LTC6905 Linear Technology, LTC6905 Datasheet - Page 8

• Manufacturer Part Number: LTC6905
• Description: 17MHz to 170MHz Resistor Set SOT-23 Oscillator
• Manufacturer: Linear Technology

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LTC6905
APPLICATIO S I FOR ATIO
ALTERNATIVE METHODS OF SETTING THE OUTPUT
FREQUENCY OF THE LTC6905
The LTC6905 may be programmed by any method that
sources a current into the SET pin (Pin 3). The accuracy of
the programming is best with a simple resistor because
the LTC6905 takes into account both the voltage at the SET
pin and the current into the SET pin when generating the
output frequency. Since the voltage at the SET pin can vary
by as much as 5%, setting the frequency using a current
rather than a resistor will result in as much as 5% addi-
tional inaccuracy in the output frequency.
RELATED PARTS
PART NUMBER
LTC1799
LTC6900
LTC6902
LTC6903/LTC6904
LTC6905-XXX Series
LTC6906
I
8
2
C is a trademark of Philips Electronics N.V.
V
+
V
+
–
= 3V
+
Figure 3. Current Controlled Oscillator
Figure 4. Voltage Controlled Oscillator
R
10k
R
10k
R
33.2k
0.1µF
SET
0.1µF
SET
CNTRL
V
0V TO 2V
I
0µA TO 60µA
CNTRL
CNTRL
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone]
1
2
3
1
2
3
V
GND
SET
V
GND
SET
DESCRIPTION
1kHz to 33MHz ThinSOT Oscillator
1kHz to 20MHz ThinSOT Oscillator
Multiphase Oscillator with Spread Spectrum Modulation
1kHz to 68MHz Serial Port Programmable Oscillator
Fixed Frequency LTC6905
Micropower, 10kHz to 1MHz Resistor Set ThinSOT Oscillator
LTC6905
+
LTC6905
+
U
●
FAX: [phone]
OUT
6905 F03
OUT
6905 F04
DIV
DIV
U
5
4
5
4
69.8MHz TO 170MHz
69.8MHz TO 170MHz
V
N = 1
V
N = 1
+
+
f
OSC
f
OSC
W
●
www.linear.com
U
V
Example (Figure 4): V
I
Example (Figure 3): V
CNTRL
CNTRL
f
f
f
f
OSC
OSC
OSC
OSC
Frequency ≤ 100kHz
=
=
=
=
Frequency ≤ 100kHz
[
N
⎡
⎢
⎣
N
1
1
168 5
168 5
⎡
⎢
⎢
⎢
⎢
⎢
⎣
⎡
⎢
⎢
⎢
⎢
⎢
⎣
168 5
Figure 3 shows a method to control the frequency of the
LTC6905 using a current source. R
maximum frequency according to the regular expression
for f
SET pin to lower the frequency.
Figure 4 shows a method for controlling the frequency of
the LTC6905 using a voltage source. In this case, R
a constant current into the SET pin, and R
tract from this current in order to change the frequency.
Increasing V
168 5
.
.
MHz
MHz
.
.
OSC
MHz
MHz
COMMENTS
Single Output, High Frequency Operation
Single Output Lower Power
2-, 3- or 4-Phase Outputs
3-Wire or I
High Accuracy, No External Resistor
Ultralow Power, Resistor Sets Frequency
. The current source will subtract current from the
• –
•
N = 1, V
(
10
SET
SET
1 10
•
•
10
10
k
Ω
CNTRL
= (V
= (V
k
k
V
Ω
Ω
•
k
2
C
+
Ω
+
⎡
⎢
⎣
TM
•
•
+
10
+
= 3V
–
⎡
⎢
⎣
•
V
⎡
⎢
⎣
Programmable
will increase the output frequency.
– 1V), R
– 1V), R
V
1
I
k
V
V
+
CNTRL
Ω
SET
+
+
–
R
R
–
–
SET
–
SET
V
V
SET
V
2
)
SET
SET
V V
+
SET
33 2
SET
© LINEAR TECHNOLOGY CORPORATION 2005
–
1 5
–
–
.
.
= 10k, R
CNTRL
I
= 10k, N = 1
LT/TP 0205 1K REV A • PRINTED IN USA
MHz
k
V
CNTRL
Ω
SET
SET
R
]
CNTRL
–
⎤
⎥ +
⎦
⎤
⎥
⎦
, in this case, sets a
V
+
CNTRL
CNTRL
1 5
1 5
.
CNTRL
.
MHz
MHz
⎤
⎥
⎦
= 33.2k,
+
⎤
⎥
⎦
⎤
⎥
⎥
⎥
⎥
⎥
⎦
will sub-
1 5
SET
.
MHz
sets
6905fa
⎤
⎥
⎥
⎥
⎥
⎥
⎦