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Texas Instruments LM34925MRX/NOPB
- Part No.:
- LM34925MRX/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- 8-PowerSOIC (0.154", 3.90mm Width)
- Datasheet:
-
LM34925MRX/NOPB.pdf
- Description:
- IC REG BUCK ADJ 100MA 8SOPWR
- Quantity:
- Payment:
- Shipping:
Inventory:1,362
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Product details
Overview
LM34925MRX/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 LM34925MRX/NOPB datasheet, LM34925MRX/NOPB pinout, LM34925MRX/NOPB application, or LM34925MRX/NOPB equivalent, key selection considerations include its 100-V input capability, integrated synchronous switch eliminating external Schottky diodes, programmable UVLO and on-time via external resistors, thermal shutdown at 165°C, and compatibility with WSON-8 and SO PowerPAD-8 packages.
Technical Context
The LM34925MRX/NOPB implements constant-on-time (COT) control with VIN-inversely proportional on-time, enabling stable frequency across 7.5–100 V input while eliminating loop compensation. Its regulation relies on a 1.225 V internal reference compared against FB voltage, with overvoltage protection triggered at 1.62 V.
It integrates a 7.6 V internal VCC regulator (with 4.5 V UVLO), bootstrap gate drive for the high-side switch (requiring 0.01 µF BST–SW capacitor), and intelligent peak current limiting (270 mA typ) with VIN- and FB-dependent off-time - ensuring robust short-circuit protection without foldback degradation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 7.5 V to 100 V - supports direct connection to 48 V telecom buses and automotive 24/48 V systems without pre-regulation. |
| Feedback Reference | 1.225 V ±2% - sets output voltage accuracy via external RFB1/RFB2 divider; enables precise 3.3 V, 5 V, or 10 V bias rails. |
| Buck Switch RDS(ON) | 0.8–1.8 Ω - low conduction loss at 100 mA test current; reduces heat generation in high-input-voltage operation. |
| Synchronous Rectifier RDS(ON) | 0.45–1.0 Ω - replaces external Schottky diode, improving efficiency and eliminating reverse recovery losses. |
| Current Limit Threshold | 150–370 mA - peak-limited protection with adaptive off-time; prevents destructive inductor saturation during overload or short circuit. |
| Operating Frequency | Up to 1 MHz - adjustable via RON resistor; enables small magnetics and fast transient response in space-constrained designs. |
| Thermal Shutdown | 165°C with 20°C hysteresis - disables switching and VCC regulator to prevent permanent damage under sustained overload or poor heatsinking. |
Pinout & Package
LM34925MRX/NOPB is packaged in an 8-pin WSON (4.00 mm × 4.00 mm) with exposed thermal pad, optimized for high-voltage isolation and thermal performance in compact bias supply layouts.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 RTN | Ground reference | System ground return for all internal circuits; must be connected to PCB ground plane and tied to exposed pad. |
| 2 VIN | Main input supply | Accepts 7.5–100 V DC; powers internal VCC regulator and high-voltage gate drivers. |
| 3 UVLO | Undervoltage lockout input | Resistor-divider programmable start-up threshold (0.66 V shutdown, 1.225 V enable); provides hysteresis via internal 20 µA current source. |
| 4 RON | On-time programming | Resistor-to-VIN sets COT on-time; minimum 100 ns required at max VIN to ensure stable operation. |
| 5 FB | Feedback input | Compares output voltage (via RFB1/RFB2) to 1.225 V reference; ripple ≥250 mV required for stable COT regulation. |
| 6 VCC | Internal bias supply output | 7.6 V regulated output (±1.35 V); powers gate drivers and logic; requires 1 µF decoupling capacitor. |
| 7 BST | Bootstrap supply | Charged from VCC through internal diode when SW is low; supplies floating gate drive for high-side N-MOSFET. |
| 8 SW | Switching node | Drives external inductor; connects to BST capacitor and output filter; withstands VIN + 0.3 V transient. |
Key Features
| Feature | Design Value |
|---|---|
| No loop compensation required | Constant-on-time architecture eliminates external compensation network, reducing BOM count and layout sensitivity. |
| No Schottky diode needed | Integrated low-side synchronous MOSFET replaces lossy external diode, improving efficiency by ~3–5% at light-to-moderate loads. |
| Adjustable UVLO with hysteresis | Programmable turn-on/off thresholds via external resistor divider; prevents erratic startup during brownout conditions. |
| Ultra-fast transient response | COT control delivers immediate on-time adjustment to load steps - no phase-margin tuning needed for dynamic line/load regulation. |
| Intelligent peak current limit | Off-time scales inversely with FB voltage and VIN; minimizes foldback during partial overloads while ensuring safe short-circuit shutdown. |
Applications
| Isolated Telecom Bias Supply | Automotive Isolated Auxiliary Rail |
|---|---|
|
Use Scenario: Generating a 5 V/100 mA isolated auxiliary rail from a 48 V backplane in telecom line cards using fly-buck topology. IC Role / Device Role / Timing Role: Secondary-side bias controller regulating output via COT control; synchronously rectifies inductor current to eliminate Schottky losses. Use Value: Enables >85% efficiency at full load without external diode or compensation components, reducing board area and thermal stress. |
Use Scenario: Providing isolated 3.3 V bias for CAN transceivers and microcontrollers in 24 V vehicle ECU designs with stringent EMC requirements. IC Role / Device Role / Timing Role: High-voltage secondary-side regulator operating from transformer-coupled winding; uses programmable UVLO to reject cold-crank dips below 6 V. Use Value: Delivers stable output during battery transients (4–16 V input dips) due to fast COT response and 165°C thermal shutdown protection. |
| Industrial PLC Isolated I/O Power | Medical Equipment Auxiliary Isolation |
|
Use Scenario: Creating a reinforced-isolation 10 V bias rail for analog front-end op-amps and ADCs in programmable logic controllers. IC Role / Device Role / Timing Role: Regulator implementing ripple-based feedback (via RC network) to meet low-noise, low-ripple requirements of precision signal chains. Use Value: Achieves <15 mVpp output ripple with proper RC filtering - critical for 16-bit ADC reference stability in noisy factory environments. |
Use Scenario: Supplying isolated 3.3 V/50 mA power to patient-connected sensor modules requiring 4 kV reinforced isolation per IEC 60601-1. IC Role / Device Role / Timing Role: Secondary-side bias IC placed on isolated side of transformer; leverages internal synchronous rectification to minimize heat in sealed enclosures. Use Value: Eliminates Schottky forward drop and reverse recovery noise - reducing EMI risk and simplifying creepage/clearance compliance. |
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 |
|---|---|---|---|
| LM5165RUMX/NOPB | Wider 3–65 V input; integrated 150 mA LDO instead of synchronous buck; no BST/SW pins; fixed 1.2 V reference. | Designed for non-isolated point-of-load; lacks secondary-side gate drive and transformer-coupled bias capability. | Choose LM5165RUMX/NOPB only for primary-side or non-isolated bias; not suitable for fly-buck or transformer-derived secondaries. |
| UCC28740DR | Primary-side QR flyback controller with HV start-up; no integrated switches; requires external MOSFETs and optocoupler feedback. | Targets primary-controlled isolated supplies; adds complexity and cost versus secondary-side self-regulating LM34925MRX/NOPB. | UCC28740DR suits high-efficiency, variable-frequency flyback designs where primary-side regulation is mandatory; LM34925MRX/NOPB offers simpler, lower-cost secondary-side implementation. |
Compared with LM5165RUMX/NOPB and UCC28740DR, the LM34925MRX/NOPB uniquely combines high-voltage secondary-side integration, synchronous rectification, and COT control - delivering faster transient response, smaller solution size, and reduced component count specifically for transformer-coupled bias rails.
Availability
LM34925MRX/NOPB is available at Aetrix Electronics and suitable for isolated telecom bias supply, automotive auxiliary rail, and industrial PLC I/O power applications requiring stable component supply, long-term manufacturability, and TI-qualified reliability.
Supply support for LM34925MRX/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 leader specializing in analog, embedded processing, and power management technologies, with decades of expertise in high-reliability power conversion ICs.
The LM34925MRX/NOPB belongs to TI's isolated bias regulator product line, engineered specifically to simplify and miniaturize secondary-side power in fly-buck, forward, and push-pull isolated DC-DC topologies.
FAQ
What is the recommended minimum on-time for LM34925MRX/NOPB, and why does it matter?
The LM34925MRX/NOPB requires a minimum on-time of 100 ns at maximum input voltage (100 V) to ensure stable constant-on-time (COT) operation. This constraint arises from internal timing resolution limits and ensures reliable switch activation and feedback sampling. Selecting RON too small risks violating this minimum, causing erratic regulation or failure to start - verified in TI's Electrical Characteristics table (Section 6.6).
Can LM34925MRX/NOPB operate without an external bootstrap capacitor?
No - LM34925MRX/NOPB requires a 0.01 µF ceramic capacitor between BST and SW pins. This capacitor supplies gate drive voltage to the high-side N-MOSFET during its on-time. Without it, the high-side switch cannot turn on, halting regulation. The internal diode charges this capacitor during SW low periods, as confirmed in Pin Functions (Section 5) and Feature Description (Section 7.3.7).
How does the LM34925MRX/NOPB achieve stable regulation without loop compensation?
The LM34925MRX/NOPB uses constant-on-time (COT) control: on-time is set by RON and VIN, while off-time ends when FB falls below 1.225 V. This ripple-based feedback inherently stabilizes the system without external compensation components. Stability depends on ≥250 mV ripple at FB - achieved via output capacitor ESR or added RC network - as specified in Section 7.3.11.
What is the purpose of the UVLO pin on LM34925MRX/NOPB, and how is it configured?
The UVLO pin on LM34925MRX/NOPB enables programmable input undervoltage lockout using an external resistor divider from VIN to RTN. Thresholds are 0.66 V (shutdown) and 1.225 V (enable), with hysteresis generated by an internal 20 µA current source. Direct connection to VIN allows operation once VCC reaches 4.5 V - details are in Section 7.3.9 and Pin Functions (Section 5).
Does LM34925MRX/NOPB support discontinuous conduction mode (DCM)?
No - LM34925MRX/NOPB forces continuous conduction mode (CCM) across all loads due to its synchronous rectifier design with no diode emulation. The low-side MOSFET remains active even at light loads, preventing inductor current reversal from reaching zero. This behavior is explicitly stated in Section 7.3.8 and ensures predictable COT timing and ripple-based regulation.
LM34925MRX/NOPB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 8-PowerSOIC (0.154", 3.90mm Width)
- 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-SO PowerPad
LM34925MRX/NOPB FAQ
1.How can I place an order for LM34925MRX/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM34925MRX/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 LM34925MRX/NOPB reliable?
The price and inventory of LM34925MRX/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM34925MRX/NOPB is usually 5 days.
3.What payment methods are accepted for LM34925MRX/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM34925MRX/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM34925MRX/NOPB?
LM34925MRX/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM34925MRX/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 LM34925MRX/NOPB?
For technical support, including LM34925MRX/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM34925MRX/NOPB requirements.
6.How does Aetrix verify that LM34925MRX/NOPB is sourced from the original manufacturer or authorized distributors?
All LM34925MRX/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 LM34925MRX/NOPB meets industry standards.
7.What is the process for return or replacement of LM34925MRX/NOPB?
All LM34925MRX/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM34925MRX/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 LM34925MRX/NOPB part is unused and in its original packaging.
Return procedure for LM34925MRX/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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