NXP Semiconductors 74HC191D,652

Overview

74HC191D,652 from Nexperia is a presettable synchronous 4-bit binary up/down counter with asynchronous parallel load, count enable control, and dual outputs (TC and RC) for multistage cascade. It operates from 2.0 V to 6.0 V, supports -40 °C to +125 °C, and delivers 39 MHz max clock frequency at 6.0 V - used in digital timing control, programmable logic sequencers, and industrial encoder interfaces.

For engineers reviewing the 74HC191D,652 datasheet, 74HC191D,652 pinout, 74HC191D,652 application, or 74HC191D,652 equivalent, key selection considerations include synchronous reversible counting behavior, active-LOW parallel load and count enable, TC/RC output timing relationships, and SO16 package thermal derating above 110 °C.

Technical Context

The 74HC191D implements four master/slave D-type flip-flops with internal steering logic to support fully synchronous count-up/count-down operation triggered on LOW-to-HIGH clock edges, while retaining asynchronous parallel load capability independent of clock state. Its U/D input determines direction, and CE must be LOW for state transitions - with strict timing constraints requiring CE to transition only when CP is HIGH.

Terminal Count (TC) is an active-HIGH status flag indicating overflow (15→0 in up-mode) or underflow (0→15 in down-mode), remaining asserted until preset, count, or U/D change. Ripple Clock (RC) is an active-LOW output enabled only when TC=HIGH and CE=LOW, enabling direct cascading without external gating.

Key Specifications

Pinout & Package

74HC191D,652 is housed in a plastic small outline package (SO16, SOT109-1) with 16 leads and 3.9 mm body width. Thermal derating begins at 110 °C (12.4 mW/K).

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HC191D,652, the 74HC193D offers independent clocking at the cost of directional coordination complexity, while the SN74LV191ADBR delivers higher speed and lower voltage support but mandates layout and interface redesign - making the 74HC191D optimal for drop-in replacement in existing HC-based systems.

Availability

74HC191D,652 is available at Aetrix Electronics and suitable for industrial motor control, programmable logic sequencers, and legacy bus interface designs requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 74HC191D,652 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 efficiency technologies, delivering high-performance logic, analog, and MOSFET solutions for automotive, industrial, and consumer markets.

The 74HC191 belongs to Nexperia's 74HC logic family - engineered for robustness in harsh environments, with emphasis on wide voltage operation, high ESD tolerance, and guaranteed performance from -40 °C to +125 °C.

FAQ

Can 74HC191D,652 be used as a divide-by-N counter?

Yes, but not natively. The 74HC191D,652 lacks built-in reset-on-match logic. To implement divide-by-N, external combinational logic (e.g., NAND gate) must detect the target count on Q0–Q3 and assert PL to reload a starting value on the next clock edge. This adds propagation delay and requires careful timing analysis to avoid race conditions.

What is the maximum recommended clock rise/fall time for reliable operation?

At VCC = 6.0 V, the maximum input transition rate is 83 ns/V, meaning rise/fall times must not exceed 500 ns (6.0 V × 83 ns/V). Slower edges increase susceptibility to noise-induced false triggering. For best results, keep tr/tf ≤ 10 ns using controlled-impedance traces and local series termination.

Is the TC output safe to drive an LED directly?

No. TC has a typical VOH of 5.48 V at VCC = 6.0 V and IOH = -5.2 mA, but its output structure is not designed for sustained DC current. Driving an LED risks exceeding the 25 mA absolute maximum output current rating. Use a buffer transistor or dedicated LED driver IC instead.

How does the RC output behave when CE is HIGH?

When CE is HIGH, RC remains HIGH (inactive) regardless of TC state or clock activity. RC only goes LOW (active) when both TC = HIGH and CE = LOW simultaneously. This ensures RC pulses are strictly gated by valid terminal count and enabled counting - preventing spurious carry signals during hold or preset modes.