LTC6990_10

LTC6990 TimerBlox: Voltage Controlled Silicon Oscillator FEATURES n DESCRIPTION The LTC®6990 is a precision silicon oscillator with a programmable frequency range of 488Hz to 2MHz. It can be used as a fixed-frequency or voltage-controlled oscillator (VCO). The LTC6990 is part of the TimerBlox™ family of versatile silicon timing devices. A single resistor, RSET, programs the LTC6990’s internal master oscillator frequency. The output frequency is determined by this master oscillator and an internal frequency divider, NDIV, programmable to eight settings from 1 to 128. fOUT = 1MHz 50kΩ • , N = 1, 2, 4 …128 NDIV RSET DIV n n n n n n n n n n Fixed-Frequency or Voltage-Controlled Operation – Fixed: Single Resistor Programs Frequency with 300kHz at 1MHz CMOS Logic Output Sources/Sinks 20mA 50% Duty Cycle Square Wave Output Output Enable (Selectable Low or Hi-Z When Disabled) –40°C to 125°C Operating Temperature Range Available in Low Profile (1mm) SOT-23 (ThinSOT™) and 2mm × 3mm DFN Package APPLICATIONS n n n n n Low Cost Precision Programmable Oscillator Voltage-Controlled Oscillator High Vibration, High Acceleration Environments Replacement for Fixed Crystal and Ceramic Oscillators Portable and Battery-Powered Equipment Optionally, a second resistor at the SET input provides linear voltage control of the output frequency and can be used for frequency modulation. A narrow or wide VCO tuning range can be configured by the appropriate selection of the two resistors. The LTC6990 includes an enable function that is synchronized with the master oscillator to ensure clean, glitch-free output pulses. The disabled output can be configured to be high impedance or forced low. The LTC6990 is available in the 6-lead SOT-23 (ThinSOT) package or a 6-lead 2mm × 3mm DFN. L, LT, LTC and LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. TimerBlox and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 6342817, 6614313. TYPICAL APPLICATION Voltage Controlled Oscillator with 16:1 Frequency Range 1000 V+ OE OUT LTC6990 GND RVCO 100k SET RSET 100k DIV 6990 TA01a VCO Transfer Function f OUT 1MHz VCTRL • 0.5 MHz V 750 fOUT (kHz) V+ V+ C1 0.1μF 500 VCTRL 250 0 0 0.5 1 VCTRL (V) 1.5 2 6990 TA01b 6990f 1 LTC6990 ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (V+) to GND ........................................6V Maximum Voltage on Any Pin ............................. (GND – 0.3V) ≤ VPIN ≤ (V+ + 0.3V) Operating Temperature Range (Note 2) LTC6990C ............................................–40°C to 85°C LTC6990I .............................................–40°C to 85°C LTC6990H .......................................... –40°C to 125°C Specified Temperature Range (Note 3) LTC6990C ................................................ 0°C to 70°C LTC6990I .............................................–40°C to 85°C LTC6990H .......................................... –40°C to 125°C Junction Temperature ........................................... 150°C Storage Temperature Range .................. –65°C to 150°C Lead Temperature (Soldering, 10sec) ................... 300°C PIN CONFIGURATION TOP VIEW V+ 1 DIV 2 SET 3 7 6 OUT 5 GND 4 OE OE 1 GND 2 SET 3 TOP VIEW 6 OUT 5 V+ 4 DIV DCB PACKAGE 6-LEAD (2mm × 3mm) PLASTIC DFN TJMAX = 150°C, θJA = 64°C/W EXPOSED PAD (PIN 7) CONNECTED TO GND, PCB CONNECTION OPTIONAL S6 PACKAGE 6-LEAD PLASTIC TSOT-23 TJMAX = 150°C, θJA = 230°C/W ORDER INFORMATION LEAD FREE FINISH LTC6990CDCB#PBF LTC6990IDCB#PBF LTC6990HDCB#PBF LTC6990CS6#PBF LTC6990IS6#PBF LTC6990HS6#PBF TAPE AND REEL LTC6990CDCB#TRPBF LTC6990IDCB#TRPBF LTC6990HDCB#TRPBF LTC6990CS6#TRPBF LTC6990IS6#TRPBF LTC6990HS6#TRPBF PART MARKING* LDWX LDWX LDWX LTDWW LTDWW LTDWW PACKAGE DESCRIPTION 6-Lead (2mm × 3mm) Plastic DFN 6-Lead (2mm × 3mm) Plastic DFN 6-Lead (2mm × 3mm) Plastic DFN 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 SPECIFIED TEMPERATURE RANGE 0°C to 70°C –40°C to 85°C –40°C to 125°C 0°C to 70°C –40°C to 85°C –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 6990f 2 LTC6990 ELECTRICAL CHARACTERISTICS SYMBOL fOUT ΔfOUT PARAMETER Output Frequency Frequency Accuracy (Note 4) The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Test conditions are V+ = 2.25V to 5.5V, OE = V+, DIVCODE = 0 to 15 (NDIV = 1 to 128), RSET = 50k to 800k, RLOAD = 5k, CLOAD = 5pF unless otherwise noted. CONDITIONS Recommended Range: RSET = 50k to 800k Extended Range: RSET = 25k to 800k Recommended Range RSET = 50k to 800k Extended Range RSET = 25k to 800k ΔfOUT/ΔT ΔfOUT/ΔV+ Frequency Drift Over Temperature Frequency Drift Over Supply Period Jitter (Note 10) V+ = 4.5V to 5.5V V+ = 2.25V to 4.5V NDIV = 1 NDIV = 2 NDIV = 128 Duty Cycle BW tS Analog Inputs VSET ΔVSET /ΔT ΔVSET /ΔV+ Voltage at SET Pin VSET Drift Over Temperature VSET Drift Over Supply Recommended Range Extended Range Deviation from Ideal VDIV/V+ = (DIVCODE + 0.5)/16 l l l l l l l l l l l l l MIN 0.488 0.488 TYP MAX 1000 2000 UNITS kHz kHz % % % % %/°C %/V %/V %P-P %P-P %RMS %P-P %RMS ±0.8 ±1.5 ±2.2 ±2.4 ±3.2 ±0.005 0.23 0.06 0.38 0.22 0.027 0.022 0.004 0.55 0.16 NDIV = 1, RSET = 25k to 800k NDIV > 1, RSET = 25k to 800k tMASTER = tOUT /NDIV l l 47 48 50 50 0.4•fOUT 6•tMASTER 53 52 % % kHz μs Frequency Modulation Bandwidth Frequency Change Settling Time (Note 9) 0.97 1.00 ±75 –150 –7 1.03 V μV/°C μV/V Ω ΔVSET /ΔISET VSET Droop with ISET Frequency-Setting Resistor RSET VDIV ΔVDIV /V+ DIV Pin Voltage DIV Pin Valid Code Range (Note 5) DIV Pin Input Current Power Supply V+ IS Operating Supply Voltage Range Power-On Reset Voltage Supply Current 50 25 0 800 800 V+ ±1.5 ±10 kΩ kΩ V % nA V V μA μA μA μA μA μA μA μA 2.25 235 145 71 59 137 106 66 56 5.5 1.95 283 183 105 92 180 145 100 90 RSET = 25k to 800k RL = ∞, NDIV = 1, RSET = 50k RL = ∞, NDIV = 1 RSET = 800k RL = ∞, NDIV = 128, RSET = 50k RL = ∞, NDIV = 128, RSET = 800k V+ = 5.5V V+ = 2.25V V+ = 5.5V V+ = 2.25V V+ = 5.5V V+ = 2.25V V+ = 5.5V V+ = 2.25V l l l l l l l l l 6990f 3 LTC6990 ELECTRICAL CHARACTERISTICS SYMBOL Digital I/O OE Pin Input Capacitance OE Pin Input Current VIH VIL IOUT(MAX) VOH High Level OE Pin Input Voltage Low Level OE Pin Input Voltage OUT Pin Hi-Z Leakage Maximum Output Current High Level Output Voltage (Note 7) V+ = 5.5V V+ = 3.3V V+ = 2.25V VOL Low Level Output Voltage (Note 7) V+ = 5.5V V+ = 3.3V V+ = 2.25V tPD Output Disable Propagation Delay V+ = 5.5V V+ = 3.3V V+ = 2.25V Output Enable Time Output Rise Time (Note 8) NDIV ≤ 2, tOUT = 1/fOUT NDIV ≥ 4, tMASTER = tOUT/NDIV V+ = 5.5V V+ = 3.3V V+ = 2.25V V+ = 5.5V V+ = 3.3V V+ = 2.25V IOH = –1mA IOH = –16mA IOH = –1mA IOH = –10mA IOH = –1mA IOH = –8mA IOL = 1mA IOL = 16mA IOL = 1mA IOL = 10mA IOL = 1mA IOL = 8mA l l l l l l l l l l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Test conditions are V+ = 2.25V to 5.5V, OE = V+, DIVCODE = 0 to 15 (NDIV = 1 to 128), RSET = 25k to 800k, RLOAD = ∞, CLOAD = 5pF unless otherwise noted. PARAMETER CONDITIONS MIN TYP 2.5 OE = 0V to V+ (Note 6) (Note 6) OE = 0V, DIVCODE ≥ 8, OUT = 0V to V+ ±20 5.45 4.84 3.24 2.75 2.17 1.58 5.48 5.15 3.27 2.99 2.21 1.88 0.02 0.26 0.03 0.22 0.03 0.26 17 26 44 tPD to tOUT tPD to 2•tMASTER 1.1 1.7 2.7 1.0 1.6 2.4 0.04 0.54 0.05 0.46 0.07 0.54 l l l MAX UNITS pF ±10 0.7•V+ 0.3•V+ ±10 nA V V μA mA V V V V V V V V V V V V ns ns ns μs μs ns ns ns ns ns ns tENABLE tr tf Output Fall Time (Note 8) 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: The LTC6990C is guaranteed functional over the operating temperature range of –40°C to 85°C. Note 3: The LTC6990C is guaranteed to meet specified performance from 0°C to 70°C. The LTC6990C is designed, characterized and expected to meet specified performance from –40°C to 85°C but it is not tested or QA sampled at these temperatures. The LTC6990I is guaranteed to meet specified performance from –40°C to 85°C. The LTC6990H is guaranteed to meet specified performance from –40°C to 125°C. Note 4: Frequency accuracy is defined as the deviation from the fOUT equation, assuming RSET is used to program the frequency. Note 5: See Operation section, Table 1 and Figure 2 for a full explanation of how the DIV pin voltage selects the value of DIVCODE. Note 6: The OE pin has hysteresis to accommodate slow rising or falling signals. The threshold voltages are proportional to V+. Typical values can be estimated at any supply voltage using VOE(RISING) ≈ 0.55 • V+ + 185mV and VOE(FALLING) ≈ 0.48 • V+ – 155mV. Note 7: To conform to the Logic IC Standard, current out of a pin is arbitrarily given a negative value. Note 8: Output rise and fall times are measured between the 10% and the 90% power supply levels with 5pF output load. These specifications are based on characterization. Note 9: Settling time is the amount of time required for the output to settle within ±1% of the final frequency after a 0.5x or 2x change in ISET. Note 10: Jitter is the ratio of the deviation of the period to the mean of the period. This specification is based on characterization and is not 100% tested. 6990f 4 LTC6990 TYPICAL PERFORMANCE CHARACTERISTICS Frequency Error vs RSET 4 3 FREQUENCY ERROR (%) 2 1 0 –1 –2 –3 –4 10 GUARANTEED MIN OVER TEMPERATURE 100 RSET (kΩ) 1000 6990 G01 V+ = 3.3V, unless otherwise noted. Frequency Error vs Supply Voltage 0.5 0.4 FREQUENCY ERROR (%) 0.3 0.2 0.1 0 –0.1 –0.2 –0.3 –0.4 –0.5 2 3 4 5 SUPPLY VOLTAGE (V) 6 6990 G02 Frequency Error vs Temperature 1.5 1.0 V+ = 3.3V DIVCODE = 4 TA = 25°C GUARANTEED MAX OVER TEMPERATURE TA = 25°C RSET = 800k ERROR (%) 0.5 RSET = 50k 0.0 RSET = 800k –0.5 RSET = 267k –1.0 –1.5 –50 TYPICAL MAX 90% OF UNITS TYPICAL MIN RSET = 200k RSET = 50k –25 0 25 50 75 TEMPERATURE (°C) 100 125 6990 G03 VSET vs ISET 1.003 V+ = 3.3V TA = 25°C 1.003 VSET vs Supply Voltage RSET = 200k TA = 25°C 1.020 VSET vs Temperature RSET = 200k 1.015 3 TYPICAL PARTS 1.010 1.002 VSET (V) 1.002 VSET (V) VSET (V) 1.005 1.000 0.995 0.990 0.985 1.001 1.001 1.000 0 10 20 ISET (μA) 30 40 6990 G04 1.000 2 3 4 5 SUPPLY VOLTAGE (V) 6 6990 G05 0.980 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 6990 G06 Typical VSET Distribution 300 250 NUMBER OF UNITS 200 150 100 50 0 TA = 25°C 2 LOTS DFN AND SOT-23 1416 UNITS 250 POWER SUPPLY CURRENT (μA) Supply Current vs Supply Voltage TA = 25°C 250 RSET = 50k, ÷1 POWER SUPPLY CURRENT (μA) RSET = 50k, ÷2 200 Supply Current vs Temperature 5.5V, RSET = 50k, ÷1 200 150 RSET = 50k, ÷128 150 2.25V, RSET = 50k, ÷1 5.5V, RSET = 50k, ÷128 100 RSET = 800k, ÷1 50 RSET = 800k, ÷128 100 5.5V, RSET = 800k, ÷1 50 2.25V, RSET = 800k, ÷128 0 0.986 0.994 1.002 1.010 VSET (V) 1.018 6990 G07 2 3 4 5 SUPPLY VOLTAGE (V) 6 6990 G05 0 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 6990 G09 6990f 5 LTC6990 TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Frequency, 5V 400 350 POWER SUPPLY CURRNET (μA) 300 ÷2 250 200 150 100 50 0 0.1 1 V+ = 5V TA = 25°C 10 100 1000 FREQUENCY (kHz) 10000 6990 G10 V+ = 3V, unless otherwise noted. Supply Current vs Frequency, 2.5V 400 350 POWER SUPPLY CURRNET (μA) 300 250 200 150 100 50 0 0.1 1 ÷128 V+ = 2.5V TA = 25°C 10 100 1000 FREQUENCY (kHz) 10000 6990 G11 RECOMMENDED RANGE EXTENDED RANGE RECOMMENDED RANGE EXTENDED RANGE ÷1 ÷2 ÷128 ÷1 Supply Current vs OE Pin Voltage 200 POWER SUPPLY CURRENT (μA) TA = 25°C RSET = 800k 175 DIVCODE = 7 150 125 100 75 50 5V, OE FALLING 3.3V, OE FALLING 3.3V, OE RISING 0.50 5V, OE RISING Peak-to-Peak Jitter vs Frequency TA = 25°C 0.45 V+ = 5V PEAK-TO-PEAK PERIOD 0.40 DEVIATION MEASURED 0.35 OVER 30sec INTERVALS JITTER (%P-P) 0.30 0.25 0.20 0.15 0.10 0.05 ÷128 1 10 100 FREQUENCY (kHz) 1000 6990 G13 ÷1 ÷2 ÷4 0 20 40 60 VOE /V+ (%) 80 100 6990 G12 0 0.1 OE Threshold Voltage vs Supply Voltage 3.5 3.0 OE PIN VOLTAGE (V) 2.5 2.0 NEGATIVE-GOING 1.5 1.0 0.5 0 OUTPUT RESISTANCE (Ω) POSITIVE-GOING TA = 25°C 50 45 40 35 30 25 20 15 10 5 2 3 4 5 SUPPLY VOLTAGE (V) 6 6990 G14 Output Resistance vs Supply Voltage TA = 25°C OUTPUT SOURCING CURRENT OUTPUT SINKING CURRENT 0 2 3 4 5 SUPPLY VOLTAGE (V) 6 6990 G16 6990f 6 LTC6990 TYPICAL PERFORMANCE CHARACTERISTICS Rise and Fall Time vs Supply Voltage 3.0 2.5 PROPAGATION DELAY (ns) RISE/FALL TIME (ns) 2.0 tRISE 1.5 tFALL 1.0 0.5 0 TA = 25°C CLOAD = 5pF 50 45 40 35 30 25 20 15 10 5 2 3 4 5 SUPPLY VOLTAGE (V) 6 6990 G16 V+ = 3V, unless otherwise noted. Output Disable Propagation Delay (tPD) vs Supply Voltage TA = 25°C CLOAD = 5pF 0 2 3 4 5 SUPPLY VOLTAGE (V) 6 6990 G17 Typical ISET Current Limit vs V+ 1000 TA = 25°C SET PIN SHORTED TO GND Typical Output Waveform V+ = 3.3V DIVCODE = 2 RSET = 200k 800 OE 2V/DIV OUT 2V/DIV ISET (μA) 600 400 200 0 2 3 4 5 SUPPLY VOLTAGE (V) 6 6990 G18 20μs/DIV 6990 G19 Frequency Modulation VCTRL 2V/DIV OUT 2V/DIV VCTRL 2V/DIV OUT 2V/DIV Frequency Modulation fOUT 50kHz/DIV fOUT 50kHz/DIV 20μs/DIV V+ = 3.3V, DIVCODE = 0 RSET = 200k, RVCO = 464k fOUT = 175kHz to 350kHz 6990 G20 20μs/DIV V+ = 3.3V, DIVCODE = 0 RSET = 200k, RVCO = 464k fOUT = 175kHz to 350kHz 6990 G21 6990f 7 LTC6990 PIN FUNCTIONS (DCB/S6) V+ (Pin 1/Pin 5): Supply Voltage (2.25V to 5.5V). This supply must be kept free from noise and ripple. It should be bypassed directly to the GND pin with a 0.1μF capacitor. DIV (Pin 2/Pin 4): Programmable Divider and Hi-Z Mode Input. A V+ referenced A/D converter monitors the DIV pin voltage (VDIV) to determine a 4-bit result (DIVCODE). VDIV may be generated by a resistor divider between V+ and GND. Use 1% resistors to ensure an accurate result. The DIV pin and resistors should be shielded from the OUT pin or any other traces that have fast edges. Limit the capacitance on the DIV pin to less than 100pF so that VDIV settles quickly. The MSB of DIVCODE (Hi-Z) determines the behavior of the output when OE is driven low. If Hi-Z = 0 the output is pulled low when disabled. If Hi-Z = 1 the output is placed in a high impedance condition when disabled. SET (Pin 3/Pin 3): Frequency-Setting Input. The voltage on the SET pin (VSET) is regulated to 1V above GND. The amount of current sourced from the SET pin (ISET) programs the master oscillator frequency. The ISET current range is 1.25μA to 40μA. The output oscillation will stop if ISET drops below approximately 500nA. A resistor connected between SET and GND is the most accurate way to set the frequency. For best performance, use a precision metal or thin film resistor of 0.5% or better tolerance and 50ppm/°C or better temperature coefficient. For lower accuracy applications an inexpensive 1% thick film resistor may be used. Limit the capacitance on the SET pin to less than 10pF to minimize jitter and ensure stability. Capacitance less than 100pF maintains the stability of the feedback circuit regulating the VSET voltage. V+ OE OUT LTC6990 GND V+ C1 0.1μF V+ R1 SET RSET DIV 6990 PF R2 OE (Pin 4/Pin 1): Output Enable. Drive high to enable the output driver (Pin 6). Driving OE low disables the output asynchronously, so that the output is immediately forced low (Hi-Z = 0) or floated (Hi-Z = 1). When enabled, the output may temporarily remain low to synchronize with the internal oscillator in order to eliminate pulse slivers. GND (Pin 5/Pin 2): Ground. Tie to a low inductance ground plane for best performance. OUT (Pin 6/Pin 6): Oscillator Output. The OUT pin swings from GND to V+ with an output resistance of approximately 30Ω. When driving an LED or other low-impedance load a series output resistor should be used to limit source/sink current to 20mA. 6990f 8 LTC6990 BLOCK DIAGRAM (S6 Package Pin Numbers Shown) V+ 5 R1 DIV 4 R2 Hi-Z WHEN DISABLED MASTER OSCILLATOR tMASTER 1μs VSET • ISET 50k MCLK PROGRAMMABLE DIVIDER ÷1, 2, 4, 8, 16, 32, 64, 128 Hi-Z BIT 1 OE 4-BIT A/D CONVERTER DIGITAL FILTER OUT 6 tOUT HALT OSCILLATOR IF ISET < 500nA ISET Hi-Z OUTPUT UNTIL SETTLED + – 2 + – 1V VSET = 1V 3 GND SET RSET POR 6990 BD 6990f 9 LTC6990 OPERATION The LTC6990 is built around a master oscillator with a 1MHz maximum frequency. The oscillator is controlled by the SET pin current (ISET) and voltage (VSET), with a 1MHz • 50k conversion factor that is accurate to ±0.8% under typical conditions. I 1 f MASTER = = 1MHz • 50k • SET tMASTER VSET A feedback loop maintains VSET at 1V ±30mV, leaving ISET as the primary means of controlling the output frequency. The simplest way to generate ISET is to connect a resistor (RSET) between SET and GND, such that ISET = VSET/RSET. The master oscillator equation reduces to: f MASTER = 1 tMASTER = 1MHz • 50k RSET LTC6990 DIV R2 GND 6990 F01 DIVCODE The DIV pin connects to an internal, V+ referenced 4-bit A/D converter that monitors the DIV pin voltage (VDIV) to determine the DIVCODE value. DIVCODE programs two settings on the LTC6990: 1. DIVCODE determines the output frequency divider setting, NDIV. 2. DIVCODE determines the state of the output when disabled, via the Hi-Z bit. VDIV may be generated by a resistor divider between V+ and GND as shown in Figure 1. 2.25V TO 5.5V V+ R1 From this equation it is clear that VSET drift will not affect the output frequency when using a single program resistor (RSET). Error sources are limited to RSET tolerance and the inherent frequency accuracy ΔfOUT of the LTC6990. RSET values between 50k and 800k (equivalent to ISET between 1.25μA and 20μA) produce the best results, although RSET may be reduced to 25k (ISET = 40μA) with reduced accuracy. The LTC6990 includes a programmable frequency divider which can further divide the frequency by 1, 2, 4, 8, 16, 32, 64 or 128 before driving the OUT pin. The divider ratio NDIV is set by a resistor divider attached to the DIV pin. fOUT = 1 tOUT 1 tOUT = 1MHz • 50k ISET • NDIV VSET 1MHz • 50k NDIV • RSET Figure 1. Simple Technique for Setting DIVCODE With RSET in place of VSET /ISET the equation reduces to: fOUT = = 6990f 10 LTC6990 OPERATION Table 1. DIVCODE Programming DIVCODE 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Hi-Z 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 NDIV 1 2 4 8 16 32 64 128 128 64 32 16 8 4 2 1 Recommended fOUT 62.5kHz to 1MHz 31.25kHz to 500kHz 15.63kHz to 250kHz 7.813kHz to 125kHz 3.906kHz to 62.5kHz 1.953kHz to 31.25kHz 976.6Hz to 15.63kHz 488.3Hz to 7.813kHz 488.3Hz to 7.813kHz 976.6Hz to 15.63kHz 1.953kHz to 31.25kHz 3.906kHz to 62.5kHz 7.813kHz to 125kHz 15.63kHz to 250kHz 31.25kHz to 500kHz 62.5kHz to 1MHz R1 (k) Open 976 976 1000 1000 1000 1000 1000 887 681 523 392 280 182 102 Short R2 (k) Short 102 182 280 392 523 681 887 1000 1000 1000 1000 1000 976 976 Open VDIV /V+ ≤ 0.03125 ±0.015 0.09375 ±0.015 0.15625 ±0.015 0.21875 ±0.015 0.28125 ±0.015 0.34375 ±0.015 0.40625 ±0.015 0.46875 ±0.015 0.53125 ±0.015 0.59375 ±0.015 0.65625 ±0.015 0.71875 ±0.015 0.78125 ±0.015 0.84375 ±0.015 0.90625 ±0.015 ≥ 0.96875 ±0.015 Table 1 offers recommended 1% resistor values that accurately produce the correct voltage division as well as the corresponding NDIV and Hi-Z values for the recommended resistor pairs. Other values may be used as long as: 1. The VDIV /V+ ratio is accurate to ±1.5% (including resistor tolerances and temperature effects) 2. The driving impedance (R1||R2) does not exceed 500kΩ. If the voltage is generated by other means (i.e. the output of a DAC) it must track the V+ supply voltage. The last Hi-Z BIT = 0 1000 0 fOUT (kHz) 100 1 2 3 4 10 5 6 7 1 column in Table 1 shows the ideal ratio of VDIV to the supply voltage, which can also be calculated as: VDIV V+ = DIVCODE + 0.5 ± 1.5% 16 For example, if the supply is 3.3V and the desired DIVCODE is 4, VDIV = 0.281 • 3.3V = 928mV ± 50mV. Figure 2 illustrates the information in Table 1, showing that NDIV is symmetric around the DIVCODE midpoint. Hi-Z BIT = 1 15 14 13 12 11 10 9 8 RECOMMENDED RANGE EXTENDED RANGE 0.1 0V 0.5•V+ INCREASING VDIV V+ 6990 F02 Figure 2. Frequency Range and Hi-Z Bit vs DIVCODE 6990f 11 LTC6990 OPERATION On start-up, the DIV pin A/D converter must determine the correct DIVCODE before the output is enabled. If VDIV is not stable, it will increase the start-up time as the converter waits for a stable result. Therefore, capacitance on the DIV pin should be minimized so it will settle quickly. Less than 100pF will not affect performance. Output Enable The OE pin controls the state of the LTC6990’s output as seen on the OUT pin. Pulling the OE pin high enables the oscillator output. Pulling it low disables the output. When the output is disabled, it is either held low or placed in a high impedance state as dictated by the Hi-Z bit value (determined by the DIVCODE as described earlier). Table 2 summarizes the output control states. Table 2. Output States OE Pin 1 0 0 Hi-Z X 1 0 OUT Enabled, Output is Active Disabled, Output is Hi-Z Disabled, Output is Held Low Figure 3 illustrates the timing for the OE function when Hi-Z = 0. When OE is low, the output is disabled and OUT is held low. Bringing OE high enables the output after a delay, tENABLE, which synchronizes the enable to eliminate sliver pulses and guarantee the correct width for the first pulse. If NDIV = 1 or 2 this delay will be no longer than the output period, tOUT. If NDIV > 2 the delay is limited to twice the internal master oscillator period (or 2 • tMASTER). Forcing OE low will bring OUT low after a propagation delay, tPD. If the output is high when OE falls, the output pulse will be truncated. As shown in Figure 4, setting Hi-Z = 1 places the output in a high-impedance state when OE = 0. This feature allows for “wired-OR” connections of multiple devices. Driving OE high enables the output. The output will usually be forced low during this time, although it is possible for OUT to transition directly from high-impedance to a high output, depending on the timing of the OE transition relative to the internal oscillator. Once high, the first output pulse will have the correct width (unless truncated by bringing OE low again). OE tPD tPD OUT tENABLE tOUT tENABLE 6990 F03 Figure 3. OE Timing Diagram (Hi-Z = 0) OE tPD OUT Hi-Z tPD tPD tPD tENABLE tOUT tENABLE 6990 F04 Figure 4. OE Timing Diagram (Hi-Z = 1) 6990f 12 LTC6990 OPERATION Changing DIVCODE After Start-Up Following start-up, the A/D converter will continue monitoring VDIV for changes. Changes to DIVCODE will be recognized slowly, as the LTC6990 places a priority on eliminating any “wandering” in the DIVCODE. The typical delay depends on the difference between the old and new DIVCODE settings and is proportional to the master oscillator period. tDIVCODE = 16 • ( ΔDIVCODE + 6) • tMASTER A change in DIVCODE will not be recognized until it is stable, and will not pass through intermediate codes. A digital filter is used to guarantee the DIVCODE has settled to a new value before making changes to the output. Then the output will make a clean (glitchless) transition to the new divider setting. Start-Up Time When power is first applied to the LTC6990 the power-on reset (POR) circuit will initiate the start-up time, tSTART. The OUT pin is floated (high-impedance) during this time. The typical value for tSTART ranges from 0.5ms to 8ms depending on the master oscillator frequency (independent of NDIV): t START(TYP) = 500 • tMASTER The start-up time may be longer if the supply or DIV pin voltages are not stable. For this reason, it is recommended to minimize the capacitance on the DIV pin so it will properly track V+. DIV 1V/DIV 576μs V+ 1V/DIV 470μs OUT 1V/DIV OUT 1V/DIV OUTPUT CONNECTED TO 1.25V THROUGH 25k TO SHOW Hi-Z V+ = 2.5V DIVCODE = 4 RSET = 50k 100μs/DIV 6990 F06 V+ = 3.3V RSET = 200k 100μs/DIV 6990 F05 Figure 5. DIVCODE Change from 5 to 2 Figure 6. Typical Start-Up 6990f 13 LTC6990 APPLICATIONS INFORMATION OE OUT Hi-Z tSTART 1/2 tOUT tOUT 6990 F07 Figure 7. Start-Up Timing Diagram (OE = 1, NDIV = 1 or 2, Hi-Z = 0 or 1) OE OUT Hi-Z tSTART tMASTER tOUT 6990 F08 Figure 8. Start-Up Timing Diagram (OE = 1, NDIV ≥ 4, Hi-Z = 0 or 1) OE OUT Hi-Z tSTART tENABLE tOUT 6990 F09 Figure 9. Start-Up Timing Diagram (OE = 0, NDIV = Any, Hi-Z = 0) OE tPD OUT Hi-Z tSTART REMAINS Hi-Z tENABLE UNTIL OE = 1 tOUT 6990 F10 Figure 10. Start-Up Timing Diagram (OE = 0, NDIV = Any, Hi-Z = 1) 6990f 14 LTC6990 APPLICATIONS INFORMATION Start-Up Behavior When first powered up, the output is high impedance. If the output is enabled (OE = 1) at the end of the start-up time, the output will go low for one tMASTER cycle (or half a tOUT cycle if NDIV < 4) before the first rising edge. If the output is disabled (OE = 0) at the end of the start-up time, the output will drop to a low output if the Hi-Z bit = 0, or simply remain floating if Hi-Z = 1. Basic Fixed Frequency Operation The simplest and most accurate method to program the LTC6990 for fixed frequency operation is to use a single resistor, RSET, between the SET and GND pins. The design procedure is a simple two step process. First select the NDIV value and then calculate the value for the RSET resistor. Step 1: Selecting the NDIV Frequency Divider Value As explained earlier, the voltage on the DIV pin sets the DIVCODE which determines both the Hi-Z bit and the NDIV value. For a given output frequency, NDIV should be selected to be within the following range. 1MHz 62.5kHz ≤ NDIV ≤ fOUT fOUT (1a) Example: Design a 20kHz Oscillator with Minimum Power Consumption Step 1: Selecting the NDIV Frequency Divider Value First, choose an NDIV value that meets the requirements of Equation (1a). 3.125 ≤ NDIV ≤ 50 Potential settings for NDIV include 4, 8, 16, and 32. NDIV = 4 is the best choice, as it minimizes supply current by using a large RSET resistor. Using Table 1, choose the R1 and R2 values to program DIVCODE to either 2 or 13, depending on the desired behavior when the output is disabled. Step 2: Select RSET Calculate the correct value for RSET using Equation (1b). RSET = 1MHz • 50k = 625k 4 • 20kHz Since 625k is not available as a standard 1% resistor, substitute 619k if a 0.97% frequency shift is acceptable. Otherwise, select a parallel or series pair of resistors such as 309k and 316k to attain a more precise resistance. Frequency Modulated Operation (Voltage-Controlled Oscillator) Operating the LTC6990 as a voltage-controlled oscillator in its simplest form is achieved with one additional resistor. As shown in Figure 11, voltage VCTRL sources/sinks a current through RVCO to vary the ISET current, which in turn modulates the output frequency as described in Equation (2). fOUT = 1MHz • 50k NDIV • R VCO V+ OE OUT LTC6990 GND RVCO SET RSET DIV 6990 F08 To minimize supply current, choose the lowest NDIV value (generally recommended). For faster start-up or decreased jitter, choose a higher NDIV setting. Alternatively, use Table 1 as a guide to select the best NDIV value for the given application. After choosing the value for NDIV, use Table 1 to select the proper resistor divider or VDIV/V+ ratio to apply to the DIV pin. Step 2: Calculate and Select RSET The final step is to calculate the correct value for RSET using the following equation. RSET = 1MHz • 50k NDIV • fOUT (1b) ⎛R ⎞ V • ⎜ 1+ VCO − CTRL ⎟ ⎝ RSET VSET ⎠ (2) V+ V+ C1 0.1μF Select the standard resistor value closest to the calculated value. R1 VCTRL R2 Figure 11. Voltage Controlled Oscillator 6990f 15 LTC6990 APPLICATIONS INFORMATION Equation (2) can be re-written as shown below, where f(0V) is the output frequency when VCTRL = 0V, and KVCO is the frequency gain. Note that the gain is negative (the output frequency decreases as VCTRL increases). fOUT = f(0V) – K VCO • VCTRL f(0V) = K VCO = 1MHz • 50k NDIV • (RSET P R VCO ) 1MHz • 50k NDIV • VSET • R VCO KVCO and f(0V) are not device settings or resistor values themselves. However, beyond their utility for the resistor calculations, these parameters provide a useful and intuitive way to look at the VCO application. The f(0V) parameter is the output frequency when VCTRL is at 0V. Viewed another way, it is the fixed output frequency when the RVCO and RSET resistors are in parallel. KVCO is actually the frequency gain of the circuit. With KVCO and f(0V) determined, the RVCO and RSET values can now be calculated. Step 3: Calculate and Select RVCO The next step is to calculate the correct value for RVCO using the following equation. R VCO = 1MHz • 50k NDIV • VSET • K VCO (3d) The design procedure for a VCO is a simple four step process. First select the NDIV value. Then calculate the intermediate values KVCO and f(0V). Next, calculate and select the RVCO resistor. Finally calculate and select the RSET resistor. Step 1: Select the NDIV Frequency Divider Value For best accuracy, the master oscillator frequency should fall between 62.5kHz and 1MHz. Since fMASTER = NDIV • fOUT, choose a value for NDIV that meets the following conditions 1MHz 62.5kHz ≤ NDIV ≤ fOUT(MAX) fOUT(MIN) (3a) Select the standard resistor value closest to the calculated value. Step 4: Calculate and Select RSET The final step is to calculate the correct value for RSET using the following equation: RSET = NDIV • f(0V) − VSET • K VCO The 16:1 frequency range of the master oscillator and the 2:1 divider step-size provides several overlapping frequency spans to guarantee that any 8:1 modulation range can be covered by a single NDIV setting. RVCO allows the gain to be tailored to the application, mapping the VCTRL voltage range to the modulation range. Step 2: Calculate KVCO and f(0V) KVCO and f(0V) define the VCO’s transfer function and simplify the calculation of the the RVCO and RSET resistors. Calculate these parameters using the following equations. fOUT(MAX) − fOUT(MIN) K VCO = (3b) V −V CTRL(MAX) CTRL(MIN) ( 1MHz • 50k ) (3e) Select the standard resistor value closest to the calculated value. Some applications require combinations of fOUT(MIN), fOUT(MAX), VCTRL(MIN) and VCTRL(MAX) that are not achievable. These applications result in unrealistic or unrealizable (e.g. negative value) resistors. These applications will require preconditioning of the VCTRL signal via range scaling and/or level shifting to place the VCTRL into a range that yields realistic resistor values. Frequency Error in VCO Applications Due to VSET Error As stated earlier, f(0V) represents the frequency for VCTRL = 0V, which is the same value as would be generated by a single resistor between SET and GND with a value of RSET || RVCO . Therefore, f(0V) is not affected by error or drift in VSET (i.e. ΔVSET adds no frequency error when VCTRL = 0V). 6990f f(0V) = fOUT(MAX) + KVCO • VCTRL(MIN) (3c) 16 LTC6990 APPLICATIONS INFORMATION The accuracy of KVCO does depend on VSET because the output frequency is controlled by the ratio of VCTRL to VSET. The frequency error (in Hertz) due to ΔVSET is approximated by: ΔV ΔfOUT ≅ K VCO • VCTRL • SET VSET As the equation indicates, the potential for error in output frequency due to VSET error increases with KVCO and is at its largest when VCTRL is at its maximum. Recall that when VCTRL is at its maximum, the output frequency is at its minimum. With the maximum absolute frequency error (in Hertz) occurring at the lowest output frequency, the relative frequency error (in percent) can be significant. VSET is nominally 1.0V with a maximum error of ±30mV for at most a ±3% error term. However, this ±3% potential error term is multiplied by both VCTRL and KVCO. Wide frequency range applications (high KVCO) can have frequency errors greater than ±50% at the highest VCTRL voltage (lowest fOUT). For this reason the simple, two resistor VCO circuit must be used with caution for applications where the frequency range is greater than 4:1. Restricting the range to 4:1 typically keeps the frequency error due to VSET variation below 10%. For wide frequency range applications, the non-inverting VCO circuit shown in Figure 13 is preferred because the maximum frequency error occurs when the frequency is highest, keeping the relative error (in percent) much smaller. 100 Example: Design a VCO with the Following Parameters fOUT(MAX) = 100kHz at VCTRL(MIN) = 1V fOUT(MIN) = 10kHz at VCTRL(MAX) = 4V Step 1: Select the NDIV Value First, choose an NDIV that meets the requirements of Equation (3a). 6.25 ≤ NDIV ≤ 10 The application’s desired frequency range is 10:1, which isn’t always possible. However, in this case NDIV = 8 meets both requirements of Equation (3). Step 2: Calculate KVCO and f(0V) Next, calculate the intermediate values KVCO and f(0V) using Equations (3b) and (3c). K VCO = 100kHz − 10kHz = 30kHz/V 4V − 1V f(0V) = 100kHz + 30kHz/V • 1V = 130kHz Step 3: Calculate and Select RVCO The next step is to use Equation (3d) to calculate the correct value for RVCO. R VCO = 1MHz • 50k = 208.333k 8 • 1V • 30kHz/V Select RVCO = 210k. Step 4: Calculate and Select RSET The final step is to calculate the correct value for RSET using Equation (3e). 1MHz • 50k RSET = = 62.5k 8 • (130kHz − 1V • 30kHz/V ) Select RSET = 61.9k In this design example, with its wide 10:1 frequency range, the potential output frequency error due to VSET error alone ranges from less than ±1% when VCTRL is at its minimum up to ±36% when VCTRL is at its maximum. This error must be accounted for in the system design. 6990f 80 fOUT (kHz) 60 40 20 0 1 2 VCTRL (V) 3 4 6990 F12 Figure 12. VCO Transfer Function 17 LTC6990 APPLICATIONS INFORMATION Depending on the application’s requirements, the noninverting VCO circuit in Figure 13 may be preferred for this wide of a frequency variation as its maximum inaccuracy due to VSET error is only ±9% and can be reduced to only ±3% with a small change to the voltage tuning range specification. Reducing VSET Error Effects in VCO Applications Figure 13 shows a VCO that reduces the effect of ΔVSET by adding an op-amp to make VCTRL dependent on VSET. This circuit also has a positive transfer function (the output frequency increases as VIN increases). Furthermore, for positive VIN voltages, this circuit places the greatest absolute frequency error at the highest output frequency. Compared to the simple VCO circuit of Figure 11, the absolute frequency error is unchanged. However, with the maximum absolute frequency error (in Hertz) now occurring at the highest output frequency, the relative frequency error (in percent) is greatly improved. Additionally, by choosing the VCO’s specifications shrewdly, the frequency error (in percent) due to VSET variation is reduced to ΔVSET/VSET = ±3%. To realize this improvement, the design must abide by three conditions. First, the VIN voltage must be positive throughout the range. Second, choose VMAX /VMIN ≥ fMAX /fMIN. Last, choose RVCO /RSET ≥ R4/R3. Figure 13 shows a design similar to the previous design example where the VMIN voltage is now specified to be 0.4V. This satisfies the VMAX /VMIN ≥ fMAX /fMIN condition and the design assures that the output frequency error due to VSET variation is only ±3%. 3V OE OUT LTC6990 GND VSET SET 3V DIV 6990 F13 10kHz TO 100kHz fOUT 3V V+ C1 0.1μF R1 1M DIVCODE = 3 (NDIV = 8, Hi-Z = 0) R2 280k + 0.4V TO 4V VIN R3 100k 1/2 LTC6078 VCTRL RVCO 75k RSET 249k – R4 30.1k C4 33pF f OUT IF R4 R3 R 1MHz • 50k • VCO NDIV • R VCO RSET VIN VSET 1• R4 R3 R VCO , THE EQUATION REDUCES TO: RSET V 1MHz • 50k • IN NDIV • RSET VSET VIN • 25kHz/V f OUT = Figure 13. VCO with Reduced ΔVSET Sensitivity 6990f 18 LTC6990 APPLICATIONS INFORMATION Eliminating VSET Error Effects with DAC Frequency Control Many DACs allow for the use of an external reference. If such a DAC is used to provide the VCTRL voltage, the VSET error is eliminated by buffering VSET and using it as the DAC’s reference voltage, as shown in Figure 14. The DAC’s output voltage now tracks any VSET variation and eliminates it as an error source. The SET pin cannot be tied directly to the reference input of the DAC because the current drawn by the DAC’s REF input would affect the frequency. ISET Extremes (Master Oscillator Frequency Extremes) Pushing ISET outside of the recommended 1.25μA to 20μA range forces the master oscillator to operate outside of the 62.5kHz to 1MHz range in which it is most accurate. The oscillator will still function with reduced accuracy in its extended range (see the Electrical Characteristics section). The LTC6990 is designed to function normally for ISET as low as 1.25μA. At approximately 500nA, the oscillator output will be frozen in its current state. For NDIV = 1 or 2, OUT will halt in a low state. But for larger divider ratios, it could halt in a high or low state. This avoids introducing short pulses while modulating a very low frequency output. Note that the output will not be disabled as when OE is low (e.g. the output will not enter a high impedance state if Hi-Z = 1). At the other extreme, the master oscillator frequency can reach 2MHz for ISET = 40μA (RSET = 25k). It is not recommended to operate the master oscillator beyond 2MHz because the accuracy of the DIV pin ADC will suffer. OE OUT LTC6990 V+ V+ C1 0.1μF GND V+ R1 + 1/2 LTC6078 SET DIV 6990 F14 R2 – V+ VCC REF VOUT RVCO RSET f OUT R 1MHz • 50k • 1 VCO RSET NDIV • R VCO DIN 4096 DIN μP CLK CS/LD DIN = 0 to 4095 LTC1659 GND Figure 14. Digitally Controlled Oscillator with VSET Variation Eliminated 6990f 19 LTC6990 APPLICATIONS INFORMATION Modulation Bandwidth and Settling Time The LTC6990 will respond to changes in ISET up to a –3dB bandwidth of 0.4 • fOUT (see Figure 15). This makes it easy to stabilize a feedback loop around the LTC6990, since it does not introduce a low-frequency pole. Settling time depends on the master oscillator frequency. Following a 2x or 0.5x step change in ISET, the output frequency takes approximately six master clock cycles (6 • tMASTER) to settle to within 1% of the final value. An example is shown in Figure 16. Power Supply Current The power supply current varies with frequency, supply voltage and output loading. It can be estimated under any condition using the following equation: IS(TYP) ≈ V + • fMASTER • 7pF + V + • f OUT • (13pF + CLOAD ) V+ V+ + + 1.75 •ISET + 50µA + 480kΩ 2 • RLOAD The equation is also valid for OE = 0 (output disabled), with fOUT = 0Hz. 0 fOUT (fMOD)/ fOUT(DC) (dB) VCTRL = 0.536V + 0.278V • SIN(2π•fMOD •t) fOUT =18.75kHz ±10% –3dB AT 0.4•fOUT VCTRL 2V/DIV OUT 2V/DIV –10 –20 fOUT 50kHz/DIV RSET = 200k RVCO = 464k DIVCODE = 4(÷16) –40 0.1 1 fMOD /fOUT (Hz/Hz) 6990 F15 –30 10 10μs/DIV V+ = 3.3V, DIVCODE = 0 RSET = 200k, RVCO = 464k fOUT = 175kHz AND 350kHz 6990 F16 Figure 15. Modulation Frequency Response Figure 16. Settling Time 6990f 20 LTC6990 APPLICATIONS INFORMATION SUPPLY BYPASSING AND PCB LAYOUT GUIDELINES The LTC6990 is a 2.2% accurate silicon oscillator when used in the appropriate manner. The part is simple to use and by following a few rules, the expected performance is easily achieved. The most important use issues involve adequate supply bypassing and proper PCB layout. Figure 17 shows example PCB layouts for both the SOT-23 and DCB packages using 0603 sized passive components. The layouts assume a two layer board with a ground plane layer beneath and around the LTC6990. These layouts are a guide and need not be followed exactly. 1. Connect the bypass capacitor, C1, directly to the V+ and GND pins using a low inductance path. The connection from C1 to the V+ pin is easily done directly on the top layer. For the DCB package, C1’s connection to GND is also simply done on the top layer. For the SOT-23, OUT can be routed through the C1 pads to allow a good C1 GND connection. If the PCB design rules do not allow that, C1’s GND connection can be accomplished through multiple vias to the ground plane. Multiple vias for both the GND pin connection to the ground plane and the C1 connection to the ground plane are recommended to minimize the inductance. Capacitor C1 should be a 0.1μF ceramic capacitor. 2. Place all passive components on the top side of the board. This minimizes trace inductance. 3. Place RSET as close as possible to the SET pin and make a direct, short connection. The SET pin is a current summing node and currents injected into this pin directly modulate the operating frequency. Having a short connection minimizes the exposure to signal pickup. 4. Connect RSET directly to the GND pin. Using a long path or vias to the ground plane will not have a significant affect on accuracy, but the direct, short connection is recommended and easy to apply. 5. Use a ground trace to shield the SET pin. This provides another layer of protection from radiated signals. 6. Place R1 and R2 close to the DIV pin. A direct, short connection to the DIV pin minimizes the external signal coupling. OE OUT LTC6990 GND V+ C1 0.1μF V+ R1 SET RSET V+ R1 V+ DIV R2 SET RSET C1 OUT GND OE DIV R2 C1 OE GND SET RSET R2 OUT V+ DIV R1 V+ DCB PACKAGE TSOT-23 PACKAGE 6990 F17 Figure 17. Supply Bypassing and PCB Layout 6990f 21 LTC6990 TYPICAL APPLICATIONS Programming NDIV Using an 8-Bit DAC OE OUT LTC6990 GND V+ 2.25V TO 5.5V C1 0.1μF C2 0.1μF DIVCODE 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 DAC CODE 0 24 40 56 72 88 104 120 136 152 168 184 200 216 232 255 SET RSET 619k DIV VCC SDI μP VOUT LTC2630-LZ8 SCK GND CS/LD 6990 TA02 Full Range VCO with Any NDIV Setting (fMAX to fMIN for VIN = 0V to VSET) 5V OE OUT LTC6990 RVCO1 26.1k 5V D1 IN4148 GND V+ C1 0.1μF 5V R1 RVCO2 26.1k Full Range VCO with Any NDIV Setting (Positive Frequency Control, fMIN to fMAX for VIN = 0V to VSET 5V R4 10k R3 10k 5V OE OUT LTC6990 GND RVCO 53.6k SET RSET1 412k RSET2 412k DIV 6990 TA04 22 + – VIN 0V TO 1V + RSET 826k LT1490 – LT1490 VIN 0V TO 1V SET DIV 6990 TA03 R2 V+ C1 0.1μF 5V R1 R2 6990f LTC6990 TYPICAL APPLICATIONS Speaker Alarm. Modulate Tone with RVCO within 500Hz to 8kHz Span 5V IN4004 5V 20k OE OUT LTC6990 GND STEP RAMP RVCO SET 97.6k DIV 6990 TA05 8Ω 2N2222 50k V+ 1M 5V 887k Overvoltage Detector/Alarm. Direct Drive of Piezo Alarm 24V 5V RA 787k + RB 10.7k 400mV LT6703-3 100k OE OUT LTC6990 GND RA RB V + – 5V 1M PIEZO ALARM 4kHz MURATA PKM29-3A0 V ALARM 400mV 1 30V 392k SET DIV 6990 TA06 523k Direct Piezo Alarm Driver. Adjust Frequency for Maximum Alarm Sound Pressure (Maximum Annoyance for Best Effect) 5V ON OFF 10k OE OUT LTC6990 GND V+ 1M SET 392k DIV 6990 TA07 5V PIEZO ALARM MURATA PKM29-340 f = 4kHz 523k 6990f 23 LTC6990 TYPICAL APPLICATIONS Isolated V → F Converter. VIN Provided by Isolated Measurement Circuit. 5μs Rise/Fall Time of Isolator Limits fMAX to 60kHz 5V 365Ω OE OUT LTC6990 GND VIN 0V TO 5V 75k SET 157k DIV 6990 TA08 3.3V MOC207M V+ 5V 1M 412Ω 523k fOUT Quadrature Sine Wave Oscillator. Voltage Controlled Frequency Range from 2Hz to 18kHz with 1VP-P Constant Output Amplitude 2.5V 51.1k 5.11k N S1A SINE COSINE BP LP LTC1059 OR 1/2 LTC1060 SA/B AGND 50/100 2.5V V+ 5V 10k LT1004 –2.5V 1M 2k 5V R1 1M OUT REF 1.18V 4.12k V+ OUT LTC6990 GND OE LTC1440 1M 24 – + + – VCC 124k 5V + – – CLOCK 5V RVCO 267k DIV SET 6990 TA09 R2 280k HYST 0.1μF RSET 49.9k FREQ ADJ 6990f LTC6990 TYPICAL APPLICATIONS Temperature to Frequency Converter. 3% Linearity from –20°C (fOUT ≈ 20kHz) to 75°C (fOUT ≈ 25kHz) 5V OE OUT LTC6990 GND 60.4k SET 22k AT 25°C B = 3964 21.5k DIV 6990 TA10 fOUT V+ 1M 5V 523k + THERMISTOR: VISHAY NTHS120601N2202J Full Range Temperature to Frequency Converter. 16kHz to 1kHz from –20°C to 80°C 5V OE 10k 5V OUT LTC6990 GND 100k LT1490 22k AT 25°C B = 3964 10k SET DIV 6990 TA11 fOUT V+ 1M 5V + 26k Light to Frequency Converter. fOUT ≈ –1.4kHz per Microampere of Photo Diode Current, IPD 1000pF IPD SFH213 + – + 26k 5V OE 24.9k 5V 222k LT1677 SET 619k GND – 681k THERMISTOR: VISHAY NTHS120601N2202J OUT LTC6990 V+ fOUT 5V 187k DIV 6990 TA12 1M 6990f 25 LTC6990 PACKAGE DESCRIPTION DCB Package 6-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1715) 0.70 0.05 3.55 0.05 1.65 0.05 (2 SIDES) PACKAGE OUTLINE 2.15 0.05 0.25 0.50 BSC 1.35 0.05 (2 SIDES) 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 2.00 0.10 (2 SIDES) R = 0.115 TYP 0.40 4 6 0.10 R = 0.05 TYP 3.00 0.10 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 1.65 0.10 (2 SIDES) PIN 1 NOTCH R0.20 OR 0.25 45 CHAMFER 3 1 (DCB6) DFN 0405 0.200 REF 0.75 0.05 0.25 0.50 BSC 0.05 1.35 0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (TBD) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 6990f 26 LTC6990 PACKAGE DESCRIPTION S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.95 BSC 0.80 – 0.90 0.30 – 0.45 6 PLCS (NOTE 3) 0.20 BSC DATUM ‘A’ 1.00 MAX 0.01 – 0.10 0.30 – 0.50 REF 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 0.09 – 0.20 (NOTE 3) 1.90 BSC S6 TSOT-23 0302 REV B 6990f 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. 27 LTC6990 TYPICAL APPLICATION Ultrasonic Frequency Sweep Generator fOUT = 500kHz TO 31.25kHz OE OE OUT LTC6990 GND V+ C1 0.1μF 2.25V TO 5.5V R1 976k R2 102k SET 74HC125 CSET 0.022μF RSET1 49.9k RSET2 750k DIV 6990 TA13 SWEEPS FROM 500kHz to 31.25kHz IN A FEW MILLISECONDS (CONTROLLED BY CSET). RELATED PARTS PART NUMBER LTC1799 LTC6900 LTC6930 DESCRIPTION 1MHz to 33MHz ThinSOT Silicon Oscillator 1MHz to 20MHz ThinSOT Silicon Oscillator Fixed Frequency Oscillator, 32.768kHz to 8.192MHz COMMENTS Wide Frequency Range Low Power, Wide Frequency Range Micropower, ISUPPLY = 35μA at 400kHz 0.09% Accuracy, 110μs Start-Up Time, 105μA at 32kHz LTC6906/LTC6907 10kHz to 1MHz or 40kHz ThinSOT Silicon Oscillator 6990f 28 Linear Technology Corporation (408) 432-1900 ● FAX: (408) 434-0507 ● LT 0710 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 www.linear.com © LINEAR TECHNOLOGY CORPORATION 2010