Toshiba Semiconductor and Storage 74HC4538D

Overview

74HC4538D from Toshiba is a dual high-speed CMOS monostable multivibrator in SOIC16 package, featuring independent A (positive-edge) and B (negative-edge) Schmitt-trigger inputs, retriggerable one-shot operation per channel, 2.0–6.0 V supply range, and typical propagation delay of 25 ns at 5 V. It generates precise timing pulses using external RX/CX networks-e.g., for debouncing mechanical switches in industrial control panels.

For engineers reviewing the 74HC4538D datasheet, 74HC4538D pinout, 74HC4538D application, or 74HC4538D equivalent, this device supports stable pulse generation with low quiescent current (4.0 µA max), balanced tPLH/tPHL delays, wide temperature operation (–40 to +125 °C), and robust input protection-key for noise-prone embedded timing designs.

Technical Context

The 74HC4538D implements two independent monostable circuits, each with dual-edge-trigger capability via separate A (rising-edge sensitive) and B (falling-edge sensitive) Schmitt inputs. Triggering initiates capacitor CX discharge through internal transistor QN, followed by controlled recharge via RX to determine output pulse width (twOUT ≈ 0.7 × CX × RX).

Each circuit includes a dedicated CD (clear/disable) input that forces Q low and rapidly charges CX to VCC when asserted low. Retriggering extends the monostable period only if the new trigger arrives during the rising phase of T2 node voltage-enabling flexible pulse stretching in event-driven systems.

Key Specifications

Pinout & Package

74HC4538D is housed in a 16-pin Small Outline Integrated Circuit (SOIC16) package, 7.5 mm wide, with 1.27 mm pitch and 0.15 g typical mass. Pin numbering follows standard JEDEC MS-012 outline.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar monostable multivibrator applications.

Compared with SN74LV4538D and 74HCT4538D, the 74HC4538D delivers broader supply flexibility (up to 6.0 V), lower quiescent current, and proven thermal stability across –40 to +125 °C-making it optimal for mixed-voltage industrial and automotive timing where reliability outweighs marginal speed gains.

Availability

74HC4538D is available at Aetrix Electronics and suitable for industrial control panels, automotive body electronics, test equipment timing modules, and medical device signal conditioning requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 74HC4538D includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Toshiba Electronic Devices & Storage Corporation designs and manufactures high-reliability semiconductor solutions for industrial, automotive, and consumer applications, with emphasis on logic, power, and analog ICs.

The 74HC4538D belongs to Toshiba's HC-series high-speed CMOS logic family, engineered for low-power, noise-immune timing functions in harsh environments-targeting applications where deterministic pulse generation replaces software-based delays.

FAQ

What is the maximum external resistor value supported by the 74HC4538D?

The 74HC4538D does not specify an upper limit for RX, but Toshiba cautions that susceptibility to externally induced noise increases significantly when RX exceeds 1 MΩ. For stable operation across temperature and voltage, design with RX ≤ 1 MΩ and ensure board layout minimizes leakage paths. The minimum RX is 5 kΩ at VCC = 2.0 V and 1 kΩ at VCC ≥ 3.0 V per the datasheet's operating ranges table.

Can the 74HC4538D operate reliably at 3.3 V supply?

Yes, the 74HC4538D is fully specified for operation at 3.3 V (within its 2.0–6.0 V range). At VCC = 3.3 V, DC parameters such as VOH (≥2.97 V), VOL (≤0.33 V), and VIH (≥2.31 V) meet standard 3.3 V CMOS logic levels. Propagation delay increases to ~35 ns typ. (vs. 25 ns at 5 V), and active supply current remains below 350 µA max-making it suitable for mixed-voltage 3.3 V systems.

How does the retrigger function behave when multiple triggers occur rapidly?

The 74HC4538D retriggering is effective only if a new A/B trigger arrives while the T2 node voltage is rising-i.e., during the recharge phase of CX through RX. If a second trigger occurs during the initial discharge phase or within the minimum retrigger time (trr(min) = 0.7 µs at VCC = 6.0 V), it is ignored. This prevents pulse collapse and ensures monotonic extension of the output high time.

Is the 74HC4538D pin-compatible with other 74xx4538 variants like the 74LS4538?

No, the 74HC4538D is not pin-compatible with bipolar 74LS4538. While both share the same SOIC16 footprint and functional pin assignments (A/B/CD/Q/Q/etc.), the LS version uses different internal architecture, lacks Schmitt inputs, requires higher drive current, and operates only at 5 V. Direct substitution risks incorrect triggering, excessive loading, or failure to meet timing specs-always verify logic family compatibility before replacement.

What is the recommended practice for unused inputs on the 74HC4538D?

All unused inputs on the 74HC4538D-including A, B, CD, and T1/T2-must be tied to either VCC or GND to prevent floating states that cause increased ICC, erratic triggering, or ESD vulnerability. Per Toshiba's datasheet note, unused A/B inputs should connect to VCC or GND; CD should be tied to VCC for normal operation; T1/T2 pins must remain unconnected (OPEN) unless used in custom timing configurations.