54121/DM54121/DM74121 One-Shot with
Clear and Complementary Outputs
General Description
The DM54/74121 is a monostable multivibrator featuring
both positive and negative edge triggering with complementary
outputs. An internal 2kX timing resistor is provided for
design convenience minimizing component count and layout
problems. This device can be used with a single external
capacitor. Inputs (A) are active-low trigger transition inputs
and input (B) is an active-high transition Schmitt-trigger input
that allows jitter-free triggering from inputs with transition
rates as slow as 1 volt/second. A high immunity to
VCC noise of typically 1.5V is also provided by internal circuitry
at the input stage.
To obtain optimum and trouble free operation please read
operating rules and NSC one-shot application notes carefully
and observe recommendations.
Features
Y Triggered from active-high transition or active-low transition
inputs
Y Variable pulse width from 30 ns to 28 seconds
Y Jitter free Schmitt-trigger input
Y Excellent noise immunity typically 1.2V
Y Stable pulse width up to 90% duty cycle
Y TTL, DTL compatible
Y Compensated for VCC and temperature variations
Y Input clamp diodes
Y Alternate Military/Aerospace device (54121) is available.
Contact a National Semiconductor Sales Office/
Distributor for specifications.
Functional Description
The basic output pulse width is determined by selection of
an internal resistor RINT or an external resistor (RX) and
capacitor (CX). Once triggered the output pulse width is independent
of further transitions of the inputs and is a function
of the timing components. Pulse width can vary from a
few nano-seconds to 28 seconds by choosing appropriate
RX and CX combinations. There are three trigger inputs from
the device, two negative edge-triggering (A) inputs, one positive
edge Schmitt-triggering (B) input.