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 modulation
(SSFM) can be activated for improved electromagnetic
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
outputs. 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.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
■
■
■
■
Switching Power Supply Clock Reference
Portable and Battery-Powered Equipment
Precision Programmable Oscillator
Charge Pump Driver
TYPICAL APPLICATIO
V
IN
2.8V TO 5.5V
C
BYP
0.1µF
2.25MHz, 2.5V/8A Step-Down Regulator
0
OUTPUT (dBc)
SV
IN
TRACK PV
IN
V
+
OUT1
2.2M
41.2k
R
T
LTC3418
RUN/SS
I
TH
4.99k
820pF
PGOOD
PGND
SGND
SW
C
IN
100µF
0.2µH
–10
–20
–30
–40
0
OUTPUT (dBc)
V
OUT
2.5V
8A
C
OUT
100µF
×2
LTC6908-1
GND
OUT2
44.2k
SET
f
OUT
= 10MHz • 10k/R
SET
MOD
690812 TA01a
1000pF
SYNC/MODE V
FB
4.32k
2k
U
150kHz to 30MHz Output
Frequency Spectrum
(9kHz Res BW)
SSFM DISABLED
SSFM ENABLED
–10
–20
–30
–40
150kHz
FREQUENCY
(FUNDAMENTAL AND HARMONICS SHOWN)
690812 TA01b
U
U
30MHz
690812fa
1
LTC6908-1/LTC6908-2
ABSOLUTE
(Note 1)
AXI U RATI GS
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
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
PACKAGE/ORDER I FOR ATIO
TOP VIEW
OUT2
OUT1
MOD
6
5
4
TOP VIEW
V
+
1
6 OUT1
5 OUT2
4 MOD
7
1
SET
2
V
+
3
GND
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 PART NUMBER
LTC6908CDCB-1
LTC6908IDCB-1
LTC6908CDCB-2
LTC6908IDCB-2
DCB PART MARKING*
LBXZ
LBXZ
LBYB
LBYB
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
2
U
U
W
W W
U
W
GND 2
SET 3
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
T
JMAX
= 150°C,
θ
JA
= 230°C/W
ORDER PART NUMBER
LTC6908CS6-1
LTC6908IS6-1
LTC6908HS6-1
LTC6908CS6-2
LTC6908IS6-2
LTC6908HS6-2
S6 PART MARKING*
LTBYC
LTBYC
LTBYC
LTBYD
LTBYD
LTBYD
690812fa
LTC6908-1/LTC6908-2
The
●
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.
SYMBOL
Δf
OUT
PARAMETER
Frequency Accuracy (Note 4)
CONDITIONS
V
+
= 2.7V
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%
●
●
●
●
●
●
●
●
●
●
●
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
TYP
±0.5
±2
±2.5
±1
±2.5
±3
±3.5
MAX
±1.5
±2.5
±3.5
±2
±3
±4
±4.5
400
400
2000
400
400
2000
20
UNITS
%
%
%
%
%
%
%
k
k
k
k
k
k
k
%/°C
%/V
%/V
%
ppm/√kHr
V
+
= 5V
R
SET
Frequency Setting Resistor Range
V
+
= 2.7V
20
20
400
20
20
400
10
±0.004
0.04
0.4
±7.5
±10
300
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
= 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
V
OL
Low Level Output Voltage (Note 6)
V
+
= 5V
V
+
= 2.7V
t
r
t
f
Output Rise Time (Note 7)
Output Fall Time (Note 7)
V
+
= 5V
V
+
= 2.7V
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
No Modulation, 250kHz ≤ f
OUT
≤ 1MHz
R
SET
= 100k, MOD Pin = V
+
, GND or OPEN
0.25
0.9
±12.5
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
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
0.15
0.5
0.3
0.7
V
V
V
V
ns
ns
ns
ns
690812fa
3
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 QA
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.
