LTC6908-1/LTC6908-2
Resistor Set SOT-23 Oscillator with
Spread Spectrum Modulation
FEATURES
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DESCRIPTION
The
LTC
®
6908
is an easy-to-use precision oscillator that
provides 2-outputs, shifted by either 180° or 90°. The
oscillator frequency is programmed by a single external
resistor (R
SET
) and spread spectrum frequency modula-
tion (SSFM) can be activated for improved electromag-
netic compatibility (EMC) performance.
The LTC6908 operates with a single 2.7V to 5.5V supply
and provides rail-to-rail, 50% duty cycle square wave out-
puts. A single resistor from 10k to 2M is used to select an
oscillator frequency from 50kHz to 10MHz (5V supply).
The oscillator can be easily programmed using the simple
formula outlined below:
f
OUT
=10MHz • 10k/R
SET
The LTC6908’s SSFM capability modulates the output
frequency by a pseudorandom noise (PRN) signal to
decrease the peak electromagnetic radiation level and
improve EMC performance. The amount of frequency
spreading is fixed at ±10% of the center frequency. When
SSFM is enabled, the rate of modulation is selected by
the user. The three possible modulation rates are f
OUT
/16,
f
OUT
/32 and f
OUT
/64.
All registered trademarks and trademarks are the property of their respective owners.
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LTC6908-1: Complementary Outputs (0°/180°)
LTC6908-2: Quadrature Outputs (0°/90°)
50kHz to 10MHz Frequency Range
One External Resistor Sets the Frequency
Optional Spread Spectrum Frequency Modulation
for Improved EMC Performance
±10% Frequency Spreading
400µA Supply Current Typical (V
+
= 5V, 50kHz)
Frequency Error ≤1.5% Max (T
A
= 25°C, V
+
= 3V)
±40ppm/°C Temperature Stability
Fast Start-Up Time: 260µs Typical (1MHz)
Outputs Muted Until Stable
Operates from a Single 2.7V to 5.5V Supply
Available in Low Profile (1mm) ThinSOT and DFN
(2mm
×
3mm) Packages
APPLICATIONS
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Switching Power Supply Clock Reference
Portable and Battery-Powered Equipment
Precision Programmable Oscillator
Charge Pump Driver
TYPICAL APPLICATION
2.25MHz, 2.5V/8A Step-Down Regulator
OUTPUT (dBc)
V
IN
2.8V TO 5.5V
C
BYP
0.1 F
44.2k
SET
f
OUT
= 10MHz • 10k/R
SET
MOD
690812 TA01a
150kHz to 30MHz Output
Frequency Spectrum
(9kHz Res BW)
0
C
IN
100 F
0.2 H
V
OUT
2.5V
8A
C
OUT
100 F
×2
–10
–20
–30
–40
0
SSFM DISABLED
SV
IN
TRACK PV
IN
V
+
OUT1
2.2M
41.2k
R
T
SW
LTC3418
PGOOD
PGND
SGND
LTC6908-1
GND
OUT2
1000pF
4.99k
820pF
OUTPUT (dBc)
RUN/SS
I
TH
SYNC/MODE V
FB
4.32k
2k
–10
–20
–30
–40
150kHz
SSFM ENABLED
30MHz
FREQUENCY
(FUNDAMENTAL AND HARMONICS SHOWN)
690812 TA01b
Document Feedback
For more information
www.analog.com
1
Rev B
LTC6908-1/LTC6908-2
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Total Supply Voltage (V
+
to GND)................................6V
Maximum Voltage on any Pin
(GND – 0.3V) ≤ V
PIN
≤ (V
+
+ 0.3V)
Output Short Circuit Duration .......................... Indefinite
Operating Temperature Range (Note 2)
LTC6908CS6-1/LTC6908CS6-2............–40°C to 85°C
LTC6908IS6-1/LTC6908IS6-2 ..............–40°C to 85°C
LTC6908HS6-1/LTC6908HS6-2 ......... –40°C to 125°C
LTC6908CDCB-1/LTC6908CDCB-2 ......–40°C to 85°C
LTC6908IDCB-1/LTC6908IDCB-2 .........–40°C to 85°C
Specified Temperature Range (Note 3)
LTC6908CS6-1/LTC6908CS6-2................ 0°C to 70°C
LTC6908IS6-1/LTC6908IS6-2 ..............–40°C to 85°C
LTC6908HS6-1/LTC6908HS6-2 ......... –40°C to 125°C
LTC6908CDCB-1/LTC6908CDCB-2 .......... 0°C to 70°C
LTC6908IDCB-1/LTC6908IDCB-2 .........–40°C to 85°C
Storage Temperature Range (S6) ........... –65°C to 150°C
Storage Temperature Range (DCB) ........ –65°C to 125°C
Lead Temperature (Soldering, 10sec).................... 300°C
PIN CONFIGURATION
TOP VIEW
OUT2
5
OUT1
4
TOP VIEW
V
+
1
7
GND 2
SET 3
1
SET
2
V
+
3
GND
6 OUT1
5 OUT2
4 MOD
MOD
6
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
T
JMAX
= 150°C,
θ
JA
= 230°C/W
DCB PACKAGE
6-LEAD (2mm × 3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 64°C/W
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC6908CDCB-1#PBF
LTC6908IDCB-1#PBF
LTC6908CDCB-2#PBF
LTC6908IDCB-2#PBF
LTC6908CS6-1#PBF
LTC6908IS6-1#PBF
LTC6908HS6-1#PBF
LTC6908CS6-2#PBF
LTC6908IS6-2#PBF
LTC6908HS6-2#PBF
TAPE AND REEL
http://www.linear.com/product/LTC6908#orderinfo
PART MARKING
LBXZ
LBXZ
LBYB
LBYB
LTBYC
LTBYC
LTBYC
LTBYD
LTBYD
LTBYD
PACKAGE DESCRIPTION
8-Lead Plastic DFN
8-Lead Plastic DFN
8-Lead Plastic DFN
8-Lead Plastic DFN
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
0°C to 70°C
–40°C to 85°C
0°C to 70°C
–40°C to 85°C
–40°C to 125°C
0°C to 70°C
–40°C to 85°C
–40°C to 125°C
LTC6908CDCB-1#TRPBF
LTC6908IDCB-1#TRPBF
LTC6908CDCB-2#TRPBF
LTC6908IDCB-2#TRPBF
LTC6908CS6-1#TRPBF
LTC6908IS6-1#TRPBF
LTC6908HS6-1#TRPBF
LTC6908CS6-2#TRPBF
LTC6908IS6-2#TRPBF
LTC6908HS6-2#TRPBF
Consult ADI Marketing for parts specified with wider operating temperature ranges.
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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
Rev B
For more information
www.analog.com
LTC6908-1/LTC6908-2
ELECTRICAL CHARACTERISTICS
SYMBOL
Δf
OUT
PARAMETER
Frequency Accuracy (Note 4)
CONDITIONS
V
+
= 2.7V
V
+
= 5V
250kHz ≤ f
OUT
≤ 5MHz
250kHz ≤ f
OUT
≤ 5MHz
50kHz ≤ f
OUT
< 250kHz
250kHz ≤ f
OUT
≤ 5MHz
250kHz ≤ f
OUT
≤ 5MHz
50kHz ≤ f
OUT
< 250kHz
5MHz < f
OUT
≤ 10MHz
|
Δf
OUT
| ≤ 1.5%
|
Δf
OUT
| ≤ 2.5%
|
Δf
OUT
| ≤ 3.5%
|
Δf
OUT
| ≤ 2%
|
Δf
OUT
| ≤ 3%
|
Δf
OUT
| ≤ 4%
|
Δf
OUT
| ≤ 4.5%
l
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The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. Test conditions are V
+
= 2.7V to 5.5V, R
L
= 5k, C
L
= 5pF unless
otherwise noted. The modulation is turned off (MOD is connected to OUT2) unless otherwise specified. R
SET
is defined as the resistor
connected from the SET pin to the V
+
pin.
MIN
TYP
±0.5
±2
±2.5
±1
±2.5
±3
±3.5
20
20
400
20
20
400
10
±0.004
0.04
0.4
±7.5
±10
300
No Modulation, 250kHz ≤ f
OUT
≤ 1MHz
R
SET
= 2000k, R
L
= ∞, f
OUT
= 50kHz, MOD Pin = V
+
V
+
= 5V
V
+
= 2.7V
R
SET
= 20k, R
L
= ∞, f
OUT
= 5MHz, MOD Pin = GND
V
+
= 5V
V
+
= 2.7V
V
IH_MOD
V
IL_MOD
I
MOD
V
OH
High Level MOD Input Voltage
Low Level MOD Input Voltage
MOD Pin Input Current (Note 6)
High Level Output Voltage (Note 6)
(OUT1, OUT2)
MOD Pin = V
+
, V
+
= 5V
MOD Pin = GND, V
+
= 5V
V
+
= 5V
V
+
= 2.7V
I
OH
= –0.3mA
I
OH
= –1.2mA
I
OH
= –0.3mA
I
OH
= –0.8mA
I
OL
= 0.3mA
I
OL
= 1.2mA
I
OL
= 0.3mA
I
OL
= 0.8mA
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
MAX
±1.5
±2.5
±3.5
±2
±3
±4
±4.5
400
400
2000
400
400
2000
20
0.25
0.9
±12.5
UNITS
%
%
%
%
%
%
%
k
k
k
k
k
k
k
%/°C
%/V
%/V
%
ppm/√kHr
R
SET
Frequency Setting Resistor Range
V
+
= 2.7V
V
+
= 5V
Δf
OUT
/ΔT
Frequency Drift Over Temperature
R
SET
= 100k
Δf
OUT
/ΔV
+
Frequency Drift Over Supply (Note 4) V
+
= 2.7V to 3.6V, R
SET
= 100k
V
+
= 4.5V to 5.5V, R
SET
= 100k
Period Variation
(Frequency Spreading)
Long-Term Stability of Output
Frequency (Note 8)
Duty Cycle (Note 5)
V
+
I
S
Operating Supply Range
Power Supply Current
R
SET
= 100k, MOD Pin = V
+
, GND or OPEN
45
2.7
50
55
5.5
%
V
mA
mA
mA
mA
V
V
µA
µA
V
V
V
V
0.4
0.4
1.25
0.9
V
+
– 0.4
0.65
0.6
1.7
1.3
0.4
–4
4.75
4.4
2.35
1.85
2
–2
4.9
4.7
2.6
2.2
0.05
0.2
0.1
0.4
6
11
5
9
4
V
OL
Low Level Output Voltage (Note 6)
V
+
= 5V
V
+
= 2.7V
0.15
0.5
0.3
0.7
V
V
V
V
ns
ns
ns
ns
t
r
t
f
Output Rise Time (Note 7)
Output Fall Time (Note 7)
V
+
= 5V
V
+
= 2.7V
V
+
= 5V
V
+
= 2.7V
For more information
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3
Rev B
LTC6908-1/LTC6908-2
ELECTRICAL CHARACTERISTICS
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:
LTC6908C and LTC6908I are guaranteed functional over the
operating temperature range of –40°C to 85°C.
Note 3:
LTC6908C is guaranteed to meet specified performance from 0°C
to 70°C. The LTC6908C is designed, characterized and expected to meet
specified performance from –40°C to 85°C but is not tested or Q
A
sampled
at these temperatures. The LTC6908I is guaranteed to meet the specified
performance limits from –40°C to 85°C. The LTC6908H is guaranteed to
meet the specified performance limits from –40°C to 125°C.
Note 4:
Frequency accuracy is defined as the deviation from the f
OUT
equation.
Note 5:
Guaranteed by 5V test
Note 6:
To conform to the Logic IC Standard, current out of a pin is
arbitrarily given a negative value.
Note 7:
Output rise and fall times are measured between the 10% and the
90% power supply levels with no output loading. These specifications are
based on characterization.
Note 8:
Long term drift on silicon oscillators is primarily due to the
movement of ions and impurities within the silicon and is tested at 30°C
under otherwise nominal operating conditions. Long term drift is specified
as ppm/√kHr due to the typically non-linear nature of the drift. To calculate
drift for a set time period, translate that time into thousands of hours, take
the square root and multiply by the typical drift number. For instance, a
year is 8.77kHr and would yield a drift of 888ppm at 300ppm/√kHr. Ten
years is 87.7kHr and would yield a drift of 2,809 ppm at 300 ppm/√kHr.
Drift without power applied to the device may be approximated as 1/10th
of the drift with power, or 30ppm/√kHr for a 300ppm/√kHr device.
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Error vs R
SET
,
V
+
= 3V
5
4
3
FREQUENCY ERROR (%)
2
1
0
–1
–2
–3
–4
GUARANTEED MIN
OVER TEMPERATURE
100k
R
SET
(Ω)
690812 G01
Frequency Error vs R
SET
,
V
+
= 5V
T
A
= 25°C
5
4
3
FREQUENCY ERROR (%)
2
1 TYPICAL MAX
0
–1
–2 TYPICAL MIN
–3
–4
–5
10k
GUARANTEED MIN
OVER TEMPERATURE
T
A
= 25°C
GUARANTEED MAX
OVER TEMPERATURE
1.00
0.75
FREQUENCY ERROR (%)
0.50
0.25
0
–0.25
–0.50
–0.75
Frequency Error vs Temperature
GUARANTEED MAX
OVER TEMPERATURE
TYPICAL MAX
TYPICAL MAX
TYPICAL MIN
TYPICAL MIN
–5
10k
1M
10M
100k
R
SET
(Ω)
1M
10M
690812 G02
–1.00
–40
–20
40
20
TEMPERATURE (°C)
0
60
80
690812 G03
Peak to Peak Jitter vs Output
Frequency
1.0
0.9
0.8
Supply Current vs Output
Frequency
800
2.0
SUPPLY CURRENT (mA)
Supply Current vs Temperature
C
L
5pF ON BOTH OUTPUTS
FREQUENCY = 1MHz
750
SSFM DISABLED
0.7
JITTER (%
P-P
)
0.6
0.5
0.4
0.3
0.2
0.1
0
10k
5V
3V
1.5
5V SSFM ENABLED
3V SSFM ENABLED
SUPPLY CURRENT ( A)
700
650
600
550
500
450
V
+
= 3V
V
+
= 5V
1.0
0.5
3V SSFM DISABLED
0
10k
5V SSFM DISABLED
100k
1M
FREQUENCY (Hz)
10M
690812 G05
100k
1M
FREQUENCY (Hz)
10M
690812 G04
400
–40
–20
0
40
20
TEMPERATURE (°C)
60
80
690812 G06
4
Rev B
For more information
www.analog.com
LTC6908-1/LTC6908-2
TYPICAL PERFORMANCE CHARACTERISTICS
Output Resistance vs Supply
Voltage
500
450
OUTPUT RESISTANCE (Ω)
400
350
300
250
200
150
100
50
0
2.5
3.0
3.5
4.5 5.0
SUPPLY VOLTAGE (V)
4.0
5.5
6.0
OUTPUT SINKING CURRENT
T
A
= 25°C
Output Operating at 5MHz,
V
+
= 3V
Output Operating at 10MHz,
V
+
= 5V
V
OUT
(1V/DIV)
OUTPUT SOURCING CURRENT
80ns/DIV
690812 G08
V
OUT
(1V/DIV)
40ns/DIV
690812 G09
690812 G07
Output Frequency Spectrum with
SSFM Enabled and Disabled
20dBm
SSFM ENABLED
(N = 16)
10dB/DIV
10dB/DIV
RES BW = 220Hz
20dBm
Output Frequency Spectrum with
SSFM Enabled and Disabled
RES BW = 9kHz
SSFM ENABLED
(N = 16)
SSFM DISABLED
–80dBm
150kHz
FREQUENCY (7.5kHz/DIV)
690812 G10
SSFM DISABLED
–80dBm
5MHz
FREQUENCY (250kHz/DIV)
690812 G11
For more information
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5
Rev B
嵌入式系统
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