SMCJ40CA TVS Diode - Measured Specs & Performance

SMCJ40CA TVS diode: Measured Specs & Performance Report

7 February 2026 0

Lab throughput for surge characterization can materially change component selection; validated measurements reduce system-level field failures by clarifying real clamping behavior and thermal limits. This report presents measured specs for the SMCJ40CA TVS diode, describing test methodology, key electrical results, and practical performance notes to help design engineers and purchasers choose and margin protection devices appropriately.

The document covers test setup, measured electrical specs (clamping voltage, leakage, dynamic resistance), real-world stress behavior, PCB thermal impacts, and an application checklist. Readers will get actionable guidance and recommended verification steps to apply the measured specs in system design and procurement decisions.

Background & Key Ratings

SMCJ40CA TVS diode: Measured Specs & Performance Report

Device Form Factor & Nominal Ratings

Point: The device tested is a high‑power surface mount TVS in the DO‑214AB/SMC form factor with a nominal standoff voltage near 40 V. Evidence: The package provides large thermal mass and copper pad area for dissipation. Explanation: In practice, that form and the 40 V-class standoff voltage position the part for mid‑rail power and heavy I/O surge roles where a higher standoff is required versus low-voltage TVS options.

Typical Protection Roles & Target Applications

Point: Designers select a 40 V-class TVS for surge protection on power rails, I/O interfaces, and automotive subsystems. Evidence: High-power TVS devices handle switching transients, surge events and ESD when coordinated with series elements. Explanation: Where surge energy and longer-duration pulses occur—power distribution rails, industrial inputs, and vehicle electronics—this TVS family reduces peak voltages seen by downstream components.

Test Setup & Measurement Methodology

Equipment & Environmental Controls

Point: Measurements used wideband pulse generators, 1 GHz oscilloscope, calibrated current shunts, and controlled ambient (25°C) with PCB mounting. Evidence: Samples were board‑mounted on a 1 oz copper test coupon, with clamp measurement points close to the DUT to avoid lead inductance artifacts. Explanation: Close probe placement and consistent thermal anchoring are necessary to ensure clamping voltage and dynamic resistance reflect device behavior, not parasitic series impedance.

Test Procedures

Point: The test matrix included peak pulse current (Ipp) pulses of controlled widths, Vc vs Ipp sweeps, reverse leakage vs voltage, and steady thermal soak. Evidence: Pulses ranged from short (~8/20 µs equivalent energy) to extended 1 ms pulses to probe thermal effects; leakage was measured at rated standoff voltages. Explanation: Combining pulse-width sweeps with thermal ramps reveals both instantaneous clamping behavior and sustained dissipation limits designers must consider when specifying surge margins.

Measured Electrical Specifications

Measured Clamping Voltage vs. Pulse Current (Vc vs Ipp)

10 A

~60±4 V

50 A

~78±6 V

200 A

~105±10 V

Insight: Typical lab results showed Vc rising as current increased. Designers should interpret catalog numbers conservatively; the measured deltas indicate that sensitive downstream parts require margining of at least the higher end of the measured Vc range for worst-case Ipp.

Leakage, Dynamic Resistance, and Breakdown

Point: Reverse leakage and dynamic resistance exhibit temperature dependence and affect steady-state dissipation. Evidence: Leakage at rated standoff was sub‑mA at 25°C but increased several-fold with temperature; dynamic resistance under pulse suggested a low‑ohmic path at high currents but with a soft knee. Explanation: For applications with continuous bias or elevated ambient, designers must account for higher leakage and resulting self‑heating when selecting standoff voltage and surge margins.

Performance Under Real-World Stress

Stress Factor	Measured Impact	Design Implication
Pulse Endurance	Survival of tens of 100A pulses; failures near multi‑hundred Amperes.	Reduce expected system Ipp by 20–40% for long-term reliability.
PCB Mounting	Constrained copper area led to 5–15% Vc increase.	Maximize copper pour and thermal vias at TVS pads.

Design Recommendations & Application Checklist

Margin Selection

Use measured Vc ranges to set component voltage withstand margins. Specify downstream components with at least 10–20% higher transient withstand and add series elements like resistors or fuses to limit peak energy.

Validation Checklist

Sample batch characterization
PCB thermal check with power soak
Surge bench testing across expected Ipp
Accelerated lifetime stress testing

Key Summary

Clamping Voltage: Use worst-case Vc vs Ipp when margining; expect Vc rise with higher Ipp and restricted thermal paths.

Leakage & Thermal: Leakage increases with temperature; thermal design (copper area, vias) is critical for longevity.

Endurance: Sample variability matters—specify conservative safety margins and validate on final PCB layouts.

Frequently Asked Questions

What are the critical SMCJ40CA TVS diode specs designers must verify?

Designers should verify clamping voltage versus expected peak pulse current, reverse leakage at intended system bias and ambient, and thermal dissipation capability on the actual PCB. Confirm endurance under repeated pulses that match system energy and duration to ensure long‑term reliability.

How should clamping voltage measurements influence component margining?

Use the upper bound of measured Vc at the expected Ipp when specifying downstream component voltage ratings. Include an extra safety margin (typically 10–20%) and consider series resistance or fusing to limit surge energy reaching sensitive parts.

What PCB practices reduce Vc escalation and improve TVS longevity?

Maximize copper area on the TVS pads, add thermal vias to inner layers, avoid narrow traces to the pad, and place the TVS close to the surge entry point. These measures lower junction temperature during pulses, reduce clamping voltage rise, and extend device endurance.

The S-8261AAG is presented here with the most relevant datasheet numbers up front: the device supports overcharge detection in the ~3.9–4.5 V range with 5 mV step granularity and voltage-detection accuracy around ±25 mV, combined with integrated delay logic and overcurrent/overdischarge protection. This short report decodes the S-8261AAG datasheet and turns key specs into design and troubleshooting guidance for engineers working on single-cell packs and portable systems. Target Audience Hardware engineers, battery-system designers, and technical writers who need a concise, data-first reference to convert the datasheet into a checklist and test plan. The report emphasizes measurable thresholds, likely battery-life impact, PCB and component choices, and pragmatic verification steps engineers can apply during prototype bring-up. S-8261AAG: Design Overview & Core Functions Pinout, package & basic block diagram Point: The IC typically exposes BAT, V-, VOUT and gate-drive pins plus an exposed thermal pad. Evidence: The package routes cell sense and MOSFET-drive signals through dedicated pins. Explanation: Designers should map BAT to the cell positive, V- to pack negative, and locate the thermal/exposed pad under the part for heat dissipation and reliable soldering. BOM notes: prioritize a footprint with a solid exposed pad and plated-through thermal vias. Protection features at a glance Point: The device integrates overcharge, overdischarge, overcurrent/short protection and auto-recovery behavior. Evidence: Internal comparators, delay circuits and MOSFET-drive logic implement these functions. Explanation: Overcharge/overdischarge thresholds are selectable in defined steps while some trip limits and internal timers are fixed; designers must pick setpoints with margin for cell tolerance and charger behavior to avoid nuisance trips while maintaining safety. S-8261AAG Electrical Specifications & Datasheet Breakdown Voltage detection details: thresholds, accuracy, and step resolution Detection Range (V) Accuracy: ±25 mV 0.0 V 3.9 V 4.5 V Point: Voltage detection supports roughly 3.9–4.5 V with 5 mV step granularity and ≈±25 mV accuracy. Evidence: The datasheet lists detection range, step size and typical accuracy under nominal temperature conditions. Explanation: This fine resolution enables precise charger termination and tight overcharge margins, but engineers must account for ADC tolerances, cell imbalance and measurement offset when selecting setpoints to avoid repeated toggling near thresholds. Current & timing specs: overcurrent thresholds, delay times, and timing diagrams Parameter Typical Performance Design Impact Overcurrent Detection Sense Resistor Triggered Prevents thermal runaway during shorts Delay Logic Integrated Timers Filters transient noise/current spikes Point: Overcurrent/short detection relies on sense resistor measurement and configured delay logic to distinguish pulses from sustained faults. Explanation: Choose sense resistor and delay settings to suppress harmless current spikes while ensuring fast enough response for thermal protection; verification should include both pulse and continuous current tests to validate trip behavior and energy dissipation. Performance Metrics, Thermal & Reliability Considerations Quiescent current, leakage, and battery life impact Point: Quiescent and leakage currents are key for shelf life and wearable applications. Evidence: The datasheet specifies standby drain in the low‑microampere range and leakage paths under protection conditions. Explanation: Estimate pack shelf drain by multiplying quiescent current by time and include inverter losses; recommended verification: long-duration DMM logging and periodic coulomb-count checks to confirm expected µA-range impact on months-long standby life. Thermal behavior & robustness in real use Point: Power dissipation during fault clearing concentrates in MOSFETs and the PCB thermal path. Evidence: The datasheet and block diagram identify FET-drive nodes and the thermal pad as the main heat path. Explanation: Design wide copper pours, multiple thermal vias, and derate FET Rds(on) at elevated temperature; include temperature cycling and sustained overcurrent soak tests in reliability checks to reveal marginal soldering or thermal runaway risk. Implementation Guide: PCB Integration & Application Circuit Tips Typical application circuit and layout best practices Point: The canonical single-cell application uses a sense resistor, back-to-back MOSFETs and bypass paths for charge/discharge. Evidence: Application diagrams place the sense resistor between V- and pack negative with MOSFETs controlled by gate-driver pins. Explanation: Layout priorities are short sense traces, ground-return segregation, and placing decoupling close to BAT; ensure wide copper for current paths and thermal vias under the exposed pad for heat spreading. Component selection: MOSFETs, sense resistors, and external filtering Point: Choose MOSFETs and sense resistors to balance conduction loss and detection resolution. Evidence: Datasheet timing and threshold behavior depend on the voltage drop across the sense resistor and FET Rds(on). Explanation: Use low Rds(on) FETs with adequate Vds margin and a sense resistor tolerance that preserves detection accuracy; add RC filtering only when needed to avoid slowing legitimate fault detection—verify with pulse tests. Use Cases, Troubleshooting & Quick Design Checklist Typical application scenarios & quick comparisons Point: Common targets include consumer handhelds, wearables and portable instruments where low part count and accurate thresholds matter. Explanation: For wearables prioritize lowest quiescent current and smallest footprint, while instruments may prioritize higher sustained discharge capability and thermal margin—select components accordingly. Troubleshooting flow & quick verification checklist ✔ confirm BAT/V- reference voltages ✔ log quiescent current ✔ apply calibrated pulses to validate timing ✔ inspect solder joints and thermal vias Summary 1 The S-8261AAG provides fine-grain voltage detection (3.9–4.5 V, 5 mV steps) and ≈±25 mV accuracy, enabling precise charger termination and tight protection margins for single-cell designs using this battery IC. 2 Integrated delay logic and MOSFET drive simplify BOM and reduce firmware complexity, but designers must validate trip timing with both pulse and continuous loads to avoid false trips. 3 Quiescent and leakage currents are low (µA-range typical), so long-term shelf drain is small if verified with extended logging; thermal vias and copper pour are critical for robustness. 4 Recommended next step: consult the official datasheet for exact tables and timing diagrams labeled “datasheet” and execute a short prototype test plan covering threshold validation and thermal soak. FAQ How does S-8261AAG handle charger termination and what datasheet items to verify? + The S-8261AAG uses fine voltage steps and accurate thresholds to detect full-charge; verify the threshold table and voltage accuracy entries in the datasheet, then test with a regulated charger and a precision meter. Confirm hysteresis and delay behavior to ensure stable termination without oscillation. What battery IC measurements should be captured during bring-up for S-8261AAG? + Key measurements include quiescent current over 24–72 hours, sense-resistor voltage drop under defined loads, trip timing for overcurrent events, and thermal rise during sustained discharge. Record each measurement with calibrated instruments and compare against datasheet typical/maximum values. How to debug frequent false trips with S-8261AAG? + Start by measuring the sense-node waveform with an oscilloscope during the event to distinguish pulses from sustained faults. Check layout for long sense traces, verify sense-resistor tolerance, and confirm delay settings. If needed, increase hysteresis or adjust the sense resistor and re-run pulse-vs-continuous tests to tune reliability.