CMPZ4621 TR - 3.6V 350mW Low Noise Zener Diode | Central Semiconductor
MPN: CMPZ4621 TR β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.12 | $0.12 |
| 10 | $0.1 | $1.00 |
| 100 | $0.07 | $7.00 |
| 500 | $0.05 | $25.00 |
| 1,000 | $0.04 | $40.00 |
CMPZ4621 TR Overview
A Zener diode is a voltage reference or clamp device that conducts in reverse breakdown at a precisely defined voltage. In the system hierarchy, it belongs to the discrete diode family, sitting below linear voltage regulators and voltage reference ICs: where a regulator uses a reference plus feedback loop, a Zener provides a fixed, simple breakdown voltage directly. Low-noise Zener families like the CMPZ4621 are specifically processed for reduced avalanche noise, which matters when the breakdown voltage feeds a comparator, ADC reference, or bias point.
Key features of the CMPZ4621 include a 3.6V nominal Zener voltage with 5% tolerance, 350 mW power dissipation, low reverse breakdown noise for clean biasing, and a compact SOT-23 surface mount footprint compatible with standard reflow assembly. The PBFREE suffix indicates a lead-free, RoHS-oriented build. The 1700 ohm dynamic impedance at 75 mA test current defines how much the clamp voltage moves with current, so designs should bias the diode well above the knee for best regulation.
Technically, the device uses a silicon avalanche/planar construction optimized by Central Semiconductor for low noise operation. Avalanche noise scales with breakdown voltage and current; the CMPZ4621's 3.6V rating sits near the low end where noise is naturally modest, and the low-noise process further reduces it versus standard Zeners.
Typical applications include voltage clamping on signal lines, low-current voltage references, bias networks for transistor amplifiers, and protection in portable and consumer electronics where the SOT-23 footprint and low cost are advantageous.
Design tip: derate the 350 mW rating above 25C ambient and ensure series current limiting keeps worst-case power below the derated curve.
This page synthesizes distributor pricing context, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for CMPZ4621 TR β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
CMPZ4620 TR
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
CMPZ4622 TR
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
CMPZ4619 TR
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
CMPZ4623 TR
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
MMSZ5227B
β Drop-Inπ Reference alternative (not in catalog)
CMPZ4621 TR Maximum Ratings & Electrical Characteristics
| Zener Voltage (Nominal) | 3.6 V |
| Voltage Tolerance | Β±5% |
| Power Dissipation | 350 mW |
| Test Current | 75 mA |
| Zener Impedance (Zzt) | 1700 ohm at 75 mA |
| Configuration | Single Zener |
| Noise Characteristic | Low Noise |
| Mounting Type | Surface Mount |
| Package | SOT-23 |
| Polarity | Single Anode / Single Cathode |
| Lead Finish | Lead-free (PBFREE) |
| RoHS Status | Compliant (PBFREE suffix) |
| Packaging | Tape and Reel (TR) |
| Product Type | Surface Mount Low Noise Silicon Zener Diode |
CMPZ4621 TR Pin Configuration
| Pin 1 | Anode β Zener anode terminal (per SOT-23 Zener convention - confirm in datasheet) |
| Pin 2 | NC β Not connected internally (per SOT-23 two-terminal diode convention) |
| Pin 3 | Cathode β Zener cathode terminal (per SOT-23 Zener convention - confirm in datasheet) |
Typical Applications
CMPZ4621 TR is suitable for 6 applications: Analog Bias Networks, Voltage Clamping and Protection, Portable and Battery-Powered Electronics, Comparator and ADC Threshold References, Audio Equipment Bias Rails, Industrial Control Input Conditioning.
Analog Bias Networks
The CMPZ4621 fits transistor and amplifier bias networks where its low-noise breakdown is the primary value: a 3.6V clamp on a bias node with 75 mA test bias exhibits a dynamic impedance of 1700 ohm, so current should be held near the test point for stable bias voltage. Because the diode's avalanche noise is process-reduced versus standard Zeners, it injects minimal noise into base-bias or offset networks of audio and instrumentation stages. Use a series resistor sized for the target current and confirm worst-case dissipation stays well below the 350 mW rating at maximum ambient.
Recommended
Voltage Clamping and Protection
As a 3.6V Β±5% clamp rated 350 mW, the CMPZ4621 protects low-voltage signal lines and IC inputs from overvoltage excursions. Placed from the protected node to ground in reverse bias, it conducts above approximately 3.6V, shunting fault energy through the diode; the series impedance of 1700 ohm at 75 mA defines the clamp slope. The SOT-23 surface mount footprint keeps the clamp close to the connector or IC pin, minimizing parasitic loop inductance. For repetitive transient events, ensure average power stays under 350 mW and derate above 25C ambient per the datasheet curve.
Recommended
Portable and Battery-Powered Electronics
In portable devices, the CMPZ4621's SOT-23 package (approximately 3 x 1.4 mm body) and low cost make it attractive for rail clamping, LED bias, and simple 3.6V status references on battery-powered boards. The 350 mW rating comfortably covers low-current duties from lithium-cell-adjacent nodes, while the lead-free PBFREE construction supports RoHS consumer manufacturing. Designers should bias the diode near its 75 mA test current only where power budget allows; for ultra-low-power designs, note that at very low currents the 3.6V nominal will sag toward the knee and tolerance widens, so verify the operating point empirically.
Recommended
Comparator and ADC Threshold References
For comparator thresholds and coarse ADC references, the CMPZ4621 provides a fixed 3.6V breakdown with reduced avalanche noise - valuable because noise on a comparator reference directly translates to trip-point jitter. At the 75 mA test current, regulation is best defined; feed the diode from a stable rail through a series resistor and buffer the node with an op-amp or comparator input with low bias current so the 1700 ohm impedance does not shift the threshold. The Β±5% tolerance suits non-critical thresholds; for sub-1% accuracy, select a calibrated shunt reference instead.
Recommended
Audio Equipment Bias Rails
Audio stages benefit directly from the CMPZ4621's low-noise specification: microphonics-free silicon avalanche construction keeps bias voltage noise off microphone preamp and phono input stages where a standard Zener would inject audible hiss. Operate the 3.6V diode at a bias current near 75 mA with adequate series resistance and bypass the node with a capacitor (for example 100 nF to 10 uF) to shunt residual noise further. The SOT-23 package suits dense mixed-signal audio PCBs, and the Β±5% tolerance is acceptable for headroom-setting bias rails rather than gain-critical references.
Recommended
Industrial Control Input Conditioning
On industrial I/O boards, the CMPZ4621 clamps 24V-logic-derived sensor signals down to safe 3.6V levels for MCU inputs: placed after a series input resistor, it shunts overvoltage while the resistor limits diode current to keep dissipation within the 350 mW envelope. The lead-free SOT-23 construction withstands standard industrial reflow profiles, and the low-noise process avoids corrupting slow analog sensor readings with clamp noise. Designers should calculate worst-case fault current (for example, 24V fault with 10k series resistor yields about 2 mA, roughly 7 mW in the diode - far below rating), confirming large safety margin.
Recommended
Recommended Products Summary
Engineering reference data for CMPZ4621 TR β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | CMPZ4620 TR | CMPZ4622 TR | MMSZ5227B |
|---|---|---|---|---|
| Package | SOT-23 | SOT-23 - same | SOT-23 - same | SOT-23 - same |
| Brand | Central Semiconductor | Central Semiconductor | Central Semiconductor | onsemi |
| Zener Voltage (Nominal) | 3.6 V | 3.3 V | 3.9 V | 3.6 V |
| Tolerance | Β±5% | Β±5% | Β±5% | Β±5% (B suffix) |
| Power Dissipation | 350 mW | 350 mW | 350 mW | 500 mW |
| Noise Characteristic | Low Noise | Low Noise | Low Noise | Standard Zener process |
| Mounting Type | Surface Mount | Surface Mount | Surface Mount | Surface Mount |
Key Differentiators
- Dedicated low-noise Zener processing (vs MMSZ5227B)
- Fine voltage granularity within the low-noise family (vs CMPZ4620 TR)
- Lead-free PBFREE construction with commodity cost (vs CMPZ4622 TR)
Design Notes
The CMPZ4621's 350 mW rating applies at a specified reference ambient and must be derated at higher temperatures. Estimated example: with a 12V rail clamped to 3.6V through a 1k ohm series resistor, diode current is roughly (12 - 3.6)/1000 = 8.4 mA and diode dissipation is about 3.6 V x 8.4 mA = 30 mW - comfortably within rating. Always compute worst-case (maximum input rail, minimum series resistance, maximum temperature) before finalizing the series resistor value.
Place the CMPZ4621 directly at the node being clamped or referenced, with a short, wide trace to the ground return to minimize parasitic inductance and impedance. For noise-critical bias nodes, add a ceramic bypass capacitor (100 nF to 10 uF depending on the application) directly across the diode to shunt residual avalanche noise and broadband interference. Standard SOT-23 land patterns apply; the part is compatible with lead-free reflow profiles given the PBFREE construction.
Do not operate the CMPZ4621 far below its 75 mA test current and then expect the full nominal 3.6V: at knee currents the clamp voltage falls and the effective tolerance widens, because the dynamic impedance is 1700 ohm at the test point. Also, SOT-23 Zener pin assignments vary between manufacturers - verify the anode/cathode lead mapping in the Central Semiconductor datasheet before layout, and never assume a competitor's SOT-23 Zener pinout carries over to this footprint.
Compliance Information
PBFREE suffix indicates lead-free construction; DigiKey/Mouser list the part as RoHS-oriented. REACH, halogen-free, and conflict-minerals declarations not stated in available data.
