MIC1555/1557 IttyBitty® RC Timer / Oscillator General Description Features ® The MIC1555 IttyBitty CMOS RC timer/oscillator and MIC1557 IttyBitty® CMOS RC oscillator are designed to provide rail-to-rail pulses for precise time delay or frequency generation. The devices are similar in function to the industry standard “555”, without a frequency control (FC) pin or an opencollector discharge (D) pin. The threshold pin (TH) has precedence over the trigger (TR) input, ensuring that the BiCMOS output is off when TR is high. The MIC1555 may be used as an astable (oscillator) or monostable (one-shot) with separate threshold and trigger inputs. In the one-shot mode, the output pulse width is precisely controlled by an external resistor and a capacitor. Time delays may be accurately controlled from microseconds to hours. In the oscillator mode, the output is used to provide precise feedback, with a minimum of one resistor and one capacitor producing a 50% duty cycle square wave. The MIC1557 is designed for astable (oscillator) operation only, with a chip select/reset (CS) input for low power shutdown. One resistor and one capacitor provide a 50% duty cycle square wave. Other duty-cycle ratios may be produced using two diodes and two resistors. The MIC1555/7 is powered from a +2.7V to +18V supply voltage. The MIC1555/7 is available in the SOT-23-5 5-pin package, and is rated for –40°C to +85°C ambient temperature range • +2.7V to +18V operation • Low current − <1µA typical shutdown mode (MIC1557) − 200µA typical (TRG and THR low) at 3V supply • Timing from microseconds to hours • “Zero” leakage trigger and threshold inputs • 50% square wave with one Resistor, one Capacitor • Threshold input precedence over trigger input • <15Ω output on resistance • No output cross-conduction current spikes • <0.005%/°C temperature stability • <0.055%/V supply stability • Small SOT-23-5 surface mount package Applications • • • • • • • • • • • • Precision timer Pulse generation Sequential timing Time-delay generation Missing pulse detector Micropower oscillator to 5MHz Charge-pump driver LED blinker Voltage converter Linear sweep generator Variable frequency and duty cycle oscillator Isolated feedback for power supplies Typical Application +5V +5V 100µs MIC1555 13 Standby Trigger 4 2 VS OUT 1k THR 4 Output TRG GND 8kHz MIC1557 5 Enabled Disabled 3 2 VS OUT 5 CS GND 1k T/T 1 0.1µF Monostable (One-Shot) Output 0.1µF Astable (Oscillator) IttyBitty is a registered trademark of Micrel, Inc. Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com May 2010 M9999-052610-D Micrel, Inc. MIC1555/1557 Ordering Information Part Number Marking Temperature Range Package T10 –40° to +85°C 5-Pin SOT-23 T11 –40° to +85°C 5-Pin SOT-23 Standard Pb-Free Standard Pb-Free MIC1555BM5 MIC1555YM5 T10 MIC1557BM5 MIC1557YM5 T11 Note: Under bar ( __ ) may not be to scale. Pin Configuration OUT GND VS 3 2 CS GND T/T 1 3 Part Identification T10 2 1 Part Identification T11 4 5 4 5 TRG THR VS OUT MIC1555 5-Pin SOT-23 (M) MIC1557 5-Pin SOT-23 (M) Pin Description Pin Number MIC1555 Pin Number 1 4 VS 2 2 GND Pin Name Supply (Input): +2.7 to +18V supply. Ground: Supply return. Chip Select/Reset (Input): Active high at >2/3VS. Output off when low at<1/3VS. 3 CS 5 OUT Output: CMOS totem-pole output. 4 TRG Trigger (Input): Sets output high. Active low (at ≤ 2/3VS nominal). 5 THR Threshold (Dominant Input): Sets output low. Active high (at ≥ 2/3VS nominal). T/T Trigger/Threshold (Input): Internally connected to both threshold and trigger functions. See TRG and THR. 3 1 May 2010 Pin Name MIC1557 2 M9999-052610-D Micrel, Inc. MIC1555/1557 Absolute Maximum Ratings Operating Ratings Supply Voltage (VS)......................................................+22V Threshold Voltage (VTHR, VT/T). ....................................+22V Trigger Voltage (VTGR, VT/T) ..........................................+22V Lead Temperature (soldering, 10sec.)....................... 300°C Maximum Storage Temperature ................................ 150°C Supply voltage (VS) ....................................... +2.7V to +18V Ambient Temperature (TA) .......................... –40°C to +85°C Package Thermal Resistance (θJA) .................................................................220°C/W (θJC) .................................................................130°C/W Electrical Characteristics TA = 25°C, bold values indicate –40°C< TA < +85°C, unless noted. Parameter Condition Typ Max Units Supply current VS = 5V 240 300 µA VS = 15V 350 400 µA 1161 µs Monostable Timing Accuracy Min RA = 10k, C =0.1µF, VS = 5V 2 RA = 10k, C =0.1µF, VS = 5V Monostable Drift over Temp Monostable Drift over Supply Astable Timing Accuracy 858 % VS = 5V, –55 ≤ TA ≤ +125°C, Note 1 100 ppm/°C VS = 10V, –55 ≤ TA ≤ +125°C, Note 1 150 ppm/°C VS = 15V, –55 ≤ TA ≤ +125°C, Note 1 200 ppm/°C VS = 5V to 15V, Note 1 0.5 %/V RA = RB = 10k, C = 0.1µF, VS = 5V 2 RA = RB = 10k, C = 0.1µF, VS = 5V 1717 % 2323 µs Maximum Astable Frequency RT = 1k, CT = 47pF, VS = 8V 5 MHz Astable Drift over Temp VS = 5V, –55 ≤ TA ≤ +125°C, Note 1 100 ppm/°C VS = 10V, –55 ≤ TA ≤ +125°C, Note 1 150 ppm/°C VS = 15V, –55 ≤ TA ≤ +125°C, Note 1 200 ppm/°C Astable Drift over Supply VS = 5V to 15V, Note 1 0.5 %/V Threshold Voltage VS = 15V 61 67 72 %/VS Trigger Voltage VS = 15V 27 32 37 %/VS Trigger Current VS = 15V 50 nA Threshold Current VS = 15V 50 nA Chip Select Output Voltage Drop on > 2/3 VS 50 67 72 %/VS off > 1/3 VS 28 33 50 %/VS VS = 15V, ISINK = 20mA 0.3 1.25 V VS = 5V, ISINK = 3.2mA 0.08 0.5 V VS = 15V, ISOURCE = 20mA 14.1 14.7 V VS = 5V, ISOURCE = 3.2mA 3.8 4.7 V Supply Voltage functional operation, Note 1 2.7 Output Rise Time RL = 10M, CL = 10pF, VS = 5V, Note 1 15 ns Output Fall Time RL = 10M, CL = 10pF, VS = 5V, Note 1 15 ns 18 V General Note: Devices are ESD protected, however handling precautions recommended. Note 1. Not tested. May 2010 3 M9999-052610-D Micrel, Inc. MIC1555/1557 Typical Characteristics (TA = 25°C, VIN = +5) ON RESISTANCE ( ) 70 On Resistance vs. Temperature 60 50 40 30 20 10 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 10 May 2010 k Factors Times RC 14 CHIP SELECT VOLTAGE (V) k FACTOR 0 -40 -20 0 20 40 60 80 100 TEMPERATURE °C) ( f=1k1 RC t=k2 RC 100 RC (µs) 1000 MIC1557 Chip Select vs. Supply Voltage 12 10 ON 8 6 4 2 0 OFF 36 9 12 15 18 SUPPLY VOLTAGE (V) 4 M9999-052610-D Micrel, Inc. MIC1555/1557 Functional Diagram VSUPPLY VS MIC1555 Bias THR 100µs S Q R Output OUT Standby Trigger <100µs TRG GND 1k 0.1µF MIC1555 Block Diagram with External Components (Monostable Configuration) VSUPPLY VS 1M MIC1557 CS Bias 8kHz S Q R Output OUT T/T GND 1k 0.1µF MIC1557 Block Diagram with External Components (Astable Configuration) May 2010 5 M9999-052610-D Micrel, Inc. MIC1555/1557 Trigger Comparator The trigger comparator is connected to R (reset) on the RS flip-flop. When TRG (trigger) goes below the trigger voltage (1/3VS), the flip-flop resets, making the output high. Functional Description Refer to the block diagrams. The MIC1555/7 provides the logic for creating simple RC timer or oscillator circuits. The MIC1555 has separate THR (threshold) and TRG (trigger) connections for monostable (one-shot) or astable (oscillator) operation. The MIC1557 has a single T/T (threshold and trigger) connection for astable (oscillator) operation only. The MIC1557 includes a CS (chip select/reset) control. Flip-Flop and Output A reset signal causes Q to go low, turning on the Pchannel MOSFET and turning off the N-channel MOSFET. This makes the output rise to nearly VS. A set signal causes Q to go high, turning off the Pchannel MOSFET, and turning on the N-channel MOSFET, grounding OUT. Supply VS (supply) is rated for +2.7V to +18V. An external capacitor is recommended to decouple noise. Basic Monostable Operation Refer to the MIC1555 functional diagram. A momentary low signal applied to TRG causes the output to go high. The external capacitor charges slowly through the external resistor. When VTHR (threshold voltage) reaches 2/3VS, the output is switched off, discharging the capacitor. During power-on, a single pulse may be generated. Resistive Divider The resistive voltage divider is constructed of three equal value resistors to produce 1/3VS and 2/3VS voltage for trigger and threshold reference voltages. Chip Select/Reset (MIC1557 only) CS (chip select/reset) controls the bias supply to the oscillator’s internal circuitry. CS must be connected to CMOS logic-high or logic-low levels. Floating CS will result in unpredictable operation. When the chip is deselected, the supply current is less than 1µA. Forcing CS low resets the MIC1557 by setting the flip flop, forcing the output low. Basic Astable Operation Refer to the MIC1557 functional diagram. The MIC1557 starts with T/T low, causing the output to go high. The external capacitor charges slowly through the external resistor. When VT/T reaches 2/3VS (threshold voltage), the output is switched off, slowly discharging the capacitor. When VT/T decreases to 1/3VS (trigger voltage), the output is switched on, causing VT/T to rise again, repeating the cycle. Threshold Comparator The threshold comparator is connected to S (set) on the RS flip-flop. When the threshold voltage (2/3VS) is reached, the flip-flop is set, making the output low. THR is dominant over TRG. May 2010 6 M9999-052610-D Micrel, Inc. MIC1555/1557 Basic Astable (Oscillator) Circuits An astable oscillator switches between two states, “on” and “off”, producing a continuous square wave. The IttyBitty® MIC1557 is optimized for this function, with the two comparator inputs, threshold and trigger (T/T), tied together internally. Chip select (CS) is brought out to allow on-off control of the oscillator. The MIC1555 may also be used as an astable oscillator by tying the threshold and trigger pins together, forming a T/T pin. If a resistor (RT) is connected from the output to a grounded timing capacitor, (CT) the voltage at their junction will ramp up from ground when the output goes high. If the T/T pin is connected to this junction, the output will switch low when the ramp exceeds 2/3 of the input voltage. The junction's voltage ramps down toward ground while the output is low. When the ramp is below 1/3 of the input voltage, the output switches to high, and the junction ramps up again. The continuing frequency of an MIC1555/7 astable oscillator depends on the RC time constant, and is approximately 0.7/RC below 1MHz. At frequencies above 1MHz the RC multiplier increases as capacitance is decreased, and propagation delay becomes dominant. Non-symmetrical oscillator operation is possible at frequencies up to 5MHz. If a duty cycle other than 50% is desired, a low-power signal diode may be connected in series with the timing resistor (RA), and a second resistor (RB) in series with an opposite facing diode connected in parallel. The frequency is then made up of two components, the charging time (tA) and the discharging time (tB) tA= 0.7RAC and tB= 0.7RBC. The frequency is the reciprocal of the sum of the two times tA + tB, so the total time is 1.4RTCT. The first half-cycle of an astable, after poweron or CS enable, is lengthened since the capacitor is charging from ground instead of the 1/3 input trigger trip voltage, to 1.1RC, the same as a monostable pulse. Application Information Basic Monostable (One-Shot) Circuit A monostable oscillator produces a single pulse each time that it is triggered, and is often referred to as a “one-shot”. The pulse width is constant, while the time between pulses depends on the trigger input. One-shots are generally used to “stretch” incoming pulses, of varying widths, to a fixed width. The IttyBitty® MIC1555 is designed for monostable operation, but may also be connected to provide astable oscillations. The pulse width is determined by the time it takes to charge a capacitor from ground to a comparator trip point. If the capacitor (CT) is charged through a resistor (RT) connected to the output of an MIC1555, the trip point is approximately 1.1RCT (the same time as the initial power-on cycle of an astable circuit.) If the trigger pulse of an MIC1555 remains low longer than the output pulse width, short oscillations may be seen in the output of a one-shot circuit, since the threshold pin has precedence over the trigger pin. These occur since the output goes low when the threshold is exceeded, and then goes high again as the trigger function is asserted. AC coupling the input with a series capacitor and a pull-up resistor, with an RC time constant less than the pulse width, will prevent these short oscillations. A diode (DT) in parallel with (RT) resets the one-shot quickly. 2.7V to 18V RT DT RPU Trigger 1 3V S VS 1 tON = 1.1R T CT THR CIN 5 CS TRG OUT 2.7V to 18V OUT 4 3 CB CT VS MIC1555 GND 4 2 RE T/T Figure 1. One-Shot Diagram CS 1 The period of a monostable circuit is: t = k2 RC where: t = period (s) k2 = constant [from Typical Characteristics graph] R = resistance (Ω) C = capacitance (F) CS 3 t OUT OUT 5 t = 0.7( RA+RB)CT MIC1557 RA GND 2 1k to 1M RB CT 100pF to 10µF Figure 2. Oscillator Diagram May 2010 7 M9999-052610-D Micrel, Inc. MIC1555/1557 The MIC1555 or MIC1557 can be used to construct an oscillator. The frequency of an astable oscillator is: f = Rising-Edge Triggered Monostable Circuit The MIC1555 may be triggered by an ac-coupled risingedge, as shown in figure 6. The pulse begins when the ac-coupled input rises, and a diode from the output holds the THR input low until TRG discharges to 1/3VS. This circuit provides a low-going output pulse. 1 k 1RC where: +5V +5V 1 OUT VS 4 3 4 2 THR 0.1µF Figure 3. MIC1555 Oscillator Configuration The MIC1557 features a CS input. When logic-low, CS places the MIC1557 into a <1µA shutdown state. If unused, the MIC1557 CS input on must be pulled up. 8kHz MIC1557 4 1M 3 2 OUT VS 5 Output CS 1k GND T/T 1 0.1µF Falling-Edge Triggered Monostable Circuit The MIC1555 may be triggered by an ac-coupled fallingedge, as shown in figure 5. The RC time constant of the input capacitor and pull-up resistor should be less than the output pulse time, to prevent multiple output pulses. A diode across the timing resistor provides a fast reset at the end of the positive timing pulse. 1M Input 100µs 4 2 VS OUT GND Output 1k TRG THR 1N4148 5 0.1µF Figure 5. Falling-Edge Trigger Configuration May 2010 Input Inverting Schmitt Trigger Refer to figure 7. The trip points of the MIC1555/7 are defined as 1/3 and 2/3VS, which allows either device to be used as a signal conditioning inverter, with hysteresis. A slowly changing input on T/T will be converted to a fast rise or fall-time opposite direction railto-rail output voltage. This output maybe used to directly drive the gate of a logic-level P-channel MOSFET with a gate pull-up resistor. This is an inverted logic low-side logic level MOSFET driver. A standard N-channel MIC1555 13 THR 1N4148 5 Long Time Delays Timing resistors larger than 1MΩ or capacitors larger than 10µF are not recommended due to leakage current inaccuracies. Time delays greater than 10 seconds are more accurately produced by dividing the output of an oscillator by a chain of flip-flop counter stages. To produce an accurate one-hour delay, for example, divide an 4.55Hz MIC1557 oscillator by 16,384 (4000hex, 214) using a CD4020 CMOS divider. 4.5Hz may be generated with a 1µF CT and approximately 156kΩ. Figure 4. MIC1557 Oscillator Configuration +5V 1k TRG GND Output Accuracy The two comparators in the MIC1555/7 use a resistor voltage divider to set the threshold and trigger trip points to approximately 2/3 and 1/3 of the input voltage, respectively. Since the charge and discharge rates of an RC circuit are dependent on the applied voltage, the timing remains constant if the input voltage varies. If a duty cycle of exactly 50% (or any other value from 1 to 99%), two resistors (or a variable resistor) and two diodes are needed to vary the charge and discharge times. The forward voltage of diodes varies with temperature, so some change in frequency will be seen with temperature extremes, but the duty cycle should track. For absolute timing accuracy, the MIC1555/7 output could be used to control constant current sources to linearly charge and discharge the capacitor, at the expense of added components and board space. 5 +5V OUT Figure 6. Rising-Edge Trigger Configuration 1k GND VS 0.1µF Output TRG 2 13 8kHz MIC1555 100µs MIC1555 f = frequency (Hz) k1 = constant [from Typical Characteristics graph] R = resistance (Ω) C = capacitance (F) To use the MIC1555 as an oscillator, connect TRG to THR. 8 M9999-052610-D Micrel, Inc. MIC1555/1557 +12V MOSFET may be driven by a second MIC1555/7, powered by 12V to 15V, to level-shift the input. +5V +12V N-Channel MOSFET RL (IRF540) TTL High = ON +5V 5 ON 1.6V 15V MIC1555 OFF 3.3V 4 2 THR VS MIC1557 1 43 RL 1 TRG GND OUT 2 C1 100pF to 10µF 3 VS CS T/T GND OUT 5 RE 100k RT 1k to 1M Figure 7. Schmitter Trigger Figure 8. Charge-Pump Charge-Pump Low-Side MOSFET Drivers A standard MOSFET requires approximately 15V to fully enhance the gate for minimum RDS(on). Substituting a logic-level MOSFET reduces the required gate voltage, allowing an MIC1557 to be used as an inverting Schmitt Trigger, described above. An MIC1557 may be configured as a voltage quadrupler to boost a 5V input to over 15V to fully enhance an N-channel MOSFET which may have its drain connected to a higher voltage, through a high-side load. ATTL high signal applied to CS enables a 10kHz oscillator, which quickly develops 15V at the gate of the MOSFET, clamped by a zener diode. A resistor from the gate to ground ensures that the FET will turn off quickly when the MIC1557 is turned off. Audible Voltmeter If an additional charge or discharge source is connected to the timing capacitor, the frequency may be shifted by turning the source on or off. An MIC1555 oscillator, powered by the circuit under test, may be used to drive a small loud speaker or piezo-electric transducer to provide a medium frequency for an open or high impedance state at the probe. A high tone is generated for a high level, and a lower frequency for a logic low on the probe. RT 10k +5V to +18V MIC1555 1N914 47k 10k CT 0.01µF 5 THR 4 TRG 2 GND VS 1 0.001µF OUT 3 10k 100 Figure 9. Audible Voltmeter May 2010 9 M9999-052610-D Micrel, Inc. MIC1555/1557 Package Information 5-Pin SOT-23 (M) MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http:/www.micrel.com The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2004 Micrel, Incorporated. May 2010 10 M9999-052610-D