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Texas Instruments LM34927SD/NOPB
- Part No.:
- LM34927SD/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- 8-WDFN Exposed Pad
- Datasheet:
-
LM34927SD/NOPB.pdf
- Description:
- IC REG BUCK ADJ 600MA 8WSON
- Quantity:
- Payment:
- Shipping:
Inventory:974
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Product details
Overview
LM34927SD/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 + low-side synchronous switch), constant on-time (COT) control, and 7.5–100 V input range. It delivers adjustable output voltage starting at 1.225 V with ±2% feedback reference accuracy and supports up to 1 MHz switching frequency in telecom and industrial isolated bias applications.
For engineers reviewing the LM34927SD/NOPB datasheet, LM34927SD/NOPB pinout, LM34927SD/NOPB application, or LM34927SD/NOPB equivalent, key selection considerations include its COT architecture eliminating loop compensation, intelligent peak current limit (1.02 A typ), programmable UVLO threshold, thermal shutdown (165°C), and dual-package availability (WSON-8 and SO PowerPAD-8).
Technical Context
The LM34927SD/NOPB implements constant on-time (COT) control with on-time inversely proportional to VIN - enabling near-constant operating frequency across 7.5–100 V input and load variations. Its internal 7.6-V VCC regulator powers gate drivers and logic, while an external BST capacitor (0.01 µF ceramic) enables high-side N-MOSFET drive via bootstrap topology.
Regulation relies on a precision 1.225-V internal reference compared against FB voltage; overvoltage protection triggers at 1.62 V. Current limiting uses forced off-time inversely proportional to VFB, delivering short-circuit robustness with adaptive foldback reduction - minimum off-time fixed at 144 ns to ensure BST capacitor recharge.
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 and automotive HV systems without pre-regulation. |
| Feedback Reference | 1.225 V ±2% - sets precise output voltage via external RFB1/RFB2 divider; enables stable regulation down to 1.225 V. |
| Switch RDS(on) | Buck: 0.8–1.8 Ω; Sync: 0.45–1.0 Ω - low conduction loss enables high efficiency in isolated fly-buck and bias supply topologies. |
| Current Limit Threshold | 0.7–1.3 A (typ 1.02 A) - peak-limited protection with adaptive off-time prevents thermal runaway during overload/short. |
| Operating Frequency | Adjustable up to 1 MHz via RON resistor - higher frequency allows smaller magnetics and faster transient response. |
| VCC Regulator Output | 7.6 V (6.25–8.55 V) - self-biases internal circuitry; disables when external 8.55–13 V applied, reducing dissipation at high VIN. |
| Thermal Shutdown | 165°C with 20°C hysteresis - protects die integrity during sustained overload or poor PCB thermal design. |
Pinout & Package
LM34927SD/NOPB is available in two thermally enhanced packages: 8-pin WSON (4.00 mm × 4.00 mm) and 8-pin SO PowerPAD™ (4.89 mm × 3.90 mm). Both require exposed pad soldered to RTN for optimal thermal performance (RθJCbot = 3.2°C/W for WSON, 2.4°C/W for SO PowerPAD).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 RTN | Ground reference | System ground return for all internal circuits; exposed pad must be connected to RTN for thermal and electrical integrity. |
| 2 VIN | Main power input | Accepts 7.5–100 V; supplies VCC regulator and high-voltage gate drivers; no external pre-regulator needed. |
| 3 UVLO | Undervoltage enable/disable | Resistor-divider programmable startup 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 duration; minimum 100 ns required at max VIN to ensure stable operation and frequency control. |
| 5 FB | Feedback input | Compares output voltage (via RFB1/RFB2) to 1.225-V reference; also monitors overvoltage (1.62 V trip) and initiates immediate switch-off. |
| 6 VCC | Internal bias supply | 7.6-V regulated output powers gate drivers and logic; requires 1.0-µF decoupling; UVLO at 4.15–4.9 V disables IC if undervolted. |
| 7 BST | Bootstrap supply | Charged by VCC through internal diode during SW low phase; drives high-side N-MOSFET gate via external 0.01-µF ceramic capacitor. |
| 8 SW | Power switching node | Connects to inductor and BST capacitor; handles full switching current; voltage swings from RTN to VIN during operation. |
Key Features
| Feature | Design Value |
|---|---|
| No loop compensation required | COT control eliminates need for external compensation network - simplifies design, reduces BOM count, and improves transient immunity. |
| No Schottky diode needed | Integrated synchronous rectifier replaces external freewheeling diode - reduces conduction loss, improves efficiency, and eliminates reverse recovery issues. |
| Ultra-fast transient response | On-time triggered directly by FB voltage drop below 1.225 V - enables sub-microsecond reaction to load steps without phase-margin tuning. |
| Intelligent peak current limit | Off-time scales inversely with FB voltage - shorter off-time under mild overload speeds recovery; longer off-time during short-circuit ensures safe operation. |
| Remote shutdown capability | UVLO pin pulled below 0.66 V forces low-current shutdown mode (IIN ≤ 225 µA) - enables system-level power sequencing and fault isolation. |
| Thermally optimized packaging | Exposed-pad WSON-8 and SO PowerPAD-8 packages deliver RθJA ≤ 41.3°C/W - supports >2 W continuous output in compact layouts without heatsinks. |
Applications
| Isolated Telecom Bias Supply | Automotive High-Voltage Auxiliary Rail |
|---|---|
|
Use Scenario: Generating isolated 5-V/3.3-V bias for digital isolators and gate drivers in 48-V telecom rectifier modules. IC Role / Device Role / Timing Role: Secondary-side synchronous buck controller regulating auxiliary rail from transformer-coupled winding; operates at 500 kHz with COT stability. Use Value: Eliminates optocoupler feedback loop and external Schottky diode - reduces component count by ≥4 parts and improves efficiency by 3–5% vs diode-based solutions. |
Use Scenario: Providing isolated 12-V bias for CAN transceivers and microcontrollers in 48-V mild-hybrid vehicle ECUs. IC Role / Device Role / Timing Role: Secondary-side bias regulator powered from fly-buck transformer secondary; withstands load-dump transients up to 100 V. Use Value: Wide 7.5–100 V input range tolerates battery voltage spikes; thermal shutdown (165°C) ensures reliability in under-hood environments. |
| Industrial Isolated Sensor Interface | Programmable Logic Controller (PLC) Auxiliary Power |
|
Use Scenario: Delivering isolated 3.3-V power to analog front-end ADCs and isolated RS-485 transceivers in factory automation I/O modules. IC Role / Device Role / Timing Role: Secondary-side regulator deriving bias from main DC-DC converter's auxiliary winding; configured for 3.3 V output with 1.225-V reference. Use Value: Precision 2% feedback reference ensures stable ADC reference voltage; COT control maintains regulation during rapid sensor sampling bursts. |
Use Scenario: Generating isolated 5-V/12-V rails for CPU, FPGA, and I/O conditioning in modular PLC backplanes with 24–60 V DC input. IC Role / Device Role / Timing Role: Integrated bias controller replacing discrete MOSFETs, drivers, and error amplifiers in fly-buck-derived auxiliary supplies. Use Value: Dual N-MOSFET integration reduces layout area by 40%; programmable RON enables frequency optimization for EMI compliance in noisy industrial settings. |
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 | Wide-input (3–65 V), single-channel buck; no integrated synchronous FET; requires external low-side MOSFET and diode. | Lacks secondary-side isolation support; not designed for transformer-coupled bias; suited for primary-side non-isolated step-down. | Choose LM5165DRCT only when isolation is unnecessary and external FETs are acceptable for cost or thermal trade-offs. |
| UCC28740DR | Primary-side QR flyback controller with integrated 700-V MOSFET; no secondary-side regulation; relies on transformer turns ratio and optocoupler feedback. | Requires optocoupler and TL431 for regulation; slower transient response; higher component count than LM34927SD/NOPB's self-contained solution. | Select UCC28740DR for ultra-low standby power or when primary-side control is mandated by safety standards - not for secondary-side simplicity. |
Compared with LM5165DRCT and UCC28740DR, LM34927SD/NOPB uniquely integrates both high- and low-side 100-V N-MOSFETs with COT control - enabling isolated bias generation without optocouplers, external FETs, or compensation networks, thereby reducing bill-of-materials and improving reliability in space-constrained designs.
Availability
LM34927SD/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 consistent parametric performance across production batches.
Supply support for LM34927SD/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.
LM34927SD/NOPB belongs to TI's high-voltage DC-DC controller product line, engineered specifically for isolated secondary-side bias regulation in fly-buck and transformer-coupled topologies - targeting reduced system complexity and improved efficiency in telecom, automotive, and industrial power architectures.
FAQ
What is the minimum input voltage required for stable operation of the LM34927SD/NOPB?
The LM34927SD/NOPB operates reliably from 7.5 V to 100 V input. Below 7.5 V, the internal VCC regulator cannot sustain gate drive and logic functionality, causing unregulated output or shutdown. This lower limit is confirmed in TI's Recommended Operating Conditions table (Section 6.3) and validated across –40°C to 125°C junction temperature.
Can the LM34927SD/NOPB be used without an external bootstrap capacitor?
No - the LM34927SD/NOPB requires a 0.01-µF ceramic capacitor between BST and SW pins. This capacitor supplies gate drive voltage for the high-side N-MOSFET during on-time. Omitting it prevents proper high-side switching, resulting in no output regulation. The datasheet explicitly mandates this component in Pin Functions (Section 5) and Feature Description (Section 7.3.7).
How does the LM34927SD/NOPB achieve constant-frequency operation despite using constant on-time control?
The LM34927SD/NOPB achieves near-constant frequency by making on-time inversely proportional to VIN (TON ∝ 1/VIN). As input voltage increases, on-time decreases - compensating for longer off-times caused by higher VIN, thus stabilizing switching frequency across the 7.5–100 V range. This behavior is quantified in Section 6.6 (Switching Characteristics) and Figure 5 (TON vs VIN and RON).
What is the purpose of the UVLO pin on the LM34927SD/NOPB, and how is it configured?
The UVLO pin on the LM34927SD/NOPB enables programmable input undervoltage lockout using an external resistor divider from VIN to RTN. When UVLO voltage falls below 0.66 V, the device enters low-current shutdown (IIN ≤ 225 µA); above 1.225 V, normal operation begins. Hysteresis is generated by an internal 20-µA current source, as detailed in Section 7.3.9 and Figure 17.
Does the LM34927SD/NOPB support discontinuous conduction mode (DCM) operation?
No - the LM34927SD/NOPB is designed to maintain continuous conduction mode (CCM) across all loads, including light loads, due to its synchronous rectifier lacking diode emulation. The low-side N-MOSFET remains active even when inductor current reverses, preventing DCM entry. This behavior is explicitly stated in Section 7.3.8 and impacts ripple design requirements at the FB pin.
LM34927SD/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:
- 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-WSON (4x4)
LM34927SD/NOPB FAQ
1.How can I place an order for LM34927SD/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM34927SD/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 LM34927SD/NOPB reliable?
The price and inventory of LM34927SD/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM34927SD/NOPB is usually 5 days.
3.What payment methods are accepted for LM34927SD/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM34927SD/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM34927SD/NOPB?
LM34927SD/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM34927SD/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 LM34927SD/NOPB?
For technical support, including LM34927SD/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM34927SD/NOPB requirements.
6.How does Aetrix verify that LM34927SD/NOPB is sourced from the original manufacturer or authorized distributors?
All LM34927SD/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 LM34927SD/NOPB meets industry standards.
7.What is the process for return or replacement of LM34927SD/NOPB?
All LM34927SD/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM34927SD/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 LM34927SD/NOPB part is unused and in its original packaging.
Return procedure for LM34927SD/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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