View LTC6905_196526.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

LTC6905 17MHz to 170MHz Resistor Set SOT-23 Oscillator
FEATURES

DESCRIPTIO
One External Resistor Sets the Frequency Fast Start-Up Time: 100s Typical Frequency Range: 17MHz to 170MHz Frequency Error 0.5% Typ 17MHz to 170MHz (TA = 0C to 70C, Over All Settings) 20ppm/C Temperature Stability Rise Time: 0.5ns, CL = 5pF Timing Jitter: 50ps at 170MHz 50% 2.5% Duty Cycle 6mA Typical Supply Current, fOSC = 100MHz CMOS Output Drives 500 Load (VS = 3V) Operates from a Single 2.7V to 5.5V Supply Low Profile (1mm) ThinSOTTM Package
The LTC(R)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, RSET, 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 RSET value. The LTC6905 features a proprietary feedback loop that linearizes the relationship between RSET 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 1 = + 1.5MHz * , N = 2, DIV Pin = Open N RSET 4, DIV Pin = GND
APPLICATIO S

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.
fOSC
For higher accuracy, fixed frequency versions that include an internal frequency-setting resistor, see the LTC6905XXX Series datasheet.
TYPICAL APPLICATIO
Typical Distribution of Frequency Error, TA = 25C
60 50 40 V+ = 3V RSET = 12k DIV = 1
Basic Connection
UNITS
5V 0.1F 10k RSET 25k 17.225MHz fOSC 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, RSET, 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 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 ....................................... - 40C to 85C LTC6905H ........................................ - 40C to 125C Specified Temperature Range (Note 8) LTC6905C ............................................... 0C to 70C LTC6905I .............................................-40C to 85C LTC6905H .........................................-40C to 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC6905CS5 LTC6905IS5 LTC6905HS5 S5 PART MARKING LTBJC
GND 2 SET 3 4 DIV
S5 PACKAGE 5-LEAD PLASTIC SOT-23
TJMAX = 125C, JA = 150C/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 TA = 25C or as noted. V+ = 2.7V to 5.5V, RL = 15k, CL = 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 (25C T 125C), LTC6905IS5 (25C T 85C) V+ = 2.7V, 17.225MHz < f < 170MHz V+ = 5V, 17.225MHz < f < 170MHz LTC6905HS5 (-40C T 125C), LTC6905IS5 (-40C T 85C) V+ = 2.7V, 17.225MHz < f < 170MHz V+ = 5V, 17.225MHz < f < 170MHz 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

MIN
TYP 0.5
MAX 1.4 2.2 1.7 2.5
UNITS % % % %

1.9 2.9

3.5 3.5 10 25 170 17.225
RSET fMAX fMIN f/T f/V
Pin 4 = V +, N = 1 Pin 4 = 0V, N = 4 RSET = 10k V+ = 2.7V to 5.5V, RSET = 10k

20 0.5 0.8 300 47.5 2.7 14 7 5 3 50 52.5 5.5 20 12 7 5
ppm/C %/V % ppm/kHr % V mA mA mA mA V
6905fa
V+ IS
Operating Supply Range Power Supply Current RSET = 10k, N = 1, RL = , fOSC = 170MHz, CL = 5pF RSET = 20k, N = 4, RL = , fOSC = 21.44MHz, CL = 5pF V + = 5.5V V + = 2.7V V + = 5.5V V + = 2.7V
V+ - 0.15
VIH
High Level DIV Input Voltage
2
U
% % % % k MHz MHz
W
U
U
WW
W
LTC6905
ELECTRICAL CHARACTERISTICS
SYMBOL VIL IDIV VOH 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 TA = 25C or as noted. V+ = 2.7V to 5.5V, RL= 15k, CL = 5pF, Pin 4 = V+ unless otherwise noted. All voltages are with respect to GND.
CONDITIONS
MIN V + = 5.5V V + = 5.5V IOH = - 1mA IOH = - 4mA IOH = - 1mA IOH = - 4mA IOL = 1mA IOL = 4mA IOL = 1mA IOL = 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 A A V V V V
Pin 4 = V + Pin 4 = 0V V+ = 5.5V
- 40 5.25 5.20 2.5 2.4
V + = 2.7V VOL Low Level Output Voltage (Note 4) V + = 5.5V V + = 2.7V tr, tf VSET OUT Rise/Fall Time (Note 5) Voltage at RSET Pin 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
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 fOSC 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 0C to 70C. The LTC6905C-XXX is designed, characterized and expected to meet specified performance from -40C to 85C but is not tested or QA sampled at these temperatures. The LTC6905I-XXX is guaranteed to meet specified performance from -40C to 85C. 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
UW
Frequency Error vs RSET
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
RSET (k)
6905fa
3
LTC6905 TYPICAL PERFOR A CE CHARACTERISTICS
ROUT vs V+
45 40
OUTPUT RESISTANCE ()
/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, VS = 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 0.1F 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+ determines 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 requires sourcing approximately 15A. Likewise, driving DIV low requires sinking 15A. 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 coupling from other PCB traces. OUT (Pin 5): Oscillator Output. This pin can drive 5k and/or 5pF loads. For larger loads, refer to the Applications Information section.
6905fa
4
UW
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, VS = 3V
1V/DIV
12.5ns/DIV
6905 G06
1ns/DIV
6905 G07
U
U
U
LTC6905
BLOCK DIAGRA
1 RSET IRES 3 SET V+
+ -
2 GND
-
VBIAS IRES
+
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 (IRES). The voltage on the SET pin is forced to approximately 1V below V+ by the PMOS transistor and its gate bias voltage. A resistor RSET, connected between the V+ and SET pins, "locks together" the voltage (V + - VSET) and current, IRES, variation. This provides the LTC6905's high precision. The master oscillation frequency reduces to:
RSET ()
168.5MHz * 10k f MO = + 1.5MHz RSET
To extend the output frequency range, the master oscillator 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 frequencies between 17.225MHz and 170MHz. The divideby 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
VRES = 1V 5% (V+ - VSET)
+
GAIN = 1 MASTER OSCILLATOR
PROGRAMMABLE DIVIDER (/1, 2 OR 4)
fOSC =
fMO
N
OUT
5
-
DIVIDER SELECT
V+ 15A
THREE-STATE INPUT DETECT
DIV
4
15A
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 overlapping frequencies.
30
25 /4 /2 20 /1
15
10
5
10
110 60 160 OUTPUT FREQUENCY (MHz)
6905 F01
Figure 1. RSET vs Output Frequency
6905fa
5
LTC6905
APPLICATIO S I FOR ATIO
SELECTING THE DIVIDER SETTING AND RESISTOR The LTC6905's master oscillator has a frequency range spanning 68.9MHz to 170MHz. A programmable divider extends the frequency range from 17.225MHz to 170MHz. Table 1 describes the recommended frequencies for each divider setting. Note that the ranges overlap; at some frequencies there are two divider/resistor combinations that result in the same frequency. Choosing a higher divider setting will result in less jitter at the expense of slightly higher supply current.
Table 1. Frequency Range vs Divider Setting
DIVIDER SETTING /1 DIV (Pin 4) = V+ /2 DIV (Pin 4) = Floating /4 DIV (Pin 4) = GND FREQUENCY RANGE 68.9MHz to 170MHz 34.45MHz to 85MHz 17.225MHz to 43MHz
After choosing the proper divider setting, determine the correct frequency-setting resistor. Because of the linear correspondence between oscillation period and resistance, a simple equation relates resistance with frequency. 1 168.5MHz * , N = 2 fOSC - 1.5MHz 4 (RSETMIN = 10k, RSETMAX = 25k) RSET = 10k N Any resistor, RSET, tolerance adds to the inaccuracy of the oscillator, fOSC. START-UP TIME The start-up time and settling time to within 1% of the final frequency is typically 100s. MAXIMUM OUTPUT LOAD The LTC6905 output (Pin 5) can drive a capacitive load (CLOAD) of 5pF or more. Driving a CLOAD greater than 5pF depends on the oscillator's frequency (fOSC) and output resistance (ROUT). The output rise time or fall time due to ROUT and CLOAD is equal to 2.2 * ROUT * CLOAD (from 10% to 90% of the rise or fall transition). If the total output rise time plus fall time is arbitrarily specified to be equal to or less than 20% of the oscillator's period (1/fOSC), then the maximum output CLOAD in picofarads (pF) should be equal to or less than [45454/(ROUT * fOSC)] (ROUT in ohms and fOSC in MHz).
6
U
Example: An LTC6905 is operating with a 3V power supply and is set for a fOSC = 50MHz. ROUT with V+ = 3V is 27 (using the ROUT vs V+ graph in the Typical Performance Characteristics). The maximum output CLOAD should be equal to or less than [45454/(27 * 50)] = 33.6pF. The lowest resistive load Pin 5 can drive can be calculated using the minimum high level output voltage in the Electrical Characteristics. With a V+ equal to 5.5V and 4mA output current, the minimum high level output voltage is 5V and the lowest resistive load Pin 5 can drive is 1.25k (5V/4mA). With a V+ equal to 2.7V and 4mA output current, the minimum high level output voltage is 1.9V and the lowest resistive load Pin 5 can drive is 475 (1.9V/4mA). FREQUENCY ACCURACY AND POWER SUPPLY NOISE The frequency accuracy of the LTC6905 may be affected when its power supply generates noise with frequency contents equal to fMO/64 or its multiples (fMO is the internal LTC6905 master oscillator frequency before the divider and fMO/64 is the master oscillator control loop frequency). If for example, the master oscillator frequency is set equal to 80MHz and the LTC6905 is powered by a switching regulator, then the oscillator frequency may show an additional error if the switching frequency is 1.4MHz (80MHz/64). JITTER AND POWER SUPPLY NOISE If the LTC6905 is powered by a supply that has frequency contents equal to the output frequency then the oscillators jitter may increase. In addition, power supply ripple in excess of 20mV at any frequency may increase jitter. JITTER AND DIVIDE RATIO At a given output frequency, a higher master oscillator frequency and a higher divide ratio will result in lower jitter and higher power supply dissipation. Indeterminate jitter percentage will decrease by a factor of slightly less than the square root of the divider ratio, while determinate jitter will not be similarly attenuated. Please consult the specification tables and Jitter vs Frequency graph showing jitter at various divider ratios.
6905fa
W
UU
LTC6905
APPLICATIO S I FOR ATIO
JITTER AND STRAY CAPACITANCE ON THE SET PIN (PIN 3) The stray capacitance on the SET pin (Pin 3) should be limited to 10pF or less to avoid increased jitter or unstable oscillation. LTC6905 SUGGESTED CRITICAL COMPONENT LAYOUT In order to provide the specified performance, it is required that the frequency setting resistor RSET and the supply bypass capacitor be placed as close as possible to the LTC6905. The following additional rules should be followed for best performance: 1) The bypass capacitor must be placed as close as possible to the LTC6905, and no vias should be placed between the capacitor and the LTC6905. The bypass capacitor must be on the same side of the circuit board as the LTC6905.
PACKAGE DESCRIPTIO
0.62 MAX
(Reference LTC DWG # 05-08-1635)
0.95 REF 2.90 BSC (NOTE 4)
3.85 MAX 2.62 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.20 BSC 1.00 MAX DATUM `A'
0.30 - 0.50 REF 0.09 - 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
2) The resistor RSET should be placed as close as possible to the LTC6905, and the connection of RSET to VCC should be closely shared with the bypass capacitor. The resistor RSET may be placed on the opposite side of the board from the LTC6905, directly underneath the bypass capacitor. 3) If a ground plane is used, the connection of the LTC6905 to the ground plane should be as close as possible to the LTC6905 GND pin and should be composed of multiple, high current capacity vias.
R C LTC6905
6905 F02
U
W
UU
Figure 2. LTC6905 Suggested Critical Component Layout
S5 Package 5-Lead Plastic TSOT-23
1.22 REF
1.4 MIN
2.80 BSC
1.50 - 1.75 (NOTE 4)
PIN ONE 0.30 - 0.45 TYP 5 PLCS (NOTE 3)
0.95 BSC
0.80 - 0.90 0.01 - 0.10
1.90 BSC
S5 TSOT-23 0302
6905fa
7
LTC6905
APPLICATIO S I FOR ATIO
ALTERNATIVE METHODS OF SETTING THE OUTPUT FREQUENCY OF THE LTC6905 The LTC6905 may be programmed by any method that sources a current into the SET pin (Pin 3). The accuracy of the programming is best with a simple resistor because the LTC6905 takes into account both the voltage at the SET pin and the current into the SET pin when generating the output frequency. Since the voltage at the SET pin can vary by as much as 5%, setting the frequency using a current rather than a resistor will result in as much as 5% additional inaccuracy in the output frequency.
V+ 0.1F RSET 10k ICNTRL 0A TO 60A
1 2 3
OUT V+ LTC6905 GND SET DIV
6905 F03
5 fOSC 69.8MHz TO 170MHz 4 V+ N=1
Figure 3. Current Controlled Oscillator
V + = 3V 0.1F RSET 10k RCNTRL 33.2k
1 2 3
V+ OUT LTC6905 GND SET DIV
6905 F04
5 fOSC 69.8MHz TO 170MHz 4 V+ N=1
+ -
VCNTRL 0V TO 2V
Figure 4. Voltage Controlled Oscillator
RELATED PARTS
PART NUMBER LTC1799 LTC6900 LTC6902 LTC6903/LTC6904 LTC6905-XXX Series LTC6906 DESCRIPTION 1kHz to 33MHz ThinSOT Oscillator 1kHz to 20MHz ThinSOT Oscillator Multiphase Oscillator with Spread Spectrum Modulation 1kHz to 68MHz Serial Port Programmable Oscillator Fixed Frequency LTC6905 Micropower, 10kHz to 1MHz Resistor Set ThinSOT Oscillator COMMENTS Single Output, High Frequency Operation Single Output Lower Power 2-, 3- or 4-Phase Outputs 3-Wire or I2CTM Programmable High Accuracy, No External Resistor Ultralow Power, Resistor Sets Frequency
6905fa LT/TP 0205 1K REV A * PRINTED IN USA
I2C is a trademark of Philips Electronics N.V.
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
www.linear.com
U
Figure 3 shows a method to control the frequency of the LTC6905 using a current source. RSET, in this case, sets a maximum frequency according to the regular expression for fOSC. The current source will subtract current from the SET pin to lower the frequency. Figure 4 shows a method for controlling the frequency of the LTC6905 using a voltage source. In this case, RSET sets a constant current into the SET pin, and RCNTRL will subtract from this current in order to change the frequency. Increasing VCNTRL will increase the output frequency.
V + - VSET - ICNTRL 168.5MHz * 10k * 1 RSET + 1.5MHz fOSC = N V + - VSET
W
UU
ICNTRL Frequency 100kHz Example (Figure 3): VSET = (V+ - 1V), RSET = 10k, N = 1
fOSC = 168.5MHz * (1 - 10k * ICNTRL ) + 1.5MHz
[
]
V + - VSET VSET - VCNTRL - 168.5MHz * 10k * RCNTRL 1 RSET fOSC = + 1.5MHz + -V N V SET
VCNTRL Frequency 100kHz Example (Figure 4): VSET = (V+ - 1V), RSET = 10k, RCNTRL = 33.2k, N = 1, V+ = 3V
2V - VCNTRL 1 - fOSC = 168.5MHz * 10k * + 1.5MHz 33.2k 10k
(c) LINEAR TECHNOLOGY CORPORATION 2005

▲Up To Search▲

Price & Availability of LTC6905

	To Download LTC6905 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .