and a voltage controlled oscillator. These circuits are
not highly accurate if used alone, but can be very useful if
they are enclosed in an overall feedback circuit such as a
phase-locked loop.
V
+
V
+
Figure 12. Current Controlled Oscillator
Figure 13. Voltage Controlled Oscillator
V
GND
DIV
+
LTC6907
V
GND
DIV
+
LTC6907
GRD
OUT
SET
GRD
OUT
SET
499k
49.9k
6907 F12
4MHz TO 400kHz
10k
6907 F13
56.2k
R
4MHz TO 400kHz
SET
V
0V TO 0.675V (V
CTRL
0µA
TO 11.25µA
SET
)
6907fa