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Texas Instruments LM34925MR/NOPB
- Part No.:
- LM34925MR/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- 8-PowerSOIC (0.154", 3.90mm Width)
- Datasheet:
-
LM34925MR/NOPB.pdf
- Description:
- IC REG BUCK ADJ 100MA 8SOPWR
- Quantity:
- Payment:
- Shipping:
Inventory:3,851
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Product details
Overview
LM34925MR/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 + 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 fly-buck and isolated telecom architectures.
For engineers reviewing the LM34925MR/NOPB datasheet, LM34925MR/NOPB pinout, LM34925MR/NOPB application, or LM34925MR/NOPB equivalent, key selection criteria include its integrated dual-switch topology, UVLO programmability via external resistor divider, bootstrap gate drive architecture, thermal shutdown at 165°C, and compatibility with low-ESR output capacitor configurations requiring ≥250 mV FB ripple.
Technical Context
The LM34925MR/NOPB implements a constant-on-time (COT) control scheme where on-time is inversely proportional to VIN and set by RON, enabling near-constant switching frequency across 7.5–100 V input. Its regulation relies on comparing FB voltage to a 1.225 V internal reference, with overvoltage protection triggered at 1.62 V.
It integrates a self-biased 7.6 V VCC regulator (with 4.5 V UVLO), a bootstrap gate driver supporting 0.01 µF BST–SW ceramic capacitance, and intelligent peak current limiting (270 mA typ) with VIN- and FB-dependent off-timing - ensuring short-circuit robustness 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, 24–72 V automotive, and industrial HV rails without pre-regulation. |
| Feedback Reference | 1.225 V ±2% - sets precise output voltage via external RFB1/RFB2 divider; enables adjustable VOUT from 1.225 V. |
| Switching Frequency | Up to 1 MHz - programmable via RON; maintains stability across line/load due to COT architecture and minimum 144 ns off-time. |
| Buck RDS(on) | 0.8–1.8 Ω @ 100 mA - low conduction loss in high-side N-MOSFET, optimized for efficiency in 10–100 mA bias supply loads. |
| Synchronous RDS(on) | 0.45–1.0 Ω @ 200 mA - eliminates Schottky diode, sustains continuous conduction mode (CCM) even at light load. |
| Current Limit Threshold | 150–370 mA - peak-limited protection with intelligent off-time scaling (e.g., 16 µs max at FB = 0 V, VIN = 48 V). |
| VCC Regulator Output | 7.6 V ±1.3 V @ 20 mA - powers internal gate drivers and logic; disables when externally biased 8.55–13 V. |
Pinout & Package
LM34925MR/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 space-constrained bias supplies.
| 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 for thermal and EMI integrity. |
| 2 VIN | Main power input | Accepts 7.5–100 V DC; feeds VCC regulator and high-side switch; requires local 1 µF ceramic decoupling. |
| 3 UVLO | Undervoltage lockout input | Resistor-divider programmable threshold (0.66 V shutdown / 1.225 V enable); enables remote shutdown and brownout protection. |
| 4 RON | On-time programming | Connects to VIN via resistor to set COT period (e.g., 100 kΩ yields ~250 ns at 48 V); ensures >100 ns min on-time at 100 V. |
| 5 FB | Feedback input | Compares to 1.225 V reference; requires ≥250 mV ripple for stable COT operation; sensitive to RC network for low-ripple configurations. |
| 6 VCC | Internal bias supply output | 7.6 V regulated output; powers gate drivers; requires 1 µF ceramic capacitor; UVLO triggers at 4.5 V. |
| 7 BST | Bootstrap supply | Charged from VCC through internal diode during SW low phase; drives high-side gate via 0.01 µF BST–SW capacitor. |
| 8 SW | Switching node | Drives external inductor; connects to BST capacitor; withstands transient voltages up to VIN + 0.3 V (100 ns). |
Key Features
| Feature | Design Value |
|---|---|
| No loop compensation required | COT control eliminates external compensation network, reducing BOM count and design iteration time for isolated bias supplies. |
| No Schottky diode needed | Integrated synchronous rectifier replaces lossy external diode, improving light-load efficiency and eliminating reverse recovery noise. |
| Programmable UVLO with hysteresis | External resistor divider sets turn-on threshold; internal 20 µA current source provides clean hysteresis without extra components. |
| Intelligent peak current limit | Off-time scales with FB voltage and VIN - delivers full protection during short circuit while minimizing foldback in overload conditions. |
| Thermal shutdown with 20°C hysteresis | Shuts down at 165°C junction temperature and resumes at ~145°C, preventing thermal runaway in enclosed or high-ambient environments. |
Applications
| Isolated Telecom Bias Supply | Automotive Isolated Auxiliary Rail |
|---|---|
Use Scenario: Generating a stable 5 V or 12 V auxiliary bias rail from a 48 V telecom bus in a fly-buck converter, powering gate drivers and optocouplers in isolated half-bridge inverters. IC Role / Device Role / Timing Role: Secondary-side controller regulating isolated output; provides self-contained switching, sensing, and protection without opto-feedback loop. Use Value: Eliminates external Schottky and compensation components, reduces solution size by >30%, and achieves <5% output deviation across –40°C to 125°C. |
Use Scenario: Powering isolated CAN transceivers and microcontroller peripherals in 24 V/48 V commercial vehicle ECUs where primary-side regulation is unavailable or noisy. IC Role / Device Role / Timing Role: Standalone secondary-side bias IC; operates independently of primary controller timing; maintains regulation during input transients per ISO 7637-2. Use Value: Withstands 100 V load-dump pulses on VIN, delivers 100 mA at 5 V with <100 mV line regulation, and meets AEC-Q100 Grade 1 ambient requirements. |
| Industrial Isolated Sensor Interface | Medical Equipment Auxiliary Supply |
Use Scenario: Providing galvanically isolated 3.3 V power to analog front-end sensors in PLC I/O modules, fed from a 24 V or 48 V backplane. IC Role / Device Role / Timing Role: Isolated secondary regulator; uses transformer-coupled winding to derive VOUT; maintains CCM via synchronous rectification for low-noise analog bias. Use Value: Enables <10 µV RMS output noise with proper RC filtering; supports EN 61000-4-5 surge immunity up to 4 kV due to high-VIN ruggedness. |
Use Scenario: Delivering isolated 5 V/3.3 V bias to patient-connected monitoring circuits (e.g., ECG front-ends) in Class II medical devices using reinforced insulation. IC Role / Device Role / Timing Role: Safety-isolated secondary-side regulator; avoids reliance on primary-side feedback, simplifying creepage/clearance compliance. Use Value: Meets IEC 60601-1 2× MOPP requirements when paired with appropriately rated transformer; thermal shutdown prevents fault propagation under single-point failure. |
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 | Wide-input (3–65 V) buck regulator with integrated 500 mA FET; no secondary-side isolation capability; requires opto-feedback for isolation. | Designed for primary-side non-isolated step-down; lacks integrated high-side/low-side switch pairing for transformer-coupled topologies. | Select when designing non-isolated bias rails or when primary-side regulation suffices; not suitable as drop-in replacement for fly-buck secondary-side use. |
| UCC28740DR | Primary-side QR flyback controller with valley switching; no integrated secondary-side switches; relies on external MOSFETs and optocoupler feedback. | Targets cost-sensitive AC/DC adapters; adds complexity and latency vs. LM34925MR/NOPB's self-contained secondary regulation. | Choose for universal AC input designs; avoid when secondary-side simplicity, fast transient response, or Schottky elimination are critical. |
Compared with LM5165RUMX/NOPB and UCC28740DR, the LM34925MR/NOPB uniquely integrates both high- and low-side 100-V switches for transformer-coupled secondary regulation - delivering faster transient response, no opto-loop delay, and reduced component count in isolated DC-DC bias applications.
Availability
LM34925MR/NOPB is available at Aetrix Electronics and suitable for isolated telecom bias supply, automotive auxiliary rail, and industrial sensor interface applications requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.
Supply support for LM34925MR/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 LM34925MR/NOPB belongs to TI's isolated bias regulator product line, engineered specifically to simplify secondary-side power delivery in fly-buck, forward, and push-pull isolated DC-DC converters - targeting telecom, automotive, and industrial systems demanding compact, robust, and loop-compensation-free solutions.
FAQ
What is the recommended minimum on-time for stable operation of the LM34925MR/NOPB?
The LM34925MR/NOPB requires a minimum on-time greater than 100 ns at maximum input voltage (100 V) to ensure reliable switching and COT control stability. This is achieved by selecting an appropriate RON resistor value - for example, 250 kΩ yields ~370 ns at 75 V per datasheet test conditions. Operating below this threshold risks pulse skipping and regulation instability.
Can the LM34925MR/NOPB operate without an external bootstrap capacitor?
No - the LM34925MR/NOPB requires a 0.01 µF ceramic capacitor between BST and SW pins to sustain high-side gate drive voltage. The internal bootstrap diode charges this capacitor during the SW low phase; omitting it causes immediate high-side switch failure and loss of regulation. TI specifies X7R or better dielectric with tight tolerance and low ESR.
How does the LM34925MR/NOPB achieve constant frequency behavior despite using constant-on-time control?
The LM34925MR/NOPB achieves nearly constant frequency by making on-time inversely proportional to VIN (TON ∝ 1/VIN), while off-time is primarily determined by output ripple decay at FB. As VIN increases, on-time decreases proportionally - compensating for higher dI/dt and maintaining consistent switching periods across 7.5–100 V input, verified up to 1 MHz in typical applications.
What is the purpose of the 250 mV minimum ripple requirement at the FB pin of the LM34925MR/NOPB?
The 250 mV minimum ripple at the FB pin ensures monotonic decay of the feedback signal during the off-time - a fundamental requirement for stable COT control. Without sufficient resistive ripple (from COUT ESR), capacitive ripple dominates and violates the COT timing condition, causing subharmonic oscillation or erratic switching. An RC network may be added to meet this requirement.
Does the LM34925MR/NOPB support remote shutdown, and how is it implemented?
Yes - the LM34925MR/NOPB supports remote shutdown via the UVLO pin. Pulling UVLO below 0.66 V (e.g., with an open-drain transistor or microcontroller GPIO) forces the device into low-current shutdown mode (<225 µA). Hysteresis is provided internally via a 20 µA current source, eliminating need for external hysteresis components.
LM34925MR/NOPB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 8-PowerSOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- 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
LM34925MR/NOPB FAQ
1.How can I place an order for LM34925MR/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM34925MR/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 LM34925MR/NOPB reliable?
The price and inventory of LM34925MR/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM34925MR/NOPB is usually 5 days.
3.What payment methods are accepted for LM34925MR/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM34925MR/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM34925MR/NOPB?
LM34925MR/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM34925MR/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 LM34925MR/NOPB?
For technical support, including LM34925MR/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM34925MR/NOPB requirements.
6.How does Aetrix verify that LM34925MR/NOPB is sourced from the original manufacturer or authorized distributors?
All LM34925MR/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 LM34925MR/NOPB meets industry standards.
7.What is the process for return or replacement of LM34925MR/NOPB?
All LM34925MR/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM34925MR/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 LM34925MR/NOPB part is unused and in its original packaging.
Return procedure for LM34925MR/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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