Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsLinear ICsLTC6906IS6#TRMPBF

LTC6906

6906fc

TYPICAL APPLICATION

FEATURES DESCRIPTION

Micropower, 10kHz to 1MHz

Resistor Set Oscillator

in SOT-23

The LTC

6906 is a precision programmable oscillator that

is versatile, compact and easy to use. Micropower opera-

tion benefits portable and battery-powered equipment. At

100kHz, the LTC6906 consumes 12μA on a 3.3V supply.

A single resistor programs the oscillator frequency over

a 10:1 range with better than 0.5% initial accuracy. The

output frequency can be divided by 1, 3 or 10 to span a

100:1 total frequency range, 10kHz to 1MHz.

The LTC6906 is easily programmed according to this

simple formula:

OUT

1M H z

•

10 0k

SET

⎛

⎝

⎜

⎞

⎠

⎟

,N=

10,

⎧

⎨

⎪

⎩

⎪

DIV Pin = V

DIV Pin = Open

DIV Pin = GND

No decoupling capacitor is needed in most cases, yield-

ing an extremely compact solution occupying less than

20mm2. Contact LTC Marketing for a version of the part

with a shutdown feature or lower frequency operation.

The LTC6906 is available in the 6-lead SOT-23 (ThinSOT)

package.

Micropower Clock Generator

APPLICATIONS

Supply Current: 12μA at 100kHz

<0.65% Frequency Accuracy (from 0°C to 70°C)

Frequency Range: 10kHz to 1MHz

One Resistor Sets the Oscillator Frequency

Single Supply: 2.25V to 5.5V

–40°C to 125°C Operating Temperature Range

No Decoupling Capacitor Needed

Start-Up Time Under 200μs at 1MHz

First Cycle After Power-Up is Accurate

150Ω CMOS Output Driver

Low Profile (1mm) SOT-23 (ThinSOT™) Package

Low Cost Precision Programmable Oscillator

Rugged, Compact Micropower Replacement for

Crystal and Ceramic Oscillators

High Shock and Vibration Environments

Portable and Battery-Powered Equipment

PDAs and Cellular Phones

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property

of their respective owners.

Typical Supply Current vs Frequency

10kHz TO 1MHz

NO DECOUPLING

CAPACITOR

NEEDED

6906 TA01

SET

100k TO 1M

2.25V TO 3.6V

GND

DIV

OUT

GRD

SET

LTC6906

FREQUENCY (kHz)

POWER SUPPLY CURRENT (A)

800

6906 TA01b

400

200

1000

600 1200

= 3.6V

= 2.25V

= 5pF

= 25°C

Summary of content (14 pages)

PAGE 1
LTC6906 Micropower, 10kHz to 1MHz Resistor Set Oscillator in SOT-23 DESCRIPTION FEATURES n n n n n n n n n n n Supply Current: 12μA at 100kHz <0.65% Frequency Accuracy (from 0°C to 70°C) Frequency Range: 10kHz to 1MHz One Resistor Sets the Oscillator Frequency Single Supply: 2.25V to 5.
PAGE 2
LTC6906 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) V+ ................................................................ –0.3V to 6V DIV to GND .....................................–0.3V to (V+ + 0.3V) SET to GND .....................................–0.3V to (V+ + 0.3V) GRD to GND ....................................–0.3V to (V+ + 0.3V) TOP VIEW Operating Temperature Range (Note 7) LTC6906C ............................................–40°C to 85°C LTC6906I ........................................
PAGE 3
LTC6906 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. SYMBOL PARAMETER CONDITIONS RSET Frequency-Setting Resistor Range Δf/ΔT Frequency Drift Over Temp (Note 3) RSET = 316k Δf/ΔV Frequency Drift Over Supply (Note 3) Timing Jitter (Note 4) Sf MIN l 100 l 0.06 %/V Pin 3 = V+, 100k ≤ RSET ≤ 1000k Pin 3 = Open, 100k ≤ RSET ≤ 1000k Pin 3 = 0V, 100k ≤ RSET ≤ 1000k 0.03 0.07 0.
PAGE 4
LTC6906 TYPICAL PERFORMANCE CHARACTERISTICS Typical Frequency Error vs Temperature Typical Frequency Error vs Power Supply 0.50 0.40 0.40 1 0.20 0.10 RSET = 1M 0 RSET = 100k –0.10 –0.20 RSET = 100k 0.30 2.25V 0 0.20 3.6V –1 ERROR (%) FREQUENCY ERROR (%) 0.30 FREQUENCY ERROR (%) Typical Frequency Error vs RSET 0.50 2 2.25V 3.6V –2 V+ = 2.25V 0 V+ = 5V –0.10 RSET = 1M –3 –0.20 –0.30 –0.30 –4 –0.40 3 4 SUPPLY VOLTAGE (V) –0.
PAGE 5
LTC6906 PIN FUNCTIONS OUT (Pin 1): Oscillator Output. The OUT pin swings from GND to V+ with an output resistance of approximately 150Ω. For micropower operation, the load resistance must be kept as high as possible and the load capacitance as low as possible. GND (Pin 2): Ground. DIV (Pin 3): Divider Setting Input. This three-level input selects one of three internal digital divider settings, determining the value of N in the frequency equation.
PAGE 6
LTC6906 TEST CIRCUIT LTC6906 SUPPLY VOLTAGE V+ OUT GND GRD DIV SET CTEST EQUIVALENT CIRCUIT OF OSCILLOSCOPE OR FREQUENCY COUNTER PROBE CPROBE RPROBE 10M RSET 0.01% 10ppm/°C 6906 F01 CTEST = 1/(1/5pF – 1/CPROBE) = 7.5pF FOR A 15pF SCOPE PROBE Figure 1. Test Circuit with 5pF Effective Load EQUIVALENT INPUT AND OUTPUT CIRCUITS 6 V+ 6 V+ 20Ω 4 SET 6 1k 5 V+ GRD 200Ω TOTAL OUTPUT RESISTANCE 800pF 2 GND 2 6906 F02 Figure 2. V+ Pin 6 GND 2 6906 F03 Figure 3.
PAGE 7
LTC6906 THEORY OF OPERATION The LTC6906 is a precision, resistor programmable oscillator (see the Block Diagram). It generates a square wave at the OUT pin with a period directly proportional to the value of an external resistor, RSET. A feedback circuit measures and controls the oscillator frequency to achieve the highest possible accuracy. In equilibrium, this circuit ensures that the current in the SET pin, ISET, is balanced by IFB.
PAGE 8
LTC6906 APPLICATIONS INFORMATION Selecting RSET and the Divider Ratio 10000 10 1000 3 1 RSET (kΩ) The LTC6906 contains a master oscillator followed by a digital divider (see the Block Diagram). RSET determines the master oscillator frequency and the DIV pin sets the divider ratio, N. The range of frequencies accessible in each divider ratio overlap, as shown in Figure 7. This figure is derived from the equations in Table 1.
PAGE 9
LTC6906 APPLICATIONS INFORMATION Guarding Against PC Board Leakage Bypassing the Power Supply The LTC6906 uses relatively large resistance values for RSET to minimize power consumption. For RSET = 1M, the SET pin current is typically only 0.65μA. Thus, only 0.65nA leaking into the SET pin causes a 0.1% frequency error. Similarly, 1G of leakage resistance across RSET (1000 • RSET) causes the same 0.1% error.
PAGE 10
LTC6906 APPLICATIONS INFORMATION LS 330nH 3.3V LTC6906 V+ OUT GND GRD DIV SET RS 100Ω 1MHz 3.3V CLOAD RSET 100k LTC6906 V+ OUT GND GRD DIV SET 1MHz CLOAD RSET 100k 6906 F14 6906 F12 Figure 14. Test Circuit with a Resistive Power Supply 3.5 3.5 3 3 VOUT (V) VOUT (V) Figure 12. Test Circuit with an Inductive Power Supply 2 1 1 CLOAD = 5pF CLOAD = 10pF CLOAD = 20pF CLOAD = 50pF 0 4.65 4.75 4.95 4.85 TIME (s) 2 5.05 5.15 6906 F13 Figure 13.
PAGE 11
LTC6906 APPLICATIONS INFORMATION If the SET pin is driven with a current source generating ISET, the oscillator output frequency will be: V+ 3.6V TO 5.5V DC 100Ω 1μF LTC6906 V+ OUT GND GRD DIV SET ƒOSC ≅ RSET 6906 F16 Figure 16. Using the LTC6906 at Higher Supply Voltages Alternative Methods for Setting the Output Frequency Any means of sinking current from the SET pin will control the output frequency of the LTC6906.
PAGE 12
LTC6906 TYPICAL APPLICATIONS Setting Frequency to 0.1% Resolution with Standard Resistors LTC6906 V+ 2.25V TO 3.6V GND 10 3 1 DIV Trimming the Frequency 10kHz TO 1MHz 2.25V TO 3.6V GRD SET 1MHz WITH 2.5% RANGE LTC6906 OUT RA RA < RB/10 1% THIN FILM RB 100k TO 1M 0.1% THIN FILM Sine Wave Oscillator V+ OUT GND GRD DIV SET 1MHz LTC6906 2.25V TO 3.6V RA 97.6k V+ OUT GND GRD DIV SET 0.
PAGE 13
LTC6906 REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION PAGE NUMBER B 12/10 Added Note 9. 2-3 C 11/11 Reinsert symbols missing from Rev B Revised values in the Guarding Against PC Board Leakage section. 9 1, 4, 5, 6, 8, 9, 10, 11, 12 6906fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 14
LTC6906 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1799 1kHz to 33MHz ThinSOT Oscillator Single Output, Greater Frequency Range LTC6900 1kHz to 20MHz ThinSOT Oscillator Single Output, Greater Frequency Range LTC6902 Multiphase Oscillator with Spread Spectrum Frequency Modulation 2-, 3- or 4-Phase Outputs LTC6903/LTC6904 1kHz to 68MHz Serial Port Programmable Oscillator Very Wide Frequency Range with Digital Programmability LTC6905 17MHz to 170MHz ThinSOT Oscillator Single Output, Hig