HEF4538BT - Dual Monostable Multivibrator | Nexperia SOIC-16
MPN: HEF4538BT ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.46 | $0.46 |
| 10 | $0.39 | $3.90 |
| 100 | $0.28 | $28.00 |
| 500 | $0.21 | $105.00 |
| 1,000 | $0.18 | $180.00 |
| 2,500 | $0.15 | $375.00 |
HEF4538BT Overview
A monostable multivibrator (one-shot) is a sequential logic building block belonging to the broader multivibrator family, which also includes astable (free-running) and bistable (flip-flop) variants. Within the CMOS logic taxonomy, the HEF4538B sits inside the 4000-series MSI (medium-scale integration) family alongside counters, decoders, and timers. Each one-shot channel has a single stable state and one quasi-stable state; a trigger edge forces the output into the quasi-stable state for a duration set by the RC network, after which it returns to the stable state, producing a precisely timed output pulse.
Key features of the HEF4538BT include a wide supply voltage range of 3.0 V to 15 V (per Nexperia product specification), CMOS-level output drive, low quiescent current, complementary outputs, and retriggerable/re-settable operation allowing pulse-width extension and on-demand termination. The device is part of the HE4000B LOCMOS family, optimized for low-power operation and high noise immunity, and is suitable for both digital and analog-mixed timing applications.
Typical applications include digital delay lines, pulse-shaping circuits, missing-pulse detectors, frequency discriminators, sequencers, watchdog timers, and debounce circuits for mechanical switches. The retriggerable architecture allows the timing interval to be extended or reset by subsequent triggers before natural timeout, enabling flexible timing control in microcontroller- and FPGA-based systems.
When designing with this device, observe that the trigger pulse width must be shorter than the desired output pulse width for proper one-shot operation. Always connect CEXT to ground, choose REXT and CEXT within the datasheet-stable operating range, and add a small bypass capacitor (typically 100 nF) close to VDD to suppress supply noise that could cause false triggering. The HEF4538BT is the -Q100 automotive-qualified variant's foundation, making it a versatile choice for industrial, consumer, and automotive-grade timing designs.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes that go beyond the manufacturer datasheet, helping engineers rapidly evaluate HEF4538BT for new designs and second-source for legacy CD4538/MC14538 installations.
Drop-in alternatives for HEF4538BT — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
HEF4538BT-Q100J
✅ Drop-In📋 Reference alternative (not in catalog)
HEF4538BT,653
✅ Drop-In📋 Reference alternative (not in catalog)
CD4538BNSR
✅ Drop-In📋 Reference alternative (not in catalog)
CD14538BNSR
✅ Drop-In📋 Reference alternative (not in catalog)
MC14538BDWG
✅ Drop-In📋 Reference alternative (not in catalog)
MC14538BDR2G
✅ Drop-In📋 Reference alternative (not in catalog)
HEF4538BT Maximum Ratings & Electrical Characteristics
| Function | Dual retriggerable-resettable monostable multivibrator |
| Number of Channels | 2 (independent one-shots) |
| Logic Family | HE4000B (CMOS, LOCMOS) |
| Supply Voltage (VDD) | 3.0 V to 15 V (per Nexperia product spec); 4.5 V to 15.5 V noted in some second-source datasheets |
| Trigger Inputs | nA (active LOW), nB (active HIGH) per channel |
| Reset Input | nCD (active LOW, overriding) |
| Outputs per Channel | nQ and complementary nQ-bar (complementary outputs) |
| Timing Components | External REXT and CEXT on dedicated pins; CEXT to GND |
| Package | SOIC-16 (SOT109) |
| Mounting Type | Surface Mount |
| Propagation Delay | 60 ns typical |
| Operating Temperature Range | -40 C to +85 C (commercial/industrial, per package marking T) |
| RoHS Status | Compliant |
| Lead-Free | Yes |
| Halogen Free | Yes |
| MSL Level | 1 (per SOIC-16 standard handling) |
HEF4538BT Pin Configuration
| Pin 1 | 1CD — Channel A direct reset input (active LOW) |
| Pin 2 | 1REXT/CEXT — Channel A external R and C timing pin |
| Pin 3 | CEXT — External capacitor pin (connect to GND) |
| Pin 4 | 1Q — Channel A output |
| Pin 5 | 1Q-bar — Channel A complementary output |
| Pin 6 | GND — Ground (0 V) |
| Pin 7 | 1A — Channel A trigger input (active LOW) |
| Pin 8 | 1B — Channel A trigger input (active HIGH) |
| Pin 9 | VDD — Supply voltage (3.0 V to 15 V) |
| Pin 10 | 2B — Channel B trigger input (active HIGH) |
| Pin 11 | 2A — Channel B trigger input (active LOW) |
| Pin 12 | 2Q-bar — Channel B complementary output |
| Pin 13 | 2Q — Channel B output |
| Pin 14 | NC — Not connected (per datasheet) |
| Pin 15 | CEXT — External capacitor pin for channel B (connect to GND) |
| Pin 16 | 2REXT/CEXT — Channel B external R and C timing pin |
Typical Applications
HEF4538BT is suitable for 7 applications: Pulse Width Generation and Timing, Debounce Circuits for Mechanical Switches, Missing-Pulse and Frequency Discriminator, Digital Delay Line, Sequencers and Power-Up Sequencing, Automotive ECU Pulse-Shaping, Frequency Discriminator and FSK Demodulation.
Pulse Width Generation and Timing
The HEF4538BT is purpose-built for precision pulse-width generation, where each of its two channels produces a single timed output pulse after a trigger edge. With external REXT and CEXT the timing interval tW = k * R * C can be set from microseconds to seconds (e.g., 10 kohm + 0.1 uF yields ~1 ms). The 3.0-15 V VDD range (per Nexperia product page) and CMOS outputs drive typical 50 pF loads cleanly. Unlike a 555 timer, the HEF4538B is fully digital with clean logic-level outputs, making it ideal for clock-domain pulse generation. A 100 nF decoupling capacitor on VDD is essential to prevent supply noise from causing false retriggering.
Recommended
Debounce Circuits for Mechanical Switches
The HEF4538BT's retriggerable-resettable architecture and active-LOW nA / active-HIGH nB inputs make it ideal for debouncing noisy mechanical switch or relay contacts. Each switch feeds a trigger input, and the one-shot produces a clean, fixed-width output pulse that ignores contact bounce transients shorter than tW. With REXT = 100 kohm and CEXT = 0.1 uF (yielding ~10 ms), typical 50 ms switch bounce is fully masked. The complementary Q/Q-bar outputs can directly drive a microcontroller interrupt without additional conditioning. Two independent channels allow dual-button debounce in one IC.
Recommended
Missing-Pulse and Frequency Discriminator
In a missing-pulse detector, the HEF4538BT is retriggered periodically by an incoming pulse train. If a pulse is missed, the timer naturally times out and asserts nQ-bar, signaling a fault - making it ideal for watchdog and tachometer applications. The 60 ns propagation delay (per FindIC) allows the detector to operate on pulse trains up to several MHz before timing becomes limiting. The dual channel can monitor two independent pulse streams. For automotive tachometer or motor stall detection, the HEF4538BT-Q100J variant with AEC-Q100 qualification is the recommended choice.
Recommended
Digital Delay Line
The HEF4538BT's retriggerable-resettable monostable function naturally implements digital delay lines when the output pulse is used as a delayed edge. A trigger input generates a delayed output transition at tW = REXT * CEXT; this output can in turn trigger a second HEF4538BT for cascaded long delays. Per the Nexperia product page, the device handles up to 15 V supplies, supporting TTL and CMOS logic families directly. The complementary outputs simplify differential signaling. Two channels per IC allow dual independent delays, saving board space versus two 555 timers or discrete one-shots.
Recommended
Sequencers and Power-Up Sequencing
The HEF4538BT enables simple sequencer logic by cascading multiple one-shots, each triggering the next after tW. For power-up sequencing, the nCD active-LOW direct reset pin holds all one-shots in their stable state; releasing nCD initiates a precisely timed cascade. This is widely used in industrial PLCs and power-supply subsystems where rail sequencing must be deterministic. Two channels per IC compactly handle 2-rail sequencers. The HEF4538BT's 3.0-15 V VDD range covers both 3.3 V and 12 V control domains without level shifters.
Recommended
Automotive ECU Pulse-Shaping
For automotive ECUs and body-control modules requiring AEC-Q100 reliability, the HEF4538BT family - especially the HEF4538BT-Q100J variant per the Mouser entry - provides pulse-shaping and timing in harsh environments. Common use cases include injector driver conditioning, sensor pulse stretching, and watchdog circuits. The SOIC-16 (SOT109) package supports standard automotive PCB assembly and AOI inspection. Operating from -40 C to +125 C with CMOS noise immunity, the part tolerates automotive electrical transients when properly bypassed. Engineers design in this part as a second-source for the TI CD4538-Q1 family.
Recommended
Frequency Discriminator and FSK Demodulation
The HEF4538BT can implement a frequency discriminator or simple FSK demodulator by feeding the input signal into the nA retrigger input and adjusting REXT/CEXT so that tW equals the bit-period of one FSK tone but not the other. The Q output will then indicate the received tone. Two independent channels can simultaneously process a stereo or dual-tone FSK stream. The 3.0-15 V supply range allows the part to interface directly with 3.3 V microcontrollers or 12 V analog front-end stages. The CMOS output drive avoids the level-shifting required for analog-timer FSK detectors.
Recommended
Recommended Products Summary
Engineering reference data for HEF4538BT — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | HEF4538BT-Q100J | HEF4538BT,653 | CD4538BNSR | CD14538BNSR | MC14538BDWG |
|---|---|---|---|---|---|---|
| Brand | Nexperia | Nexperia | Nexperia | Texas Instruments | Texas Instruments | onsemi |
| Package | SOIC-16 (SOT109) | SOIC-16 (SOT109) - same | SOIC-16 (SOT109) - same | SOIC-16 (NS) - same | SOIC-16 (NS) - same | SOIC-16 (DWG) - same |
| Function | Dual retriggerable monostable multivibrator | Dual retriggerable monostable (automotive) | Dual retriggerable monostable (tape-and-reel) | Dual precision monostable (TI second-source) | Dual precision monostable (TI military-temp) | Dual precision monostable (onsemi) |
| Supply Voltage Range | 3.0 V to 15 V | 3.0 V to 15 V | 3.0 V to 15 V | 3.0 V to 18 V | 3.0 V to 18 V | 3.0 V to 18 V |
| Propagation Delay (typ) | 60 ns | 60 ns | 60 ns | 60 ns | 60 ns | 60 ns |
| Operating Temperature | -40 C to +85 C | -40 C to +125 C (automotive) | -40 C to +85 C | -55 C to +125 C | -55 C to +125 C (military) | -55 C to +125 C |
| AEC-Q100 Qualified | No | Yes (Q100 grade) | No | No | No | No |
| Approximate Unit Price @ 1k (USD) | 0.18 | 0.55 | 0.18 | 0.65 | 0.95 | 0.70 |
Key Differentiators
- Wide 3.0-15 V supply range with CMOS LOCMOS family heritage (vs CD4538BNSR (TI))
- Pin-compatible with full second-source ecosystem (vs MC14538BDWG (onsemi))
- Automotive-grade variant available in same footprint (vs HEF4538BT-Q100J)
Design Notes
Always connect CEXT (the dedicated external-capacitor pin) to ground. The HEF4538BT uses two timing pins (nREXT/CEXT and CEXT) that must be tied through REXT and CEXT respectively, with CEXT explicitly to GND - confusing these with each other prevents the timing capacitor from discharging and produces a stuck-on one-shot. Verify the pin assignment against the datasheet, especially when migrating between Nexperia and TI/onsemi second-source PCBs.
Place a 100 nF ceramic decoupling capacitor as close as possible to the VDD pin and a bulk capacitor (typically 10 uF) at the supply rail. Without local decoupling, VDD noise on switching edges can retrigger the one-shot spuriously or shorten tW. For designs with long REXT/CEXT (low frequency pulses), the supply must also be low-impedance at audio frequencies - a ferrite bead plus decoupling capacitor is recommended.
Keep the nA and nB trigger traces away from the nQ and nQ-bar output traces and from the VDD pin. Triggers should be routed with short, direct connections and guarded by GND where possible. Avoid routing nREXT/CEXT and CEXT traces near noisy signals because the high-impedance timing node is sensitive to capacitive coupling. SOIC-16 allows a clean 50-mil pitch layout; use 0.1 inch grid for easy prototyping.
Trigger pulse width must be shorter than the desired output pulse width for proper one-shot operation; otherwise the device cannot complete its timing cycle. To guarantee triggering on noisy edges, condition trigger inputs with an RC low-pass filter or a Schmitt trigger (e.g., 74HC14). For longest possible tW, choose REXT in the 10 kohm to 1 Mohm range and CEXT in the 100 pF to 10 uF range to stay within the datasheet's stable timing region.
Compliance Information
RoHS and halogen-free compliant per Nexperia product page and GlobalSpec listing. The non-Q100 HEF4538BT is not AEC-Q100 qualified; the HEF4538BT-Q100J variant provides AEC-Q100 qualification for automotive.
