Nexperia USA Inc. HEF4021BT,652

Overview

HEF4021BT,652 from Nexperia is an 8-bit static shift register (parallel-to-serial converter) with asynchronous parallel load (PL), synchronous serial data input (DS), LOW-to-HIGH edge-triggered clock (CP), and buffered Q5–Q7 outputs. It operates from 3 V to 15 V, supports -40 °C to +125 °C ambient range, and features Schmitt-trigger CP input for noise immunity. Used in industrial control logic, LED matrix drivers, and legacy microcontroller I/O expansion.

For engineers reviewing the HEF4021BT,652 datasheet, HEF4021BT,652 pinout, HEF4021BT,652 application, or HEF4021BT,652 equivalent, key selection criteria include its wide VDD range (3–15 V), asynchronous PL capability, Q5–Q7 output buffering, SO16 package compatibility, and CMOS-level static operation without clock dependency for parallel loading.

Technical Context

The HEF4021BT implements eight cascaded D-type master-slave flip-flops, each with independent SD and CD inputs. Parallel load occurs asynchronously when PL = HIGH, overriding CP and DS timing - enabling immediate register capture of D0–D7 states regardless of clock phase.

During serial shift mode (PL = LOW), data advances rightward on each CP rising edge: DS enters Q0, Q0→Q1, ..., Q6→Q7, with Q5–Q7 buffered for drive strength. Schmitt-trigger CP input ensures reliable triggering even with slow-rising clock edges up to 40 MHz at VDD = 15 V.

Key Specifications

Pinout & Package

HEF4021BT,652 is housed in a plastic small outline package (SO16) per SOT109-1 standard: 16-pin, 3.9 mm body width, 1.27 mm lead pitch, gull-wing leads, and JEDEC MS-012 compliant footprint.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit parallel-to-serial shift register applications.

Compared with CD4021BE and 74HC165PW, HEF4021BT,652 uniquely combines asynchronous PL, Schmitt-trigger CP, and buffered Q5–Q7 outputs - making it the only option among the three capable of noise-tolerant, zero-latency parallel capture and direct-drive capability in 3–15 V mixed-voltage industrial systems.

Availability

HEF4021BT,652 is available at Aetrix Electronics and suitable for industrial PLC I/O expansion, LED matrix row driving, legacy microcontroller bus interfacing, and serial-to-parallel protocol conversion requiring stable component supply across extended temperature and voltage ranges.

Supply support for HEF4021BT,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 leading Dutch semiconductor manufacturer specializing in high-volume logic, discrete, and MOSFET solutions with emphasis on reliability, efficiency, and automotive-grade quality.

The HEF4021B belongs to Nexperia's legacy 4000-series CMOS logic family, designed specifically for industrial control, instrumentation, and retro-compatibility applications demanding wide supply range and robust static operation.

FAQ

What is the minimum pulse width required for the PL input to ensure reliable parallel loading?

The minimum PL HIGH pulse width is 12 ns at VDD = 15 V and +125 °C, per Table 7. This ensures full propagation through all eight stages during asynchronous load. At lower VDD or temperature, the requirement relaxes to 24 ns (VDD = 5 V, +125 °C), allowing compatibility with slower microcontroller GPIO toggle rates without added timing constraints.

Can unused inputs like SD and CD be left floating, or must they be tied?

Unused SD and CD inputs must not be left floating. Per Section 1 of the datasheet, all unused inputs must be connected to VDD, VSS, or another driven input. Floating SD/CD risks metastability or unintended set/clear of internal flip-flops, potentially corrupting register state during PL or CP transitions.

Does the HEF4021BT,652 support hot insertion or live-state preservation during VDD ramp-up?

No. The device lacks power-on reset (POR) or Ioff protection. During VDD ramp-up, undefined logic states may occur on outputs until VDD exceeds VIH thresholds. To preserve state, PL must be held HIGH and CP held LOW until VDD stabilizes above 3 V, and a known-good parallel load should be applied before enabling serial shift mode.

How does the Schmitt-trigger CP input affect maximum achievable clock frequency?

The Schmitt trigger does not limit maximum clock frequency - tPHL/tPLH remains 40 ns at VDD = 15 V regardless of input edge rate. Instead, it guarantees reliable recognition of slow-rising edges (down to 0.08 μs/V), enabling use with RC clocks or long traces where conventional CMOS inputs would oscillate or miss edges - without sacrificing top-end speed.