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ManualsBrandsLinear Technology ManualsClockProgrammable Oscillator SOT-23

LTC1799

1799fc

Typical applicaTion

FeaTures DescripTion

1kHz to 33MHz

Resistor Set SOT-23 Oscillator

The LTC

1799 is a precision oscillator that is easy to use

and occupies very little PC board space. The oscillator

frequency is programmed by a single external resistor

SET

). The LTC1799 has been designed for high accuracy

operation (≤1.5% frequency error) without the need for

external trim components.

The LTC1799 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. The frequency-setting

resistor can vary from 3k to 1M to select a master oscil-

lator frequency between 100kHz and 33MHz (5V supply).

The three-state DIV input determines whether the master

clock is divided by 1, 10 or 100 before driving the out-

put, providing three frequency ranges spanning 1kHz to

33MHz (5V supply). The LTC1799 features a proprietary

feedback loop that linearizes the relationship between R

SET

and frequency, eliminating the need for tables to calculate

frequency. The oscillator can be easily programmed using

the simple formula outlined below:

OSC

=10MHz •

10k

N • R

SET













, N=

100,

10,











DIV Pin = V

DIV Pin =Open

DIV Pin =GND

applicaTions

One External Resistor Sets the Frequency

Fast Start-Up Time: <1ms

1kHz to 33MHz Frequency Range

Frequency Error ≤1.5% 5kHz to 20MHz

= 25°C)

Frequency Error ≤2% 5kHz to 20MHz

= 0°C to 70°C)

±40ppm/°C Temperature Stability

0.05%/V Supply Stability

50% ±1% Duty Cycle 1kHz to 2MHz

50% ±5% Duty Cycle 2MHz to 20MHz

1mA Typical Supply Current

100Ω CMOS Output Driver

Operates from a Single 2.7V to 5.5V Supply

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

Low Cost Precision Oscillator

Charge Pump Driver

Switching Power Supply Clock Reference

Clocking Switched Capacitor Filters

Fixed Crystal Oscillator Replacement

Ceramic Oscillator Replacement

Small Footprint Replacement for Econ Oscillators

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. Protected by U.S. Patents including 6342817 and 6614313.

Basic Connection

Typical Distribution of Frequency Error,

= 25°C (5kHz ≤ f

OSC

≤ 20MHz, V

= 5V)

TSOT-23 Actual Size

1kHz ≤ f

OSC

≤ 33MHz

3k ≤ R

SET

≤ 1M

0.1µF

1799 TA01

GND

LTC1799

SET

OUT

DIV

OPEN

÷10

÷100

÷1

UNITS (%)

–1.25 –0.75 –0.25 0 0.25 0.75 1.25

FREQUENCY ERROR (%)

1799 TA02

Summary of content (14 pages)

PAGE 1
LTC1799 1kHz to 33MHz Resistor Set SOT-23 Oscillator Features n n n n n n n n n n n n n Description One External Resistor Sets the Frequency Fast Start-Up Time: <1ms 1kHz to 33MHz Frequency Range Frequency Error ≤1.5% 5kHz to 20MHz (TA = 25°C) Frequency Error ≤2% 5kHz to 20MHz (TA = 0°C to 70°C) ±40ppm/°C Temperature Stability 0.05%/V Supply Stability 50% ±1% Duty Cycle 1kHz to 2MHz 50% ±5% Duty Cycle 2MHz to 20MHz 1mA Typical Supply Current 100Ω CMOS Output Driver Operates from a Single 2.7V to 5.
PAGE 2
LTC1799 Absolute Maximum Ratings Pin Configuration (Note 1) TOP VIEW 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) Operating Temperature Range LTC1799C................................................. 0°C to 70°C LTC1799I..............................................–40°C to 85°C LTC1799H...........................................
PAGE 3
LTC1799 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+ = 2.7V to 5.5V, RL = 5k, CL = 5pF, unless otherwise noted. All voltages are with respect to GND. SYMBOL PARAMETER Duty Cycle (Note 7) V+ Operating Supply Range IS Power Supply Current CONDITIONS Pin 4 = V+ or Open (DIV Either by 100 or 10) Pin 4 = 0V (DIV by 1), RSET = 5k to 200k l 2.
PAGE 4
LTC1799 Typical Performance Characteristics 4 Frequency Variation Over Temperature Frequency Variation vs RSET 1.00 TA = 25°C GUARANTEED LIMITS APPLY OVER 5k TO 200k RANGE 3 0.75 0.50 TYPICAL HIGH 1 VARIATION (%) VARIATION (%) 2 0 TYPICAL LOW –1 –0.25 –3 –0.75 10 100 RSET (kΩ) 0.7 Supply Current vs Output Frequency 4.0 SUPPLY CURRENT (mA) ÷1 0.4 ÷10 0.2 ÷100 0.1 3.5 TA = 25°C CL = 5pF RL = 1M 3.0 ÷1 (5V) 2.5 ÷10 (5V) 2.0 ÷100 (5V) 1.5 1.0 0.
PAGE 5
LTC1799 Pin Functions 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 a ground plane with a 0.1µF capacitor. 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 LTC1799 to approximately 1.13V below the V+ voltage.
PAGE 6
LTC1799 Theory of Operation As shown in the Block Diagram, the LTC1799’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 1.13V below V+ by the PMOS transistor and its gate bias voltage. This voltage is accurate to ± 7% at a particular input current and supply voltage (see Figure 1). The effective input resistance is approximately 2k.
PAGE 7
LTC1799 Applications Information Selecting the Divider Setting and Resistor The LTC1799’s master oscillator has a frequency range spanning 0.1MHz to 33MHz. However, accuracy may suffer if the master oscillator is operated at greater than 10MHz with a supply voltage lower than 4V. A programmable divider extends the frequency range to greater than three decades. Table 1 describes the recommended frequencies for each divider setting.
PAGE 8
LTC1799 Applications Information Power Supply Rejection Start-Up Time Low Frequency Supply Rejection (Voltage Coefficient) The start-up time and settling time to within 1% of the final value can be estimated by tSTART ≅ RSET(2.8µs/kΩ) + 20µs. Note the start-up time depends on RSET and it is independent from the setting of the divider pin. For instance with RSET = 50k, the LTC1799 will settle with 1% of its 200kHz final value (N = 10) in approximately 160µs.
PAGE 9
LTC1799 Applications Information Jitter The typical jitter is listed in the Electrical Characteristics and shown in the Typical Performance Characteristics. These specifications assume that the capacitance on SET (Pin 3) is limited to less than 10pF, as suggested in the Pin Functions description. If this requirement is not met, the jitter will increase. For more information, contact Linear Technology Applications group.
PAGE 10
LTC1799 Applications Information Once RIN/RSET is known, calculate RSET from: RSET = ( 10MHz 10k • • N fOSC(MAX) )   RIN   +   VIN(MAX) − V + VRES  1+  RSET       R    VRES  IN   RSET    (3) Maximum VCO Modulation Bandwidth The maximum VCO modulation bandwidth is 10kHz; that is, the LTC1799 will respond to changes in VIN at a rate up to 25kHz.
PAGE 11
LTC1799 Typical Application Low Power 80Hz to 8kHz Sine Wave Generator (IQ < 4mA) 3V 1 C1 0.1µF RSET 2 3 V+ OUT LTC1799 GND SET DIV fOSC 5 3V 3V, N = 100 SW1 OPEN, N = 10 4 74HC4520 1 3V 2 16 C2 0.1µF 10 7 8 800Hz ≤ fSINE 8kHz, N = 10 80Hz ≤ fSINE 800Hz, N = 100 9 15 CLOCK A Q1A ENABLE A Q2A VDD Q3A ENABLE B Q4A RESET A Q1B VSS Q2B CLOCK B Q3B RESET B Q4B 3 ÷2 4 ÷4 5 ÷8 6 ÷16 11 ÷32 12 ÷64 1 2 3 R61 10k 4 R51 5.11k R31 51.
PAGE 12
LTC1799 Package Description S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 TYP 5 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 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.
PAGE 13
LTC1799 Revision History (Revision history begins at Rev C) REV DATE DESCRIPTION PAGE NUMBER C 1/11 Revised part number in Maximum VCO Modulation Bandwidth section. 10 1799fc 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.
PAGE 14
LTC1799 Typical Applications Shutting Down the LTC1799 5V ON/SHDN 74AC04 R1 10k 1 C1 0.1µF 2 3 V+ OUT LTC1799 5 OUT GND SET DIV 4 1799 TA08 Output Frequency vs Temperature 1400 Temperature-to-Frequency Converter RT 100k THERMISTOR 1 C1 0.