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Texas Instruments LM34926MR/NOPB
- Part No.:
- LM34926MR/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- 8-PowerSOIC (0.154", 3.90mm Width)
- Datasheet:
-
LM34926MR/NOPB.pdf
- Description:
- IC REG BUCK ADJ 300MA 8SOPWR
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
LM34926MR/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, and operation across 7.5 V to 100 V input. It delivers regulated output voltage adjustable from 1.225 V via external resistor divider, includes precision 2% feedback reference, and supports up to 1 MHz switching frequency in telecom and industrial isolated bias supplies.
For engineers reviewing the LM34926MR/NOPB datasheet, LM34926MR/NOPB pinout, LM34926MR/NOPB application, or LM34926MR/NOPB equivalent, key selection criteria include its integrated 300-mA switches, no-loop-compensation COT architecture, programmable UVLO threshold, thermal shutdown at 165°C, and WSON-8 package with exposed thermal pad.
Technical Context
The LM34926MR/NOPB implements constant on-time (COT) control where on-time is inversely proportional to VIN and set by RON, enabling near-constant frequency across input voltage variations. 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), bootstrap gate drive for the high-side switch (requiring 0.01 µF BST–SW capacitor), and intelligent peak current limiting (575 mA typical) with off-time scaling based on FB voltage and VIN - ensuring robust short-circuit and overload protection without foldback degradation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 7.5 V to 100 V - enables 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; determines regulation accuracy and load/line transient response. |
| Switch RDS(ON) | Buck: 0.8–1.8 Ω; Sync: 0.45–1 Ω - defines conduction loss, thermal rise, and minimum achievable output voltage drop at full load. |
| Current Limit Threshold | 390–750 mA - provides peak-current-based short-circuit protection; off-time scales with FB voltage to minimize foldback during partial overloads. |
| VCC Regulator Output | 7.6 V (6.25–8.55 V) - powers internal gate drivers and logic; disables when externally supplied 8.55–13 V applied, reducing die dissipation at high VIN. |
| Thermal Shutdown | 165°C (20°C hysteresis) - forces reset state to prevent catastrophic failure; resumes operation only after junction cools to ~145°C. |
| Operating Junction Temp | –40°C to +125°C - specifies full performance envelope for industrial and automotive under-hood environments. |
Pinout & Package
The LM34926MR/NOPB is packaged in an 8-pin WSON (NGU) with 4.00 mm × 4.00 mm body and exposed thermal pad (EP) that must be soldered to RTN for optimal thermal performance (RθJA = 41.3°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 RTN | Ground reference | System ground return for all internal circuits; EP must be connected to this node for thermal and EMI integrity. |
| 2 VIN | Main power input | Accepts 7.5–100 V; supplies VCC regulator and high-voltage switch drains; requires local 10 µF+ ceramic input capacitor. |
| 3 UVLO | Undervoltage enable/disable | Resistor-divider programmable start-up threshold; pulled below 0.66 V forces shutdown; >1.225 V enables regulation. |
| 4 RON | On-time programming | Resistor to VIN sets COT duration; minimum 100 ns on-time required at max VIN to ensure stable switching. |
| 5 FB | Feedback sensing | Inverting input of regulation comparator; 1.225 V reference sets output voltage; requires ≥25 mV ripple for COT stability. |
| 6 VCC | Internal bias supply | 7.6 V output powering gate drivers; must be decoupled with 1.0 µF ceramic; UVLO at 4.5 V disables IC if undervolted. |
| 7 BST | Bootstrap supply | Charged from VCC through internal diode during SW low phase; drives high-side gate; requires 0.01 µF ceramic to SW. |
| 8 SW | Power switching node | Drain of high-side FET and source of sync FET; connects to inductor, BST capacitor, and transformer secondary winding in fly-buck topologies. |
Key Features
| Feature | Design Value |
|---|---|
| No loop compensation required | COT architecture eliminates external compensation network, reducing BOM count and design iteration time for isolated bias supplies. |
| Integrated high- and low-side switches | 100-V N-channel buck + sync FETs eliminate external MOSFETs and Schottky diodes, simplifying fly-buck and isolated secondary designs. |
| Adjustable UVLO with hysteresis | External resistor divider sets turn-on threshold; internal 20 µA current source adds hysteresis to prevent chatter during brownout conditions. |
| Ultra-fast transient response | COT control enables immediate on-time retriggering upon FB dip, delivering sub-microsecond recovery from load steps without phase-margin tuning. |
| Thermal and overvoltage protection | Dual safeguards: 165°C thermal shutdown with 20°C hysteresis and 1.62 V FB overvoltage cutoff prevent damage during fault conditions. |
Applications
| Isolated Telecom Bias Supply | Automotive Domain Controller Bias |
|---|---|
Use Scenario: Generating isolated 5 V or 12 V auxiliary bias from a 48 V telecom bus to power gate drivers, optocouplers, and monitoring ICs in AC/DC front-end PSUs. IC Role / Device Role / Timing Role: Secondary-side synchronous buck controller implementing fly-buck topology; regulates output using transformer-coupled energy transfer and COT timing. Use Value: Eliminates need for separate isolated bias IC or discrete MOSFETs, reducing solution size by >30% while maintaining <2% output regulation across –40°C to +85°C. | Use Scenario: Providing isolated 3.3 V bias to microcontroller and CAN transceiver in 12 V/24 V automotive domain controllers with strict EMC and thermal constraints. IC Role / Device Role / Timing Role: High-voltage secondary regulator operating from transformer secondary winding; uses COT control to maintain stable 500 kHz switching under wide input transients (ISO 7637-2 pulses). Use Value: Withstands 100 V load-dump surges on primary side; integrated switches and thermal shutdown ensure reliability in under-hood environments up to 125°C junction temperature. |
| Industrial PLC I/O Module Bias | Medical Isolated Sensor Interface |
Use Scenario: Delivering isolated 5 V/3.3 V bias to analog front-ends and digital isolators in programmable logic controller (PLC) I/O modules requiring reinforced isolation per IEC 61000-4-5. IC Role / Device Role / Timing Role: Secondary-side regulator in fly-buck configuration; leverages transformer turns ratio and RON resistor to fix switching frequency near 750 kHz for predictable EMI filtering. Use Value: Achieves >85% efficiency at 100 mA load with 24 V input; programmable UVLO prevents false start-up during brownouts common in factory floor power distribution. | Use Scenario: Powering isolated ADCs, amplifiers, and digital isolators in patient-connected medical sensors requiring 4 kV reinforced isolation and low leakage. IC Role / Device Role / Timing Role: Low-noise secondary bias generator; operates in CCM mode via synchronous rectification to avoid discontinuous-mode noise injection into sensitive analog paths. Use Value: Synchronous rectification maintains continuous inductor current even at light loads (<1 mA), eliminating burst-mode switching noise that could corrupt sub-µV biomedical signals. |
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 |
|---|---|---|---|
| LM5160QPWPRQ1 | Wider 3–65 V input; integrated 1.5-A FETs; requires external compensation; no BST pin - uses integrated charge pump. | Designed for primary-side regulation in automotive; lacks dedicated secondary-side fly-buck optimization and UVLO programmability. | Prefer LM34926MR/NOPB for transformer-coupled secondary bias where COT stability, UVLO flexibility, and BST-driven high-side gate are critical. |
| UCC28740DR | Primary-side QR flyback controller; no integrated switches; requires external MOSFET and optocoupler feedback; supports <100 mW output. | Targets ultra-low-power isolated supplies; not suitable for >500 mW secondary bias due to lack of integrated power stage. | Choose LM34926MR/NOPB when >500 mW isolated bias is needed with minimal component count and no optocoupler dependency. |
Compared with LM5160QPWPRQ1 and UCC28740DR, the LM34926MR/NOPB uniquely combines secondary-side placement, integrated dual 100-V switches, COT control for zero-compensation design, and programmable UVLO - making it the only option optimized for efficient, compact, transformer-coupled bias generation in high-reliability isolated systems.
Availability
LM34926MR/NOPB is available at Aetrix Electronics and suitable for isolated telecom bias supply, automotive domain controller power, and industrial PLC I/O module designs requiring stable component supply across extended temperature and high-voltage operating conditions.
Supply support for LM34926MR/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 technologies, with leadership in high-reliability industrial and automotive power solutions.
The LM34926MR/NOPB belongs to TI's isolated DC-DC bias regulator product line, engineered specifically to simplify secondary-side power delivery in fly-buck and transformer-coupled topologies while eliminating external Schottky diodes and loop compensation components.
FAQ
What is the recommended minimum on-time for stable operation of the LM34926MR/NOPB?
The LM34926MR/NOPB requires a minimum on-time of 100 ns at maximum input voltage (100 V) to ensure reliable COT control and stable switching. This is enforced by selecting RON such that TON = K × RON / VIN remains ≥100 ns across the full VIN range. For example, at VIN = 100 V, RON must be ≥250 kΩ to meet this requirement. Violating this causes pulse-skipping and regulation instability.
Does the LM34926MR/NOPB require an external Schottky diode in fly-buck configurations?
No, the LM34926MR/NOPB does not require an external Schottky diode because it integrates both a high-side buck switch and a low-side synchronous rectifier MOSFET. The synchronous rectification eliminates conduction losses associated with Schottky diodes and enables continuous conduction mode (CCM) operation across all load conditions - a key advantage for noise-sensitive isolated bias applications.
How is the output voltage set on the LM34926MR/NOPB, and what tolerance does it achieve?
The output voltage of the LM34926MR/NOPB is set using an external resistor divider (RFB1 and RFB2) connected to the FB pin, where VOUT = 1.225 V × (1 + RFB1/RFB2). The internal 1.225 V reference has ±2% initial tolerance over temperature, and total output regulation error - including resistor tolerance and layout effects - typically stays within ±3% across line, load, and temperature when using 1% resistors and proper PCB layout.
Can the LM34926MR/NOPB operate with an externally supplied VCC voltage?
Yes, the LM34926MR/NOPB supports external VCC biasing between 8.55 V and 13 V, which disables the internal 7.6 V VCC regulator. This reduces power dissipation in high-input-voltage applications (e.g., 75 V–100 V), improves overall efficiency, and avoids thermal derating. When externally powered, the VCC pin must be bypassed with a 1.0 µF ceramic capacitor, and the internal regulator remains inactive as long as external voltage exceeds 8.55 V.
What is the purpose of the RON pin on the LM34926MR/NOPB, and how is it used?
The RON pin on the LM34926MR/NOPB sets the switch on-time duration via an external resistor connected between RON and VIN. Because on-time is inversely proportional to VIN (TON = K × RON / VIN), this resistor allows designers to fix the nominal switching frequency across the input voltage range - for example, selecting RON = 100 kΩ yields ~750 kHz at VIN = 48 V. RON also directly impacts light-load efficiency and minimum output voltage capability.
LM34926MR/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:
- 300mA
- 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
LM34926MR/NOPB FAQ
1.How can I place an order for LM34926MR/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM34926MR/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 LM34926MR/NOPB reliable?
The price and inventory of LM34926MR/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM34926MR/NOPB is usually 5 days.
3.What payment methods are accepted for LM34926MR/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM34926MR/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM34926MR/NOPB?
LM34926MR/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM34926MR/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 LM34926MR/NOPB?
For technical support, including LM34926MR/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM34926MR/NOPB requirements.
6.How does Aetrix verify that LM34926MR/NOPB is sourced from the original manufacturer or authorized distributors?
All LM34926MR/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 LM34926MR/NOPB meets industry standards.
7.What is the process for return or replacement of LM34926MR/NOPB?
All LM34926MR/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM34926MR/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 LM34926MR/NOPB part is unused and in its original packaging.
Return procedure for LM34926MR/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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