Linear Technology LTC6908CS6-2, LTC6908 Datasheet

LTC6908-1/LTC6908-2

1

690812fa

690812 TA01b

FREQUENCY

(FUNDAMENTAL AND HARMONICS SHOWN)

150kHz

0

–10

–20

–30

–40

0

–10

–20

–30

–40

OUTPUT (dBc) OUTPUT (dBc)

30MHz

SSFM DISABLED

SSFM ENABLED

Resistor Set SOT-23
Oscillator with Spread
Spectrum Modulation

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 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 fi xed 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.

■

Switching Power Supply Clock Reference

■

Portable and Battery-Powered Equipment

■

Precision Programmable Oscillator

■

Charge Pump Driver

■

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 (TA = 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 Profi le (1mm) ThinSOT and DFN

(2mm × 3mm) Packages

APPLICATIO S

U

FEATURES

DESCRIPTIO

U

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

2.25MHz, 2.5V/8A Step-Down Regulator

TYPICAL APPLICATIO

U

C

BYP

44.2k

OUT1

OUT2

f

OUT

= 10MHz • 10k/R

SET

MOD

V

+

GND

SET

690812 TA01a

SVINTRACK

LTC3418

R

T

C

IN

100µF

0.2µH

LTC6908-1

RUN/SS
I

TH

PGOOD

SW

PGND
SGND

SYNC/MODE V

FB

PV

IN

820pF

1000pF

0.1µF
C

OUT

100µF
×2

V

OUT

2.5V
8A

4.32k

2k

41.2k

2.2M

V

IN

2.8V TO 5.5V

4.99k

150kHz to 30MHz Output

Frequency Spectrum

(9kHz Res BW)

LTC6908-1/LTC6908-2

2

690812fa

Total Supply Voltage (V+ to GND) ...............................6V

Maximum Voltage on any Pin
(GND – 0.3V) ≤ V

PIN

≤ (V+ + 0.3V)

Output Short Circuit Duration .......................... Indefi nite

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

(Note 1)

ABSOLUTE AXI U RATI GS

W

WW

U

PACKAGE/ORDER I FOR ATIO

UUW

TOP VIEW

MOD

OUT2

OUT1

SET

V

+

GND

DCB PACKAGE

6-LEAD (2mm × 3mm) PLASTIC DFN

4

5

7

6

3

2

1

T

JMAX

= 125°C, θJA = 64°C/W

EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB

V+ 1

GND 2

SET 3

6 OUT1

5 OUT2

4 MOD

TOP VIEW

S6 PACKAGE

6-LEAD PLASTIC TSOT-23

T

JMAX

= 150°C, θJA = 230°C/W

ORDER PART NUMBER DCB PART MARKING* ORDER PART NUMBER S6 PART MARKING*

LTC6908CDCB-1
LTC6908IDCB-1
LTC6908CDCB-2
LTC6908IDCB-2

LBXZ
LBXZ
LBYB
LBYB

LTC6908CS6-1
LTC6908IS6-1
LTC6908HS6-1
LTC6908CS6-2
LTC6908IS6-2
LTC6908HS6-2

LTBYC
LTBYC
LTBYC
LTBYD
LTBYD
LTBYD

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 specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.

Specifi ed 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

LTC6908-1/LTC6908-2

3

690812fa

The

●

denotes the specifi cations which apply over the full operating

temperature range, otherwise specifi cations are at T

A

= 25°C. Test conditions are V+ = 2.7V to 5.5V, RL = 5k, CL = 5pF unless otherwise

noted. The modulation is turned off (MOD is connected to OUT2) unless otherwise specifi ed. R

SET

is defi ned as the resistor connected

from the SET pin to the V

+

pin.

ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Δf

OUT

Frequency Accuracy (Note 4) V+ = 2.7V 250kHz ≤ f

OUT

≤ 5MHz

250kHz ≤ f

OUT

≤ 5MHz

50kHz ≤ f

OUT

< 250kHz

●

●

±0.5

±2

±2.5

±1.5
±2.5
±3.5

%
%
%

V

+

= 5V 250kHz ≤ f

OUT

≤ 5MHz

250kHz ≤ f

OUT

≤ 5MHz

50kHz ≤ f

OUT

< 250kHz

5MHz < f

OUT

≤ 10MHz

●

●

●

±1

±2.5

±3

±3.5

±2
±3
±4

±4.5

%
%
%
%

R

SET

Frequency Setting Resistor Range V+ = 2.7V | Δf

OUT

| ≤ 1.5%

| Δf

OUT

| ≤ 2.5%

| Δf

OUT

| ≤ 3.5%

●

●

20
20

400

400
400

2000

k
k
k

V

+

= 5V | Δf

OUT

| ≤ 2%

| Δf

OUT

| ≤ 3%

| Δf

OUT

| ≤ 4%

| Δf

OUT

| ≤ 4.5%

●

●

●

20
20

400

10

400
400

2000

20

k
k
k
k

Δf

OUT

/ΔT Frequency Drift Over Temperature R

SET

= 100k

●

±0.004 %/°C

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

●

●

0.04

0.4

0.25

0.9

%/V
%/V

Period Variation
(Frequency Spreading)

R

SET

= 100k, MOD Pin = V+, GND or OPEN

●

±7.5 ±10 ±12.5 %

Long-Term Stability of Output
Frequency (Note 8)

300 ppm/√kHr

Duty Cycle (Note 5) No Modulation, 250kHz ≤ f

OUT

≤ 1MHz

●

45 50 55 %

V

+

Operating Supply Range

●

2.7 5.5 V

I

S

Power Supply Current R

SET

= 2000k, RL = ∞, f

OUT

= 50kHz, MOD Pin = V

+

V+ = 5V
V

+

= 2.7V

●

●

0.4

0.4

0.65

0.6

mA
mA

R

SET

= 20k, RL = ∞, f

OUT

= 5MHz, MOD Pin = GND

V

+

= 5V

V

+

= 2.7V

●

●

1.25

0.9

1.7

1.3

mA
mA

V

IH_MOD

High Level MOD Input Voltage

●

V+ – 0.4 V

V

IL_MOD

Low Level MOD Input Voltage

●

0.4 V

I

MOD

MOD Pin Input Current (Note 6) MOD Pin = V+, V+ = 5V

MOD Pin = GND, V

+

= 5V

●

●

–4

2

–2

4µA

µA

V

OH

High Level Output Voltage (Note 6)
(OUT1, OUT2)

V+ = 5V IOH = –0.3mA
I

OH

= –1.2mA

●

●

4.75

4.4

4.9

4.7

V
V

V

+

= 2.7V IOH = –0.3mA

I

OH

= –0.8mA

●

●

2.35

1.85

2.6

2.2

V
V

V

OL

Low Level Output Voltage (Note 6) V+ = 5V IOL = 0.3mA

I

OL

= 1.2mA

●

●

0.05

0.2

0.15

0.5

V
V

V+ = 2.7V IOL = 0.3mA
I

OL

= 0.8mA

●

●

0.1

0.4

0.3

0.7

V
V

t

r

Output Rise Time (Note 7) V+ = 5V

V

+

= 2.7V

6

11

ns
ns

t

f

Output Fall Time (Note 7) V+ = 5V

V

+

= 2.7V

5
9

ns
ns

LTC6908-1/LTC6908-2

4

690812fa

TEMPERATURE (°C)

–

40

SUPPLY CURRENT (µA)

20

60

690812 G06

–

20 0 40

800

4

00

45

0

5

00

55

0

6

00

65

0

7

00

75

0

80

V+ = 5V

V+ = 3V

CL 5pF ON BOTH OUTPUTS
FREQUENCY = 1MHz
SSFM DISABLED

R

SET

(Ω)

10k

FREQUENCY ERROR (%)

5

4

3

2

1

0

–1

–2

–3

–4

–5

100k 1M 10M

690812 G01

TA = 25°C

TYPICAL MAX

GUARANTEED MAX
OVER TEMPERATURE

GUARANTEED MIN
OVER TEMPERATURE

TYPICAL MIN

R

SET

(Ω)

10k

FREQUENCY ERROR (%)

5

4

3

2

1

0

–1

–2

–3

–4

–5

100k 1M 10M

690812 G02

TA = 25°C

TYPICAL MAX

GUARANTEED MAX
OVER TEMPERATURE

GUARANTEED MIN
OVER TEMPERATURE

TYPICAL MIN

TEMPERATURE (°C)

–

40

FREQUENCY ERROR (%)

20

60

690812 G03

–

20 0 40

1.00

0.75

0.50

0.25

0

–

0.25

–

0.50

–

0.75

–

1.00
80

TYPICAL MAX

TYPICAL MIN

FREQUENCY (Hz)

10k

JITTER (%

P-P

)

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

100k 1M 10M

690812 G04

5V

3V

FREQUENCY (Hz)

10k

SUPPLY CURRENT (mA)

2.0

1.5

1.0

0.5

0

100k 1M 10M

690812 G05

5V SSFM DISABLED

3V SSFM DISABLED

5V SSFM ENABLED

3V SSFM ENABLED

Frequency Error vs R

SET

,

V

+

= 3V

Frequency Error vs R

SET

,

V

+

= 5V Frequency Error vs Temperature

Peak to Peak Jitter vs Output
Frequency

Supply Current vs Output
Frequency Supply Current vs Temperature

TYPICAL PERFOR A CE CHARACTERISTICS

UW

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 specifi ed performance from
0°C to 70°C. The LTC6908C is designed, characterized and expected to
meet specifi ed performance from –40°C to 85°C but is not tested or QA
sampled at these temperatures. The LTC6908I is guaranteed to meet
the specifi ed performance limits from –40°C to 85°C. The LTC6908H is
guaranteed to meet the specifi ed performance limits from –40°C to 125°C.

Note 4: Frequency accuracy is defi ned 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 specifi cations 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 specifi ed
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.

ELECTRICAL CHARACTERISTICS

LTC6908-1/LTC6908-2

5

690812fa

690812 G10

150kHz

FREQUENCY (7.5kHz/DIV)

SSFM DISABLED

RES BW = 220Hz

SSFM ENABLED

(N = 16)

20dBm

–

80dBm

10dB/DIV

690812 G11

5MHz

20dBm

–80dBm

10dB/DIV

FREQUENCY (250kHz/DIV)

SSFM DISABLED

RES BW = 9kHz

SSFM ENABLED

(N = 16)

690812 G09

40ns/DIV

V

OUT

(1V/DIV)

SUPPLY VOLTAGE (V)

2.5

OUTPUT RESISTANCE (Ω)

4.5

5.5

690812 G07

3.0 3.5

4.0 5.0

0

5

0

1

00

15

0

2

00

4

00

45

0

5

00

25

0

3

00

35

0

6.0

OUTPUT SINKING CURRENT

OUTPUT SOURCING CURRENT

TA = 25°C

Output Resistance vs Supply
Voltage

TYPICAL PERFOR A CE CHARACTERISTICS

UW

Output Operating at 5MHz,
V

+

= 3V

Output Operating at 10MHz,
V+ = 5V

Output Frequency Spectrum with
SSFM Enabled and Disabled

Output Frequency Spectrum with
SSFM Enabled and Disabled

690812 G08

80ns/DIV

V

OUT

(1V/DIV)