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Texas Instruments LM34927MR/NOPB
- Part No.:
- LM34927MR/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- 8-PowerSOIC (0.154", 3.90mm Width)
- Datasheet:
-
LM34927MR/NOPB.pdf
- Description:
- IC REG BUCK ADJ 600MA 8SOPWR
- Quantity:
- Payment:
- Shipping:
Inventory:1,560
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Product details
Overview
LM34927MR/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, and programmable 1.225-V feedback reference. It operates from 7.5 V to 100 V input, delivers up to 600 mA output current, and supports isolated telecom and industrial bias supplies.
For engineers reviewing the LM34927MR/NOPB datasheet, LM34927MR/NOPB pinout, LM34927MR/NOPB application, or LM34927MR/NOPB equivalent, key selection considerations include its COT architecture eliminating loop compensation, intelligent peak current limit with 150-ns response, adjustable UVLO threshold, thermal shutdown at 165°C, and compatibility with WSON-8 and SO PowerPAD-8 packages.
Technical Context
The LM34927MR/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 range. Its regulation relies on direct comparison of FB voltage to a precision 1.225-V internal reference, with overvoltage protection triggered at 1.62 V.
It integrates two N-channel MOSFETs: a high-side buck switch (RDS(ON) = 0.8–1.8 Ω) and a low-side synchronous rectifier (RDS(ON) = 0.45–1 Ω), both rated for 100-V operation. The device uses bootstrap gate drive (BST–SW capacitor ≥0.01 µF) and includes an internal 7.6-V VCC regulator with 4.5-V UVLO and 26-mA current limit.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 7.5 V to 100 V - enables direct connection to 48-V telecom, 24/48-V automotive, and industrial HV rails without pre-regulation. |
| Feedback Reference | 1.225 V ±2% - sets output voltage via external resistor divider; enables precise regulation down to ~1.23 V minimum. |
| Switching Frequency | Adjustable up to 1 MHz - determined by RON and VIN; maintains stability without compensation due to COT architecture. |
| Peak Current Limit | 0.7–1.3 A - provides short-circuit protection with intelligent off-time scaling based on FB voltage and VIN. |
| Thermal Shutdown | 165°C with 20°C hysteresis - disables buck switch and VCC regulator to prevent damage; resumes at ≤145°C. |
| VCC Regulator Output | 7.6 V ±1.3 V - powers internal gate drivers and logic; self-biased from VIN; UVLO at 4.5 V ensures reliable startup. |
| UVLO Threshold | 1.225 V rising / 0.66 V falling - externally programmable via resistor divider; enables remote shutdown and brownout protection. |
Pinout & Package
LM34927MR/NOPB is available in an 8-pin WSON package (4.00 mm × 4.00 mm) with exposed thermal pad connected to RTN. The pinout supports compact, thermally efficient layout for isolated bias applications.
| 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 DC; supplies VCC regulator and high-side switch; requires local 1-µF ceramic decoupling. |
| 3 UVLO | Undervoltage detection input | Resistor-divider node for programmable startup/shutdown; 20-µA hysteresis current source enables clean threshold control. |
| 4 RON | On-time programming | Connects to VIN via resistor to set minimum on-time (≥100 ns at max VIN); determines operating frequency. |
| 5 FB | Feedback input | Compares output voltage 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 for gate drivers; must be decoupled with 1-µF ceramic; UVLO at 4.5 V enables IC operation. |
| 7 BST | Bootstrap supply | Charges external 0.01-µF ceramic capacitor during SW low phase; enables floating gate drive for high-side N-MOSFET. |
| 8 SW | Power switching node | Drives external inductor; connects to BST capacitor and output filter; handles full switching current and voltage transitions. |
Key Features
| Feature | Design Value |
|---|---|
| No loop compensation required | Constant on-time (COT) control eliminates need for external compensation network - reduces BOM count and design iteration time. |
| No Schottky diode needed | Integrated low-side synchronous rectifier replaces lossy external diode - improves efficiency by ~3–5% at light-to-moderate loads. |
| Ultra-fast transient response | On-time initiation within nanoseconds of FB drop below 1.225 V - minimizes output voltage deviation during load steps. |
| Intelligent peak current limit | Off-time scales inversely with FB voltage - provides aggressive protection during short-circuit while minimizing foldback under overload. |
| Programmable undervoltage lockout | UVLO threshold set by external resistor divider - enables system-level brownout management and controlled startup sequencing. |
Applications
| Isolated Telecom Bias Supply | Automotive Isolated Auxiliary Rail |
|---|---|
Use Scenario: Generating +5 V or +12 V auxiliary bias for isolated gate drivers, ADC references, or optocoupler interfaces in 48-V telecom rectifier modules. IC Role / Device Role / Timing Role: Secondary-side synchronous buck controller regulating isolated winding output; provides stable, low-noise bias independent of primary-side regulation. Use Value: Eliminates discrete Schottky and external compensation components; achieves >85% efficiency at 100-mA load with 48-V input. | Use Scenario: Powering isolated CAN transceivers, sensor signal conditioners, or isolated microcontroller peripherals in 24-V/48-V commercial vehicle ECUs. IC Role / Device Role / Timing Role: High-voltage secondary-side regulator deriving bias from transformer auxiliary winding; withstands load-dump transients up to 100 V. Use Value: Integrated 100-V switches and thermal shutdown ensure robustness in harsh automotive environments; RON-based frequency tuning simplifies EMI filtering. |
| Industrial PLC I/O Isolation | Medical Equipment Isolated Logic Supply |
Use Scenario: Providing galvanically isolated +3.3 V or +5 V for digital I/O modules in programmable logic controllers with 24-V or 48-V backplane inputs. IC Role / Device Role / Timing Role: Compact, self-contained bias regulator on secondary side of fly-buck or forward converter; supports continuous conduction mode (CCM) at all loads. Use Value: Synchronous rectification and COT control maintain tight regulation (<±2%) across –40°C to +125°C ambient; WSON-8 footprint saves board space. | Use Scenario: Delivering certified isolated +5 V bias for patient-connected monitoring circuitry (e.g., ECG front-end, isolation amplifiers) in Class II medical devices. IC Role / Device Role / Timing Role: Safety-isolated secondary-side regulator meeting creepage/clearance requirements; operates with transformer-coupled input only. Use Value: Precision 1.225-V reference and 2% FB tolerance ensure accurate voltage setting; thermal shutdown prevents fault propagation in safety-critical paths. |
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 | Wide-input (3–65 V) synchronous buck with integrated 100-V high-side FET only; requires external low-side FET and compensation. | Designed for primary-side regulation; lacks integrated synchronous rectifier and COT simplicity for secondary-side use. | Choose when primary-side control or higher VIN (>65 V) is needed; not drop-in for LM34927MR/NOPB's secondary-side topology. |
| UCC28740DR | Secondary-side QR flyback controller with integrated 700-V MOSFET; no synchronous rectification; requires external diode or SR controller. | Optimized for flyback topologies with transformer reset; lacks integrated synchronous switch and COT benefits for buck-derived bias. | Prefer for lower-power (<5 W), transformer-reset-critical designs; does not match LM34927MR/NOPB's integrated dual-FET buck architecture. |
Compared with LM5160QPWPRQ1 and UCC28740DR, the LM34927MR/NOPB uniquely combines dual 100-V N-MOSFETs, constant on-time control, and synchronous rectification in a single 8-pin package - delivering simpler layout, faster transient response, and higher efficiency specifically for isolated buck-derived bias rails.
Availability
LM34927MR/NOPB is available at Aetrix Electronics and suitable for isolated telecom bias supply, automotive auxiliary rail generation, and industrial PLC I/O isolation requiring stable component supply and long-term manufacturability.
Supply support for LM34927MR/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 headquartered in Dallas, Texas, designing and manufacturing analog and embedded processing chips for industrial, automotive, and communications markets.
The LM34927MR/NOPB belongs to TI's high-voltage DC-DC controller product line, engineered specifically for cost-sensitive, space-constrained isolated bias applications where simplicity, reliability, and wide input range are critical.
FAQ
What is the recommended minimum on-time for stable operation of the LM34927MR/NOPB?
The LM34927MR/NOPB requires a minimum on-time of 100 ns at maximum input voltage (100 V) for reliable COT operation. This is enforced by selecting the RON resistor per the TON = K × RON / VIN equation (K = 9×10⁻¹¹). Using RON values that yield shorter on-times risks pulse skipping and instability. Designers should verify on-time using Figure 5 (TON vs VIN and RON) in the datasheet and confirm with bench testing under worst-case VIN and temperature conditions. The LM34927MR/NOPB datasheet specifies this requirement in Section 7.3.5.
Can the LM34927MR/NOPB operate without an external bootstrap capacitor?
No, the LM34927MR/NOPB cannot operate without an external bootstrap capacitor. A 0.01-µF ceramic capacitor between BST and SW pins is mandatory to provide gate drive voltage for the high-side N-channel MOSFET. During the SW low phase, the internal diode charges this capacitor from the VCC regulator; during the on-phase, it supplies the floating gate voltage. Omitting the BST capacitor causes immediate high-side gate drive failure and unregulated output. The LM34927MR/NOPB datasheet explicitly states this in Pin Functions (Section 5) and Feature Description (Section 7.3.7).
How does the LM34927MR/NOPB achieve constant frequency across varying input voltage?
The LM34927MR/NOPB achieves nearly constant switching frequency by implementing a constant on-time (COT) control scheme where on-time is inversely proportional to VIN - set by the RON resistor. As VIN increases, on-time decreases proportionally, maintaining consistent average switching period. Off-time is determined by feedback voltage decay, which remains relatively stable under steady-state load. This architecture avoids traditional voltage-mode compensation and delivers frequency stability within ±15% across 7.5–100 V input. The LM34927MR/NOPB datasheet confirms this behavior in Sections 3, 7.1, and Figure 5.
What is the purpose of the RC network in LM34927MR/NOPB feedback configurations?
The RC network (series resistor + capacitor) in LM34927MR/NOPB feedback configurations generates controlled ripple at the FB pin to satisfy the COT controller's stability requirement of ≥25 mV monotonic ripple. Since output capacitors with ultra-low ESR produce insufficient resistive ripple, RC introduces intentional resistive voltage drop synchronized with inductor current. This ensures FB voltage decreases monotonically during off-time - preventing burst-mode oscillation. The LM34927MR/NOPB datasheet details RC sizing in Section 7.3.11 and Figure 16.
Does the LM34927MR/NOPB support forced continuous conduction mode (CCM) at light loads?
Yes, the LM34927MR/NOPB inherently operates in continuous conduction mode (CCM) across all load conditions, including light loads, due to its synchronous rectifier architecture with no diode emulation. Unlike controllers that skip cycles or enter discontinuous mode, the low-side N-MOSFET remains actively controlled, allowing inductor current to reverse slightly. This maintains CCM, improves light-load regulation, and enables reliable secondary-side transformer winding derivation. The LM34927MR/NOPB datasheet confirms this in Section 7.3.8 and Figure 11–15 transient waveforms.
LM34927MR/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:
- 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
LM34927MR/NOPB FAQ
1.How can I place an order for LM34927MR/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM34927MR/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 LM34927MR/NOPB reliable?
The price and inventory of LM34927MR/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM34927MR/NOPB is usually 5 days.
3.What payment methods are accepted for LM34927MR/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM34927MR/NOPB transactions.
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4.How is shipping managed for LM34927MR/NOPB?
LM34927MR/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM34927MR/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 LM34927MR/NOPB?
For technical support, including LM34927MR/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM34927MR/NOPB requirements.
6.How does Aetrix verify that LM34927MR/NOPB is sourced from the original manufacturer or authorized distributors?
All LM34927MR/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 LM34927MR/NOPB meets industry standards.
7.What is the process for return or replacement of LM34927MR/NOPB?
All LM34927MR/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM34927MR/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 LM34927MR/NOPB part is unused and in its original packaging.
Return procedure for LM34927MR/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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