74HCT4538D,112

Overview

The Nexperia 74HCT4538D,112 is a dual retriggerable-resettable monostable multivibrator from the HCT logic family. It operates within a supply voltage range of 4.5 V to 5.5 V and supports an ambient temperature range of -40 °C to +125 °C. The device features two independent multivibrators, each with dedicated trigger inputs (nA for HIGH-to-LOW, nB for LOW-to-HIGH) and a direct reset input (nCD). Output pulse width is determined by external timing components REXT and CEXT using the formula TW = 0.7 × REXT × CEXT. Propagation delay is typically 60 ns at 4.5 V. It utilizes Schmitt-trigger inputs for noise immunity and includes clamp diodes on all inputs.

Feature Summary

• Dual precision monostable multivibrators with separate reset inputs
• Tolerant of slow trigger rise and fall times via Schmitt-trigger action
• Capable of triggering from both rising and falling edges
• CMOS low power dissipation with TTL-compatible input levels

Applications

• Pulse generation and shaping circuits
• Timing delays in digital systems
• Debouncing switches or contacts
• Frequency division applications

Procurement Notes

Verify that the ordering suffix matches the required package type. The 'D' suffix indicates an SO16 plastic small outline package (SOT109-1). Confirm the specific variant against the manufacturer's current ordering information table to ensure compatibility with PCB footprint requirements and thermal management needs.

Selection Notes

Select this component when precise pulse width control is required using external RC networks. The HCT series ensures compatibility with standard TTL logic levels while maintaining CMOS power characteristics. Ensure the application environment stays within the specified -40 °C to +125 °C operating temperature range and that the supply voltage remains between 4.5 V and 5.5 V.

Part Context

This part belongs to the 74HCT4538 family of dual monostable multivibrators. It is functionally compatible with other manufacturers' 74HCT4538 devices but may differ in pinout or electrical specifications. The D suffix specifically denotes the SO16 package variant, distinct from the PW (TSSOP16) version. It is designed for general-purpose timing applications requiring high noise immunity and precise pulse duration.

Replacement Considerations

Direct replacements include other 74HCT4538 variants from different manufacturers, provided they match the SO16 package and electrical specifications. Verify pinout compatibility and ensure the substitute device meets the same HCT logic level requirements and operating temperature range.

FAQ

How is the output pulse width determined?

The output pulse width (TW) is determined by the external resistor (REXT) and capacitor (CEXT) connected to the device, calculated as TW = 0.7 × REXT × CEXT.

Can the device be triggered by both signal edges?

Yes, each multivibrator has two trigger inputs: nA triggers on a HIGH-to-LOW transition, and nB triggers on a LOW-to-HIGH transition.

What happens if a LOW level is applied to the reset input?

Applying a LOW level to the direct reset input (nCD) immediately terminates the output pulse, regardless of the current state.