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Texas Instruments UC29431D
- Part No.:
- UC29431D
- Manufacturer:
- Texas Instruments
- Category:
- Voltage Reference
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
UC29431D.pdf
- Description:
- IC VREF SHUNT ADJ 0.39% 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,048
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Product details
Overview
UC29431D from Texas Instruments is a precision adjustable shunt voltage regulator with 100mA sink capability, internal programmable reference divider (2.82V–12.24V), 0.4% initial reference accuracy, and dual-stage error + transconductance amplifier architecture optimized for optocoupler feedback in isolated DC-DC converters. It operates from 2.2V to 36.0V supply and delivers stable regulation across –25°C to +85°C.
For engineers reviewing the UC29431D datasheet, UC29431D pinout, UC29431D application, or UC29431D equivalent, key selection considerations include its fixed 140mS transconductance (±30mS), 5MHz error amplifier GBW, 3MHz transconductance amplifier GBW, UVLO threshold (~1V), and SOIC-8 package compatibility with standard PCB layouts for flyback and forward converter feedback networks.
Technical Context
The UC29431D implements a two-stage control architecture: a high-gain error amplifier (90dB AVOL, 5MHz GBW) compares SENSE voltage against an internal 1.3V reference, while a separate transconductance amplifier (gm = –140mS ±30mS) converts COMP voltage into output sink current at COLL. This decoupled design enables independent compensation of loop dynamics via COMP and COLL pins.
Internal resistor network (R1/R2/R3) supports six factory-programmable reference voltages (2.82V, 3.12V, 5.1V, 7.8V, 10.42V, 12.24V) without external components; configuration is set by connecting pins to SENSE, COLL, GND, or leaving open. UVLO activation at ~1V on SENSE ensures reliable startup only after reference stabilization.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Reference Voltage | 1.30V ±0.005V at 25°C - provides precise error comparison baseline unaffected by supply variation |
| Initial Accuracy | ±0.4% - enables tight output voltage tolerance in regulated power supplies without trimming |
| Sink Current | 100mA continuous - sufficient to drive standard optocoupler LEDs and maintain loop stability under full load |
| Error Amp GBW | 5MHz - supports fast transient response and flexible pole/zero placement for stable compensation |
| Transconductance | –140mS ±30mS - delivers linear, predictable current output vs. COMP voltage for consistent CTR-independent regulation |
| Operating Temp Range | –25°C to +85°C - qualified for industrial-grade power supply environments |
| Supply Voltage Range | 2.2V to 36.0V - accommodates wide-input offline and intermediate bus applications |
Pinout & Package
UC29431D is housed in an 8-pin SOIC (D package), RoHS-compliant, moisture sensitivity level 2 (260°C peak reflow).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - COLL | Collector output | Sink terminal of internal NPN transistor; rated to 36V, delivers up to 140mA; connects to optocoupler anode or magnetic amplifier gate |
| 2 - COMP | Error amp output / gm amp input | Compensation node for error amplifier; internally clamped to ~2.0V; used to add poles/zeros for loop stability |
| 3 - GND | Power & reference ground | Common return for internal reference, error amp, and transconductance stages; isolated substrate ground improves noise immunity |
| 4 - R1 | Internal resistor tap | Connection point for first internal resistor; configures reference divider ratio when tied to SENSE, COLL, GND, or left open |
| 5 - R2 | Internal resistor tap | Connection point for second internal resistor; determines programmed reference voltage per Table 1 in datasheet |
| 6 - R3 | Internal resistor tap | Connection point for third internal resistor; completes six-voltage selection matrix (2.82V–12.24V) |
| 7 - SENSE | Inverting input / UVLO sense | Feedback node for error amplifier; also triggers undervoltage lockout below ~1V to prevent erratic startup |
| 8 - VCC | Power supply input | Primary bias rail; draws 0.50–0.80mA quiescent current; supports 2.2V–36.0V operation with full spec compliance |
Key Features
| Feature | Design Value |
|---|---|
| Programmable Reference Voltages | Six factory-set outputs (2.82V–12.24V) selectable via pin-strapping - eliminates need for external resistor dividers in common feedback designs |
| Fixed Linear Transconductance | –140mS ±30mS - ensures predictable current sourcing into optocoupler LED, removing CTR dependency and supply-voltage drift |
| Dual-Stage Compensation | Independent COMP and COLL nodes - allows simultaneous optimization of error amplifier bandwidth and output stage dynamics for robust loop stability |
| UVLO with 1V Threshold | Prevents operation until internal reference stabilizes - guarantees clean startup and avoids false regulation during brownout conditions |
| High Initial Reference Accuracy | ±0.4% at 25°C - reduces system-level calibration burden and improves output voltage consistency across production batches |
Applications
| Isolated Flyback Converter Feedback | Optocoupler-Based Voltage Regulation |
|---|---|
|
Use Scenario: Primary-side sensing in offline AC-DC adapters where secondary-side voltage must be tightly regulated despite transformer leakage and line/load transients. IC Role / Device Role / Timing Role: Shunt regulator providing precise reference voltage to optocoupler LED; COLL sink current modulates optocoupler conduction to adjust PWM duty cycle on primary side. Use Value: Enables ±1% output regulation using low-cost PC817-style optocouplers, eliminating need for TL431 + external resistors and reducing BOM count by two components. |
Use Scenario: Secondary-side voltage monitoring in telecom brick PSUs requiring stable 5.1V or 12.24V outputs with minimal temperature drift. IC Role / Device Role / Timing Role: Precision shunt reference driving optocoupler LED; internal 5.1V or 12.24V divider selected via R1–R3 strapping removes external resistor network. Use Value: Achieves 0.7% overall reference tolerance over –25°C to +85°C, improving long-term output stability versus discrete Zener-based solutions. |
| Magnetic Amplifier Controller | Programmable Shunt Reference |
|
Use Scenario: Regulating auxiliary outputs in multi-rail server PSUs using saturable reactors driven by square-wave signals. IC Role / Device Role / Timing Role: Error amplifier compares sensed output to internal reference; transconductance stage generates reset current for magnetic amplifier core. Use Value: Provides linear, temperature-stable current source (vs. exponential BJT behavior), enabling accurate reset timing and >95% efficiency in mag-amp circuits. |
Use Scenario: Replacing Zener diodes in lab bench supplies where user-selectable output voltages (e.g., 2.82V, 7.8V, 10.42V) are required without hardware changes. IC Role / Device Role / Timing Role: Adjustable shunt regulator with six factory-programmed references; configured via solder-jumpers or zero-ohm resistors on R1/R2/R3 pins. Use Value: Reduces design variants from six discrete Zener parts to single UC29431D SKU, simplifying inventory and qualification testing. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar shunt regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TL431ACDR | Single-stage shunt regulator; no internal resistor network; requires external divider for all reference voltages; 2.5V fixed reference; 0.5% initial accuracy | Lacks programmable internal references and dual-stage compensation; suitable for simpler, lower-bandwidth loops | Choose TL431ACDR when cost is critical and only 2.5V reference is needed with basic compensation. |
| UC39431D | Same architecture and pinout; wider temperature range (0°C to +70°C); identical electrical specs except for temp grade and test conditions | Targeted for commercial applications; not rated for extended industrial temperature operation | Choose UC39431D for cost-sensitive commercial designs where –25°C to +85°C operation is unnecessary. |
Compared with TL431ACDR and UC39431D, the UC29431D offers guaranteed industrial temperature support (–25°C to +85°C), integrated reference selection, and dedicated COMP/COLL nodes for advanced loop shaping-making it optimal for high-reliability isolated power supplies requiring design flexibility and thermal robustness.
Availability
UC29431D is available at Aetrix Electronics and suitable for isolated flyback converters, optocoupler-based voltage regulation, magnetic amplifier controllers, and programmable shunt reference applications requiring stable component supply and long-term industrial-grade availability.
Supply support for UC29431D 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
Texas Instruments is a global semiconductor company specializing in analog and embedded processing technologies, with leadership in power management, signal chain, and high-reliability ICs.
The UC29431D belongs to TI's precision shunt regulator product line, designed specifically for high-accuracy, optocoupler-coupled feedback in isolated DC-DC converters and magnetic amplifier control systems.
FAQ
What is the operating temperature range for UC29431D?
The UC29431D is specified for operation from –25°C to +85°C ambient temperature. This industrial-grade rating ensures reliable performance in demanding power supply environments such as industrial automation and telecom infrastructure. All electrical characteristics-including reference accuracy, transconductance, and sink current-are guaranteed across this full range, unlike the commercial-grade UC39431D which is limited to 0°C to +70°C. The UC29431D datasheet confirms these limits in the Electrical Characteristics table under TA conditions.
How does UC29431D achieve 0.4% initial reference accuracy?
The UC29431D achieves ±0.4% initial reference accuracy through laser-trimmed on-chip bandgap circuitry and matched transistor pairs fabricated in TI's precision analog process. This specification applies at 25°C before any system-level calibration and is verified during final test. The internal 1.30V reference remains stable across supply voltage (2.2V–36.0V) and load, contributing directly to the device's 0.7% overall reference tolerance over temperature. This accuracy eliminates the need for post-assembly trimming in most isolated power supply designs.
Can UC29431D replace TL431 in existing designs?
The UC29431D is not a direct drop-in replacement for TL431 due to different pinout (TL431 uses cathode/anode/reference; UC29431D uses COLL/COMP/SENSE/VCC) and architecture (dual-stage vs. single op-amp). However, it can replace TL431 in new designs targeting higher loop bandwidth, programmable references, or improved CTR independence. Migration requires PCB layout changes and compensation redesign-but yields benefits like 5MHz error amp GBW, fixed transconductance, and six internal reference options not available in TL431ACDR.
What are the six programmable reference voltages supported by UC29431D?
The UC29431D supports six factory-programmable reference voltages: 2.82V, 3.12V, 5.1V, 7.8V, 10.42V, and 12.24V. These are selected by connecting its R1, R2, and R3 pins to SENSE, COLL, GND, or leaving them open-as defined in Table 1 of the UC29431D datasheet. No external resistors are needed for these voltages, reducing component count and improving long-term stability versus discrete divider networks. Each voltage is trimmed to ±0.5% tolerance at 25°C.
Does UC29431D include undervoltage lockout (UVLO) functionality?
Yes, UC29431D includes integrated undervoltage lockout (UVLO) activated on the SENSE pin with a threshold of approximately 1V. This prevents the device from regulating until the internal 1.3V reference is properly biased, ensuring clean startup and avoiding erratic behavior during brownout or soft-start conditions. The UVLO is inherent to the SENSE input structure and requires no external components-unlike many discrete shunt regulators that need added circuitry for reliable enable sequencing.
UC29431D Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Series:
- -
- Packaging:
- Tube
- Product Status:
- Obsolete
- Reference Type:
- Shunt
- Output Type:
- Adjustable
- Voltage - Output (Min/Fixed):
- 1.3V
- Voltage - Output (Max):
- 36 V
- Current - Output:
- 100 mA
- Tolerance:
- ±0.39%
- Temperature Coefficient:
- -
- Noise - 0.1Hz to 10Hz:
- -
- Noise - 10Hz to 10kHz:
- -
- Voltage - Input:
- -
- Current - Supply:
- -
- Current - Cathode:
- 800 µA
- Operating Temperature:
- -25°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
UC29431D FAQ
1.How can I place an order for UC29431D through Aetrix?
Please submit a Request for Quotation (RFQ) for UC29431D on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for UC29431D reliable?
The price and inventory of UC29431D are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC29431D is usually 5 days.
3.What payment methods are accepted for UC29431D?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC29431D transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC29431D?
UC29431D orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC29431D order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for UC29431D?
For technical support, including UC29431D datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC29431D requirements.
6.How does Aetrix verify that UC29431D is sourced from the original manufacturer or authorized distributors?
All UC29431D products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that UC29431D meets industry standards.
7.What is the process for return or replacement of UC29431D?
All UC29431D units undergo pre-shipment inspection (PSI). If there is an issue with UC29431D, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The UC29431D part is unused and in its original packaging.
Return procedure for UC29431D:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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