74HC4538D Series

The 74HC4538 is a dual retriggerable-resettable monostable multivibrator. Each multivibrator has two trigger/retrigger inputs (nAand nB), a direct reset input (nCD), two complementary outputs (nQ and nQ), and two pins (nREXT/CEXT and nCEXT) for connecting the external timing components CEXTand REXT. Typical pulse width variation over temperature range is ± 0.2 %. The device may be triggered by either the positive or the negative edges of the input pulse. The duration and accuracy of the output pulse are determined by the external timing components CEXTand REXT. The output pulse width (TW) is equal to 0.7 × REXT× CEXT. The linear design techniques guarantee precise control of the output pulse width. A LOW level at nCDterminates the output pulse immediately. Schmitt-trigger action in the trigger inputs makes the circuit highly tolerant to slower rise and fall times. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of VCC.