LTC6905
17MHz to 170MHz
Resistor Set SOT-23 Oscillator
FEATURES
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DESCRIPTIO
One External Resistor Sets the Frequency
Fast Start-Up Time: 100
µ
s 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: 50ps 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
TM
Package
The LTC
®
6905 precision, programmable silicon oscillator
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:
,
⎧
1 DIV Pin
=
V
+
⎛
168.5MHz • 10k
Ω
⎞
1
⎪
=
⎜
+
1.5MHz
⎟
• , N
=
⎨
2, DIV Pin
=
Open
⎝
⎠
N
R
SET
⎪
4, DIV Pin
=
GND
⎩
APPLICATIO S
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High Frequency Precision Oscillator
High Speed Data Bus Clock
Fixed Crystal Oscillator Replacement
Ceramic Oscillator Replacement
, LTC and LT 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.
f
OSC
For higher accuracy, fixed frequency versions that include
an internal frequency-setting resistor, see the LTC6905-
XXX Series datasheet.
TYPICAL APPLICATIO
Typical Distribution of Frequency Error, T
A
= 25°C
60
50
40
V
+
= 3V
R
SET
= 12k
DIV = 1
Basic Connection
UNITS
5V
0.1µF
10k
≤
R
SET
≤
25k
17.225MHz
≤
f
OSC
≤
170MHz
1
2
3
OUT
V
+
LTC6905
GND
SET
DIV
6905 TA01
5
5V
÷1
4
÷4
÷2
OPEN
30
20
10
0
–0.5
NOTE: RESISTOR, R
SET
, TOLERANCE WILL ADD
TO THE FREQUENCY ERROR
6905fa
U
–0.3
–0.1
0.1
% ERROR
0.3
0.5
6905 TA02
U
U
1
LTC6905
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
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
Specified Temperature Range (Note 8)
LTC6905C ............................................... 0°C to 70°C
LTC6905I .............................................–40°C to 85°C
LTC6905H .........................................–40°C to 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART NUMBER
LTC6905CS5
LTC6905IS5
LTC6905HS5
S5 PART MARKING
LTBJC
S5 PACKAGE
5-LEAD PLASTIC SOT-23
T
JMAX
= 125°C,
θ
JA
= 150°C/W
ELECTRICAL CHARACTERISTICS
SYMBOL
∆f
PARAMETER
Frequency Accuracy (Notes 2, 9)
The
●
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
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
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
Pin 4 = V
+
, N = 1
Pin 4 = 0V, N = 4
R
SET
= 10k
V
+
= 2.7V to 5.5V, R
SET
= 10k
●
●
MIN
TYP
±0.5
MAX
±1.4
±2.2
±1.7
±2.5
UNITS
%
%
%
%
●
●
±1.9
±2.9
●
●
±3.5
±3.5
10
170
17.225
±20
0.5
0.8
300
25
R
SET
f
MAX
f
MIN
∆f/∆T
∆f/∆V
Frequency-Setting Resistor Range
Maximum Frequency
Minimum Frequency
Freq Drift Over Temp (Note 2)
Freq Drift Over Supply (Notes 2, 9)
Timing Jitter (Note 3)
Long-Term Stability of Output Frequency
Duty Cycle
●
●
ppm/°C
%/V
%
ppm/√kHr
52.5
5.5
20
12
7
5
%
-
V
mA
mA
mA
mA
V
6905fa
47.5
2.7
50
14
7
5
3
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
●
●
●
●
●
V
+
– 0.15
V
IH
High Level DIV Input Voltage
2
U
%
%
%
%
kΩ
MHz
MHz
W
U
U
W W
W
LTC6905
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IL
I
DIV
V
OH
PARAMETER
Low Level DIV Input Voltage
DIV Input Current (Note 4)
High Level Output Voltage (Note 4)
The
●
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
●
MIN
V
+
= 5.5V
V
+
= 5.5V
I
OH
= – 1mA
I
OH
= – 4mA
I
OH
= – 1mA
I
OH
= – 4mA
I
OL
= 1mA
I
OL
= 4mA
I
OL
= 1mA
I
OL
= 4mA
●
●
●
●
●
●
●
●
●
●
●
●
TYP
15
– 11
5.45
5.30
2.6
2.4
0.05
0.2
0.1
0.4
0.5
MAX
0.2
40
UNITS
V
µA
µA
V
V
V
V
Pin 4 = V
+
Pin 4 = 0V
V
+
= 5.5V
V
+
= 2.7V
– 40
5.25
5.20
2.5
2.4
V
OL
Low Level Output Voltage (Note 4)
V
+
= 5.5V
V
+
= 2.7V
0.25
0.3
0.3
0.5
4.73
1.79
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:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
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 LTC6905 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 PERFOR A CE CHARACTERISTICS
Supply Current vs Frequency
18
16
5.5V
2.7V
SUPPLY CURRENT (mA)
FREQUENCY ERROR (%)
12
10
8
6
4
2
0
0
50
100
÷4
÷4
÷2
÷2
÷1
0.20
0
–0.20
–0.40
–0.60
–0.80
FREQUENCY ERROR (%)
14
÷1
150
FREQUENCY (MHz)
6905 G01
U W
Frequency Error vs R
SET
0.60
0.40
Frequency Error vs Supply Voltage
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0
–0.20
12
14
16
18
20
22
24
6905 G02
200
10
–0.40
2.5
3
3.5
4
4.5
SUPPLY VOLTAGE (V)
5
5.5
6905 G03
R
SET
(kΩ)
6905fa
3
LTC6905
TYPICAL PERFOR A CE CHARACTERISTICS
R
OUT
vs V
+
45
40
OUTPUT RESISTANCE (Ω)
÷1
PERCENTAGE ERROR (%)
35
30
25
20
15
10
JITTER (%)
5
0
2.5
3
3.5
4
4.5
SUPPLY VOLTAGE (V)
5
5.5
6905 G04
LTC6905 Output Operating at
17.5MHz, V
S
= 3V
1V/DIV
PI FU CTIO S
V
+
(Pin 1):
Voltage Supply (2.7V
≤
V
+
≤
5.5V). This supply
must be kept free from noise and ripple. It should be
bypassed directly to the GND (Pin 2) with a 0.1µF capacitor
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 re-
quires sourcing approximately 15µA. Likewise, driving DIV
low requires sinking 15µA. 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 cou-
pling 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.
6905fa
4
U W
Jitter vs Frequency
1.20
1.00
÷4
0.80
0.60
0.40
0.20
0
0
20
40
60 80 100 120 140 160 180
FREQUENCY (MHz)
6905 G05
Frequency vs Temperature
1.0
0.8
÷2
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–40 –20
0
20 40 60 80 100 120
TEMPERATURE (°C)
6905 G08
LTC6905 Output Operating at
170MHz, V
S
= 3V
1V/DIV
12.5ns/DIV
6905 G06
1ns/DIV
6905 G07
U
U
U
LTC6905
BLOCK DIAGRA
1
R
SET
I
RES
3
SET
V
+
+
–
2
GND
–
V
BIAS
I
RES
+
GND
THEORY OF OPERATIO
As shown in the Block Diagram, the LTC6905’s master
oscillator is controlled by the ratio of the voltage between
the V
+
and SET pins and the current entering the SET pin
(I
RES
). The voltage on the SET pin is forced to approxi-
mately 1V below V
+
by the PMOS transistor and its gate
bias voltage.
A resistor R
SET
, connected between the V
+
and SET pins,
“locks together” the voltage (V
+
– V
SET
) and current, I
RES
,
variation. This provides the LTC6905’s high precision. The
master oscillation frequency reduces to:
R
SET
(Ω)
f
MO
=
168.5MHz • 10k
Ω
+
1.5MHz
R
SET
To extend the output frequency range, the master oscilla-
tor 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 fre-
quencies between 17.225MHz and 170MHz. The divide-
by value is determined by the state of the DIV input
(Pin 4). Tie DIV to V
+
or drive it to within 0.4V of V
+
to
select
÷1.
This is the highest frequency range, with the
U
W
V
RES
= 1V
±5%
(V
+
– V
SET
)
+
GAIN = 1
MASTER OSCILLATOR
PROGRAMMABLE
DIVIDER
(÷1, 2 OR 4)
f
OSC
=
f
MO
N
OUT
5
–
DIVIDER
SELECT
V
+
15µA
THREE-STATE
INPUT DETECT
DIV
4
15µA
6905 BD
master output frequency passed directly to OUT. The DIV
pin may be floated 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
SET
,
divider setting and output frequency, including the over-
lapping frequencies.
30
25
÷4 ÷2
20
÷1
15
10
5
10
110
60
160
OUTPUT FREQUENCY (MHz)
6905 F01
Figure 1. R
SET
vs Output Frequency
6905fa
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