LTC6902
Multiphase Oscillator
with Spread Spectrum
Frequency Modulation
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
s
2-, 3- or 4-Phase Outputs
Optional Spread Spectrum Frequency Modulation
for Improved EMC Performance
5kHz to 20MHz Frequency Range
One External Resistor Sets the Frequency
One External Resistor Sets Percent Frequency
Spreading
400µA Typical Supply Current, V
S
= 3V, 1MHz
Frequency Error
≤1.5%
Max, 5kHz to 10MHz
(T
A
= 25°C)
Frequency Error
≤
2% Max, 5kHz to 10MHz
(T
A
= 0°C to 70°C)
±40ppm/°C
Temperature Stability
Fast Start-Up Time: 50µs to 1.5ms
100Ω CMOS Output Driver
Operates from a Single 2.7V to 5.5V Supply
Available in 10-Lead MS Package
The LTC
®
6902 is a precision, low power and easy-to-use
oscillator that provides multiphase outputs in a small
package. The oscillator frequency is set by a single exter-
nal resistor (R
SET
). The LTC6902 also provides an optional
spread spectrum frequency modulation (SSFM) capability
that can be activated and controlled by an additional
external resistor (R
MOD
).
The LTC6902’s master oscillator is controlled by the R
SET
resistor and has a range of 100kHz and 20MHz. In order
to accommodate a wider output frequency range, a pro-
grammable divider (divide by 1, 10 or 100) is included.
The integrated programmable multiphase circuit pro-
vides either 2-, 3- or 4-phase waveforms.
The LTC6902’s SSFM capability modulates the oscillator’s
frequency by a pseudorandom noise (PRN) signal to
spread the oscillator’s energy over a wide frequency band.
This spreading decreases the peak electromagnetic radia-
tion level and improves electromagnetic compatibility
(EMC) performance. The amount of frequency spreading
is programmable by a single additional external resistor
(R
MOD
) and is disabled by grounding the MOD pin.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
s
Switching Power Supply Clock Reference
Portable and Battery-Powered Equipment
PDAs
Cell Phones
Clocking Switched Capacitor Filters
TYPICAL APPLICATIO
5V
0.1µF
R
MOD
10k
R
SET
10k
LTC6902
V
+
OPEN
DIV
PH
SET
MOD
GND
Output Frequency Spectrum With and Without SSFM
0
OUTPUT
SPECTRUM
WITH SSFM
DISABLED
OUTPUT
SPECTRUM
WITH 20%
SPREADING
500kHz, 4-Phase Clock with 20% Frequency Spreading
RELATIVE AMPLITUDE (dBm)
–20
–40
–60
OUT1 OUT4
OUT2 OUT3
OUT4
OUT3
OUT2
6902 TA01
–80
–100
OUT1
400
U
550
450
500
FREQUENCY (kHz)
600
6902 TA02
U
U
6902f
1
LTC6902
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
+
1
DIV
PH
OUT1
OUT2
2
3
4
5
10
9
8
7
6
SET
MOD
GND
OUT4
OUT3
Supply Voltage (V
+
) to GND ........................– 0.3V to 6V
Voltage On Any Pin
(Referred to GND) ......................... – 0.3V to (V
+
+ 0.3V)
Operating Temperature Range (Note 9)
LTC6902C .......................................... – 40°C to 85°C
LTC6902I ............................................ – 40°C to 85°C
Specified Temperature Range (Note 10)
LTC6902C .......................................... – 40°C to 85°C
LTC6902I ............................................ – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER
PART NUMBER
LTC6902CMS
LTC6902IMS
MS PART MARKING
LTK2
LTK3
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 150°C,
θ
JA
= 250°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
∆f
OUT
PARAMETER
Frequency Accuracy (Notes 2, 3)
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
+
= 2.7V to 5.5V, R
L
= 5k, C
L
= 5pF, Pin 3 (PH) = 0V (2-phase, M = 1)
unless otherwise specified. Pin 9 (MOD) is at 0V unless otherwise specified. R
SET
is defined as a resistor connected from the SET pin
to the V
+
pin. R
MOD
is defined as a resistor connected from the MOD pin to the V
+
pin.
CONDITIONS
V
+
= 5V
5kHz
≤
f
OUT
≤
10MHz
1kHz
≤
f
OUT
≤
5kHz
10MHz
≤
f
OUT
≤
20MHz
5kHz
≤
f
OUT
≤
10MHz, LTC6902C
5kHz < f
OUT
≤
10MHz, LTC6902I
5kHz
≤
f
OUT
≤
10MHz
1kHz
≤
f
OUT
≤
5kHz
5kHz
≤
f
OUT
≤
10MHz, LTC6902C
5kHz
≤
f
OUT
≤
10MHz, LTC6902I
MIN
TYP
±0.5
±2.0
±3.0
MAX
±1.5
±4.0
±2.0
±2.5
±1.5
±2.0
±2.5
400
400
±0.004
0.04
0.1
0.2
0.6
300
Pin 2 = V
+
or Open (N = 100 or 10)
Pin 3 = 0V (2-Phase, M = 1)
Pin 3 = Open (3-Phase, M = 3)
Pin 3 = V
+
(4-Phase, M = 4)
Pin 2 = 0V (N = 1)
Pin 3 = 0V (2-Phase, M = 1)
Pin 3 = Open (3-Phase, M = 3)
Pin 3 = V
+
(4-Phase, M = 4)
0.12
UNITS
%
%
%
%
%
%
%
%
%
kΩ
kΩ
%/°C
%/V
%
%
%
ppm/√kHr
q
q
q
V
+
= 2.7V
±0.5
±2.0
q
q
q
q
q
q
R
SET
∆f
OUT
/∆T
∆f
OUT
/∆V
Frequency Setting Resistor Range
Frequency Drift Over Temperature
(Note 3)
Timing Jitter (Note 4)
∆f
OUT
< 1.5%, V
+
= 5V
∆f
OUT
< 1.5%, V
+
= 2.7V
20
20
R
SET
= 63.2k
Frequency Drift Over Supply (Note 3) V
+
= 2.7V to 5V, R
SET
= 63.2k
20k
≤
R
SET
≤
400k
Pin 2 = V
+
(N = 100)
Pin 2 = Open (N = 10)
Pin 2 = 0V (N = 1)
Long-Term Stability of
Output Frequency
Duty Cycle (Note 5)
q
q
q
q
q
q
49.0
32.3
49.0
45.0
32.3
49.0
50.0
33.3
50.0
50.0
33.3
50.0
51.0
34.3
51.0
55.0
34.3
51.0
2
U
%
%
%
%
%
%
6902f
W
U
U
W W
W
LTC6902
ELECTRICAL CHARACTERISTICS
SYMBOL
V
+
I
S
PARAMETER
Operating Supply Range
Power Supply Current
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
+
= 2.7V to 5.5V, R
L
= 5k, C
L
= 5pF, Pin 3 (PH) = 0V (2-phase, M = 1)
unless otherwise specified. Pin 9 (MOD) is at 0V unless otherwise specified. R
SET
is defined as a resistor connected from the SET pin
to the V
+
pin. R
MOD
is defined as a resistor connected from the MOD pin to the V
+
pin.
CONDITIONS
q
MIN
2.7
TYP
MAX
5.5
UNITS
V
mA
mA
mA
mA
mA
mA
mA
mA
V
V
µA
µA
V
V
µA
µA
V
V
V
V
R
SET
= 400k, R
L
=
∞,
Pin 2 = V
+
(N = 100), f
OUT
= 5kHz
V
+
= 5V
V
+
= 2.7V
R
SET
= 20k, R
L
=
∞,
Pin 2 = 0V (N = 1), f
OUT
= 10MHz
V
+
= 5V
V
+
= 2.7V
q
q
q
q
0.35
0.32
2.35
1.40
0.45
0.34
2.50
1.40
0.55
0.50
3.50
1.80
0.63
0.50
3.60
1.90
0.4
R
SET
= 400k, R
L
=
∞,
Pin 2 = V
+
(N = 100), R
MOD
= 800k
V
+
= 5V
q
+
= 2.7V
q
V
R
SET
= 20k, R
L
=
∞,
Pin 2 = 0V (N = 1), R
MOD
= 40k
V
+
= 5V
V
+
= 2.7V
V
IH_DIV
V
IL_DIV
I
DIV
V
IH_PH
V
IL_PH
I
PH
V
OH
High Level DIV Input Voltage
Low Level DIV Input Voltage
DIV Input Current (Note 6)
High Level PH Input Voltage
Low Level PH Input Voltage
PH Input Currrent (Note 6)
High Level Output Voltage (Note 6)
(OUT1, OUT2, OUT3, OUT4)
Pin 3 = V
+
, V
+
= 5V
Pin 3 = 0V, V
+
= 5V
V
+
= 5V
V
+
= 2.7V
V
OL
Low Level Output Voltage (Note 6)
(OUT1, OUT2, OUT3, OUT4)
V
+
= 5V
V
+
= 2.7V
t
r
Output Rise Time (Note 7)
(OUT1, OUT2, OUT3, OUT4)
V
+
= 5V
V
+
= 2.7V
t
f
Output Fall Time (Note 7)
(OUT1, OUT2, OUT3, OUT4)
V
+
= 5V
V
+
= 2.7V
Spread Spectrum Frequency
Modulation Spreading Percentage
(Downspread from Maximum
Frequency)
Percent = 100 • (f
MAX
– f
MIN
)/f
MAX
(Note 8)
I
OH
= – 1mA
I
OH
= – 4mA
I
OH
= – 1mA
I
OH
= – 4mA
I
OL
= 1mA
I
OL
= 4mA
I
OL
= 1mA
I
OL
= 4mA
Pin 2 = V
+
or Open (N = 100 or N = 10)
Pin 2 = 0V (N = 1)
Pin 2 = V
+
or Open (N = 100 or N = 10)
Pin 2 = 0V (N = 1)
Pin 2 = V
+
or Open (N = 100 or N = 10)
Pin 2 = 0V (N = 1)
Pin 2 = V
+
or Open (N = 100 or N = 10)
Pin 2 = 0V (N = 1)
q
q
q
q
q
q
q
V
+
– 0.4
q
Pin 2 = V
+
, V
+
= 5V
Pin 2 = 0V, V
+
= 5V
q
q
–4
2
–2
4
q
V
+
– 0.4
q
q
q
q
q
q
q
q
q
q
q
0.4
–4
4.75
4.40
2.35
1.85
2
–2
4.90
4.70
2.6
2.2
0.05
0.20
0.1
0.4
14
7
19
11
13
6
19
10
35
7.5
35
7.5
40
10
40
10
45.0
12.5
45.0
12.5
0.15
0.40
0.3
0.7
4
V
V
V
V
ns
ns
ns
ns
ns
ns
ns
ns
%
%
%
%
V
+
= 5V, N = 10, R
SET
= 20k, R
MOD
= 10k
V
+
= 5V, N = 10, R
SET
= 20k, R
MOD
= 40k
V
+
= 2.7V, N = 10, R
SET
= 20k, R
MOD
= 10k
V
+
= 2.7V, N = 10, R
SET
= 20k, R
MOD
= 40k
6902f
3
LTC6902
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
Frequencies near 100kHz and 1MHz may be generated using two
different values of R
SET
(see Applications Information). For these
frequencies, the error is specified under the following assumption:
20k < R
SET
≤
400k for 5kHz
≤
f
OUT
≤
10MHz.
Note 3:
Frequency accuracy is defined as the deviation from the f
OUT
equation.
Note 4:
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 5:
Guaranteed by 5V test.
Note 6:
To conform with the Logic IC Standard convention, current out of
a pin is arbitrarily given as 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:
f
MAX
is defined as the highest frequency excursion and is equal to
the f
OUT
frequency set by the R
SET
resistor. f
MIN
is the lowest frequency
excursion.
Note 9:
The LTC6902CMS and LTC6902IMS are guaranteed functional
over the operating temperature range of –40°C to 85°C.
Note 10:
The LTC6902CMS is guaranteed to meet 0°C to 70°C specifica-
tions and are designed, characterized and expected to meet the specified
performance from –40°C to 85°C but is not tested or QA sampled at these
temperatures. The LTC6902IMS is guaranteed to meet specified perfor-
mance from –40°C to 85°C.
TYPICAL PERFOR A CE CHARACTERISTICS
Frequency Variation vs R
SET
4
3
2
T
A
= 25°C
GUARANTEED LIMITS APPLY OVER
20kΩ
≤
R
SET
≤
400kΩ
1.00
0.75
0.50
R
SET
= 63.4k
÷1
OR
÷10
OR
÷100
VARIATION (%)
VARIATION (%)
1
0
–1
–2
–3
–4
1k
10k
0.25
0
–0.25
–0.50
–0.75
JITTER (%
P-P
)
TYPICAL HIGH
TYPICAL LOW
100k
R
SET
(Ω)
Supply Current vs Output
Frequency [SSFM Disabled,
2-Phase Mode (M = 1)]
3.5
3.0
2.5
÷1,
5V
2.0
1.5
÷100,
5V
1.0
0.5
0
÷100,
3V
÷10,
3V
1k
÷1,
3V
10M
6902 G04
OUTPUT RESISTANCE (Ω)
SUPPLY CURRENT (mA)
10k
100k
1M
OUTPUT FREQUENCY (Hz)
4
U W
1M
6902 G01
Frequency Variation Over
Temperature
1.0
0.9
0.8
TYPICAL
HIGH
0.7
0.6
0.5
0.4
0.3
0.2
0.1
–20
0
20
40
60
TEMPERATURE (°C)
80
6902 G02
Peak-to-Peak Jitter vs Output
Frequency (M = 1, 2-Phase Mode)
÷1,
V
A
= 5V
÷1,
V
A
= 3V
TYPICAL
LOW
÷10
÷100
1k
10k
100k
1M
OUTPUT FREQUENCY (Hz)
10M
6902 G03
–1.00
–40
0
Output Resistance
vs Supply Voltage
140
T
A
= 25°C
120
OUTPUT SOURCING CURRENT
100
÷10,
5V
80
60
OUTPUT SINKING CURRENT
40
2.5
3.0
3.5 4.0 4.5
5.0
SUPPLY VOLTAGE (V)
5.5
6.0
6902 G05
6902f
LTC6902
TYPICAL PERFOR A CE CHARACTERISTICS
Output Operating at 20MHz,
V
S
= 5V
V
+
= 5V, R
SET
= 10k, C
L
= 10pF
1V/DIV
0V
QUICK DESIG GUIDE
V
+
0.1µF
R
MOD
R
SET
LTC6902
V
+
DIV
PH
DIV
PH
SET
MOD
GND
OUT4
OUT3
OUT2
6902 F01
OUT1 OUT4
OUT2 OUT3
Step 1. Select Multiphase Mode, Setting M
By selecting the multiphase mode, a division parameter M
is also chosen:
2-Phase: Connect PH Pin to GND
3-Phase: Leave PH Open
4-Phase: Connect PH Pin to V+
M=1
M=3
M=4
Step 2. Choosing Programmable Divider Setting N
A. For applications using spread spectrum frequency
modulation (SSFM) or applications that are constant fre-
quency where low clock jitter is the primary specification:
U W
Output Operating at 10MHz,
V
S
= 3V
V
+
= 3V, R
SET
= 20k, C
L
= 10pF
1V/DIV
0V
12.5ns/DIV
69012 G06
25ns/DIV
69012 G07
U
10MHz
20k
Ω
•
; 5kHz
≤
f
OUT
≤
20MHz
N • M
R
SET
R
Spreading Percentage
=
20 •
SET
R
MOD
f
OUT
=
OUT1
Figure 1. Typical Application with Design Equation
DIVIDER SETTING
N=1
N = 10
N = 100
Connect DIV Pin to GND
Leave DIV Open
Connect DIV Pin to V
+
FREQUENCY RANGE (f
OUT
• M)
2MHz to 20MHz
200kHz to 2MHz
< 200kHz
Note: The frequency range numbers are for a 5V supply where a 20MHz
output is the maximum frequency supported. For low supply applications
(2.7V
≤
V
+
≤
4V), the maximum rated output frequency is 10MHz and all
of the above numbers should be halved.
B. For constant frequency applications where frequency
accuracy is the primary specification:
DIVIDER SETTING
N=1
N = 10
N = 100
Connect DIV Pin to GND
Leave DIV Open
Connect DIV Pin to V
+
FREQUENCY RANGE (f
OUT
• M)
> 500kHz*
50kHz to 500kHz
< 50kHz
*The maximum frequency (f
OUT
• M) is 20MHz for 5V applications and is
10MHz for low supply applications (2.7V
≤
V
+
≤
4V).
6902f
5
FPGA/CPLD
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