MIC1555/1557
IttyBitty
®
RC Timer / Oscillator
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 (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 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.
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
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
•
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
MIC1555
13
Standby
Trigger
4
2
100µs
VS
TRG
GND
THR
5
+5V
MIC1557
Output
4
Enabled
Disabled
3
2
8kHz
5
OUT
1k
VS
CS
GND
OUT
Output
1k
T/T
1
0.1µF
0.1µF
Monostable (One-Shot)
IttyBitty is a registered trademark of Micrel, Inc.
Astable (Oscillator)
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 [ MICREL SEMICONDUCTOR ]
