TL431CDBZR - Adjustable 2.495V Shunt Reference 100mA SOT-23-3 | TI
MPN： TL431CDBZR ✓ 啟用中TL431CDBZR 概覽
An adjustable shunt regulator (also called a programmable shunt reference) is a type of voltage reference IC that regulates voltage by sinking current from a supply rail through its cathode when the reference pin senses a voltage above an internal bandgap threshold. In the power-management hierarchy, it sits between a fixed zener diode and a full linear regulator: more precise and temperature-stable than a zener, yet far cheaper and simpler than an LDO. Because the output is set by just two external resistors, the shunt reference family is a fundamental building block in analog circuit design.
Key features include a wide adjustable output range set by two external resistors, approximately 2.495 V internal reference with 2.2% (standard C grade) initial tolerance, 0.2 ohm to 0.5 ohm order typical dynamic output impedance, and a maximum cathode current of 100 mA. The C-grade device is specified over the 0 C to 70 C commercial temperature range, and its low minimum cathode current of roughly 1 mA allows operation in low-power systems.
Technically, the TL431 combines an internal 2.495 V bandgap reference with an operational amplifier and an open-collector output transistor. When the REF pin exceeds the internal threshold, the output transistor conducts and sinks current from cathode to anode, forming the basis of error-amplifier action in isolated flyback and forward power supplies, where the TL431 is frequently paired with an optocoupler such as the PC817 for secondary-side feedback.
Typical applications include secondary-side voltage regulation and feedback in AC-DC and DC-DC switch-mode power supplies, adjustable zener replacement and overvoltage crowbar sensing, battery charger voltage monitoring, and precision threshold comparators in industrial instrumentation.
A critical design consideration is temperature drift: the C grade (2.2% at 25 C) drifts more than the A or B grades over temperature, so precision systems should select TL431ACDBZR or TL431BDBZR instead. Always provide at least the minimum cathode current for regulation.
This page adds distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
直接替換替代品，適用於 TL431CDBZR — 相同封裝，腳位對腳位相容。需重新設計 PCB 的不同封裝零件不列入。
此系列的變體
與下列產品可直接替換的同系列型號： TL431CDBZR （相同外形與佔位） — 差異在於 Package, Minimum Cathode Current for Regulation, Operating Temperature Range, Reference Voltage (Vref), Adjustable Output Range.
TL431ACDBZR
✅ 直接替換聯絡詢價
查看資料表 →TL431QDBZR
✅ 直接替換聯絡詢價
查看資料表 →TL431IDBZR
✅ 直接替換聯絡詢價
查看資料表 →TL431BDBZR
✅ 直接替換📋 參考替代品（不在目錄中）
KA431AZTA
✅ 直接替換📋 參考替代品（不在目錄中）
AZ431AZ-ATRE1
✅ 直接替換📋 參考替代品（不在目錄中）
TL431CDBZR 規格
| 輸出類型 | Adjustable Shunt |
| Reference Voltage (Vref) | 2.495 V |
| Initial Reference Tolerance | ±2.2% at 25 C |
| Adjustable Output Range | 2.495 V to 36 V |
| Maximum Cathode Current | 100 mA |
| Maximum Cathode Voltage | 36 V |
| Dynamic Output Impedance | 0.2 ohm typical |
| Minimum Cathode Current for Regulation | 1 mA (typical, max 4 mA) |
| Grade | C (standard, 2.2%) |
| 工作溫度範圍 | 0 C to +70 C |
| 封裝 | SOT-23-3 (DBZ) |
| 安裝類型 | Surface Mount |
| Configuration | TL431 pinout (REF, Anode, Cathode) |
| RoHS 狀態 | Compliant |
| Packaging | Tape & Reel (R suffix) |
TL431CDBZR 腳位配置
| 腳位 1 | REF — Reference input (2.495 V threshold, connected to resistor divider) |
| 腳位 2 | ANODE — Anode, connected to system ground / lowest potential |
| 腳位 3 | CATHODE — Cathode, current sink terminal (up to 100 mA, 36 V max) |
典型應用
TL431CDBZR 適用於 6 應用s: SMPS Secondary-Side Feedback, Adjustable Zener / Voltage Clamping, Battery Charger Voltage Monitoring, Precision Comparator / Threshold Detection, Constant-Current Sources, Instrumentation Voltage Reference.
SMPS Secondary-Side Feedback
The TL431CDBZR is the industry-standard error amplifier for secondary-side regulation in isolated flyback and forward AC-DC converters. Its 2.495 V bandgap reference and open-collector output drive an optocoupler LED, closing the feedback loop across the isolation barrier with the REF divider sensing the output rail. The 36 V cathode rating covers most 5 V, 12 V, and 24 V power supplies, and its approximately 0.2 ohm dynamic impedance keeps loop gain stable. Typical designs use 1% feedback resistors plus a 10 nF to 100 nF compensation capacitor at REF, achieving load regulation below 1% across the commercial 0 C to 70 C range.
推薦
Adjustable Zener / Voltage Clamping
Replacing fixed zener diodes, the TL431CDBZR provides any clamping voltage from 2.495 V to 36 V using two resistors, with far sharper knee characteristics and ±2.2% accuracy versus typical ±5% zeners. Its regulation begins at only about 1 mA of cathode current, whereas zeners need several milliamps for stable breakdown, making the TL431 more efficient in low-power clamp and threshold-detection circuits. In overvoltage protection, the TL431 triggers a crowbar SCR or gate-drive shutdown when the sensed rail crosses the programmed threshold. Designers should respect the 100 mA maximum cathode current and add series resistance when clamping high-energy rails.
推薦
Battery Charger Voltage Monitoring
In charger ICs and battery packs, the TL431CDBZR senses cell or pack voltage against its 2.495 V reference and indicates or terminates charge when the divider crosses threshold. The 36 V cathode rating supports multi-cell packs, and the C grade ±2.2% tolerance suits lead-acid and NiMH chargers where a final trim is acceptable; lithium applications needing tighter cutoff should select TL431ACDBZR (±1%) or TL431BDBZR (±0.5%) on the same footprint. Because the device draws under 1 mA in regulation, it adds negligible self-discharge burden to battery-powered monitoring circuits across the commercial temperature range.
推薦
Precision Comparator / Threshold Detection
The TL431CDBZR functions as a comparator with a built-in precision reference: when the REF pin rises above 2.495 V, the cathode pulls low sharply, sinking up to 100 mA. This lets one small SOT-23 device both detect a threshold and directly drive a relay, LED, or microcontroller input without a separate op-amp. Designers set the threshold with a resistor divider from the monitored rail and use a small hysteresis resistor from cathode to REF for clean switching in noisy environments. Compared with a discrete reference-plus-comparator pair, the TL431CDBZR saves board area and BOM cost in industrial sensor and alarm circuits.
推薦
Constant-Current Sources
By forcing a fixed 2.495 V across a sense resistor placed between the cathode and REF pin, the TL431CDBZR forms a two-terminal constant-current sink; for example, a 12.4 ohm resistor yields approximately 200 mA, scaled by the resistor value. The tight bandgap reference gives far better current accuracy than a zener-based circuit, and the SOT-23 package suits compact LED driver and bias-current applications within the 100 mA cathode limit and package power dissipation. Thermal design matters at higher currents: keep (Vcathode - Vref) times current within the small package capability, or move to a larger package variant.
推薦
Instrumentation Voltage Reference
Bench instruments, data-acquisition front ends, and industrial meters use the TL431CDBZR to generate a local, adjustable reference rail or offset voltage from a higher system supply. Programming to any value from 2.495 V to 36 V with two resistors eliminates custom reference values, and the approximately 0.2 ohm dynamic impedance provides good ripple rejection when fed from a switching supply. Where the ±2.2% C-grade tolerance is too loose for ADC reference duties, pin-compatible TL431ACDBZR (±1%) or TL431BDBZR (±0.5%) upgrades drop onto the same footprint, allowing one PCB layout to serve multiple accuracy and cost tiers.
推薦
推薦產品摘要
工程參考資料，適用於 TL431CDBZR — 比較、設計指引及合規資訊。
選型指南
與替代品比較
| 參數 | 本產品 | TL431ACDBZR | TL431QDBZR | KA431AZTA | AZ431AZ-ATRE1 |
|---|---|---|---|---|---|
| Package | SOT-23-3 (DBZ) | SOT-23-3 (DBZ) - same | SOT-23-3 (DBZ) - same | SOT-23-3 - same | SOT-23-3 - same |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | onsemi | Diodes Incorporated |
| Reference Tolerance | ±2.2% (C grade) | ±1% (A grade) | ±2% (automotive grade) | ±2% (AZ grade) | ±1% (A grade) |
| Reference Voltage | 2.495 V | 2.495 V | 2.495 V | 2.495 V | 2.495 V |
| Max Cathode Voltage | 36 V | 36 V | 36 V | 36 V | 36 V |
| Max Cathode Current | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA |
主要差異化特點
- Widest same-brand grade selection on one footprint (對比TL431ACDBZR)
- Commercial temperature range optimized for cost (對比TL431QDBZR)
- Cross-brand second sourcing available (對比KA431AZTA)
- Honest trade-off: not for precision lithium cutoff (對比AZ431AZ-ATRE1)
設計說明
Do not substitute the TL432CDBZR for the TL431CDBZR without checking pinout: TI states the two devices have different pin assignments in the DBZ package (cathode and REF swapped). Also do not confuse the DBZ and DBV packages - TL431CDBVR uses a different SOT-23 footprint pinout. Always verify the complete ordering code, since grade suffix (C, A, B, I, Q) changes tolerance and temperature range on an otherwise identical die.
Estimated: ensure cathode current stays above the 1 mA typical (4 mA max) minimum for regulation and below the 100 mA absolute maximum. For a 12 V rail clamped to 5 V at 10 mA, series resistor = (12 V - 5 V) / 10 mA = 700 ohm, dissipating 70 mW - safe for SOT-23. Stable regulation requires the feedback loop bias current through the resistor divider to be large relative to REF pin input current; use divider current of 0.5 mA or more.
In optocoupler feedback loops, the TL431 REF pin is sensitive to capacitance: per TI application guidance, capacitance directly on REF can destabilize the internal amplifier. Place a small series resistance (about 1 kOhm to 10 kOhm) between divider and REF when compensation is needed, and use a ceramic capacitor from cathode to REF (typically 10 nF to 100 nF) to set loop crossover. Keep divider resistors within 1% tolerance for best output accuracy.
Place the cathode-to-anode decoupling path short and keep the REF divider close to pin 1 to minimize noise pickup. The SOT-23-3 thermal path is limited; Estimated: at 100 mA and 30 V cathode voltage the device would dissipate 3 W - far beyond SOT-23 capability - so restrict worst-case dissipation to a few hundred milliwatts with adequate copper area on the anode trace.
合規資訊
RoHS compliant and lead-free per TI product page and distributor listings. AEC-Q100 qualification applies to the TL431QDBZR automotive variant, not this C-grade commercial part. REACH and halogen-free status should be confirmed via the TI material declaration page.
