october 1998 1 mic1555/1557 mic1555/1557 micrel mic1555/1557 ittybitty? rc timer / oscillator final information general description the mic1555 ittybitty cmos rc timer/oscillator and mic1557 ittybitty cmos rc oscillator are designed to pro- vide rail-to-rail pulses for precise time delay or frequency generation. the devices are similar in function to the industry standard ?55? without a frequency control (f c ) pin or an open- collector 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 microsec- onds 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 shut- down. 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-lead package, and is rated for ?0 c to +85 c ambient temperature range. typical applications features +2.7v to +18v operation low current <1 a typical shutdown mode (mic1557) 200 a typical (trg and thr low) at 3v supply timing from microseconds to hours ?ero?leakage trigger and threshold inputs 50% square wave with one resistor, one capacitor threshold input precedence over trigger input <15 ? 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 ordering information part number temp. range package marking mic1555bm5 ?0 c to +85 c sot-23-5 t10 mic1557bm5 ?0 c to +85 c sot-23-5 t11 standby trigger vs out mic1555 13 gnd 2 thr 5 +5v output trg 4 100s 1k 0.1f monostable (one-shot) 8khz enabled disabled vs cs mic1557 4 3 gnd 2 +5v out 5 t/t 1 output 1k 0.1f astable (oscillator) micrel, inc. ? 1849 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 944-0800 ? fax + 1 (408) 944-0970 ? http://www.micrel.com
mic1555/1557 micrel mic1555/1557 2 october 1998 pin configuration vs thr trg out t10 part identification 1 3 45 t/t out vs cs t11 1 3 45 22 gnd gnd sot-23-5 (m5) pin description pin number pin number pin name pin function mic1555 mic1557 1 4 vs supply (input): +2.7 to +18v supply. 2 2 gnd ground: supply return. 3 cs chip select/reset (input): active high at >2 3 v s . output off when low at < 1 3 v s . 3 5 out output: cmos totem-pole output. 4 trg trigger (input): sets output high. active low (at 2 3 v s nominal) . 5 thr threshold (dominant input): sets output low. active high (at 2 3 v s nominal). 1 t/t trigger/threshold (input): internally connected to both threshold and trigger functions. see trg and thr. part number identification mic1555bm5 t10 mic1557bm5 t11
october 1998 3 mic1555/1557 mic1555/1557 micrel electrical characteristics t a = 25 c, bold values indicate 40 c t a +85 c; unless noted. parameter condition min typ max units supply current v s = 5v 240 300 a v s = 15v 350 400 a monostable timing accuracy r a = 10k, c =0.1 f, v s = 5v 2 % r a = 10k, c =0.1 f, v s = 5v 858 1161 s monostable drift over temp v s = 5v, 55 t a +125 c, note 1 100 ppm/ c v s =10v, 55 t a +125 c, note 1 150 ppm/ c v s = 15v, 55 t a +125 c, note 1 200 ppm/ c monostable drift over supply v s = 5v to 15v, note 1 0.5 %/v astable timing accuracy r a = r b = 10k, c = 0.1 f, v s = 5v 2 % r a = r b = 10k, c = 0.1 f, v s = 5v 1717 2323 s maximum astable frequency r t = 1k, c t = 47pf, v s = 8v 5 mhz astable drift over temp v s = 5v, 55 t a +125 c, note 1 100 ppm/ c v s =10v, 55 t a +125 c, note 1 150 ppm/ c v s = 15v, 55 t a +125 c, note 1 200 ppm/ c astable drift over supply v s = 5v to 15v, note 1 0.5 %/v threshold voltage v s = 15v 61 67 72 %v s trigger voltage v s = 15v 27 32 37 %v s trigger current v s = 15v 50 na threshold current v s = 15v 50 na chip select on > 2 / 3 v s 50 67 72 %v s off < 1 / 3 v s 28 33 50 %v s output voltage drop v s = 15v, i sink = 20ma 0.3 1.25 v v s = 5v, i sink = 3.2ma 0.08 0.5 v output voltage drop v s = 15v, i source = 20ma 14.1 14.7 v v s = 5v, i source = 3.2ma 3.8 4.7 v supply voltage functional operation, note 1 2.7 18 v output rise time r l = 10m, c l = 10pf, v s = 5v, note 1 15 ns output fall time r l = 10m, c l = 10pf, v s = 5v, note 1 15 ns general note: devices are esd protected, however handling precautions are recommended. note 1: not tested. absolute maximum ratings supply voltage (v s ) .................................................... +22v threshold voltage (v thr , v t/t ) .................................. +22v trigger voltage (v trg , v t/t ) ....................................... +22v lead temperature (soldering 10sec.) ....................... 300 c operating ratings supply voltage (v s ) ..................................... +2.7v to +18v ambient temperature range (t a ) ............. 40 c to +85 c package thermal resistance ( ja ) ................................................................... 220 c/w ( jc ) .................................................................. 130 c/w
mic1555/1557 micrel mic1555/1557 4 october 1998 typical characteristics (t a = 25 c, v in = +5) 0.0001 0.001 0.01 0.1 1 10 100 1x10 -1 1x10 0 1x10 1 1x10 2 1x10 3 1x10 4 1x10 5 1x10 6 1x10 7 capacitance ( f) period ( s) pulse width 100k 10k r t =1k 1m 0 10 20 30 40 50 60 70 -40 -20 0 20 40 60 80 100 on resistance ( ? ) temperature ( c) on resistance vs. temperature 200 220 240 260 280 300 -40 -20 0 20 40 60 80 100 supply current ( a) temperature ( c) supply current vs. temperature 0 10 20 30 40 50 60 70 0 5 10 15 20 on resistance ( ? ) supply voltage (v) on resistance vs. supply voltage 0 100 200 300 400 500 0 5 10 15 20 supply current ( a) supply voltage (v) supply current vs. supply voltage 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 10 100 1000 k factor rc ( s) k factors times rc f=1 k 1 rc t=k 2 rc 0.0001 0.001 0.01 0.1 1 10 100 1x10 -2 1x10 -1 1x10 0 1x10 1 1x10 2 1x10 3 1x10 4 1x10 5 1x10 6 1x10 7 capacitance ( f) frequency (hz) astable frequenc y 1m r t =1k 10k 100k 0 2 4 6 8 10 12 14 3 6 9 12 15 18 chip select voltage (v) supply voltage (v) mic1557 chip select vs. supply voltage on off
october 1998 5 mic1555/1557 mic1555/1557 micrel 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) con- nection for astable (oscillator) operation only. the mic1557 includes a cs (chip select/reset) control. supply vs (supply) is rated for +2.7v to +18v. an external capacitor is recommended to decouple noise. resistive divider the resistive voltage divider is constructed of three equal value resistors to produce 1 3 v s and 2 3 v s 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 1 a. forcing cs low resets the mic1557 by setting the flip flop, forcing the output low. threshold comparator the threshold comparator is connected to s (set) on the rs flip-flop. when the threshold voltage ( 2 3 v s ) is reached, the flip-flop is set, making the output low. thr is dominant over trg. functional diagrams s r q t/t out vs bias gnd cs v supply mic1557 output 1k 0.1f 8khz 1m mic1557 block diagram with external components (astable configuration) s r q out gnd output trg thr standby trigger vs v supply mic1555 1k 0.1f <100s bias 100s mic1555 block diagram with external components (monostable configuration) trigger comparator the trigger comparator is connected to r (reset) on the rs flip-flop. when trg (trigger) goes below the trigger voltage ( 1 3 v s ), the flip-flop resets, making the output high. flip-flop and output a reset signal causes q to go low, turning on the p-channel mosfet and turning off the n-channel mosfet. this makes the output rise to nearly v s . a set signal causes q to go high, turning off the p-channel mosfet, and turning on the n-channel mosfet, grounding out. 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 v thr (threshold voltage) reaches 2 3 v s , the output is switched off, discharging the capacitor. during power-on, a single pulse may be generated. 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 v t/t reaches 2 3 v s (threshold volt- age), the output is switched off, slowly discharging the capacitor. when v t/t decreases to 1 3 v s (trigger voltage), the output is switched on, causing v t/t to rise again, repeating the cycle.
mic1555/1557 micrel mic1555/1557 6 october 1998 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 (c t ) is charged through a resistor (r t ) connected to the output of an mic1555, the trip point is approximately 1.1rc t (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 oscilla- tions 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 (d t ) in parallel with (r t ) resets the one-shot quickly. cs out thr trg vs gnd d t r t out c in r pu c t mic1555 trigger 1 3 v in t on = 1.1r t c t 2.7v to 18v 1 3 2 4 5 figure 1. one-shot diagram the period of a monostable circuit is: t = k 2 rc where: t = period (s) k 2 = constant [from typical characteristics graph] r = resistance ( ? ) c = capacitance (f) 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 compara- tor 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 (r t ) is connected from the output to a grounded timing capacitor, (c t ) 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 propa- gation 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 (r a ), and a second resistor (r b ) in series with an opposite facing diode connected in parallel. the frequency is then made up of two components, the charging time (t a ) and the discharging time (t b ) t a = 0.7r a c and t b = 0.7r b c. the frequency is the reciprocal of the sum of the two times t a + t b , so the total time is 1.4r t c t . the first half-cycle of an astable, after power-on or cs enable, is lengthened since the capaci- tor is charging from ground instead of the 1 3 input trigger trip voltage, to 1.1rc, the same as a monostable pulse. r a 1k to 1m cs out t/t vs gnd out mic1557 2.7v to 18v c b r e c t 100pf to 10f 5 3 2 4 1 cs t = 0.7(r a +r b )c t t r b figure 2. oscillator diagram the mic1555 or mic1557 can be used to construct an oscillator. the frequency of an astable oscillator is: f 1 k rc 1 = ? ) c = capacitance (f)
october 1998 7 mic1555/1557 mic1555/1557 micrel accuracy the two comparators in the mic1555/7 use a resistor voltage divider to set the threshold and trigger trip points to approxi- mately 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. long time delays timing resistors larger than 1m ? or capacitors larger than 10 f are not recommended due to leakage current inaccura- cies. time delays greater than 10 seconds are more accu- rately 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 (4000 hex , 2 14 ) using a cd4020 cmos divider. 4.5hz may be generated with a 1 f c t and approxi- mately 156k ? . inverting schmitt trigger refer to figure 7. the trip points of the mic1555/7 are defined as 1 / 3 and 2 / 3 v s , which allows either device to be used as a signal conditioning inverter, with hysteresis. a slowly chang- ing input on t/t will be converted to a fast rise or fall-time opposite direction rail-to-rail output voltage. this output may be 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 mosfet may be driven by a second mic1555/7, powered by 12v to 15v, to level-shift the input. thr out mic1555 1 3 gnd 2 vs 5 trg 4 +5v +12v r l off 3.3v on 1.6v figure 7. schmitt trigger charge-pump low-side mosfet drivers a standard mosfet requires approximately 15v to fully enhance the gate for minimum r ds(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 to use the mic1555 as an oscillator, connect trg to thr. vs trg mic1555 1 4 gnd 2 +5v out 3 thr 5 output 8khz 1k 0.1f figure 3. mic1555 oscillator configuration the mic1557 features a cs input. when logic-low, cs places the mic1557 into a <1 a shutdown state. if unused, the mic1557 cs input on must be pulled up. vs cs mic1557 4 3 gnd 2 +5v out 5 t/t 1 output 8khz 1m 1k 0.1f figure 4. mic1557 oscillator configuration falling-edge triggered monostable circuit the mic1555 may be triggered by an ac-coupled falling- edge, 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. vs out mic1555 13 gnd 2 thr 5 +5v output trg 4 100s 1m 1n4148 1k 0.1f input figure 5. falling-edge trigger configuration rising-edge triggered monostable circuit the mic1555 may be triggered by an ac-coupled rising- edge, 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 3 v s . this circuit provides a low-going output pulse. vs out mic1555 13 gnd 2 thr 5 +5v output trg 4 100s 1n4148 1k 0.1f input figure 6. rising-edge trigger configuration
mic1555/1557 micrel mic1555/1557 8 october 1998 connected to a higher voltage, through a high-side load. a ttl 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. vs cs mic1557 43 gnd 2 +5v out 5 t/t 1 ttl high = on 15v +12v r l n-channel mosfet (irf540) r e 100k c1 100pf to 10f r t 1k to 1m figure 8. charge-pump 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 loudspeaker 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. thr out mic1555 1 3 gnd 2 vs 5 trg 4 100 ? +5v to +18v r t 10k 10k 10k 47k c t 0.01f 1n914 0.001f figure 9. audible voltmeter package information 0.20 (0.008) 0.09 (0.004) 0.60 (0.024) 0.10 (0.004) 3.02 (0.119) 2.80 (0.110) 10 0 3.00 (0.118) 2.60 (0.102) 1.75 (0.069) 1.50 (0.059) 0.95 (0.037) ref 1.30 (0.051) 0.90 (0.035) 0.15 (0.006) 0.00 (0.000) dimensions: mm (inch) 0.50 (0.020) 0.35 (0.014) 1.90 (0.075) ref sot-23-5 (m5) micrel inc. 1849 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 web http://www.micrel.com this information is believed to be accurate and reliable, however no responsibility is assumed by micrel for its use nor for an y infringement of patents or other rights of third parties resulting from its use. no license is granted by implication or otherwise under any patent or pat ent right of micrel inc. ? 1998 micrel incorporated
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