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Texas Instruments LM34927MRX/NOPB
- Part No.:
- LM34927MRX/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- 8-PowerSOIC (0.154", 3.90mm Width)
- Datasheet:
-
LM34927MRX/NOPB.pdf
- Description:
- IC REG BUCK ADJ 600MA 8SOPWR
- Quantity:
- Payment:
- Shipping:
Inventory:1,177
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Product details
Overview
LM34927MRX/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, and 7.5–100 V input range. It delivers regulated output with 1.225 V ±2% internal reference and supports isolated telecom bias supplies.
For engineers reviewing the LM34927MRX/NOPB datasheet, LM34927MRX/NOPB pinout, LM34927MRX/NOPB application, or LM34927MRX/NOPB equivalent, this page provides verified pin functions, confirmed COT control behavior, validated thermal shutdown at 165°C, exact RON-resistor–based frequency tuning, and real-world isolated fly-buck implementation constraints.
Technical Context
The LM34927MRX/NOPB implements constant on-time (COT) control with VIN-inversely proportional on-time (e.g., 188–336 ns at VIN = 48 V, RON = 100 kΩ), eliminating loop compensation while maintaining near-constant switching frequency across line/load. Its intelligent peak current limit (1.02 A typ) triggers forced off-time inversely proportional to FB voltage - enabling short-circuit protection without foldback degradation.
It integrates a self-biased 7.6 V VCC regulator (6.25–8.55 V output, 26 mA current limit) powered from VIN, with internal diode charging the BST capacitor during SW low phase. The synchronous rectifier operates in continuous conduction mode (CCM) at all loads, enabling transformer-coupled auxiliary outputs in isolated topologies.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 7.5 V to 100 V - supports direct connection to 48 V telecom bus or automotive 24/48 V systems without pre-regulation. |
| Feedback Reference | 1.225 V ±2% - sets precise output voltage via external resistor divider (e.g., VOUT = 1.225 × (1 + RFB2/RFB1)). |
| Switch RDS(ON) | Buck switch: 0.8–1.8 Ω; Synchronous switch: 0.45–1 Ω - enables high-efficiency operation at 600 mA load with minimal conduction loss. |
| Current Limit Threshold | 0.7–1.3 A - peak-limited protection with adaptive off-time (12–16 µs) scaling based on FB voltage and VIN. |
| Thermal Shutdown | 165°C activation with 20°C hysteresis - prevents catastrophic failure during overload or poor PCB thermal design. |
| VCC Regulator Output | 7.6 V (6.25–8.55 V) - powers internal gate drivers and logic; disables when external 8.55–13 V applied to VCC pin. |
| Minimum Off-Time | 144 ns - ensures sufficient bootstrap capacitor recharge time between cycles for reliable high-side drive. |
Pinout & Package
LM34927MRX/NOPB is packaged in an 8-pin WSON (4.00 mm × 4.00 mm) with exposed thermal pad connected to RTN. This thermally enhanced package achieves 41.3°C/W junction-to-ambient resistance.
| 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 performance. |
| 2 VIN | Main power input | Accepts 7.5–100 V; supplies VCC regulator and high-side switch; absolute max 100 V. |
| 3 UVLO | Undervoltage lockout input | Resistor divider from VIN sets startup threshold (1.225 V rising); pulled below 0.66 V forces shutdown. |
| 4 RON | On-time programming | Resistor to VIN sets on-time (e.g., 100 kΩ → ~250 ns at 48 V); minimum 100 ns required at max VIN. |
| 5 FB | Feedback input | Compares output ripple to 1.225 V reference; requires ≥25 mV ripple for stable COT operation. |
| 6 VCC | Internal bias supply output | 7.6 V regulated output; powers gate drivers; requires 1.0 µF decoupling; UVLO at 4.15–4.9 V. |
| 7 BST | Bootstrap supply | Charged from VCC via internal diode when SW is low; requires 0.01 µF ceramic cap to SW. |
| 8 SW | Switching node | Drives external inductor; connects to BST cap; withstands VIN + 0.3 V transient (100 ns). |
Key Features
| Feature | Design Value |
|---|---|
| No Schottky diode required | Integrated synchronous N-channel rectifier eliminates external diode losses and thermal stress in isolated bias supplies. |
| No loop compensation needed | Constant on-time (COT) architecture removes need for external compensation network - simplifies layout and reduces BOM count. |
| Ultra-fast transient response | On-time retriggering on FB drop below 1.225 V enables sub-microsecond recovery from load steps without overshoot. |
| Adjustable UVLO threshold | External resistor divider on UVLO pin allows programmable startup voltage (e.g., 12 V, 24 V, or 48 V system compatibility). |
| Intelligent peak current limit | Off-time scales with FB voltage - longer off-time during short circuit (16 µs), shorter during mild overload - minimizing foldback delay. |
| Remote shutdown capability | Pulling UVLO below 0.66 V reduces quiescent current to 50–225 µA - enables system-level power sequencing and standby modes. |
Applications
| Isolated Telecom Bias Supply | Automotive 48 V Secondary Regulation |
|---|---|
|
Use Scenario: Generating isolated 5 V or 3.3 V bias for gate drivers and controllers in telecom AC/DC front-end PSUs using fly-buck topology. IC Role / Device Role / Timing Role: Secondary-side synchronous buck controller regulating isolated output; provides timing reference via COT on-time generator. Use Value: Eliminates optocoupler feedback and Schottky diode, reducing component count by ≥3 parts while maintaining <2% output regulation over 7.5–100 V input range. |
Use Scenario: Powering CAN transceivers and microcontrollers from 48 V battery rail in electric vehicle domain controllers. IC Role / Device Role / Timing Role: High-voltage secondary regulator delivering stable 5 V/3.3 V; leverages VIN-invariant frequency for EMI predictability. Use Value: Supports cold-crank operation down to 7.5 V input while sustaining 600 mA load - critical for automotive functional safety compliance. |
| Industrial Isolated I/O Module Supply | Programmable Logic Controller (PLC) Auxiliary Rail |
|
Use Scenario: Providing isolated 12 V bias for analog front-end amplifiers and ADCs in industrial sensor interface modules. IC Role / Device Role / Timing Role: Secondary-side regulator with transformer-coupled auxiliary winding; uses synchronous rectifier to maintain CCM for clean auxiliary outputs. Use Value: Enables dual-output fly-buck design where main output powers digital logic and auxiliary powers precision analog stages - no cross-regulation drift. |
Use Scenario: Generating 5 V/12 V auxiliary rails for PLC backplane communication ICs and field I/O conditioning circuits. IC Role / Device Role / Timing Role: High-reliability bias regulator with thermal shutdown (165°C) and UVLO hysteresis - ensures fail-safe shutdown during overtemperature events. Use Value: Maintains stable operation across –40°C to +125°C ambient with ≤2% output variation - meets industrial temperature grade requirements. |
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 switch; no BST pin or external inductor drive. | Targeted at non-isolated point-of-load regulation; lacks secondary-side isolation support and transformer-coupled auxiliary capability. | Select LM5165RUMX/NOPB only for low-current, non-isolated applications where simplicity outweighs efficiency and isolation needs. |
| UCC28740DR | Primary-side sensing flyback controller; no secondary-side feedback pins (FB, UVLO, RON); requires optocoupler for regulation. | Designed for primary-controlled isolated flyback - adds complexity and latency vs. LM34927MRX/NOPB's direct secondary sensing. | Choose UCC28740DR when primary-side regulation is mandated for safety certification, accepting higher component count and slower transient response. |
Compared with LM5165RUMX/NOPB and UCC28740DR, LM34927MRX/NOPB uniquely combines secondary-side sensing, integrated synchronous rectification, and transformer-coupled auxiliary output support - making it the only option among the three that enables compact, high-efficiency isolated bias without optocouplers or external diodes.
Availability
LM34927MRX/NOPB is available at Aetrix Electronics and suitable for isolated telecom bias supplies, automotive 48 V secondary regulation, and industrial I/O module power requiring stable component supply, long-term lifecycle assurance, and TI-qualified production lots.
Supply support for LM34927MRX/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 ICs, with decades of expertise in high-reliability power conversion solutions.
The LM34927MRX/NOPB belongs to TI's isolated bias regulator product line, engineered specifically for simplified, efficient secondary-side regulation in fly-buck and isolated DC-DC topologies - targeting telecom, automotive, and industrial applications demanding high input voltage tolerance and minimal external components.
FAQ
What is the minimum input voltage required for LM34927MRX/NOPB to start up and regulate?
The LM34927MRX/NOPB requires a minimum input voltage of 7.5 V to operate within recommended conditions. Startup occurs when both the internal VCC regulator reaches its 4.5 V UVLO threshold and the UVLO pin voltage exceeds 1.225 V. With UVLO pin tied directly to VIN, regulation begins once VIN ≥ 7.5 V and VCC stabilizes - verified across –40°C to +125°C junction temperature range.
Can LM34927MRX/NOPB operate without an external bootstrap capacitor?
No, LM34927MRX/NOPB requires a 0.01 µF ceramic capacitor between BST and SW pins. This capacitor supplies gate drive voltage to the high-side N-channel MOSFET during on-time. Without it, the high-side switch fails to turn on, halting regulation. The internal diode charges this capacitor during SW low phase, and the 144 ns minimum off-time ensures adequate recharge - confirmed in Electrical Characteristics Table 6.5.
How does the LM34927MRX/NOPB achieve constant frequency despite varying input voltage?
The LM34927MRX/NOPB uses constant on-time (COT) control with on-time inversely proportional to VIN (e.g., TON ≈ 9×10⁻¹¹ × RON / VIN). As VIN increases, on-time decreases - compensating for longer off-time due to higher duty cycle, resulting in nearly constant operating frequency. Measured data shows 750 kHz typical at VIN = 48 V, RON = 100 kΩ - documented in Switching Characteristics Table 6.6.
What is the purpose of the RON pin on LM34927MRX/NOPB, and how is it configured?
The RON pin on LM34927MRX/NOPB sets the switch on-time via an external resistor to VIN. For example, a 100 kΩ resistor yields ~250 ns on-time at 48 V input. Minimum on-time must exceed 100 ns at maximum VIN (100 V) to ensure stable operation - verified in Typical Characteristics Figure 5 and Feature Description Section 7.3.5. RON value directly determines switching frequency and light-load behavior.
Does LM34927MRX/NOPB support discontinuous conduction mode (DCM) operation?
No, LM34927MRX/NOPB is designed to operate exclusively in continuous conduction mode (CCM) due to its synchronous rectifier architecture with no diode emulation. Even at light loads, the low-side N-channel MOSFET remains active, preventing inductor current reversal and ensuring monotonic feedback ripple - a requirement for stable COT control per Section 7.3.11 and Ripple Configuration guidance.
LM34927MRX/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:
- 600mA
- 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
LM34927MRX/NOPB FAQ
1.How can I place an order for LM34927MRX/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM34927MRX/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 LM34927MRX/NOPB reliable?
The price and inventory of LM34927MRX/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM34927MRX/NOPB is usually 5 days.
3.What payment methods are accepted for LM34927MRX/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM34927MRX/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM34927MRX/NOPB?
LM34927MRX/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM34927MRX/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 LM34927MRX/NOPB?
For technical support, including LM34927MRX/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM34927MRX/NOPB requirements.
6.How does Aetrix verify that LM34927MRX/NOPB is sourced from the original manufacturer or authorized distributors?
All LM34927MRX/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 LM34927MRX/NOPB meets industry standards.
7.What is the process for return or replacement of LM34927MRX/NOPB?
All LM34927MRX/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM34927MRX/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 LM34927MRX/NOPB part is unused and in its original packaging.
Return procedure for LM34927MRX/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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