LTC6905C(RevA) Ver la hoja de datos (PDF) - Linear Technology
Número de pieza
componentes Descripción
Lista de partido
LTC6905C Datasheet PDF : 8 Pages
| |||
LTC6905
APPLICATIO S I FOR ATIO
ALTERNATIVE METHODS OF SETTING THE OUTPUT
Figure 3 shows a method to control the frequency of the
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
LTC6905 using a current source. RSET, in this case, sets a
maximum frequency according to the regular expression
for fOSC. The current source will subtract current from the
SET pin to lower the frequency.
the LTC6905 takes into account both the voltage at the SET Figure 4 shows a method for controlling the frequency of
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
the LTC6905 using a voltage source. In this case, RSET sets
a constant current into the SET pin, and RCNTRL will sub-
tract from this current in order to change the frequency.
rather than a resistor will result in as much as 5% addi- Increasing VCNTRL will increase the output frequency.
tional inaccuracy in the output frequency.
V+
1
0.1µF
2
RSET
10k
3
ICNTRL
0µA TO 60µA
V+
5
OUT
LTC6905
GND
fOSC
69.8MHz TO 170MHz
SET
4
DIV
V+
N=1
6905 F03
fOSC
=
⎡
1
⎢168.5MHz
⎢
N⎢
⎢
•
10kΩ
•
⎡
⎢
⎣
V
+ – VSET
RSET
V+ – VSET
⎤
– ICNTRL ⎥
⎦
⎤
⎥
+ 1.5MHz⎥⎥
⎥
⎣⎢
⎦⎥
ICNTRL Frequency ≤ 100kHz
Example (Figure 3): VSET = (V+ – 1V), RSET = 10k, N = 1
Figure 3. Current Controlled Oscillator
[ ] fOSC = 168.5MHz • (1– 10kΩ • ICNTRL) + 1.5MHz
V+ = 3V
0.1µF
RSET
10k
RCNTRL
33.2k
+–
VCNTRL
0V TO 2V
1 V+
5
OUT
LTC6905
2
GND
fOSC
69.8MHz TO 170MHz
3
4
SET DIV
6905 F04
V+
N=1
Figure 4. Voltage Controlled Oscillator
fOSC
=
⎡
⎢168.5MHz • 10kΩ
1⎢
N⎢
⎢
•
⎡
⎢
⎣
V+ – VSET
RSET
V+ – VSET
–
VSET – VCNTRL
RCNTRL
⎤
⎥
⎦
⎤
⎥
+ 1.5MHz⎥⎥
⎥
⎣⎢
⎦⎥
VCNTRL Frequency ≤ 100kHz
Example (Figure 4): VSET = (V+ – 1V), RSET = 10k, RCNTRL = 33.2k,
N = 1, V+ = 3V
fOSC
=
⎣⎢⎡168.5MHz
•
10kΩ
•
⎡1
⎣⎢10kΩ
–
2V – VCNTRL
33.2kΩ
⎤
⎦⎥
+
1.5MHz⎤⎦⎥
RELATED PARTS
PART NUMBER
DESCRIPTION
LTC1799
1kHz to 33MHz ThinSOT Oscillator
LTC6900
1kHz to 20MHz ThinSOT Oscillator
LTC6902
Multiphase Oscillator with Spread Spectrum Modulation
LTC6903/LTC6904 1kHz to 68MHz Serial Port Programmable Oscillator
LTC6905-XXX Series Fixed Frequency LTC6905
LTC6906
Micropower, 10kHz to 1MHz Resistor Set ThinSOT Oscillator
I2C is a trademark of Philips Electronics N.V.
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
COMMENTS
Single Output, High Frequency Operation
Single Output Lower Power
2-, 3- or 4-Phase Outputs
3-Wire or I2CTM Programmable
High Accuracy, No External Resistor
Ultralow Power, Resistor Sets Frequency
6905fa
LT/TP 0205 1K REV A • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 2005
Share Link: 