LTC6991 TimerBlox: Resettable, Low Frequency Oscillator Features Description n n n n n n n n The LTC®6991 is a silicon oscillator with a programmable period range of 1.024ms to 9.54 hours (29.1µHz to 977Hz), specifically intended for long duration timing events. The LTC6991 is part of the TimerBlox™ family of versatile silicon timing devices. n n Period Range: 1ms to 9.5 Hours Configured with 1 to 3 Resistors <1.5% Maximum Frequency Error Output Reset Function 2.25V to 5.5V Single Supply Operation 55µA to 80µA Supply Current (2ms to 9.5hr Clock Period) 500µs Start-Up Time CMOS Output Driver Sources/Sinks 20mA –40°C to 125°C Operating Temperature Range Available in Low Profile (1mm) SOT-23 (ThinSOT™) and 2mm × 3mm DFN Packages Applications n n n n n n A single resistor, RSET , programs the LTC6991’s internal master oscillator frequency. The output clock period is determined by this master oscillator and an internal frequency divider, NDIV , programmable to eight settings from 1 to 221. “Heartbeat” Timers Watchdog Timers Intervalometers Periodic “Wake-Up” Call High Vibration, High Acceleration Environments Portable and Battery-Powered Equipment L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and ThinSOT and TimerBlox are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. tOUT = NDIV • RSET • 1.024ms, NDIV = 18 , , 64,..., 221 50kΩ In normal operation, the LTC6991 oscillates with a 50% duty cycle. A reset function is provided to truncate the pulse (reducing the duty cycle). The reset pin can also be used to prevent the output from oscillating. The RST and OUT pins can be configured for active-low or active-high operation using a polarity function. POL BIT 0 0 1 1 RST PIN 0 1 0 1 OUTPUT STATE Oscillating 0 (reset) 1 (reset) Oscillating The LTC6991 is available in the 6-lead SOT-23 (ThinSOT) package or a 6-lead 2mm × 3mm DFN. Typical Application Clock Period Range over Eight Divider Settings 10Hr Low Frequency Pulse Generator RST LTC6991 GND RSET 715k OUT 2.25V TO 5.5V V + R1 1M SET DIV R2 392k tPULSE ≈ RPW • CPW ≈ 1µs 0.1µF 6991 TA01a CLOCK PERIOD (LOG SCALE) OUT RPW 2.26k CPW 470pF 1Hr 1µs PULSE WIDTH 60 SECONDS 10Min 1Min 10Sec 1Sec 100ms 10ms 1ms 0 1.25 0.625 1.875 DIV PIN VOLTAGE, VDIV (V) 2.5 6991 TA01b 6991f LTC6991 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) LTC6991C.............................................–40°C to 85°C LTC6991I..............................................–40°C to 85°C LTC6991H........................................... –40°C to 125°C Specified Temperature Range (Note 3) LTC6991C................................................. 0°C to 70°C LTC6991I..............................................–40°C to 85°C LTC6991H........................................... –40°C to 125°C Junction Temperature............................................ 150°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) S6 Package............................................................ 300°C Pin Configuration TOP VIEW V+ 1 DIV 2 TOP VIEW 6 OUT 7 5 GND 4 RST SET 3 RST 1 6 OUT GND 2 5 V+ SET 3 4 DIV DCB PACKAGE 6-LEAD (2mm s 3mm) PLASTIC DFN S6 PACKAGE 6-LEAD PLASTIC TSOT-23 TJMAX = 150°C, θJA = 64°C/W, θJC = 10.6°C/W EXPOSED PAD (PIN 7) CONNECTED TO GND, PCB CONNECTION OPTIONAL TJMAX = 150°C, θJA = 192°C/W, θJC = 51°C/W Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LTC6991CDCB#PBF LTC6991CDCB#TRPBF LDWZ 6-Lead (2mm × 3mm) Plastic DFN 0°C to 70°C LTC6991IDCB#PBF LTC6991IDCB#TRPBF LDWZ 6-Lead (2mm × 3mm) Plastic DFN –40°C to 85°C LTC6991HDCB#PBF LTC6991HDCB#TRPBF LDWZ 6-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C LTC6991CS6#PBF LTC6991CS6#TRPBF LTDWY 6-Lead Plastic TSOT-23 0°C to 70°C LTC6991IS6#PBF LTC6991IS6#TRPBF LTDWY 6-Lead Plastic TSOT-23 –40°C to 85°C LTC6991HS6#PBF LTC6991HS6#TRPBF LTDWY 6-Lead Plastic TSOT-23 –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/ 6991f LTC6991 Electrical Characteristics 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, RST = 0V, DIVCODE = 0 to 15 (NDIV = 1 to 221), RSET = 50k to 800k, RLOAD = 5k, CLOAD = 5pF unless otherwise noted. SYMBOL PARAMETER tOUT Output Clock Period fOUT Output Frequency ∆fOUT Frequency Accuracy (Note 4) ∆fOUT/∆T Frequency Drift Over Temperature CONDITIONS MIN TYP 34,360 29.1µ 977 Hz ±1.5 ±2.2 % % ±0.8 l Frequency Drift Over Supply Period Jitter (Note 10) NDIV = 1 NDIV = 8 BW Frequency Modulation Bandwidth tS Frequency Change Settling Time (Note 9) UNITS 1.024m 29.1µHz ≤ fOUT ≤ 977Hz V+ = 4.5V to 5.5V V+ = 2.25V to 4.5V MAX l ±0.005 l l 0.23 0.06 Seconds %/°C 0.55 0.16 15 7 %/V %/V ppmRMS ppmRMS 0.4 • fOUT Hz 1 Cycle Analog Inputs VSET Voltage at SET Pin l ∆VSET/∆T VSET Drift Over Temperature l RSET Frequency-Setting Resistor l 0.97 1.00 1.03 ±75 V µV/°C 50 800 kΩ 0 V+ V l ±1.5 % DIV Pin Input Current l ±10 nA Operating Supply Voltage Range l Power-On Reset Voltage l VDIV DIV Pin Voltage ∆VDIV/∆V+ DIV Pin Valid Code Range (Note 5) l Deviation from Ideal VDIV/V+ = (DIVCODE + 0.5)/16 Power Supply V+ IS Supply Current 2.25 5.5 V 1.95 V RL = ∞, RSET = 50k V+ = 5.5V V+ = 2.25V l l 135 105 170 135 µA µA RL = ∞, RSET = 100k V+ = 5.5V V+ = 2.25V l l 100 80 130 105 µA µA RL = ∞, RSET = 800k V+ = 5.5V V+ = 2.25V l l 65 55 100 85 µA µA 6991f LTC6991 Electrical Characteristics 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, RST = 0V, DIVCODE = 0 to 15 (NDIV = 1 to 221), RSET = 50k to 800k, RLOAD = ∞, CLOAD = 5pF unless otherwise noted. SYMBOL Digital I/O VIH VIL IOUT(MAX) VOH VOL PARAMETER RST Pin Input Capacitance RST Pin Input Current High Level RST Pin Input Voltage Low Level RST Pin Input Voltage Output Output Current High Level Output Voltage (Note 7) Low Level Output Voltage (Note 7) tRST Reset Propagation Delay tWIDTH tr Minimum Input Pulse Width Output Rise Time (Note 8) tf Output Fall Time (Note 8) CONDITIONS MIN TYP MAX 2.5 RST = 0V to V+ (Note 6) (Note 6) V+ = 2.7V to 5.5V V+ = 5.5V V+ = 3.3V V+ = 2.25V V+ = 5.5V V+ = 3.3V V+ = 2.25V V+ = 5.5V V+ = 3.3V V+ = 2.25V V+ = 3.3V V+ = 5.5V V+ = 3.3V V+ = 2.25V V+ = 5.5V V+ = 3.3V V+ = 2.25V 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 LTC6991C is guaranteed functional over the operating temperature range of –40°C to 85°C. Note 3: The LTC6991C is guaranteed to meet specified performance from 0°C to 70°C. The LTC6991C 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 LTC6991I is guaranteed to meet specified performance from –40°C to 85°C. The LTC6991H 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. ±10 l 0.7 • V+ 0.3 • V+ l IOUT = –1mA IOUT = –16mA IOUT = –1mA IOUT = –10mA IOUT = –1mA IOUT = –8mA IOUT = 1mA IOUT = 16mA IOUT = 1mA IOUT = 10mA IOUT = 1mA IOUT = 8mA l l l l l l l l l l l l 5.45 4.84 3.24 2.75 2.17 1.58 ±20 5.48 5.15 3.27 2.99 2.21 1.88 0.02 0.26 0.03 0.22 0.03 0.26 16 24 40 5 1.1 1.7 2.7 1.0 1.6 2.4 0.04 0.54 0.05 0.46 0.07 0.54 UNITS pF nA V V mA V V V V V V V V V V V V ns ns ns ns ns ns ns ns ns ns Note 6: The RST 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 VRST(RISING) ≈ 0.55 • V+ + 185mV and VRST(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 0.5× or 2× 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. 6991f LTC6991 Typical Performance Characteristics + V = 3.3V, RSET = 200k, TA = 25°C unless otherwise noted. Frequency Error vs Temperature Frequency Error vs Temperature 3 GUARANTEED MAX OVER TEMPERATURE RSET = 50k 3 PARTS 1 0 –1 2 RSET = 200k 3 PARTS 1 ERROR (%) ERROR (%) 1 0 GUARANTEED MIN OVER TEMPERATURE –3 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 GUARANTEED MIN OVER TEMPERATURE –2 –3 –50 –25 125 50 25 75 0 TEMPERATURE (°C) 100 6991 G01 Frequency Error vs RSET GUARANTEED MAX OVER TEMPERATURE 200 –1 NUMBER OF UNITS 0.2 DRIFT (%) ERROR (%) 250 0.3 3 PARTS 0.1 0 –0.1 –0.2 REFERENCED TO V+ = 4.5V RSET = 50k RSET = 200k RSET = 800k –0.3 GUARANTEED MIN OVER TEMPERATURE –0.4 0 200 400 RSET (kΩ) 600 –0.5 800 2 0.8 0.6 0.6 0.4 0.4 0.2 0.2 –0.6 –0.6 –1.0 0 5 10 ISET (µA) 15 20 6992 G07 100 1.020 0.988 0.996 1.004 VSET (V) VSET vs Temperature 3 PARTS 1.010 1.005 1.000 0.995 0.990 –0.8 –1.0 1.02 1.012 1.015 0 –0.4 REFERENCED TO ISET = 10µA 150 6991 G06 VSET Drift vs Supply –0.2 –0.4 –0.8 2 LOTS DFN AND SOT-23 1274 UNITS 0 0.98 VSET (V) 0.8 DRIFT (mV) VSET (mV) 1.0 125 Typical VSET Distribution 6991 G05 VSET Drift vs ISET 0 100 50 6 4 3 5 SUPPLY VOLTAGE (V) 6991 G04 –0.2 50 25 75 0 TEMPERATURE (°C) 6991 G03 0.4 1 1.0 –3 –50 –25 125 Frequency Drift vs Supply Voltage 0 GUARANTEED MIN OVER TEMPERATURE –2 0.5 –2 0 6991 G02 3 2 RSET = 800k 3 PARTS –1 –1 –2 –3 GUARANTEED MAX OVER TEMPERATURE GUARANTEED MAX OVER TEMPERATURE 2 ERROR (%) 2 Frequency Error vs Temperature 3 3 0.985 REFERENCED TO V+ = 4V 2 3 4 SUPPLY (V) 6 5 6991 G08 0.980 –50 –25 75 0 25 50 TEMPERATURE (°C) 100 125 6991 G09 6991f LTC6991 Typical Performance Characteristics + V = 3.3V, RSET = 200k, TA = 25°C unless otherwise noted. Supply Current vs Supply Voltage 250 150 125 100 RSET = 100k RSET = 200k 75 RSET = 800k 50 25 2 3 4 5 SUPPLY VOLTAGE (V) 125 POWER SUPPLY CURRENT (µA) RSET = 50k POWER SUPPLY CURRENT (µA) POWER SUPPLY CURRENT (µA) 150 0 5V, RSET = 100k 100 2.5V, RSET = 100k 75 5V, RSET = 800k 50 2.5V, RSET = 800k 25 0 –50 –25 6 50 25 75 0 TEMPERATURE (°C) 100 6991 G10 1000 75 V+ = 2.5V 50 25 200 400 RSET (kΩ) 600 3.3V RST RISING 100 50 0 0.2 0.6 0.4 VRST/V+ (V/V) 3.5 SET PIN SHORTED TO GND 3.0 POSITIVE-GOING 400 0 1.0 RST Threshold Voltage vs Supply Voltage 600 800 0.8 6991 G12 200 0 3.3V RST FALLING 0 RST PIN VOLTAGE (V) 100 V+ = 3.3V 5V RST RISING 150 125 800 V+ = 5V ISET (µA) POWER SUPPLY CURRENT (µA) 125 5V RST FALLING 200 Typical ISET Current Limit vs V+ 150 RSET = 800k 6991 G11 Supply Current vs RSET 0 Supply Current vs RST Pin Voltage Supply Current vs Temperature 2.5 2.0 NEGATIVE-GOING 1.5 1.0 0.5 2 3 4 5 SUPPLY VOLTAGE (V) 0 6 2 3 4 5 SUPPLY VOLTAGE (V) 6991 G15 6 6991 G14 6991 G13 Reset Propagation Delay (tRST) vs Supply Voltage 50 3.0 CLOAD = 5pF 35 30 25 20 15 10 2.0 tRISE 1.5 tFALL 1.0 0.5 5 0 CLOAD = 5pF 2.5 40 RISE/FALL TIME (ns) PROPAGATION DELAY (ns) 45 Rise and Fall Time vs Supply Voltage 2 4 3 5 SUPPLY VOLTAGE (V) 6 0 2 3 4 5 SUPPLY VOLTAGE (V) 6 6991 G17 6991 G16 6991f LTC6991 Typical Performance Characteristics + V = 3.3V, RSET = 200k, TA = 25°C unless otherwise noted. Output Resistance vs Supply Current Typical Start-Up with POL = 1 50 OUTPUT RESISTANCE (Ω) 45 40 35 V+ 1V/DIV OUTPUT SOURCING CURRENT 30 1µs (tMASTER) WIDE INITIAL PULSE 25 500µs 20 OUT 1V/DIV OUTPUT SINKING CURRENT 15 10 5 0 2 3 4 5 SUPPLY VOLTAGE (V) 6 6991 G22 Pin Functions V+ = 2.5V DIVCODE = 15 RSET = 50k 250µs/DIV 6991 G19 (DCB/S6) V+ (Pin 1/Pin 5): Supply Voltage (2.25V to 5.5V). This supply should be kept free from noise and ripple. It should be bypassed directly to the GND pin with a 0.1µF capacitor. 50ppm/°C or better temperature coefficient. For lower accuracy applications an inexpensive 1% thick film resistor may be used. DIV (Pin 2/Pin 4): Programmable Divider and Polarity 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 (POL) determines the polarity of the RST and OUT pins. If POL = 0, RST is active-high, and forces OUT low. If POL = 1, RST is active-low and forces OUT high. 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. 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 20µA. 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 V+ RST OUT LTC6991 GND SET RSET V+ V+ C1 0.1µF R1 DIV 6991 PF R2 RST (Pin 4/Pin 1): Output Reset. The behavior of the RST pin is dependent on the polarity bit (POL). The POL bit is configured via the DIVCODE setting. When POL = 0, setting RST high forces OUT low and setting RST low allows the output to oscillate. When POL = 1, RST is active low. In that case, setting RST low forces OUT high and setting RST high allows the output to oscillate. 6991f LTC6991 Pin Functions (DCB/S6) GND (Pin 5/Pin 2): Ground. Tie to a low inductance ground plane for best performance. 30Ω. When driving an LED or other low impedance load a series output resistor should be used to limit source/sink current to 20mA. OUT (Pin 6/Pin 6): Oscillator Output. The OUT pin swings from GND to V+ with an output resistance of approximately Block Diagram (S6 package pin numbers shown) 5 V+ R1 4 DIV 4-BIT A/D CONVERTER POL BIT DIGITAL FILTER R2 OUTPUT POLARITY V+ MASTER OSCILLATOR 1µs V = SET tMASTER = 50kΩ ISET MCLK FIXED DIVIDER ÷ 1024 PROGRAMMABLE DIVIDER ÷1, 8, 64, 512 4096, 215, 218, 221 HALT OSCILLATOR IF ISET < 500nA POR D OUT 6 tOUT Q R INPUT POLARITY ISET + – VSET = 1V + – SET 3 1V RST GND 2 1 6991 BD ISET RSET 6991f LTC6991 Operation The LTC6991 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. fMASTER = 1 tMASTER I = 1MHz • 50kΩ • SET 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: fMASTER = 1 tMASTER = DIVCODE The DIV pin connects to an internal, V+ referenced 4-bit A/D converter that determines the DIVCODE value. DIVCODE programs two settings on the LTC6991: 1.DIVCODE determines the output frequency divider setting, NDIV . 2.DIVCODE determines the polarity of the RST and OUT pins, via the POL bit. VDIV may be generated by a resistor divider between V+ and GND as shown in Figure 1. 2.25V TO 5.5V V+ 1MHz • 50kΩ RSET LTC6991 DIV R2 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 ∆fOUT of the LTC6991. RSET may range from 50k to 800k (equivalent to ISET between 1.25µA and 20µA). Before reaching the OUT pin, the oscillator frequency passes through a fixed ÷1024 divider. The LTC6991 also includes a programmable frequency divider which can further divide the frequency by 1, 8, 64, 512, 4096, 215, 218 or 221. The divider ratio NDIV is set by a resistor divider attached to the DIV pin. fOUT = tOUT = 1MHz • 50kΩ ISET • , or 1024 • NDIV VSET 1 fOUT = NDIV VSET • • 1.024ms 50kΩ ISET GND 6991 F01 Figure 1. Simple Technique for Setting DIVCODE Table 1 offers recommended 1% resistor values that accurately produce the correct voltage division as well as the corresponding NDIV and POL 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 column in Table 1 shows the ideal ratio of VDIV to the supply voltage, which can also be calculated as: VDIV with RSET in place of VSET/ISET the equation reduces to: N •R tOUT = DIV SET • 1.024ms 50kΩ R1 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. 6991f LTC6991 Operation Table 1. DIVCODE Programming DIVCODE POL NDIV RECOMMENDED tOUT R1 (kΩ) R2 (kΩ) VDIV/V+ 0 0 1 1.024ms to 16.384ms Open Short ≤0.03125 ±0.015 1 0 8 8.192ms to 131ms 976 102 0.09375 ±0.015 2 0 64 65.5ms to 1.05sec 976 182 0.15625 ±0.015 3 0 512 524ms to 8.39sec 1000 280 0.21875 ±0.015 4 0 4,096 4.19sec to 67.1sec 1000 392 0.28125 ±0.015 5 0 32,768 33.6sec to 537sec 1000 523 0.34375 ±0.015 6 0 262,144 268sec to 4,295sec 1000 681 0.40625 ±0.015 7 0 2,097,152 2,147sec to 34,360sec 1000 887 0.46875 ±0.015 8 1 2,097,152 2,147sec to 34,360sec 887 1000 0.53125 ±0.015 9 1 262,144 268sec to 4,295sec 681 1000 0.59375 ±0.015 10 1 32,768 33.6sec to 537sec 523 1000 0.65625 ±0.015 11 1 4,096 4.19sec to 67.1sec 392 1000 0.71875 ±0.015 12 1 512 524ms to 8.39sec 280 1000 0.78125 ±0.015 13 1 64 65.5ms to 1.05sec 182 976 0.84375 ±0.015 14 1 8 8.192ms to 131ms 102 976 0.90625 ±0.015 15 1 1 1.024ms to 16.384ms Short Open ≥0.96875 ±0.015 POL BIT = 0 POL BIT = 1 10000 7 6 1000 9 10 5 100 tOUT (SECONDS) 8 11 4 10 12 3 1 13 2 0.1 1 0.01 0.001 14 0 0V 15 0.5•V+ INCREASING VDIV V+ 6991 F02 Figure 2. Frequency Range and POL Bit vs DIVCODE 6991f 10 LTC6991 Operation RST Pin and Polarity (POL) Bit The RST pin controls the state of the LTC6991’s output as seen on the OUT pin. The active/inactive voltage levels depend on the POL bit setting. Table 2. Output States POL BIT RST PIN OUTPUT STATE 0 0 Oscillating 0 1 0 (reset) 1 0 1 (reset) 1 1 Oscillating Each period of the LTC6991’s internal oscillator clocks the output state latch (see Block Diagram). The reset pin (RST) can reset or hold off the output latch. The active state of the reset pin is determined by the polarity function (POL). Similarly, the output latch is followed by a buffer that can invert the output. The output polarity is also controlled by the POL bit. If POL = 0, the reset pin is active high and the output latch is not inverted. Therefore, pulling the RST pin high will reset the output latch and force the OUT pin low. Pulling RST low will allow the output to oscillate, with the next rising edge dependent on the internal oscillator. If POL = 1, the reset pin is active low and the output latch is inverted. Therefore, pulling the RST pin low will reset the output latch and force the OUT pin high. Pulling RST high will allow the output to oscillate, with the next falling edge dependent on the internal oscillator. Note that the master oscillator frequency and phase are not affected by the RST pin; The LTC6991 continues to oscillate, internally, even when RST is active. While the reset function can block an output pulse, its exact placement in time can only be changed by power cycling the LTC6991. tWIDTH RST INTERNAL OSCILLATOR tRST OUT 6991 F03 tOUT Figure 3. RST Timing Diagram (POL = 0) RST tRST OUT tOUT INTERNAL OSCILLATOR 6991 F04 Figure 4. RST Timing Diagram (POL = 1) 6991f 11 LTC6991 Operation Changing DIVCODE After Start-Up Following start-up, the A/D converter will continue monitoring VDIV for changes. The LTC6991 will respond to DIVCODE changes in less than one cycle. start-up time may increase 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+. Less than 100pF will not affect performance. tDIVCODE < 500 • tMASTER < tOUT Start-Up Behavior The output may have an inaccurate pulse width during the frequency transition. But the transition will be glitch-free and no high or low pulse can be shorter than the master clock period. A digital filter is used to guarantee the DIVCODE has settled to a new value before making changes to the output. When first powered up, the output is held low. If the polarity is set for non-inversion (POL = 0) and the output is enabled (RST = 0) at the end of the start-up time, OUT will begin oscillating. If the output is being reset (RST = 1) at the end of the start-up time, the first pulse will be skipped. Subsequent pulses will also be skipped until RST = 0. Start-Up Time In inverted operation (POL = 1), the start-up sequence is similar. However, the LTC6991 does not know the correct DIVCODE setting when first powered up, so the output defaults low. At the end of tSTART , the value of DIVCODE is recognized and OUT goes high (inactive) because POL = 1. If RST = 1 (inactive) then OUT will quickly fall after a single tMASTER cycle. If RST = 0 at the end of the start-up time, the output is held in reset and remains high. When power is first applied, the power-on reset (POR) circuit will initiate the start-up time, tSTART . The OUT pin is held low during this time. The typical value for tSTART ranges from 0.5ms to 8ms depending on the master oscillator frequency (independent of NDIV): tSTART(TYP) = 500 • tMASTER During start-up, the DIV pin A/D converter must determine the correct DIVCODE before the output is enabled. The Figures 7 to 10 detail the four possible start-up sequences. V+ 1V/DIV DIV 200mV/DIV OUT 1V/DIV OUT 1V/DIV V+ = 3.3V RSET = 200k 10ms/DIV 6991 F05 Figure 5. DIVCODE Change from 1 to 0 500µs V+ = 2.5V DIVCODE = 0 RSET = 50k 250µs/DIV 6991 F06 Figure 6. Typical Start-Up 6991f 12 LTC6991 Operation RST OUT tSTART tOUT 6991 F07 Figure 7. Start-Up Timing Diagram (RST = 0, POL = 0) RST OUT tSTART OUTPUT DISABLED FOR INTEGER MULTIPLE OF tOUT 6991 F08 Figure 8. Start-Up Timing Diagram (RST = 1, POL = 0) RST 6991 F09 OUT tSTART tMASTER OUTPUT DISABLED FOR INTEGER MULTIPLE OF tOUT Figure 9. Start-Up Timing Diagram (RST = 0, POL = 1) RST 6991 F10 OUT tSTART tOUT tMASTER Figure 10. Start-Up Timing Diagram (RST = 1, POL = 1) 6991f 13 LTC6991 Applications Information Basic Operation The simplest and most accurate method to program the LTC6991 is to use a single resistor, RSET , between the SET and GND pins. The design procedure is a 3-step process. First select the POL bit setting and NDIV value, then calculate the value for the RSET resistor. Step 1: Select the POL Bit Setting For noninverted (active-high) functionality, choose POL = 0. Step 2: Select the NDIV Frequency Divider Value Step 1: Select the POL Bit Setting The LTC6991 can operate in normal (active-high) or inverted (active-low) modes, depending on the setting of the POL bit. The best choice depends on the the application. Step 2: Select the NDIV Frequency Divider Value As explained earlier, the voltage on the DIV pin sets the DIVCODE which determines both the POL bit and the NDIV value. For a given output clock period, NDIV should be selected to be within the following range. tOUT t ≤ NDIV ≤ OUT 16.384ms 1.024ms Example: Design a 1Hz oscillator with minimum power consumption and active-high reset input. (1) To minimize supply current, choose the lowest NDIV value (generally recommended). Alternatively, use Table 1 as a guide to select the best NDIV value for the given application. With POL already chosen, this completes the selection of DIVCODE. Use Table 1 to select the proper resistor divider or VDIV/V+ ratio to apply to the DIV pin. Choose an NDIV value that meets the requirements of Equation (1), using tOUT = 1000ms: 61.04 ≤ NDIV ≤ 976.6 Potential settings for NDIV include 64 and 512. NDIV = 64 is the best choice, as it minimizes supply current by using a large RSET resistor. POL = 0 and NDIV = 64 requires DIVCODE = 2. Using Table 1, choose R1 = 976k and R2 = 182k values to program DIVCODE = 2. Step 3: Select RSET Calculate the correct value for RSET using Equation (2). RSET = 50k 1000ms • = 763k 1.024ms 64 Since 763k is not available as a standard 1% resistor, substitute 768k if a –0.7% frequency shift is acceptable. Otherwise, select a parallel or series pair of resistors such as 576k + 187k to attain a more precise resistance. The completed design is shown in Figure 11. Step 3: Calculate and Select RSET The final step is to calculate the correct value for RSET using the following equation. RSET = t 50k • OUT 1.024ms NDIV RST OUT LTC6991 GND (2) Select the standard resistor value closest to the calculated value. RST 2.25V TO 5.5V V+ R1 976k SET RSET 763k DIV DIVCODE = 2 R2 182k 6991 F11 Figure 11. 1Hz Oscillator 6991f 14 LTC6991 Applications Information LTC6991 as “Wake-Up Timer” input to filter start-up glitches from the system as it is powered on. The output latch reset function provided by the RST pin allows the LTC6991 to enable a larger system at regular intervals. The on-time can be controlled by the system. This allows the system to shut itself down immediately after performing its tasks, reducing power consumption. If the LTC6991 is enabling a switching regulator that can operate on supplies greater than 5.5V, it will be necessary to limit the supply voltage provided to the LTC6991. If the LTC6991 output is not heavily loaded, and if a large RSET resistor is used, the supply current will not be much larger than 100µA, so a simple regulator circuit can be constructed using a Zener diode. Figure 12 shows an example using “black boxes” for a switching regulator and the system being duty-cycled. In some cases, an RC filter may be necessary at the RST 3V TO 20V tOUT 3570 SECONDS RSUPPLY 4.99k 1N4733A 5.1V V+ R1 1M 0.1µF OUT VREG SWITCHING REGULATOR SHDN LTC6991 DIV R2 R SET 681k 665k VOUT VIN V+ GND SET RST SYSTEM RFILT 100k DONE CFILT 0.1µF 6991 F12 THE SYSTEM CAN EXTEND tON AS LONG AS NEEDED (UP TO 50% OF tOUT) tON tON tON VREG DONE/RST LTC6991 OUT tOUT tOUT tOUT Figure 12. Powering Up a System Once an Hour 6991f 15 LTC6991 Applications Information Self-Resetting Circuits OUT RPW 2.26k The RST pin has hysteresis to accommodate slow-changing input voltages. Furthermore, the trip points are proportional to the supply voltage (see Note 6 and the RST Threshold Voltage vs Supply Voltage curve in Typical Performance Characteristics). This allows an RC time constant at the RST input to generate a delay that is nearly independent of the supply voltage. RST CPW 470pF OUT LTC6991 2.25V TO 5.5V V+ GND 0.1µF R1 1M RSET 715k DIV SET R2 392k A simple application of this technique allows the LTC6991 output to reset itself, producing a well-controlled pulse once each cycle. Figures 13a and 13b show circuits that produce approximately 1µs pulses once a minute. The only difference is in the POL bit setting, which controls whether the pulse is positive or negative. VRST(RISING) V+ tPULSE ≈ –2.26kΩ • 470pF • In(1 – 0.61) tPULSE ≈ 1µs tPULSE = –RPW • CPW • In 1– 1µs PULSE WIDTH 60 SECONDS 6991 F13a Voltage Controlled Frequency Figure 13a. Self-Resetting Circuit (DIVCODE = 4) With one additional resistor, the LTC6991 output frequency can be manipulated by an external voltage. As shown in Figure 14, voltage VCTRL sources/sinks a current through RVCO to vary the ISET current, which in turn modulates the output frequency as described in Equation (3). OUT RPW 2.26k RST CPW 470pF GND R V 1MHz • 50kΩ fOUT = • 1+ VCO – CTRL (3) 1024 • NDIV • R VCO RSET VSET RSET 715k 16 V 0.1µF R1 392k DIV SET VRST(FALLING) V+ tPULSE ≈ –2.26kΩ • 470pF • In(0.43) tPULSE ≈ 0.9µs tPULSE = –RPW • CPW • In 0.9µs PULSE WIDTH 60 SECONDS 6991 F13b Figure 13b. Self-Resetting Circuit (DIVCODE = 11) RST OUT V+ LTC6991 GND ISET Extremes (Master Oscillator Frequency Extremes) When operating with ISET outside of the recommended 1.25µA to 20µA range, the master oscillator operates outside of the 62.5kHz to 1MHz range in which it is most accurate. 2.25V TO 5.5V + R2 1M Digital Frequency Control The control voltage can be generated by a DAC (digitalto-analog converter), resulting in a digitally-controlled frequency. Many DACs allow for the use of an external reference. If such a DAC is used to provide the VCTRL voltage, the VSET dependency can be eliminated by buffering VSET and using it as the DAC’s reference voltage, as shown in Figure 15. 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. OUT LTC6991 VCTRL RVCO SET RSET V+ C1 0.1µF R1 DIV R2 6991 F14 Figure 14. Voltage-Controlled Oscillator 6991f LTC6991 Applications Information RST OUT V+ LTC6991 0.1µF V+ V+ GND + SET 1/2 LTC6078 C1 0.1µF R1 DIV R2 – V+ 6991 F15 0.1µF DIN µP CLK VCC LTC1659 R D 1MHz • 50kΩ • 1 + VCO – IN RSET 4096 1024 • NDIV • RVCO DIN = 0 TO 4095 fOUT = REF VOUT RVCO CS/LD RSET GND Figure 15. Digitally-Controlled Oscillator The oscillator can still function with reduced accuracy for ISET < 1.25µA. At approximately 500nA, the oscillator output will be frozen in its current state. The output could halt in a high or low state. This avoids introducing short pulses when frequency modulating a very low frequency output. At the other extreme, it is not recommended to operate the master oscillator beyond 2MHz because the accuracy of the DIV pin ADC will suffer. Frequency Modulation and Settling Time The LTC6991 will respond to changes in ISET up to a –3dB bandwidth of 0.4 • fOUT . Following a 2× or 0.5× step change in ISET , the output frequency takes less than one cycle to settle to within 1% of the final value. Power Supply Current ignores CLOAD (valid for CLOAD < 1nF) and assumes the output has 50% duty cycle. V+ V+ IS(TYP) ≈ V • fMASTER • 7.8pF + + 420kΩ 2 • RLOAD + + 1.8 • ISET + 50µA Supply Bypassing and PCB Layout Guidelines The LTC6991 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. Adequate supply bypassing and proper PCB layout are important to ensure this. Figure 18 shows example PCB layouts for both the TSOT-23 and DFN packages using 0603 sized passive components. The layouts assume a two layer board with a ground plane layer beneath and around the LTC6991. These layouts are a guide and need not be followed exactly. The power supply current varies with frequency, supply voltage and output loading. It can be estimated under any condition using the following equation. This equation 6991f 17 LTC6991 Applications Information RST OUT LTC6991 GND SET V+ V+ C1 0.1µF R1 DIV RSET R2 V+ R1 R2 V+ C1 C1 V+ OUT RST OUT DIV GND GND V+ SET RST SET DIV R1 RSET RSET R2 6991 F18 DFN PACKAGE TSOT-23 PACKAGE Figure 18. Supply Bypassing and PCB Layout 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 DFN package, C1’s connection to GND is also simply done on the top layer. For the TSOT-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 a 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. 6991f 18 LTC6991 Typical Applications 5 Second On/Off Timed Relay Driver 12V 0.1µF L D1 1N4148 RESET RUN RELAY ENABLE RST OUT LTC6991 R4 15k R1 1M SET Q1 2N2219A 1 COTO 1022 RELAY 9001-12-01 5V V+ GND C NO C2 0.1µF DIV R2 392k R3 118k 6991 TA02 1.5ms Radio Control Servo Reference Pulse Generator 5V R7 10k RESET = OPEN RUN = GND 20ms FRAME RATE GENERATOR RST 20ms PERIOD OUT LTC6991 GND TRIG 5V V+ SET DIV R5 102k GND C1 0.01µF 1.5ms PULSE OUT LTC6993-1 R4 976k R6 121k 1.5ms REFERENCE PULSE 5V V+ R1 1M R3 146k SET C2 0.1µF DIV R2 280k 6991 TA03 6991f 19 LTC6991 Typical Applications Cycling (10 Seconds On/Off) Symmetrical Power Supplies M2 Si4435DY 15VIN RST R2 1k M3 Si9410 R11 5k OUT LTC6991 V+ GND 5V C1 0.1µF R8 1M SET M4 Si4435DY DIV R9 392k R10 237k 15VOUT R6 20k R1 100k R3 50k –15VIN M1 Si9410 –15VOUT F6991 TA04 Isolated AC Load Flasher 5V OPEN = OFF GND = ON R3 10k 0.1µF 5 1 RST V+ OUT LTC6991 3 RSET 237k SET GND DIV R4 215Ω 6 4 2 R1 1M R2 392k 1 U2 MOC3041M 6 R5 5.94k 2 5V ZERO CROSSING U3 NTE5642 4 10 SECONDS ON/OFF 40W LAMP R6 10k HOT 117V AC R7 100Ω C2 0.022µF 6991 TA05 NEUTRAL AC ISOLATION BARRIER = 7500V 6991f 20 LTC6991 Typical Applications Interval (Wiper) Timer 5V 5s 15s 30s 2s V+ 1m 2m 4m OFF RST 66.5k 280k 182k 18.2k OUT TRIG LTC6991 5s 15s 30s 2s GND V+ V+ 0.1µF 1m 2m 4m OFF SET OUT OUTPUT 2s LTC6993-1 DIV V+ V+ GND 0.1µF 1M DIV SET 383k 1M 2s tINTERVAL 2 SECONDS TO 4 MINUTES 681k 6991 TA06 182k 280k 113k 133k 5s 15s 30s 1m 2m 4m 2s OFF 6991f 21 LTC6991 Package Description DCB Package 6-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1715 Rev A) 0.70 p0.05 3.55 p0.05 1.65 p0.05 (2 SIDES) 2.15 p0.05 PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 1.35 p0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP R = 0.05 TYP 2.00 p0.10 (2 SIDES) 3.00 p0.10 (2 SIDES) 0.40 p 0.10 4 6 1.65 p 0.10 (2 SIDES) PIN 1 NOTCH R0.20 OR 0.25 s 45o CHAMFER PIN 1 BAR TOP MARK (SEE NOTE 6) 3 0.200 REF 0.75 p0.05 1 (DCB6) DFN 0405 0.25 p 0.05 0.50 BSC 1.35 p0.10 (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 6991f 22 LTC6991 Package Description S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 0.62 MAX 2.90 BSC (NOTE 4) 0.95 REF 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 0.30 – 0.45 6 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) 1.90 BSC 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 S6 TSOT-23 0302 REV B 6991f 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. 23 LTC6991 Typical Application Intervalometer for Time-Lapse Photography ACTIVATES SHUTTER AT 8SEC TO 8.5MIN INTERVALS RPW 100k RST CPW 33µF GND RS3 95.3k 8SEC TO 64SEC RS1 1M OUT SHUTTER LTC6991 V+ R1A 332k SET DIV R1B 1M 1µF “SLOW RANGE” 1.1MIN TO 8.5 MIN RS2 2M R2 130k 6991 TA07 Related Parts PART NUMBER DESCRIPTION COMMENTS LTC1799 1MHz to 33MHz ThinSOT Silicon Oscillator Wide Frequency Range LTC6900 1MHz to 20MHz ThinSOT Silicon Oscillator Low Power, Wide Frequency Range LTC6906/LTC6907 10kHz to 1MHz or 40kHz ThinSOT Silicon Oscillators Micropower, ISUPPLY = 35µA at 400kHz LTC6930 Fixed Frequency Oscillator, 32.768kHz to 8.192MHz 0.09% Accuracy, 110µs Start-Up Time, 105µA at 32kHz LTC6990 TimerBlox: Voltage-Controlled Silicon Oscillator Fixed-Frequency or Voltage-Controlled Operation LTC6992 TimerBlox: Voltage-Controlled Pulse Width Modulator (PWM) Simple PWM with Wide Frequency Range LTC6993 TimerBlox: Monostable Pulse Generator (One Shot) Resistor Programmable Pulse Width of 1µs to 34sec LTC6994 TimerBlox: Delay Block/Debouncer Delays Rising, Falling or Both Edges 1µs to 34sec 6991f 24 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LT 0910 • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2010