+5VMIC15551StandbyTrigger42100µsVSTRGGNDTHR5+5VMIC1557Output4EnabledDisabled328kHz5OUT3VSCSGNDOUTOutput1k1k0.1µFT/T10.1µFMonostable (One-Shot)Astable (Oscillator)
October 19981MIC1555/1557
元器件交易网www.cecb2b.comMIC1555/1557Pin Configuration
OUTGNDVS321MicrelCSGNDT/T321T10Part NumberMIC1555BM5MIC1557BM5IdentificationT10T11454T115PartIdentificationTRGTHRVSOUTSOT-23-5 (M5)Pin DescriptionPin NumberMIC155512Pin NumberMIC155742334515Pin NameVSGNDCSOUTTRGTHRT/TPin FunctionSupply (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.Output: CMOS totem-pole output.Trigger (Input): Sets output high. Active low (at ≤ 2⁄3VS nominal).Threshold (Dominant Input): Sets output low. Active high (at ≥ 2⁄3VSnominal).Trigger/Threshold (Input): Internally connected to both threshold and triggerfunctions. See TRG and THR.MIC1555/15572October 1998
元器件交易网www.cecb2b.comMIC1555/1557Absolute Maximum Ratings
Supply Voltage (VS)....................................................+22V
Threshold Voltage (VTHR, VT/T)..................................+22VTrigger Voltage (VTRG, VT/T).......................................+22VLead Temperature (soldering 10sec.).......................300°C
MicrelOperating Ratings
Supply Voltage (VS).....................................+2.7V to +18VAmbient Temperature Range (TA).............–40°C to +85°CPackage 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.ParameterSupply current
ConditionVS = 5VVS = 15V
Monostable Timing Accuracy
RA = 10k, C =0.1µF, VS = 5VRA = 10k, C =0.1µF, VS = 5V
Monostable Drift over Temp
VS = 5V, –55 ≤ TA ≤ +125°C, Note 1VS =10V, –55 ≤ TA ≤ +125°C, Note 1VS = 15V, –55 ≤ TA ≤ +125°C, Note 1
Monostable Drift over SupplyAstable Timing Accuracy
VS = 5V to 15V, Note 1
RA = RB = 10k, C = 0.1µF, VS = 5VRA = RB = 10k, C = 0.1µF, VS = 5V
Maximum Astable FrequencyAstable Drift over Temp
RT = 1k, CT = 47pF, Vs = 8VVS = 5V, –55 ≤ TA ≤ +125°C, Note 1VS =10V, –55 ≤ TA ≤ +125°C, Note 1VS = 15V, –55 ≤ TA ≤ +125°C, Note 1
Astable Drift over SupplyThreshold VoltageTrigger VoltageTrigger CurrentThreshold CurrentChip Select
VS = 5V to 15V, Note 1VS = 15VVS = 15VVS = 15VVS = 15Von > 2/3VSoff < 1/3VS
Output Voltage Drop
VS = 15V, ISINK = 20mAVS = 5V, ISINK = 3.2mA
Output Voltage Drop
VS = 15V, ISOURCE = 20mAVS = 5V, ISOURCE = 3.2mA
Supply VoltageOutput Rise TimeOutput Fall Time
Note 1:
Not tested.
MinTyp2403502
Max300400
UnitsµAµA%
858
1001502000.52
1717
51001502000.5
6127
6732
1161µsppm/°Cppm/°Cppm/°C%/V%
2323µsMHzppm/°Cppm/°Cppm/°C%/V
72375050
%VS%VSnAnA%VS%VSVVVV
5028
67330.30.08
72501.250.5
14.13.82.7
14.74.7
18
1515
functional operation, Note 1
RL = 10M, CL = 10pF, VS = 5V, Note 1RL = 10M, CL = 10pF, VS = 5V, Note 1
Vnsns
General Note:Devices are ESD protected, however handling precautions are recommended.
October 19983MIC1555/1557
元器件交易网www.cecb2b.comMIC1555/1557Typical Characteristics (TA = 25°C, VIN = +5)
Astable Frequency100CAPACITANCE (µF)100MicrelPulse Width RT=1kON RESISTANCE (Ω)7060504030201000On Resistance
vs. Supply Voltage
RT=1k100k10k10.10.010.0011x1001x10-21x10-1CAPACITANCE (µF)101010.10.010.00110k100k1M1M1x1011x1021x1031x1041x1051x1061x1070.00011x1001x1011x1021x1031x1041x1051x106FREQUENCY (Hz)1x10-1PERIOD (µs)70ON RESISTANCE (Ω)605040302010
On Resistancevs. Temperature
SUPPLY CURRENT (µA)300280260240220
Supply Currentvs. Temperature
SUPPLY CURRENT (µA)1x1070.000151015SUPPLY VOLTAGE (V)
205004003002001000Supply Currentvs. Supply Voltage
0
-40-20020406080100TEMPERATURE (°C)200
-40-20020406080100TEMPERATURE (°C)
051015SUPPLY VOLTAGE (V)
202.01.91.8k FACTOR1.71.61.51.41.31.21.11.010k FactorsTimes RC
f=1⁄k1 RCt=k2 RC100RC (µs)
100014CHIP SELECT VOLTAGE (V)1210864203MIC1557 Chip Selectvs. Supply Voltage
ONOFF691215SUPPLY VOLTAGE (V)
18MIC1555/15574October 1998
元器件交易网www.cecb2b.comMIC1555/1557Functional Diagrams
VSUPPLYVSMIC15551MMIC1557VSUPPLYVSMicrelBiasTHRSQRStandbyTriggerCSBias100µsS8kHzQOUTOutputOUTOutputR<100µsTRGT/TGND1kGND1k0.1µF0.1µFMIC1555 Block Diagram with External Components
(Monostable Configuration)MIC1557 Block Diagram with External Components
(Astable Configuration)
Functional Description
Refer to the block diagrams.
The MIC1555/7 provides the logic for creating simple RCtimer 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 MIC1557includes a CS (chip select/reset) control.Supply
VS (supply) is rated for +2.7V to +18V. An external capacitoris recommended to decouple noise.Resistive Divider
The resistive voltage divider is constructed of three equalvalue resistors to produce 1⁄3VS and 2⁄3VS voltage for triggerand threshold reference voltages.Chip Select/Reset (MIC1557 only)
CS (chip select/reset) controls the bias supply to the oscillator’sinternal circuitry. CS must be connected to CMOS logic-highor logic-low levels. Floating CS will result in unpredictableoperation. When the chip is deselected, the supply current isless than 1µA. Forcing CS low resets the MIC1557 by settingthe flip flop, forcing the output low.
Threshold Comparator
The threshold comparator is connected to S (set) on the RSflip-flop. When the threshold voltage (2⁄3VS) is reached, theflip-flop is set, making the output low. THR is dominant overTRG.October 1998
5
Trigger Comparator
The trigger comparator is connected to R (reset) on the RSflip-flop. When TRG (trigger) goes below the trigger voltage(1⁄3VS), the flip-flop resets, making the output high.Flip-Flop and Output
A reset signal causes Q to go low, turning on the P-channelMOSFET and turning off the N-channel MOSFET. Thismakes the output rise to nearly VS.
A set signal causes Q to go high, turning off the P-channelMOSFET, and turning on the N-channel MOSFET, groundingOUT.
Basic Monostable Operation
Refer to the MIC1555 functional diagram.
A momentary low signal applied to TRG causes the output togo high. The external capacitor charges slowly through theexternal 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.Basic Astable Operation
Refer to the MIC1557 functional diagram.
The MIC1557 starts with T/T low, causing the output to gohigh. The external capacitor charges slowly through theexternal resistor. When VT/T reaches 2⁄3VS (threshold volt-age), the output is switched off, slowly discharging thecapacitor. When VT/T decreases to 1⁄3VS (trigger voltage), theoutput is switched on, causing VT/T to rise again, repeatingthe cycle.
MIC1555/1557
元器件交易网www.cecb2b.comMIC1555/1557Application Information
Basic Monostable (One-Shot) Circuit
A monostable oscillator produces a single pulse each timethat it is triggered, and is often referred to as a “one-shot”. Thepulse width is constant, while the time between pulsesdepends on the trigger input. One-shots are generally usedto “stretch” incoming pulses, of varying widths, to a fixedwidth. The IttyBitty MIC1555 is designed for monostableoperation, but may also be connected to provide astableoscillations. The pulse width is determined by the time it takesto 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 isapproximately 1.1RCT (the same time as the initial power-oncycle of an astable circuit.) If the trigger pulse of an MIC1555remains low longer than the output pulse width, short oscilla-tions may be seen in the output of a one-shot circuit, since thethreshold pin has precedence over the trigger pin. Theseoccur since the output goes low when the threshold isexceeded, and then goes high again as the trigger function isasserted. AC coupling the input with a series capacitor anda pull-up resistor, with an RC time constant less than thepulse width, will prevent these short oscillations. A diode (DT)in parallel with (RT) resets the one-shot quickly.
2.7V to 18VRTDTRPUVS1MicrelThe MIC1555 may also be used as an astable oscillator bytying the threshold and trigger pins together, forming a T/Tpin. If a resistor (RT) is connected from the output to a
grounded timing capacitor, (CT) the voltage at their junctionwill ramp up from ground when the output goes high. If the T/T pin is connected to this junction, the output will switch lowwhen the ramp exceeds 2⁄3 of the input voltage. The junction'svoltage ramps down toward ground while the output is low.When the ramp is below 1⁄3 of the input voltage, the outputswitches to high, and the junction ramps up again.The continuing frequency of an MIC1555/7 astable oscillatordepends on the RC time constant, and is approximately 0.7/RC below 1MHz. At frequencies above 1MHz the RCmultiplier increases as capacitance is decreased, and propa-gation delay becomes dominant. Non-symmetrical oscillatoroperation is possible at frequencies up to 5MHz.
If a duty cycle other than 50% is desired, a low-power signaldiode may be connected in series with the timing resistor(RA), and a second resistor (RB) in series with an oppositefacing diode connected in parallel. The frequency is thenmade up of two components, the charging time (tA) and thedischarging time (tB) tA= 0.7RAC and tB= 0.7RBC. Thefrequency 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 power-on or CS enable, is lengthened since the capaci-tor is charging from ground instead of the 1⁄3 input trigger tripvoltage, to 1.1RC, the same as a monostable pulse.
2.7V to 18VCBTHR5tON = 1.1RTCTCSOUT3VS4RETrigger1⁄3VINCINCTTRG4T/T1OUTCSCS3tMIC1555GND2OUTOUT5t = 0.7(RA+RB)CTMIC1557RA1k to 1MRBCT100pF to 10µFGNDFigure 1.One-Shot Diagram
The period of a monostable circuit is:
t = k2 RCwhere:
t = period (s)
k2 = constant [from Typical Characteristics graph]R = resistance (Ω)C = capacitance (F)Basic Astable (Oscillator) Circuits
An astable oscillator switches between two states, “on” and“off”, producing a continuous square wave. The IttyBittyMIC1557 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 theoscillator.
2Figure 2.Oscillator Diagram
The MIC1555 or MIC1557 can be used to construct anoscillator.
The frequency of an astable oscillator is:
f=1k1RCwhere:
f = frequency (Hz)
k1 = constant [from Typical Characteristics graph]R = resistance (Ω)C = capacitance (F)6
October 1998
MIC1555/1557
元器件交易网www.cecb2b.comMIC1555/1557To use the MIC1555 as an oscillator, connect TRG to THR.
+5VMIC1555142MicrelAccuracy
The two comparators in the MIC1555/7 use a resistor voltagedivider to set the threshold and trigger trip points to approxi-mately 2⁄3 and 1⁄3 of the input voltage, respectively. Since thecharge and discharge rates of an RC circuit are dependent onthe applied voltage, the timing remains constant if the inputvoltage varies. If a duty cycle of exactly 50% (or any othervalue from 1 to 99%), two resistors (or a variable resistor) andtwo diodes are needed to vary the charge and dischargetimes. The forward voltage of diodes varies with temperature,so some change in frequency will be seen with temperatureextremes, but the duty cycle should track. For absolute timingaccuracy, the MIC1555/7 output could be used to controlconstant current sources to linearly charge and discharge thecapacitor, at the expense of added components and boardspace.
Long Time Delays
Timing resistors larger than 1MΩ or capacitors larger than10µF 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 achain of flip-flop counter stages. To produce an accurateone-hour delay, for example, divide an 4.55Hz MIC1557oscillator by 16,384 (4000hex, 214) using a CD4020 CMOSdivider. 4.5Hz may be generated with a 1µF CT and approxi-mately 156kΩ.
Inverting Schmitt Trigger
Refer to figure 7. The trip points of the MIC1555/7 are definedas 1/3 and 2/3VS, which allows either device to be used as asignal conditioning inverter, with hysteresis. A slowly chang-ing input on T/T will be converted to a fast rise or fall-timeopposite direction rail-to-rail output voltage. This output maybe used to directly drive the gate of a logic-level P-channelMOSFET with a gate pull-up resistor. This is an inverted logiclow-side logic level MOSFET driver. A standard N-channelMOSFET may be driven by a second MIC1555/7, powered by12V to 15V, to level-shift the input.
+5V+12V8kHz3VSTRGGNDOUTOutput1kTHR50.1µFFigure 3.MIC1555 Oscillator ConfigurationThe MIC1557 features a CS input. When logic-low, CSplaces the MIC1557 into a <1µA shutdown state. If unused,the MIC1557 CS input on must be pulled up.
+5VMIC155748kHzVSCSGNDT/T1OUT5Output1k0.1µF1M32Figure 4.MIC1557 Oscillator ConfigurationFalling-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 theinput capacitor and pull-up resistor should be less than theoutput pulse time, to prevent multiple output pulses. A
diode across the timing resistor provides a fast reset at theend of the positive timing pulse.
+5V1MInputMIC1555142100µsVSTRGGNDTHROUT3Output1N41480.1µF1k5Figure 5.Falling-Edge Trigger ConfigurationRising-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 theTHR input low until TRG discharges to 1⁄3VS. This circuitprovides a low-going output pulse.
+5VMIC1555142OFF ≥ 3.3V542MIC1555THRTRGGNDOUT3VS1RLON ≤ 1.6V100µs3VSTRGGNDOUTOutput1N4148InputFigure 7. Schmitt trigger
Charge-Pump Low-Side MOSFET Drivers
A standard MOSFET requires approximately 15V to fullyenhance the gate for minimum RDS(on). Substituting a logic-level MOSFET reduces the required gate voltage, allowingan MIC1557 to be used as an inverting Schmitt Trigger,described above. An MIC1557 may be configured as avoltage quadrupler to boost a 5V input to over 15V to fullyenhance an N-channel MOSFET which may have its drain
1kTHR50.1µFFigure 6.Rising-Edge Trigger Configuration
October 19987MIC1555/1557
元器件交易网www.cecb2b.comMIC1555/1557connected 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 groundensures that the FET will turn off quickly when the MIC1557is turned off.
+12VN-ChannelMOSFET(IRF540)15VMIC1557VST/TGND53MicrelAudible Voltmeter
If an additional charge or discharge source is connected tothe timing capacitor, the frequency may be shifted by turningthe source on or off. An MIC1555 oscillator, powered by thecircuit under test, may be used to drive a small loudspeakeror piezo-electric transducer to provide a medium frequencyfor an open or high impedance state at the probe. A high toneis generated for a high level, and a lower frequency for a logiclow on the probe.
RT 10kMIC15551N91447k10kCT0.01µF5421RLTTL High = ON+5V412+5V to +18VCSTHRTRGGNDVS0.001µFOUT310kC1100pFto 10µFOUTRE100kRT 1k to 1M100ΩFigure 8. Charge-PumpFigure 9. Audible Voltmeter
Package Information
1.90 (0.075) REF0.95 (0.037) REF1.75 (0.069)1.50 (0.059)3.00 (0.118)2.60 (0.102)DIMENSIONS:MM (INCH)3.02 (0.119)2.80 (0.110)1.30 (0.051)0.90 (0.035)10°0°0.15 (0.006)0.00 (0.000)0.60 (0.024)0.10 (0.004)0.20 (0.008)0.09 (0.004)0.50 (0.020)0.35 (0.014)SOT-23-5 (M5)
MICREL INC.1849 FORTUNE DRIVESAN JOSE, CA95131USA
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 any 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 patent right of Micrel Inc.
© 1998 Micrel Incorporated
MIC1555/15578October 1998
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