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Texas Instruments LM34925SDX/NOPB
- Part No.:
- LM34925SDX/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- 8-WDFN Exposed Pad
- Datasheet:
-
LM34925SDX/NOPB.pdf
- Description:
- IC REG BUCK ADJ 100MA 8WSON
- Quantity:
- Payment:
- Shipping:
Inventory:1,406
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Product details
Overview
LM34925SDX/NOPB from Texas Instruments is a high-voltage integrated secondary-side bias regulator for isolated DC-DC converters, featuring dual 100-V N-channel MOSFET switches (high-side buck and low-side synchronous), constant-on-time (COT) control, 7.5–100 V input range, 1.225 V precision feedback reference, and operation up to 1 MHz. It enables compact, loop-compensation-free bias supplies in telecom and industrial isolated power architectures.
For engineers reviewing the LM34925SDX/NOPB datasheet, LM34925SDX/NOPB pinout, LM34925SDX/NOPB application, or LM34925SDX/NOPB equivalent, key selection considerations include its integrated dual-switch topology, UVLO programmability via external resistor divider, bootstrap gate drive architecture, thermal shutdown at 165°C, and compatibility with WSON-8 and SO PowerPAD-8 packages.
Technical Context
The LM34925SDX/NOPB implements constant-on-time (COT) control with on-time inversely proportional to VIN and set by RON, enabling near-constant switching frequency across 7.5–100 V input without loop compensation. Its intelligent peak current limit uses forced off-time inversely proportional to FB voltage and VIN, delivering graded foldback during overload while maintaining short-circuit protection up to 100 V.
It integrates a 7.6-V internal VCC regulator (with 4.5 V UVLO and 26 mA current limit) for self-biasing gate drivers and logic, plus an external BST-SW bootstrap capacitor (0.01 µF) for high-side drive. The synchronous rectifier operates in continuous conduction mode (CCM) at all loads, supporting transformer-coupled secondary outputs.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 7.5 V to 100 V - supports direct connection to 48 V telecom, 24/42 V automotive, and industrial HV rails without pre-regulation. |
| Feedback Reference | 1.225 V ±2% - sets output voltage accuracy and enables precise external resistor-divider programming (e.g., 10 V out with RFB1/RFB2 = 7.16). |
| Buck Switch RDS(ON) | 0.8–1.8 Ω - limits conduction loss in high-side switch at 100 mA test current; impacts efficiency at medium-to-high load. |
| Synchronous Switch RDS(ON) | 0.45–1.0 Ω - reduces rectification loss vs. Schottky diode, eliminating need for external diode and improving light-load efficiency. |
| Current Limit Threshold | 150–370 mA - peak-limited protection; off-time scales with FB voltage to minimize foldback during partial overloads. |
| Thermal Shutdown | 165°C with 20°C hysteresis - disables buck switch and VCC regulator to prevent catastrophic failure; resumes at ~145°C. |
| VCC Regulator Output | 7.6 V (6.25–8.55 V) - powers internal gate drivers and logic; externally bypassed with 1 µF ceramic capacitor. |
Pinout & Package
LM34925SDX/NOPB is available in 8-pin WSON (4.00 mm × 4.00 mm) and 8-pin SO PowerPAD™ (4.89 mm × 3.90 mm) packages, both with exposed thermal pad connected to RTN for enhanced thermal dissipation.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 RTN | Ground reference | System ground return for all internal circuits; exposed pad must be soldered to PCB ground plane. |
| 2 VIN | Main power input | Accepts 7.5–100 V; feeds VCC regulator and high-side switch drain; requires local 10 µF+ input capacitor. |
| 3 UVLO | Undervoltage lockout input | Resistor divider from VIN sets startup threshold (1.225 V trip); 0.66 V shutdown; enables remote enable/disable. |
| 4 RON | On-time programming | Resistor to VIN sets minimum on-time (e.g., 100 kΩ → ~250 ns at 48 V); determines operating frequency. |
| 5 FB | Feedback input | Compares output voltage (via RFB1/RFB2) to 1.225 V reference; ripple ≥250 mV required for stable COT operation. |
| 6 VCC | Internal bias supply | 7.6 V regulated output; powers gate drivers; requires 1 µF decoupling; UVLO at 4.5 V disables IC. |
| 7 BST | Bootstrap supply | Charged via internal diode from VCC when SW is low; supplies high-side gate driver; needs 0.01 µF ceramic to SW. |
| 8 SW | Switching node | Drain of high-side FET and source of low-side FET; connects to inductor, bootstrap cap, and transformer primary winding. |
Key Features
| Feature | Design Value |
|---|---|
| No loop compensation required | Constant-on-time (COT) architecture eliminates external compensation network, reducing BOM count and layout sensitivity. |
| Integrated dual N-channel switches | Eliminates external high-voltage MOSFETs and Schottky diode, reducing solution size and cost in isolated bias supplies. |
| Programmable UVLO and shutdown | External resistor divider on UVLO pin allows system-level brownout control and remote ON/OFF sequencing. |
| Intelligent peak current limiting | Off-time dynamically scales with FB voltage and VIN, minimizing output foldback during moderate overloads and speeding recovery. |
| Thermally enhanced packaging | WSON-8 and SO PowerPAD-8 packages deliver RθJCbot as low as 2.4°C/W, enabling >1 W output in compact layouts without heatsinks. |
Applications
| Isolated Telecom Bias Supply | Automotive Isolated Auxiliary Rail |
|---|---|
Use Scenario: Generating +12 V or +5 V bias for gate drivers and controllers in 48 V telecom DC-DC bricks with primary-side isolation. IC Role / Device Role / Timing Role: Secondary-side synchronous buck controller regulating isolated auxiliary rail; provides fast transient response to digital load steps. Use Value: Eliminates optocoupler feedback and external MOSFETs, reducing component count by ≥4 and board area by 30% vs. discrete solutions. | Use Scenario: Powering isolated CAN transceivers and sensor interfaces in 12 V/42 V hybrid vehicle subsystems with reinforced insulation. IC Role / Device Role / Timing Role: High-voltage secondary-side bias regulator; maintains regulation during cold-crank (6.5 V) and load-dump (80 V) events. Use Value: 100 V absolute max rating and programmable UVLO ensure reliable start-up and shutdown across full automotive voltage range. |
| Industrial PLC I/O Isolation | Medical Equipment Auxiliary Power |
Use Scenario: Providing isolated +3.3 V/5 V rails for analog front-ends and digital isolators in programmable logic controller modules. IC Role / Device Role / Timing Role: Compact secondary-side regulator on isolated fly-buck transformer secondary; supports CCM operation down to zero load. Use Value: Synchronous rectifier and CCM operation ensure low output ripple and predictable EMI behavior for sensitive analog signal chains. | Use Scenario: Delivering certified isolated bias for patient-connected monitoring circuits requiring reinforced creepage/clearance per IEC 60601-1. IC Role / Device Role / Timing Role: Secondary-side bias controller on transformer-coupled auxiliary winding; enables compact, low-noise, low-leakage auxiliary supply. Use Value: No external Schottky diode eliminates reverse leakage path, improving isolation integrity and reducing risk of fault propagation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar secondary-side bias regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LM5165RGET | Wide-input (3–65 V) buck regulator with integrated 150-V MOSFET; no synchronous rectifier; requires external compensation. | Designed for primary-side non-isolated step-down; lacks secondary-side bias optimization and transformer-coupled support. | Choose LM5165RGET only if primary-side regulation is acceptable and transformer coupling is not required. |
| UCC28740DR | PSR flyback controller with primary-side sensing; no integrated power switches; requires external MOSFET and transformer. | Targets lower-cost isolated supplies where primary-side regulation suffices; higher design complexity and component count. | Prefer UCC28740DR when BOM cost is critical and transformer design flexibility outweighs integration benefits. |
Compared with LM5165RGET and UCC28740DR, the LM34925SDX/NOPB uniquely integrates dual N-channel switches optimized for secondary-side operation, enabling transformer-coupled bias generation without optocouplers or external rectifiers-reducing solution size by ≥40% and simplifying safety certification.
Availability
LM34925SDX/NOPB is available at Aetrix Electronics and suitable for isolated telecom bias supply, automotive auxiliary rail, and industrial PLC I/O isolation requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for LM34925SDX/NOPB 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, embedded processing, and power management ICs, with leadership in high-reliability industrial and automotive power solutions.
The LM34925SDX/NOPB belongs to TI's isolated bias regulator product line, designed specifically to simplify secondary-side power delivery in fly-buck, forward, and push-pull isolated topologies while minimizing component count and layout complexity.
FAQ
What is the recommended minimum output capacitor ESR for stable operation of the LM34925SDX/NOPB?
The LM34925SDX/NOPB requires ≥250 mV of ripple voltage at the FB pin for stable constant-on-time control. This mandates sufficient output capacitor ESR to generate resistive ripple in phase with inductor current. If ceramic capacitors with low ESR are used, a series RC network (e.g., 1 Ω + 100 nF) must be added between VOUT and FB to meet the ripple requirement. Failure to do so causes erratic switching or instability.
Can the LM34925SDX/NOPB operate with an externally supplied VCC voltage?
Yes, the LM34925SDX/NOPB supports external VCC biasing between 8.55 V and 13 V. When an external voltage in this range is applied to the VCC pin, the internal high-voltage linear regulator is disabled, reducing power dissipation-especially beneficial at high input voltages like 75 V or 100 V. The internal VCC UVLO (4.5 V) no longer applies in this configuration.
How does the LM34925SDX/NOPB implement undervoltage lockout (UVLO) control?
The LM34925SDX/NOPB features dual-level UVLO: a 0.66 V shutdown threshold (low-current mode) and a 1.225 V enable threshold on the UVLO pin. An internal 20 µA current source provides hysteresis by injecting current into the external resistor divider. This allows precise, temperature-stable startup and shutdown points independent of VIN fluctuations.
What is the purpose of the RON pin on the LM34925SDX/NOPB, and how is it configured?
The RON pin on the LM34925SDX/NOPB sets the minimum on-time via an external resistor to VIN. On-time is inversely proportional to VIN (e.g., 100 kΩ yields ~250 ns at 48 V). This resistor directly determines operating frequency and must be selected to ensure ≥100 ns minimum on-time at maximum VIN (100 V) for reliable switching.
Does the LM34925SDX/NOPB support discontinuous conduction mode (DCM) operation?
No, the LM34925SDX/NOPB forces continuous conduction mode (CCM) at all loads due to its synchronous rectifier architecture and lack of diode emulation. The low-side N-channel MOSFET remains active even at light loads, preventing inductor current reversal and ensuring predictable ripple and EMI behavior-critical for noise-sensitive isolated applications.
LM34925SDX/NOPB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 8-WDFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Function:
- Step-Down
- Output Configuration:
- Positive, Isolation Capable
- Topology:
- Buck
- Output Type:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 7.5V
- Voltage - Input (Max):
- 100V
- Voltage - Output (Min/Fixed):
- 1.225V
- Voltage - Output (Max):
- 100V
- Current - Output:
- 100mA
- Frequency - Switching:
- Adj to 1MHz
- Synchronous Rectifier:
- Yes
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-WSON (4x4)
LM34925SDX/NOPB FAQ
1.How can I place an order for LM34925SDX/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM34925SDX/NOPB 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 LM34925SDX/NOPB reliable?
The price and inventory of LM34925SDX/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM34925SDX/NOPB is usually 5 days.
3.What payment methods are accepted for LM34925SDX/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM34925SDX/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM34925SDX/NOPB?
LM34925SDX/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM34925SDX/NOPB 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 LM34925SDX/NOPB?
For technical support, including LM34925SDX/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM34925SDX/NOPB requirements.
6.How does Aetrix verify that LM34925SDX/NOPB is sourced from the original manufacturer or authorized distributors?
All LM34925SDX/NOPB 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 LM34925SDX/NOPB meets industry standards.
7.What is the process for return or replacement of LM34925SDX/NOPB?
All LM34925SDX/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM34925SDX/NOPB, 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 LM34925SDX/NOPB part is unused and in its original packaging.
Return procedure for LM34925SDX/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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