LTC6905
17MHz to 170MHz
Resistor Set SOT-23 Oscillator
FEATURES
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DESCRIPTION
The LTC
®
6905 precision, programmable silicon oscilla-
tor is easy to use and occupies very little board space. It
requires only a single resistor to set the output frequency
from 17MHz to 170MHz with a typical frequency error of
0.5% or less.
The LTC6905 operates with a single 2.7V to 5.5V power
supply and provides a rail-to-rail, 50% duty cycle square
wave output. The CMOS output driver ensures fast rise/fall
times and rail-to-rail switching. Operation is simple: A
single resistor, R
SET
, between 10k to 25k is used to set
the frequency, and an internal three-state divider (DIV
input) allows for division of the master clock by 1, 2 or 4,
providing three frequencies for each R
SET
value.
The LTC6905 features a proprietary feedback loop that
linearizes the relationship between R
SET
and frequency,
eliminating the need for tables to calculate frequency. The
oscillator can be easily programmed using the simple
formula outlined below:
f
OSC
,
⎧
1 DIV Pin
=
V
+
⎛
168.5MHz • 10k
Ω
⎞
1
⎪
=
⎜
+
1.5MHz
⎟
• , N
=
⎨
2, DIV Pin
=
Open
⎝
⎠
N
R
SET
⎪
4, DIV Pin
=
GND
⎩
One External Resistor Sets the Frequency
Fast Start-Up Time: 100μs Typical
Frequency Range: 17MHz to 170MHz
Frequency Error ±0.5% Typ 17MHz to 170MHz
(T
A
= 0°C to 70°C, Over All Settings)
±20ppm/°C Temperature Stability
Rise Time: 0.5ns, C
L
= 5pF
Timing Jitter: 7.2ps RMS at 170MHz
50% ±2.5% Duty Cycle
6mA Typical Supply Current, f
OSC
= 100MHz
CMOS Output Drives 500Ω Load (V
S
= 3V)
Operates from a Single 2.7V to 5.5V Supply
Low Profile (1mm) ThinSOT ™ Package
APPLICATIONS
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High Frequency Precision Oscillator
High Speed Data Bus Clock
Fixed Crystal Oscillator Replacement
Ceramic Oscillator Replacement
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 6614313, 6342817.
For higher accuracy, fixed frequency versions that
include an internal frequency-setting resistor, see the
LTC6905-XXX Series data sheet.
TYPICAL APPLICATION
Basic Connection
Typcial Distribution of Frequency Error, T
A
= 25°C
60
50
40
V
+
= 3V
R
SET
= 12k
DIV = 1
1
0.1μF
2
3
V
+
OUT
LTC6905
GND
SET
DIV
6905 TA01
5
5V
÷1
4
÷4
÷2
OPEN
UNITS
5V
17.225MHz ≤ f
OSC
≤ 170MHz
30
20
10
0
–0.5
10k ≤ R
SET
≤ 25k
–0.3
–0.1
0.1
% ERROR
0.3
0.5
6905 TA02
NOTE: RESISTOR, R
SET
, TOLERANCE WILL ADD
TO THE FREQUENCY ERROR
6905fd
1
LTC6905
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
V
+
1
GND 2
SET 3
4 DIV
5 OUT
Supply Voltage (V
+
) to GND .........................– 0.3V to 6V
DIV to GND .................................... – 0.3V to (V
+
+ 0.3V)
SET to GND .................................... – 0.3V to (V
+
+ 0.3V)
Output Short-Circuit Duration (Note 6) ........... Indefinite
Operating Temperature Range (Note 7)
LTC6905C, I .........................................– 40°C to 85°C
LTC6905H ..........................................– 40°C to 125°C
LTC6905MP .......................................– 55°C to 125°C
Specified Temperature Range (Note 8)
LTC6905C ................................................ 0°C to 70°C
LTC6905I..............................................– 40°C to 85°C
LTC6905H ..........................................– 40°C to 125°C
LTC6905MP .......................................– 55°C to 125°C
Storage Temperature Range...................– 65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
S5 PACKAGE
5-LEAD PLASTIC SOT-23
T
JMAX
= 125°C,
θ
JA
= 160°C/W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
LTC6905CS5#TRMPBF
LTC6905CS5#TRPBF
LTBJC
5-Lead Plastic SOT-23
LTC6905IS5#TRMPBF
LTC6905IS5#TRPBF
LTBJC
5-Lead Plastic SOT-23
LTC6905HS5#TRMPBF
LTC6905HS5#TRPBF
LTBJC
5-Lead Plastic SOT-23
LTC6905MPS5#TRMPBF
LTC6905MPS5#TRPBF
LTDVW
5-Lead Plastic SOT-23
LEAD BASED FINISH
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
LTC6905MPS5#TRM
LTC6905MPS5#TR
LTDVW
5-Lead Plastic SOT-23
TRM = 500 pieces. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
–40°C to 125°C
–55°C to 125°C
TEMPERATURE RANGE
–55°C to 125°C
6905fd
2
LTC6905
ELECTRICAL CHARACTERISTICS
SYMBOL
Δf
PARAMETER
Frequency Accuracy (Notes 2, 9)
The
l
denotes the specifications which apply over the full specified
temperature range, otherwise specifications are at T
A
= 25°C or as noted. V
+
= 2.7V to 5.5V, R
L
= 15k, C
L
= 5pF, Pin 4 = V
+
unless
otherwise noted. All voltages are with respect to GND.
CONDITIONS
V
+
= 2.7V, 17.225MHz < f < 170MHz
V
+
= 5V, 17.225MHz < f < 170MHz
LTC6905CS5
V
+
= 2.7V, 17.225MHz < f < 170MHz
V
+
= 5V, 17.225MHz < f < 170MHz
LTC6905MPS5 (25°C ≤ T ≤ 125°C),
LTC6905HS5 (25°C ≤ T ≤ 125°C),
LTC6905IS5 (25°C ≤ T ≤ 85°C)
V+ = 2.7V, 17.225MHz < f < 170MHz
V+ = 5V, 17.225MHz < f < 170MHz
LTC6905MPS5 (–55°C < T < 125°C),
LTC6905HS5 (–40°C ≤ T ≤ 125°C),
LTC6905IS5 (–40°C ≤ T ≤ 85°C)
V
+
= 2.7V, 17.225MHz < f < 170MHz
V
+
= 5V, 17.225MHz < f < 170MHz
MIN
TYP
±0.5
l
l
MAX
±1.4
±2.2
±1.7
±2.5
UNITS
%
%
%
%
±1.9
±2.9
%
%
l
l
±3.5
±3.5
10
25
170
17.225
%
%
kΩ
MHz
MHz
ppm/°C
%/V
%
ppm/√kHr
Δf
R
SET
f
MAX
f
MIN
Δf/ΔT
Δf/ΔV
Frequency Accuracy (Notes 2, 9)
Frequency-Setting Resistor Range
Maximum Frequency
Minimum Frequency
Freq Drift Over Temp (Note 2)
Freq Drift Over Supply (Notes 2, 9)
Peak-to-Peak Timing Jitter (Note 3)
Long-Term Stability of Output Frequency
Duty Cycle
l
l
Pin 4 = V
+
, N = 1
Pin 4 = 0V, N = 4
R
SET
= 10k
V
+
= 2.7V to 5.5V, R
SET
= 10k
l
l
±20
0.5
0.8
300
47.5
2.7
14
7
5
3
V
+
– 0.15
0.2
–40
15
–11
5.45
5.30
2.6
2.4
40
50
52.5
5.5
20
12
7
5
%
V
mA
mA
mA
mA
V
V
μA
μA
V
V
V
V
V
+
I
S
Operating Supply Range
Power Supply Current
R
SET
= 10k, N = 1, R
L
= ∞,
f
OSC
= 170MHz, C
L
= 5pF
R
SET
= 20k, N = 4, R
L
= ∞,
f
OSC
= 21.44MHz, C
L
= 5pF
V
+
= 5.5V
V
+
= 2.7V
V
+
= 5.5V
V
+
= 2.7V
l
l
l
l
l
l
V
IH
V
IL
I
DIV
V
OH
High Level DIV Input Voltage
Low Level DIV Input Voltage
DIV Input Current (Note 4)
High Level Output Voltage (Note 4)
Pin 4 = V
+
Pin 4 = 0V
V
+
= 5.5V, Pin 4 = 0V
V
+
= 2.7V, Pin 4 = 0V
V
+
= 5.5V
V
+
= 5.5V
I
OH
= –1mA
I
OH
= –4mA
I
OH
= –1mA
I
OH
= –4mA
l
l
l
l
l
5.25
5.20
2.5
2.4
6905fd
3
LTC6905
ELECTRICAL CHARACTERISTICS
SYMBOL
V
OL
PARAMETER
Low Level Output Voltage (Note 4)
The
l
denotes the specifications which apply over the full specified
temperature range, otherwise specifications are at T
A
= 25°C or as noted. V
+
= 2.7V to 5.5V, R
L
= 15k, C
L
= 5pF, Pin 4 = V
+
unless
otherwise noted. All voltages are with respect to GND.
CONDITIONS
V
+
= 5.5V, Pin 4 = 0V
V
+
= 2.7V, Pin 4 = 0V
I
OL
= 1mA
I
OL
= 4mA
I
OL
= 1mA
I
OL
= 4mA
l
l
l
l
l
l
MIN
TYP
0.05
0.2
0.1
0.4
0.5
MAX
0.25
0.3
0.3
0.5
4.73
1.79
UNITS
V
V
V
V
ns
V
V
t
r
, t
f
V
SET
OUT Rise/Fall Time (Note 5)
Voltage at R
SET
Pin
V
+
= 5.5V
V
+
= 2.7V
4.27
1.61
4.5
1.7
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
Frequency accuracy is defined as the deviation from the f
OSC
equation. Accuracy is tested with DIV = V
+
, N = 1 and other divide ratios
are guaranteed by design.
Note 3:
Jitter is the ratio of the peak-to-peak distribution of the period to
the mean of the period. This specification is based on characterization and
is not 100% tested.
Note 4:
To conform with the Logic IC Standard convention, current out of
a pin is arbitrarily given as a negative value.
Note 5:
Output rise and fall times are measured between the 10% and
90% power supply levels.
Note 6:
A heat sink may be required to keep the junction temperature
below the absolute maximum when the output is shorted indefinitely.
Note 7:
The LTC6905C is guaranteed functional over the operating
temperature range.
Note 8:
The LTC6905C is guaranteed to meet specified performance from
0°C to 70°C. The LTC6905C-XXX is designed, characterized and expected
to meet specified performance from –40°C to 85°C but is not tested or QA
sampled at these temperatures. The LTC6905I-XXX is guaranteed to meet
specified performance from –40°C to 85°C.
Note 9:
The LTC6905 is optimized for the performance with a 3V power
supply voltage. Please consult LTC Marketing for parts optimized for 5V
operation.
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Frequency
18
16
SUPPLY CURRENT (mA)
14
÷1
12
10
8
6
4
2
0
0
50
100
FREQUENCY (MHz)
150
200
6905 G01
Frequency Error vs R
SET
0.60
0.40
FREQUENCY ERROR (%)
0.20
0
–0.20
–0.40
–0.60
–0.80
10
12
14
16
18
20
22
24
6905 G02
Frequency Error vs Supply Voltage
1.40
1.20
FREQUENCY ERROR (%)
1.00
0.80
0.60
0.40
0.20
0
5.5V
2.7V
÷2
÷4
÷2
÷4
÷1
–0.20
–0.40
2.5
3
3.5
4
4.5
SUPPLY VOLTAGE (V)
5
5.5
6905 G03
R
SET
(kΩ)
6905fd
4
LTC6905
TYPICAL PERFORMANCE CHARACTERISTICS
R
OUT
vs V
+
45
40
PEAK-TO-PEAK JITTER (%)
OUTPUT RESISTANCE (Ω)
35
30
25
20
15
10
5
0
2.5
3
3.5
4
4.5
SUPPLY VOLTAGE (V)
5
5.5
6905 G04
Jitter vs Frequency
1.20
1.00
÷1
PERCENTAGE ERROR (%)
÷4
0.80
0.60
0.40
0.20
0
0
20
40
÷2
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
60 80 100 120 140 160 180
FREQUENCY (MHz)
6905 G05
Frequency vs Temperature
–1.0
–40 –20
0
20 40 60 80 100 120
TEMPERATURE (°C)
6905 G08
LTC6905 Output Operating at
17.5MHz, V
S
= 3V
LTC6905 Output Operating at
170MHz, V
S
= 3V
1V/DIV
1V/DIV
12.5ns/DIV
6905 G06
1ns/DIV
6905 G07
PIN FUNCTIONS
V
+
(Pin 1):
Voltage Supply (2.7V ≤ V
+
≤ 5.5V). This sup-
ply must be kept free from noise and ripple. It should be
bypassed directly to the GND (Pin 2) with a 0.1μF capaci-
tor or higher.
GND (Pin 2):
Ground. Should be tied to a ground plane
for best performance.
SET (Pin 3):
Frequency-Setting Resistor Input. The value
of the resistor connected between this pin and V
+
deter-
mines the oscillator frequency. The voltage on this pin is
held by the LTC6905 to approximately 1V below the V
+
voltage. For best performance, use a precision metal film
resistor with a value between 10k and 25k and limit the
capacitance on this pin to less than 10pF
.
DIV (Pin 4):
Divider-Setting Input. This three-state input
selects among three divider settings, determining the value
of N in the frequency equation. Pin 4 should be tied to V
+
for the ÷1 setting, the highest frequency range. Floating
Pin 4 divides the master oscillator by 2. Pin 4 should
be tied to GND for the ÷4 setting, the lowest frequency
range. To detect a floating DIV pin, the LTC6905 attempts
to pull the pin toward midsupply. This is realized with two
internal current sources, one tied to V
+
and Pin 4 and the
other one tied to ground and Pin 4. Therefore, driving
the DIV pin high requires sourcing approximately 15μA.
Likewise, driving DIV low requires sinking 11μA. When
Pin 4 is floated, it should be bypassed by a 1nF capacitor
to ground or it should be surrounded by a ground shield
to prevent excessive coupling from other PCB traces.
OUT (Pin 5):
Oscillator Output. This pin can drive 5kΩ
and/or 5pF loads. For larger loads, refer to the Applications
Information section.
6905fd
5
单片机
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