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Texas Instruments LM34925SD/NOPB
- Part No.:
- LM34925SD/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- 8-WDFN Exposed Pad
- Datasheet:
-
LM34925SD/NOPB.pdf
- Description:
- IC REG BUCK ADJ 100MA 8WSON
- Quantity:
- Payment:
- Shipping:
Inventory:2,586
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Product details
Overview
LM34925SD/NOPB from Texas Instruments is a high-voltage, integrated secondary-side bias regulator for isolated DC-DC converters, featuring dual 100-V N-channel MOSFETs (high-side buck and low-side synchronous switches), 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 transformer-coupled topologies.
For engineers reviewing the LM34925SD/NOPB datasheet, LM34925SD/NOPB pinout, LM34925SD/NOPB application, or LM34925SD/NOPB equivalent, key selection criteria include its integrated dual-switch architecture, UVLO programmability via external resistor divider, bootstrap gate drive implementation, thermal shutdown at 165°C, and compatibility with isolated telecom and automotive auxiliary rail designs.
Technical Context
The LM34925SD/NOPB implements a constant-on-time (COT) control scheme where on-time is inversely proportional to VIN and set by an external RON resistor - 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 7.6 V internal VCC regulator (with 4.5 V UVLO and 26 mA current limit), a bootstrap capacitor charging path (BST–SW, requiring 0.01 µF ceramic), and intelligent peak-current limiting (270 mA typical threshold) with adaptive off-time inversely proportional to VFB and VIN - 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, 24/48 V industrial, and 12–96 V automotive bus rails without pre-regulation. |
| Feedback Reference | 1.225 V ±2% - sets output voltage accuracy via external RFB1/RFB2 divider; enables stable regulation down to ~1.23 V. |
| Switch RDS(ON) | Buck switch: 0.8–1.8 Ω; Sync switch: 0.45–1 Ω - defines conduction loss and thermal budget at full load in continuous conduction mode. |
| Current Limit Threshold | 150–370 mA - peak-limited protection with adaptive off-time ensures safe short-circuit operation up to 100 V input. |
| VCC Regulator Output | 7.6 V (6.25–8.55 V) - powers internal gate drivers and logic; self-biased from VIN; disables when externally supplied 8.55–13 V applied. |
| Thermal Shutdown | 165°C (±5°C) with 20°C hysteresis - prevents catastrophic failure; resumes operation at ~145°C after cooling. |
| UVLO Threshold | 1.225 V rising (UVLO pin); 0.66 V falling - enables programmable startup voltage via resistor divider from VIN to RTN. |
Pinout & Package
LM34925SD/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; must connect exposed pad to RTN for thermal and EMI integrity. |
| 2 VIN | Main power input | High-voltage input (7.5–100 V); supplies VCC regulator and switch drivers; requires local 100 nF + 10 µF input capacitance. |
| 3 UVLO | Undervoltage enable control | Resistor-divider input to set startup threshold; 0.66 V shutdown, 1.225 V enable; internal 20 µA hysteresis current source. |
| 4 RON | On-time programming | Connects to VIN via resistor to set minimum on-time (≥100 ns at max VIN); determines operating frequency (up to 1 MHz). |
| 5 FB | Feedback sensing | Inverting input of regulation comparator; 1.225 V reference; requires ≥250 mV ripple for COT stability; RC network may be needed for low-ESR caps. |
| 6 VCC | Internal bias supply output | 7.6 V regulated output for gate drivers; requires 1 µF ceramic decoupling; UVLO at 4.5 V disables IC if undervolted. |
| 7 BST | Bootstrap supply node | Charged from VCC through internal diode during SW low phase; powers high-side driver; needs 0.01 µF ceramic to SW. |
| 8 SW | Power switching node | Drives external inductor; connects to BST cap and output filter; withstands VIN + 0.3 V transient; critical for EMI layout. |
Key Features
| Feature | Design Value |
|---|---|
| No loop compensation required | COT architecture eliminates external compensation components, reducing BOM count and design iteration time for isolated bias rails. |
| Integrated dual N-channel switches | Eliminates external high-voltage MOSFETs and Schottky diodes - simplifies fly-buck transformer secondary-side design and improves efficiency. |
| Programmable UVLO and shutdown | External resistor divider on UVLO pin allows precise input voltage turn-on/off thresholds - essential for brownout immunity in automotive and telecom systems. |
| Intelligent peak current limit | Adaptive off-time scaling with VFB and VIN reduces foldback during overload - maintains faster recovery and stable start-up under varying loads. |
| Thermal shutdown with hysteresis | 165°C trip with 20°C hysteresis ensures reliable fault recovery without oscillation - critical for unattended operation in industrial power modules. |
Applications
| Isolated Telecom Bias Supply | Automotive Auxiliary Rail |
|---|---|
Use Scenario: Generating isolated 5 V or 12 V bias for gate drivers, optocouplers, and control ICs in 48 V telecom rectifier modules. IC Role / Device Role / Timing Role: Secondary-side synchronous buck controller regulating transformer-coupled winding output; provides stable, low-noise bias independent of primary-side regulation. Use Value: Eliminates discrete high-voltage MOSFETs and Schottky diodes - reduces solution size by >30% and improves efficiency by 5–8% vs. diode-rectified fly-buck. | Use Scenario: Powering CAN transceivers, sensor interfaces, and microcontrollers from 12 V or 24 V battery rails in ADAS domain controllers. IC Role / Device Role / Timing Role: Isolated auxiliary regulator delivering clean, regulated 3.3 V or 5 V from main DC-DC converter secondary windings. Use Value: Wide 7.5–100 V input range accommodates cold-crank (6.5 V) to load-dump (100 V) transients without external protection - enhancing system robustness. |
| Industrial Isolated I/O Module | Medical Equipment Auxiliary Power |
Use Scenario: Providing galvanically isolated 5 V/3.3 V rails for digital isolators and ADC front-ends in PLC analog input modules. IC Role / Device Role / Timing Role: Secondary-side bias regulator referenced to isolated ground; operates with transformer-coupled feedback for reinforced insulation. Use Value: Integrated synchronous rectification maintains CCM at light loads - avoids subharmonic oscillation and ensures predictable EMI profile for EMC compliance. | Use Scenario: Generating patient-isolated 5 V bias for monitoring sensors and communication interfaces in portable ultrasound or infusion pumps. IC Role / Device Role / Timing Role: Compact, thermally efficient secondary-side regulator meeting 2×MOPP creepage/clearance requirements via transformer isolation. Use Value: 8-pin WSON package with exposed pad enables <15°C/W junction-to-board thermal resistance - meets stringent temperature rise limits in sealed enclosures. |
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 |
|---|---|---|---|
| LM5165DRCT | Wider 3–65 V input; no integrated low-side switch; requires external sync FET; 600 kHz max frequency. | Suitable for non-isolated or transformer-fed primary-side bias; lacks secondary-side synchronous rectification. | Select when primary-side regulation is preferred or when lower input voltage (<7.5 V) is required. |
| UCC28740DR | PSR flyback controller; no integrated power switches; requires external HV MOSFET and diode; 100 kHz fixed frequency. | Designed for transformer-isolated output with primary-side sensing; higher component count but better cross-regulation. | Select when tight multi-output cross-regulation or lower standby power (<30 mW) is critical. |
Compared with LM34925SD/NOPB, LM5165DRCT offers broader low-voltage support but requires external FETs and lacks secondary-side integration; UCC28740DR achieves tighter output tolerance via PSR but increases bill-of-materials and layout complexity - making LM34925SD/NOPB optimal for cost-sensitive, space-constrained isolated bias rails needing minimal external components.
Availability
LM34925SD/NOPB is available at Aetrix Electronics and suitable for isolated telecom bias supply, automotive auxiliary rail, and industrial I/O module designs requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.
Supply support for LM34925SD/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 LM34925SD/NOPB belongs to TI's isolated bias regulator product line, engineered specifically for simplified, high-efficiency secondary-side power delivery in fly-buck, forward, and push-pull converter topologies used in telecom, automotive, and industrial systems.
FAQ
What is the recommended minimum on-time for LM34925SD/NOPB and how is it set?
The LM34925SD/NOPB requires a minimum on-time ≥100 ns at maximum input voltage (100 V) for stable COT operation. This is set using the RON resistor between VIN and the RON pin, with values selected per the TON = K × RON/VIN equation (K = 9×10−11). For example, at 100 V input, RON ≈ 250 kΩ yields ~370 ns on-time - ensuring reliable switching and avoiding pulse-skipping.
Does LM34925SD/NOPB require an external Schottky diode?
No, LM34925SD/NOPB does not require an external Schottky diode. It integrates both a high-side buck N-channel MOSFET and a low-side synchronous N-channel MOSFET, enabling fully synchronous rectification. This eliminates conduction losses associated with Schottky diodes and improves efficiency - especially at light loads - while simplifying PCB layout and reducing component count.
How is the output voltage programmed on LM34925SD/NOPB?
The output voltage of LM34925SD/NOPB is programmed using two external resistors (RFB1 and RFB2) forming a voltage divider from VOUT to RTN, connected to the FB pin. The regulation equation is VOUT = 1.225 V × (1 + RFB1/RFB2). For example, RFB2 = 10 kΩ and RFB1 = 39 kΩ yields VOUT ≈ 12 V. The FB pin bias current is only 60 nA, minimizing divider error.
What thermal considerations apply to LM34925SD/NOPB in WSON-8 package?
LM34925SD/NOPB in WSON-8 has RθJA = 41.3°C/W and RθJCbot = 3.2°C/W. To maintain TJ ≤125°C at full load, the PCB must provide adequate copper area under the exposed pad (connected to RTN) and minimize thermal resistance to ambient. Derating is required above 85°C ambient; thermal shutdown activates at 165°C with 20°C hysteresis to prevent damage.
Can LM34925SD/NOPB operate with an externally supplied VCC?
Yes, LM34925SD/NOPB can operate with an externally supplied VCC. When a voltage between 8.55 V and 13 V is applied to the VCC pin, the internal high-voltage linear regulator is disabled - reducing power dissipation and improving efficiency at high input voltages (e.g., 75–100 V). External VCC must be well-regulated and bypassed with ≥1 µF ceramic capacitance.
LM34925SD/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)
LM34925SD/NOPB FAQ
1.How can I place an order for LM34925SD/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM34925SD/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 LM34925SD/NOPB reliable?
The price and inventory of LM34925SD/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM34925SD/NOPB is usually 5 days.
3.What payment methods are accepted for LM34925SD/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM34925SD/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM34925SD/NOPB?
LM34925SD/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM34925SD/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 LM34925SD/NOPB?
For technical support, including LM34925SD/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM34925SD/NOPB requirements.
6.How does Aetrix verify that LM34925SD/NOPB is sourced from the original manufacturer or authorized distributors?
All LM34925SD/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 LM34925SD/NOPB meets industry standards.
7.What is the process for return or replacement of LM34925SD/NOPB?
All LM34925SD/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM34925SD/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 LM34925SD/NOPB part is unused and in its original packaging.
Return procedure for LM34925SD/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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