SDLS042 - MAY 1983 - REVISED MARCH 1988
PRODUCTION DATA documents contain information current as of publicationdate. Products conform to specifications per the terms of Texas Instrumentsstandard warranty. Production processing does not necessarily include testingof all parameters.
These multivibrators feature dual negative-transition-triggered inputsand a single positive-transition-triggered input which can be used as an inhibitinput. Complementary output pulses are provided.
Pulse triggering occurs at a particular voltage level and is not directlyrelated to the transition time of the input pulse. Schmitt-trigger input circuitry(TTL hysteresis) for the B input allows jitter-free triggering from inputswith transition rates as slow as 1 volt/second, providing the circuit withan excellent noise immunity of typically 1.2 volts. A high immunity to VCC noise of typically 1.5 volts is also provided by internal latchingcircuitry.
Once fired, the outputs are independent of further transitions of the inputsand are a function only of the timing components. Input pulses may be of anyduration relative to the output pulse. Output pulse length may be varied from40 nanoseconds to 28 seconds by choosing appropriate timing components. Withno external timing components (i.e., Rint connected to VCC, Cext and Rext/Cext open), an outputpulse of typically 30 or 35 nanoseconds is achieved which may be used as ad-c triggered reset signal. Output rise and fall times are TTL compatibleand independent of pulse length.
Pulse width stability is achieved through internal compensation and isvirtually independent of VCC and temperature. In most applications,pulse stability will only be limited by the accuracy of external timing components.
Jitter-free operation is maintained over the full temperature and VCC ranges for more than six decades of timing capacitance (10 pF to10 μF) and more than one decade of timing resistance (2 k
to 30k for the SN54121 and 2 k to 40 k for the SN74121). Throughoutthese ranges, pulse width is defined by the relationship tw(out)= CextRTIn2 ≈ 0.7 CextRT. Incircuits where pulse cutoff is not critical, timing capacitance up to 1000 μFand timing resistance as low as 1.4 k may be used. Also, the rangeof jitter-free output pulse widths is extended if VCC is held to5 volts and free-air temperature is 25°C. Duty cycles as high as 90% areachieved when using maximum recommended RT'. Higher duty cyclesare available if a certain amount of pulse-width jitter is allowed.
View more information about generic part numbers:SN54121, SN74121
Go to the Engineering Design Center to locate information on other TI Semiconductor devices.