Nexperia USA Inc. 74HC191DB,112

Overview

74HC191DB,112 from Nexperia is a presettable synchronous 4-bit binary up/down counter with asynchronous parallel load, count enable control, and dual overflow/underflow outputs (TC and RC). It operates from 2.0 V to 6.0 V, supports -40 °C to +125 °C ambient range, and delivers 39 MHz max clock frequency at 6.0 V. Used in digital timing, frequency division, and multistage counter chains in industrial control panels and programmable logic interfaces.

For engineers reviewing the 74HC191DB,112 datasheet, 74HC191DB,112 pinout, 74HC191DB,112 application, or 74HC191DB,112 equivalent, key selection considerations include synchronous reversible counting behavior, active-LOW parallel load and count enable, TC/RC output timing relationships, and SO16 package compatibility with legacy 74HC logic layouts.

Technical Context

The 74HC191DB,112 implements a master/slave flip-flop architecture with internal steering logic enabling true synchronous up/down counting on LOW-to-HIGH clock transitions while supporting asynchronous preset via active-LOW PL. Its U/D input determines direction without requiring state-hold delays, and CE must be LOW for counting - but only when CP is HIGH during CE transition.

Terminal count (TC) asserts HIGH at 0 (count-down) or 15 (count-up), remaining latched until state change or U/D toggle; ripple clock (RC) follows CP only when TC = HIGH and CE = LOW, enabling cascaded counter designs without external gating. TC is not clock-safe due to decoding spikes, and RC is active-LOW with propagation delay as low as 14 ns at 6.0 V.

Key Specifications

Pinout & Package

74HC191DB,112 is housed in a 16-lead SO16 plastic small outline package (SOT109-1), 3.9 mm body width, with standard 1.27 mm lead pitch and gull-wing leads compatible with IPC-7351B footprint IPC-SOIC-16-1.27.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 4-bit synchronous up/down counter applications.

Compared with 74HC191DB,112, the 74HC193D lacks unified U/D control and RC-based synchronous expansion, while the SN74LS191N sacrifices voltage flexibility, power efficiency, and modern reliability specs - making the 74HC191DB,112 optimal for new designs requiring robust, scalable, and energy-efficient counting.

Availability

74HC191DB,112 is available at Aetrix Electronics and suitable for industrial PLC counter modules, automotive dashboard odometer logic, and digital test equipment frequency dividers requiring stable component supply across extended temperature and voltage ranges.

Supply support for 74HC191DB,112 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

Nexperia is a global semiconductor expert focused on essential semiconductors, delivering high-performance, reliable components for automotive, industrial, and consumer applications.

The 74HC191DB,112 belongs to Nexperia's 74HC logic family - engineered for low-power, high-noise-immunity digital control in space-constrained and thermally demanding environments.

FAQ

Can 74HC191DB,112 operate reliably at 2.0 V supply?

Yes - the device is fully specified from 2.0 V to 6.0 V per JEDEC JESD7A. At 2.0 V, it maintains guaranteed functionality including 625 ns/V input transition rate, 220 ns max CP→Qn propagation, and -40 °C to +125 °C operation. Static current remains below 80 μA, and VIH/VIL thresholds scale proportionally to VCC, ensuring robust noise margins even at minimum voltage.

What is the correct way to cascade multiple 74HC191DB,112 counters for synchronous operation?

Use the RC output of each stage to drive the CP input of the next, with all CE pins tied together and controlled globally. Ensure TC of stage N enables CE of stage N+1 via an AND gate (or direct connection if only overflow matters), and maintain RC load ≤50 pF. Avoid using TC as a clock - its decoding spikes can cause metastability; RC is the intended ripple-synchronized clock source for multistage designs.

Is the PL (parallel load) input truly asynchronous?

Yes - PL is asynchronous: asserting PL LOW immediately loads D0–D3 into Q0–Q3 regardless of CP state or CE level, overriding all counting functions. The load occurs within 18 ns (max at 6 V), and outputs reflect new values before the next CP edge. However, D0–D3 must be stable for ≥6 ns before PL goes LOW (tsu) and held for ≥2 ns after (th), per datasheet timing requirements.

Why does the datasheet warn against using TC as a clock signal?

TC exhibits decoding spikes during state transitions due to internal combinatorial logic resolving terminal conditions (0 or 15). These narrow, unpredictable glitches violate clock signal integrity requirements - causing false triggering, metastability, or race conditions in downstream logic. RC is specifically designed as the clean, edge-aligned ripple output; TC serves only as a level-sensitive status flag or enable signal, not a timing reference.