General Description
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 open-collector discharge (D) pin. The threshold pin (THR) has precedence over the trigger (TRG) input, ensuring that the BiCMOS output is off when TRG is high.
The MIC1555 can 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 micro-seconds 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 and is rated for –40°C to +85°C ambient temperature range. The MIC1555/7 is available in SOT-23-5, and thin SOT23-5 5-pin packages. A low profile, ultra-thin, (UTDFN), version of the MIC1555 (with chip select) is also available.
Datasheets and support documentation are available on Micrel’s website at: www.micrel.com.

Features
• +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
• 10-pin ultra-thin DFN package (2mm × 2mm × 0.4mm)
• 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