LTC1799CS5#TRMPBF

LTC1799 

## 1kHz to 33MHz Resistor Set SOT-23 Oscillator 

## **FEATURES** 

- n **One External Resistor Sets the Frequency** 

- n **Fast Start-Up Time: <1ms** 

- n **1kHz to 33MHz Frequency Range** 

- n Frequency Error ≤1.5% 5kHz to 20MHz (TA = 25°C) 

- n Frequency Error ≤2% 5kHz to 20MHz (TA = 0°C to 70°C) 

- n ±40ppm/°C Temperature Stability 

- n 0.05%/V Supply Stability 

- n 50% ±1% Duty Cycle 1kHz to 2MHz 

- n 50% ±5% Duty Cycle 2MHz to 20MHz 

- n 1mA Typical Supply Current 

- n 100Ω CMOS Output Driver 

- n Operates from a Single 2.7V to 5.5V Supply 

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

- n AEC-Q100 Qualified for Automotive Applications 

## **APPLICATIONS** 

- n Low Cost Precision Oscillator 

- n Switching Power Supply Clock Reference 

- n Clocking Switched Capacitor Filters 

- n Fixed Crystal Oscillator Replacement 

- n Ceramic Oscillator Replacement 

All registered trademarks and trademarks are the property of their respective owners. Protected by U.S. Patents including 6342817 and 6614313. 

## **DESCRIPTION** 

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 (RSET). 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 oscillator 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 output, providing three frequency ranges spanning 1kHz to 33MHz (5V supply). The LTC1799 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: 

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## **TYPICAL APPLICATION** 

## **Basic Connection** 

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5V 1kHz ≤ fOSC ≤ 33MHz<br>1 5<br>V [+] OUT<br>0.1µF LTC1799<br>3k ≤ RSET ≤ 1M 2 GND 5V<br>÷100<br>3 4 ÷10<br>SET DIV OPEN<br>1799 TA01 ÷1<br>**----- End of picture text -----**<br>


**TSOT-23 Actual Size** 

**Typical Distribution of Frequency Error, TA = 25°C (5kHz ≤ fOSC ≤ 20MHz, V[+] = 5V)** 

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25<br>20<br>15<br>10<br>5<br>0<br>–1.25 –0.75 –0.25 0 0.25 0.75 1.25<br>FREQUENCY ERROR (%)<br>1799 TA02<br>UNITS (%)<br>**----- End of picture text -----**<br>


Rev. E 

1 

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## LTC1799 

## **ABSOLUTE MAXIMUM RATINGS** 

## **PIN CONFIGURATION** 

## **(Note 1)** 

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 .......................................... –40°C to 125°C Storage Temperature Range ..................–65°C to 150°C Lead Temperature (Soldering, 10 sec) ...................300°C 

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TOP VIEW<br>V [+] 1 5 OUT<br>GND 2<br>SET 3 4 DIV<br>S5 PACKAGE<br>5-LEAD PLASTIC TSOT-23<br>TJMAX = 150°C, θJA = 256°C/W<br>**----- End of picture text -----**<br>


## **ORDER INFORMATION** 

|**TAPE AND REEL (MINI)**|**TAPE AND REEL**|**PART MARKING***|**PACKAGE DESCRIPTION**|**TEMPERATURE RANGE**|
|---|---|---|---|---|
|LTC1799CS5#TRMPBF|LTC1799CS5#TRPBF|LTND|5-Lead Plastic TSOT-23|0°C to 70°C|
|LTC1799IS5#TRMPBF|LTC1799IS5#TRPBF|LTNE|5-Lead Plastic TSOT-23|–40°C to 85°C|
|LTC1799HS5#TRMPBF|LTC1799HS5#TRPBF|LTND|5-Lead Plastic TSOT-23|–40°C to 125°C|
|**AUTOMOTIVE PRODUCTS****|||||
|LTC1799IS5#WTRMPBF|LTC1799IS5#WTRPBF|LTNE|5-Lead Plastic TSOT-23|–40°C to 85°C|
|LTC1799HS5#WTRMPBF|LTC1799HS5#WTRPBF|LTND|5-Lead Plastic TSOT-23|–40°C to 125°C|



TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container. 

Contact the factory for parts specified with wider operating temperature ranges. Contact the factory for information on lead based finish parts. 

Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. 

****** Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for these models. 

Rev. E 

2 

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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.** 

|<br>**voltages**|<br>**are with respect to GND.**|||||||
|---|---|---|---|---|---|---|---|
|**SYMBOL**|**PARAMETER**|**CONDITIONS**||||**MIN**<br>**TYP**<br>**MAX**|**UNITS**|
|∆f|Frequency Accuracy<br>(Notes 2, 3)|V+= 5V|5kHz ≤ f ≤ 20MHz<br>5kHz ≤ f ≤ 20MHz, LTC1799C<br>5kHz ≤ f ≤ 20MHz, LTC1799I/H<br>1kHz ≤ f ≤ 5kHz<br>20MHz ≤ f ≤ 33MHz||l<br>l|<br>±0.5<br>±2.5<br>±2.5<br>±1.5<br>±2<br>±2.5|%<br>%<br>%<br>%<br>%|
|||V+= 3V|5kHz ≤ f ≤ 10MHz<br>5kHz ≤ f ≤ 10MHz, LTC1799C<br>5kHz ≤ f ≤ 10MHz, LTC1799I/H<br>1kHz ≤ f ≤ 5kHz<br>10MHz ≤ f ≤ 20MHz||l<br>l|<br>±0.5<br>±2.5<br>±2.5<br>±1.5<br>±2<br>±2.5|%<br>%<br>%<br>%<br>%|
|RSET|Frequency-Setting Resistor Range||∆f| < 1.5%||V+= 5V<br>V+= 3V||5<br>10<br>200<br>200|kΩ<br>kΩ|
|fMAX|Maximum Frequency||∆f| < 2.5%, Pin 4 = 0V||V+= 5V<br>V+= 3V||33<br>20|MHz<br>MHz|
|fMIN|Minimum Frequency||∆f|< 2.5%, Pin 4 = V+||||1|kHz|
|∆f/∆T|Freq Drift Over Temp(Note 3)|RSET= 31.6k|||l|±0.004|%/°C|
|∆f/∆V|Freq Drift Over Supply(Note 3)|V+= 3V to 5V, RSET= 31.6k|||l|0.05<br>0.1|%/V|
||Timing Jitter<br>(Note 4)|Pin 4 = V+<br>Pin 4 = Open<br>Pin 4 = 0V||||0.06<br>0.13<br>0.4|%<br>%<br>%|
||Long-Term Stability of Output Frequency|||||300|ppm/√kHr|
||Duty Cycle (Note 7)|Pin 4 = V+or Open (DIV Either by 100 or 10)<br>Pin 4 = 0V(DIV by 1), RSET= 5k to 200k|||l<br>l|<br>49<br>45<br>50<br>50<br>51<br>55|%<br>%|
|V+|Operating Supply Range||||l|2.7<br>5.5|V|
|IS|Power Supply Current|RSET= 200k, Pin 4 = V+, RL= ∞||V+= 5V|l|0.7<br>1.1|mA|
|||RSET= 10k, Pin 4 = 0V, RL= ∞||V+= 5V<br>V+= 3V|l<br>l|<br>2.4<br>2|mA<br>mA|
|VIH|High Level DIV Input Voltage||||l|V+– 0.4|V|
|VIL|Low Level DIV Input Voltage||||l|0.5|V|
|IDIV|DIV Input Current (Note 5)|Pin 4 = V+<br>Pin 4 = 0V||V+= 5V<br>V+= 5V|l<br>l|<br>–8<br>5<br>–5<br>8|µA<br>µA|



Rev. E 

3 

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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**|**CONDITIONS**|**CONDITIONS**|**CONDITIONS**|**MIN**<br>**TYP**<br>**MAX**|**UNITS**|<br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br>|
|---|---|---|---|---|---|---|---|
|VOH|High Level Output Voltage (Note 5)|V+= 5V,<br>LTC1799C/I|IOH= –1mA<br>IOH= –4mA|l<br>l|<br>4.8<br>4.5<br>4.95<br>4.8|V<br>V||
|||V+= 5V,<br>LTC1799H|IOH= –1mA<br>IOH= –4mA|l<br>l|<br>4.75<br>4.40<br>4.95<br>4.75|V<br>V||
|||V+= 3V,<br>LTC1799C/I|IOH= –1mA<br>IOH= –4mA|l<br>l|<br>2.7<br>2.2<br>2.9<br>2.6|V<br>V||
|||V+= 3V,<br>LTC1799H|IOH= –1mA<br>IOH= –4mA|l<br>l|<br>2.65<br>2.10<br>2.90<br>2.55|V<br>V||
|VOL|Low Level Output Voltage (Note 5)|V+= 5V,<br>LTC1799C/I|IOL= 1mA<br>IOL= 4mA|l<br>l|<br>0.05<br>0.2<br>0.15<br>0.4|V<br>V||
|||V+= 5V,<br>LTC1799H|IOL= 1mA<br>IOL= 4mA|l<br>l|<br>0.05<br>0.25<br>0.20<br>0.50|V<br>V||
|||V+= 3V,<br>LTC1799C/I|IOL= 1mA<br>IOL= 4mA|l<br>l|<br>0.1<br>0.4<br>0.3<br>0.7|V<br>V||
|||V+= 3V,<br>LTC1799H|IOL= 1mA<br>IOL= 4mA|l<br>l|<br>0.10<br>0.45<br>0.35<br>0.80|V<br>V||
|tr|OUT Rise Time<br>(Note 6)|V+= 5V<br>Pin 4 = V+or Floating, RL = ∞<br>Pin 4 = 0V, RL = ∞|||14<br>7|ns<br>ns||
|||V+= 3V<br>Pin 4 = V+or Floating, RL = ∞<br>Pin 4 = 0V, RL = ∞|||19<br>11|ns<br>ns||
|tf|OUT Fall Time<br>(Note 6)|V+= 5V<br>Pin 4 = V+or Floating, RL = ∞<br>Pin 4 = 0V, RL = ∞|||13<br>6|ns<br>ns||
|||V+= 3V<br>Pin 4 = V+or Floating, RL = ∞<br>Pin 4 = 0V, RL = ∞|||19<br>10|ns<br>ns||



**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:** Frequencies near 100kHz and 1MHz may be generated using two different values of RSET (see the Table 1 in the Applications Information section). For these frequencies, the error is specified under the following assumption: 10k < RSET ≤ 100k. The frequency accuracy for fOSC = 20MHz is guaranteed by design and test correlation. 

**Note 4:** 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 5:** To conform with the Logic IC Standard convention, current out of a pin is arbitrarily given as a negative value. 

**Note 6:** Output rise and fall times are measured between the 10% and 90% power supply levels. These specifications are based on characterization. **Note 7:** Guaranteed by 5V test. 

**Note 3:** Frequency accuracy is defined as the deviation from the fOSC equation. 

Rev. E 

4 

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LTC1799 

## **TYPICAL PERFORMANCE CHARACTERISTICS** 

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Frequency Variation<br>vs RSET<br>**----- End of picture text -----**<br>


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Frequency Variation<br>Over Temperature<br>**----- End of picture text -----**<br>


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4 1.00<br>TA = 25°C RSET = 31.6k<br>3 GUARANTEED LIMITS APPLY  0.75 ÷1 OR ÷10 OR ÷100<br>OVER 5k TO 200k RANGE<br>2 pl 0.50<br>TYPICAL TYPICAL<br>10 neHT FH Hon HIGH aiiilcal l 0.250 HIGH<br>–1 TYPICAL –0.25<br>LOW<br>–2 SeieeeelilTAME –0.50 TYPICAL<br>–3 ELLIE [LLIN] ssn [LET] LETH –0.75 LOW<br>–4 ELIE LUI LL –1.00<br>1 10 100 1000 –40 –20 0 20 40 60 80<br>RSET (kΩ) TEMPERATURE (°C)<br>1799 G01 1799 G02<br>Supply Current<br>Peak-to-Peak Jitter vs Frequency vs Output Frequency<br>0.7 4.5<br>TA = 25°C<br>0.6 4.0 CL = 5pF<br>TAT ÷1 3.5 poe RL = 1M<br>0.5 SN an mn<br>3.0<br>0.4 BU TT EN Cen ÷1 (5V) c<br>0 0 a 2.5 CH E<br>÷10 (5V)<br>0.3 2.0<br>Es ÷10 Bw ÷100 (5V)<br>1.5<br>0.2<br>÷100 1.0<br>0.1 Ne TC<br>vil ts A 0.5 N= ÷100 (3V) ÷10 (3V) ÷1 (3V)<br>0 0<br>1k HEFT 10k 100k 1M 10M 100M 1k fue 10k l= 100k lial w 1M 10M l 100M<br>OUTPUT FREQUENCY, fOUT (Hz) OUTPUT FREQUENCY, fOUT (Hz)<br>1799 G03 1799 G04<br>VARIATION (%) VARIATION (%)<br>JITTER (%)<br>SUPPLY CURRENT (mA)<br>**----- End of picture text -----**<br>


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Output Resistance   LTC1799 Output Operating at  LTC1799 Output Operating at<br>vs Supply Voltage 20MHz, VS = 5V 10MHz, VS = 3V<br>140<br>TA = 25°C V [+]  = 5V, RSET = 5k, CL = 10pF V [+]  = 3V, RSET = 10k, CL = 10pF<br>120<br>NITE] fe py 1<br>OUTPUT SOURCING CURRENT<br>100 1V/DIV 1V/DIV<br>80<br>AN Pye) oP<br>60 1799 G06 1799 G07<br>12.5ns/DIV 25ns/DIV<br>NESS OUTPUT SINKING CURRENT een |<br>40 ER<br>2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0<br>SUPPLY VOLTAGE (V)<br>1799 G05<br>OUTPUT RESISTANCE (Ω)<br>**----- End of picture text -----**<br>


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5 

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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. For best performance, use a precision metal film resistor with a value between 10k and 200k 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 GND for the ÷1 setting, the highest frequency range. 

Floating Pin 4 divides the master oscillator by 10. Pin 4 should be tied to V[+] for the ÷100 setting, the lowest frequency range. To detect a floating DIV pin, the LTC1799 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 5µA. Likewise, driving DIV low requires sinking 5µA. When Pin 4 is floated, preferably 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 5kΩ and/or 10pF loads. Larger loads may cause inaccuracies due to supply bounce at high frequencies. Transients will not cause latchup if the current into/out of the OUT pin is limited to 50mA. 

## **BLOCK DIAGRAM** 

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VRES = 1.13V ±25%<br>V [+] (V [+]  – VSET) PROGRAMMABLE OUT<br>1 DIVIDER 5<br>(÷1, 10 OR 100)<br>+<br>RSET V [+]<br>IRES 3 SET +– VBIAS –GAIN = 1 ƒMO = 100MHz • kΩ •MASTER OSCILLATOR(V [+]  – VIRESSET) DIVIDERSELECT 5µA<br>THREE-STATE DIV<br>2 GND IRES INPUT DETECT 4<br>5µA<br>GND<br>1799 BD<br>**----- End of picture text -----**<br>


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6 

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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. 

A resistor RSET, connected between the V[+] and SET pins, “locks together” the voltage (V[+] – VSET) and current, IRES, variation. This provides the LTC1799’s high precision. The master oscillation frequency reduces to: 

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The LTC1799 is optimized for use with resistors between 10k and 200k, corresponding to master oscillator frequencies between 0.5MHz and 10MHz. Accurate frequencies up to 20MHz (RSET = 5k) are attainable if the supply voltage is greater than 4V. 

(Pin 5). The divide-by value is determined by the state of the DIV input (Pin 4). Tie DIV to GND or drive it below 0.5V to select ÷1. This is the highest frequency range, with the master output frequency passed directly to OUT. The DIV pin may be floated or driven to midsupply to select ÷10, the intermediate frequency range. The lowest frequency range, ÷100, is selected by tying DIV to V[+] or driving it to within 0.4V of V[+] . Figure 2 shows the relationship between RSET, divider setting and output frequency, including the overlapping frequency ranges near 100kHz and 1MHz. 

The CMOS output driver has an on resistance that is typically less than 100Ω. In the ÷1 (high frequency) mode, the rise and fall times are typically 7ns with a 5V supply and 11ns with a 3V supply. These times maintain a clean square wave at 10MHz (20MHz at 5V supply). In the ÷10 and ÷100 modes, where the output frequency is much lower, slew rate control circuitry in the output driver increases the rise/fall times to typically 14ns for a 5V supply and 19ns for a 3V supply. The reduced slew rate lowers EMI (electromagnetic interference) and supply bounce. 

To extend the output frequency range, the master oscillator signal may be divided by 1, 10 or 100 before driving OUT 

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1.4<br>TA = 25°C<br>1.3<br>V [+]  = 5V<br>1.2<br>V [+]  = 3V<br>1.1<br>1.0<br>0.9<br>0.8<br>1 10 100 1000<br>IRES (µA)<br>1799 F01<br>SET<br>+ – V<br> = V<br>RES<br>V<br>**----- End of picture text -----**<br>


**Figure 1. V[+] – VSET Variation with IRES** 

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1000<br>÷100 ÷10 ÷1 MOST<br>100 ACCURATE<br>OPERATION<br>10<br>1<br>1k 10k 100k 1M 10M 100M<br>DESIRED OUTPUT FREQUENCY (Hz)<br>1799 F02<br> (kΩ)<br>SET<br>R<br>**----- End of picture text -----**<br>


**Figure 2. RSET vs Desired Output Frequency** 

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7 

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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. Note that the ranges overlap; at some frequencies there are two divider/resistor combinations that result in the desired frequency. 

In general, any given oscillator frequency (fOSC) should be obtained using the lowest master oscillator frequency. Lower master oscillator frequencies use less power and are more accurate. For instance, fOSC = 100kHz can be obtained by either RSET = 10k, N = 100, master oscillator = 10MHz or RSET = 100k, N = 10, master oscillator = 1MHz. The RSET = 100k is preferred for lower power and better accuracy. 

**Table 1. Frequency Range vs Divider Setting** 

|**DIVIDER SETTING**|**FREQUENCY RANGE**|
|---|---|
|÷1<br>⇒<br>DIV(Pin 4)= GND|>500kHz*|
|÷10<br>⇒<br>DIV(Pin 4)= Floating|50kHz to 1MHz|
|÷100⇒<br>DIV(Pin 4)= V+|<100kHz|



*At master oscillator frequencies greater than 10MHz (RSET < 10kΩ), the LTC1799 may suffer reduced accuracy with a supply voltage less than 4V. 

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. 

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RSETMAX = 1M) 

Any resistor, RSET, tolerance adds to the inaccuracy of the oscillator, fOSC. 

## **ALTERNATIVE METHODS OF SETTING THE OUTPUT FREQUENCY OF THE LTC1799** 

The oscillator may be programmed by any method that sources a current into the SET pin (Pin 3). The circuit in Figure 3 sets the oscillator frequency using a programmable current source and in the expression for fOSC, the resistor RSET is replaced by the ratio of 1.13V/ICONTROL. As already explained in the “Theory of Operation,” the voltage difference between V[+] and SET is approximately 1.13V, therefore, the Figure 3 circuit is less accurate than if a resistor controls the oscillator frequency. 

Figure 4 shows the LTC1799 configured as a VCO. A voltage source is connected in series with an external 10k resistor. The output frequency, fOSC, will vary with VCONTROL, that is the voltage source connected between V[+] and the SET pin. Again, this circuit decouples the relationship between the input current and the voltage between V[+] and SET; the frequency accuracy will be degraded. The oscillator frequency, however, will monotonically increase with decreasing VCONTROL. 

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400kHz TO 21MHz<br>(APPROXIMATE, SEE TEXT)<br>V [+]<br>1 5<br>V [+] OUT<br>ICONTROL 0.1µF 2 LTC1799<br>5µA TO 200µA GND<br>3 4 N = 1<br>SET DIV<br>1799 F03<br>ƒOSC ≅ 10MHzN • 1.13V10kΩ • ICONTROL<br>ICONTROL EXPRESSED IN (A)<br>**----- End of picture text -----**<br>


**Figure 3. Current Controlled Oscillator** 

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V [+]<br>1 5<br>V [+] OUT<br>0V TO 1.13VVCONTROL +– 0.1µFRSET 2 GNDLTC1799<br>10k 3 4 N = 1<br>SET DIV<br>1799 F04<br>ƒOSC ≅ 10MHz • 10k • 1 –  [V][CONTROL]<br>N RSET ( 1.13V )<br>**----- End of picture text -----**<br>


**Figure 4. Voltage Controlled Oscillator** 

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8 

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LTC1799 

## **APPLICATIONS INFORMATION** 

## **POWER SUPPLY REJECTION** 

## **Low Frequency Supply Rejection (Voltage Coefficient)** 

Figure 5 shows the output frequency sensitivity to power supply voltage at several different temperatures. The LTC1799 has a conservative guaranteed voltage coefficient of 0.1%/V but, as Figure 5 shows, the typical supply sensitivity is lower. 

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0.15<br>RSET = 31.6k<br>PIN 4 = FLOATING (÷10)<br>0.10<br>25°C<br>–40°C<br>0.05<br>85°C<br>0<br>–0.05<br>2.5 3.0 3.5 4.0 4.5 5.0 5.5<br>SUPPLY VOLTAGE (V)<br>1799 F05<br>FREQUENCY DEVIATION (%)<br>**----- End of picture text -----**<br>


**Figure 5. Supply Sensitivity** 

## **High Frequency Power Supply Rejection** 

The accuracy of the LTC1799 may be affected when its power supply generates significant noise with frequency contents in the vicinity of the programmed value of fOSC. If a switching power supply is used to power up the LTC1799, and if the ripple of the power supply is more than a few tens of millivolts, make sure the switching frequency and its harmonics are not related to the output frequency of the LTC1799. Otherwise, the oscillator may show an additional 0.1% to 0.2% of frequency error. 

If the LTC1799 is powered by a switching regulator and the switching frequency or its harmonics coincide with the output frequency of the LTC1799, the jitter of the oscillator output may be affected. This phenomenon will become noticeable if the switching regulator exhibits ripples beyond 30mV. 

## **START-UP TIME** 

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. Figure 6 shows start-up times for various RSET resistors. 

Figure 7 shows an application where a second set resistor RSET2 is connected in parallel with set resistor RSET1 via switch S1. When switch S1 is open, the output frequency of the LTC1799 depends on the value of the resistor RSET1. When switch S1 is closed, the output frequency of the LTC1799 depends on the value of the parallel combination of RSET1 and RSET2. 

The start-up time and settling time of the LTC1799 with switch S1 open (or closed) is described by tSTART shown above. Once the LTC1799 starts and settles, and switch S1 closes (or opens), the LTC1799 will settle to its new output frequency within approximately 25µs. 

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60<br>TA = 25°C<br>V [+]  = 5V<br>50<br>40<br>30<br>20<br>200k<br>10 10k<br>31.6k<br>0<br>–10<br>0 100 200 300 400 500 600<br>TIME AFTER POWER APPLIED (µs)<br>1799 F06<br>FREQUENCY ERROR (%)<br>**----- End of picture text -----**<br>


**Figure 6. Start-Up Time** 

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3V OR 5V 1 5 10k<br>V [+] OUT fOSC = 10MHz • (N • RSET1)<br>S1 LTC1799 OR<br>RRSET2SET1 23 GND 4 ÷100 V [+] fOSC = 10MHz • (N • RSET110k//RSET2)<br>SET DIV ÷10<br>÷1<br>1799 F07<br>**----- End of picture text -----**<br>


**Figure 7.** 

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LTC1799 

## **APPLICATIONS INFORMATION** 

When VIN = V[+] , the output frequency of the LTC1799 assumes the highest value and it is set by the parallel combination of RIN and RSET. Also note, the output frequency, fOSC, is independent of the value of VRES = (V[+] – VSET) so the accuracy of fOSC is within the data sheet limits. 

## **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. 

When VIN is less than V[+] , and especially when VIN approaches the ground potential, the oscillator frequency, fOSC, assumes its lowest value and its accuracy is affected by the change of VRES = (V[+] – VSET). At 25°C VRES varies by ±8%, assuming the variation of V[+] is ±5%. The temperature coefficient of VRES is 0.02%/°C. 

## **A Ground Referenced Voltage Controlled Oscillator** 

The LTC1799 output frequency can also be programmed by steering current in or out of the SET pin, as conceptually shown in Figure 8. This technique can degrade accuracy as the ratio of (V[+] – VSET) / IRES is no longer uniquely dependent of the value of RSET, as shown in the LTC1799 Block Diagram. This loss of accuracy will become noticeable when the magnitude of IPROG is comparable to IRES. The frequency variation of the LTC1799 is still monotonic. 

By manipulating the algebraic relation for fOSC above, a simple algorithm can be derived to set the values of external resistors RSET and RIN, as shown in Figure 9. 

1. Choose the desired value of the maximum oscillator frequency, fOSC(MAX), occurring at maximum input voltage VIN(MAX) ≤ V[+] . 

2. Set the desired value of the minimum oscillator frequency, fOSC(MIN), occurring at minimum input voltage V ≥ 0. IN(MIN) 

Figure 9 shows how to implement the concept shown in Figure 8 by connecting a second resistor, RIN, between the SET pin and a ground referenced voltage source, VIN. 

3. Choose VRES = 1.1 and calculate the ratio of RIN/RSET from the following: 

For a given power supply voltage in Figure 9, the output frequency of the LTC1799 is a function of VIN, RIN, RSET and (V[+] – VSET) = VRES:SET) = VRES:) = VRES:RES:: 

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 – VSET) = VRES:SET) = VRES:) = VRES:RES:: RIN =<br>10k RSET<br>[10MHz] • •<br>N RIN RSET ⎛ fOSC(MAX) ⎞<br>INVRES − V [+] ) • ⎛⎜⎜⎜⎜ 1+ R1 [R][IN] ⎞⎟⎟⎟⎟⎤⎥⎥⎥⎥ (1) (VIN(MAX) − VVRES [+] ) [−] ⎡⎢⎢⎣⎜⎜⎝(ffOSCfOSC(MIN)OSC((MAXMIN)))⎟⎟⎠−(V1IN(MIN)⎤⎥⎥⎦  − V [+] ) − 1 (2)<br>⎝ SET ⎠⎦<br>1 5 1 5<br>V [+] V [+] OUT V [+] V [+] OUT fOSC<br>0.1µF LTC1799 + 0.1µF LTC1799<br>2 2<br>RSET GND 5V VRES RSET GND 5V<br>÷100 – ÷100<br>3 4 ÷10 RIN 3 4 ÷10<br>SET DIV OPEN SET DIV OPEN<br>+<br>IRES ÷1 ÷1<br>IPR VIN<br>1799 F08 1799 F09<br>–<br>**----- End of picture text -----**<br>


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**Figure 8. Concept for Programming via Current Steering** 

**Figure 9. Implementation of Concept Shown in Figure 8 Steering** 

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LTC1799 

## **APPLICATIONS INFORMATION** 

Once RIN/RSET is known, calculate RSET from: 

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## **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. In lower frequency applications however, the modulation frequency may need to be limited to a lower rate to prevent an increase in output jitter. This lower limit 

is the master oscillator frequency divided by 20, (fOSC/20). In general, for minimum output jitter the modulation frequency should be limited to fOSC/20 or 10kHz, whichever is less. For best performance at all frequencies, the value for fOSC should be the master oscillator frequency (N = 1) when VIN is at the lowest level. 

**Table 2. Variation of VRES for Various Values of RIN || RSET** 

|**RIN || RSET (VIN = V+)**|**VRES, V+ = 3V**|**VRES, V+ = 5V**|
|---|---|---|
|10k|0.98V|1.06V|
|20k|1.03V|1.11V|
|40k|1.09V|1.17V|
|80k|1.13V|1.21V|
|160k|1.16V|1.24V|



VRES = Voltage across RSET 

**Note:** All of the calculations above assume VRES = 1.1V, although VRES ≈ 1.1V. For completeness, Table 2 shows the variation of VRES against various parallel combinations of RIN and RSET (VIN = V[+] ). Calculate first with VRES ≈ 1.1V, then use Table 2 to get a better approximation of VRES, then recalculate the resistor values using the new value for VRES. 

## **TYPICAL APPLICATION** 

## **Low Power 80Hz to 8kHz Sine Wave Generator (IQ < 4mA)** 

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3V<br>1 5 fOSC<br>V [+] OUT<br>0.1µFC1 RSET 2 GNDLTC1799 SW13V 3V, N = 100 3V LTC1067-50<br>3 SET DIV 4 OPEN, N = 10 C4 C3 1 V [+] CLK 16<br>74HC4520 1µF 0.1µF 2 15<br>NC AGND<br>1 CLOCK A Q1A 3 ÷2 R61 3 V [+] V [–] 14 R62 14k<br>3V 2 ENABLE A Q2A 4 ÷4 10k 4 SA SB 13 R52<br>16 5 ÷8 R51 5.11k 5 12 5.11k SINEWAVE<br>C2 10 ENABLE BVDD Q3AQ4A 6 ÷16 R31 51.1k 6 LPABPA BPBLPB 11 R32 51.1k OUT<br>0.1µF 7 RESET A Q1B 11 ÷32 R11 7 HPA/NA HPB/NB 10 fSINE = 10MHzN • 64R10kSET<br>8 12 ÷64 100k R21 20k 8 9 R22 20k<br>VSS Q2B INV A INV B<br>800Hz ≤ fSINE  8kHz, N = 10 9 13 ÷128<br>80Hz ≤ fSINE  800Hz, N = 100 CLOCK B Q3B<br>15 14 ÷256 RH1 249k<br>RESET B Q4B fOSC<br>64 RL1 51.1k<br>1799 TA05<br>CLOCK-TUNABLE LOWPASS FILTER WITH<br>A STOPBAND NOTCH AT THE 3rd HARMONIC<br>fOSC • 3<br>( 64 )<br>**----- End of picture text -----**<br>


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LTC1799 

## **PACKAGE DESCRIPTION** 

## **S5 Package 5-Lead Plastic TSOT-23** 

(Reference LTC DWG # 05-08-1635) 

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0.62 0.95<br>2.90 BSC<br>MAX REF<br>(NOTE 4)<br>1.22 REF<br>1.50 – 1.75<br>3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC (NOTE 4)<br>PIN ONE<br>RECOMMENDED SOLDER PAD LAYOUT 0.30 – 0.45 TYP<br>0.95 BSC<br>PER IPC CALCULATOR 5 PLCS (NOTE 3)<br>0.80 – 0.90<br>0.20 BSC<br>0.01 – 0.10<br>1.00 MAX<br>DATUM ‘A’<br>0.30 – 0.50 REF<br>0.09 – 0.20 1.90 BSC<br>NOTE: (NOTE 3) S5 TSOT-23 0302<br>1. DIMENSIONS ARE IN MILLIMETERS<br>2. DRAWING NOT TO SCALE<br>**----- End of picture text -----**<br>


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 

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LTC1799 

## **REVISION HISTORY (Revision history begins at Rev C)** 

|**RE**|**ISIO**|**N HISTORY**<br>**(Revision history begins at Rev C)**||
|---|---|---|---|
|**REV**|**DATE**|**DESCRIPTION**|**PAGE NUMBER**|
|C|1/11|Revised part number in Maximum VCO Modulation Bandwidth section.|10|
|D|07/16|Updated TJMAX(150°C)|2|
|E|01/20|Added AEC-Q100 Qualified Note<br>Added W Grade Automotive Products to Order Information|1<br>2|



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LTC1799 

## **TYPICAL APPLICATIONS** 

## **Shutting Down the LTC1799** 

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5V<br>74AC04 1 5<br>ON/SHDN V [+] OUT OUT<br>C1 LTC1799<br>R1 0.1µF 2<br>10k GND<br>3 4<br>SET DIV<br>1799 TA08<br>**----- End of picture text -----**<br>


## **Output Frequency vs Temperature** 

## **Temperature-to-Frequency Converter** 

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5V<br>100kRT 0.1µFC1 12 VGNDLTC1799 [+] OUT 5 fOSC = 10MHz10 • 10kRT<br>THERMISTOR<br>3 4<br>SET DIV<br>1799 TA03<br>RT: YSI 44011  800 765-4974<br>**----- End of picture text -----**<br>


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1400<br>MAX<br>TYP<br>1200<br>MIN<br>1000<br>800<br>600<br>400<br>200<br>0<br>–20 –10 0 10 20 30 40 50 60 70 80 90<br>TEMPERATURE (°C)<br>1799 TA04<br>FREQUENCY (kHz)<br>**----- End of picture text -----**<br>


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