STMicroelectronics M74HC393B1R

Overview

M74HC393B1R from STMicroelectronics is a high-speed CMOS dual 4-bit binary ripple-carry counter with independent negative-edge-triggered clock inputs and asynchronous clear. It operates from 2V to 6V, delivers 79 MHz max clock frequency at 6V, and features symmetrical 4 mA output drive, balanced propagation delays (tPLH ≅ tPHL), and high noise immunity (28% VCC). Used in digital timing, frequency division, and address sequencing in industrial control logic.

For engineers reviewing the M74HC393B1R datasheet, M74HC393B1R pinout, M74HC393B1R application, or M74HC393B1R equivalent, key selection criteria include dual independent counter operation, negative-edge triggering, asynchronous reset behavior, propagation delay consistency across QA–QD outputs, and DIP-14 package compatibility with legacy 74-series layouts.

Technical Context

The M74HC393B1R implements two electrically isolated 4-bit binary counters, each incremented on the falling edge of its dedicated clock input (CLK1/CLK2) and cleared asynchronously via separate /CLR1 and /CLR2 inputs. No internal cascading - external wiring required for divide-by-256 operation.

Each counter stage uses silicon gate C2MOS technology, enabling low ICC (4 µA max at 25°C), wide VCC range (2–6 V), and rail-to-rail output swing. Input thresholds are fixed percentages of VCC (VIH = 70%, VIL = 30%), ensuring robust noise margin across supply voltages.

Key Specifications

Pinout & Package

Package: Plastic Dual In-line Package (DIP-14), 0.3" wide, through-hole mount, JEDEC MS-001 compliant.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual binary counter applications.

Compared with SN74HC393N and CD74HC393E, the M74HC393B1R offers the highest guaranteed maximum clock frequency (79 MHz) and lowest quiescent current (4 µA), making it optimal for power-constrained, high-speed digital timing where both metrics are simultaneously critical.

Availability

M74HC393B1R is available at Aetrix Electronics and suitable for industrial PLC timer modules, digital panel meter counting, legacy equipment clock dividers, and test fixture sequencing logic requiring stable component supply and long-term obsolescence management.

Supply support for M74HC393B1R 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing microcontrollers, power ICs, sensors, and logic devices for industrial, automotive, and consumer markets.

The M74HC393B1R belongs to ST's high-speed CMOS logic family, engineered specifically for reliable, low-power digital counting and timing functions in harsh industrial environments with wide temperature (-55°C to +125°C) and voltage (2–6 V) ranges.

FAQ

Can M74HC393B1R be operated at 3.3 V?

Yes. The device is fully specified from 2 V to 6 V, including 3.3 V. At VCC = 3.3 V, VIH = 2.31 V (min), VIL = 0.99 V (max), and fMAX ≈ 50 MHz (typ.), meeting standard 3.3 V logic interface requirements without level shifting.

Is the clear function synchronous or asynchronous?

The clear inputs (/CLR1 and /CLR2) are asynchronous - they force all four Q outputs of their respective counter to logic low immediately, regardless of clock state. This behavior is confirmed by the truth table and timing chart showing tPHL(CLEAR→Qn) ≤ 38 ns at 6 V.

What is the maximum capacitive load this device can drive reliably?

Driving CL = 50 pF is validated in AC specifications (propagation delay, fMAX). With 4 mA output drive and 10 pF input capacitance, it can reliably drive up to three additional 74HC inputs (≈30 pF total) while maintaining timing margins per the datasheet's tW(H)/tW(L) requirements.

Does M74HC393B1R support cascading between the two counters internally?

No. The two 4-bit counters are electrically independent - no internal cascade path exists. To build a divide-by-256 counter, QA1 must be externally wired to CLK2, as shown in the functional description and logic diagram. This requires external routing but enables flexible truncation points.