My Inquiry
My Account
Analog Devices Inc. LT3781IG#TRPBF
- Part No.:
- LT3781IG#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 20-SSOP (0.209", 5.30mm Width)
- Datasheet:
-
LT3781IG#TRPBF.pdf
- Description:
- IC REG CTRLR FWRD CONV 20SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,477
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
LT3781IG#TRPBF from Analog Devices (formerly Linear Technology) is a high-voltage synchronous forward controller IC for isolated and nonisolated DC/DC converters, supporting input voltages up to 72V, fixed-frequency current-mode control up to 350kHz, and dual N-channel MOSFET drive with ≤50% duty cycle enforcement. It integrates a 5V reference (±1%), undervoltage lockout with 6V hysteresis, soft-start, and fault protection for telecom power supplies.
For engineers reviewing the LT3781IG#TRPBF datasheet, LT3781IG#TRPBF pinout, LT3781IG#TRPBF application, or LT3781IG#TRPBF equivalent, key selection considerations include bootstrap gate drive capability (VBST up to 90V), synchronous switch timing control (SG/BG/TG phase relationships), thermal and overvoltage fault response, and compatibility with quarter-brick forward converter footprints.
Technical Context
The LT3781IG#TRPBF employs fixed-frequency current-mode control with internal logic enforcing ≤50% maximum duty cycle to prevent transformer saturation in forward topologies. Its oscillator runs at twice the switching frequency and supports synchronization up to 350kHz via TTL-compatible SYNC input with phase-locking capability.
Fault detection includes independent OVLO and THERM comparators (1.25V threshold, 40mV hysteresis), VCC UVLO (8.4V/14.5V thresholds), and 5VREF overcurrent shutdown. Adaptive blanking on the SENSE pin disables current sensing until BG exceeds 5V, ensuring accurate peak-current detection regardless of FET size.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Operating Input Voltage | Up to 72V VIN - enables direct use in 48V telecom and industrial bus systems without pre-regulation. |
| Switching Frequency Range | Programmable up to 350kHz - allows optimization of magnetics size vs. efficiency in high-power forward converters. |
| Max Duty Cycle | ≤50% enforced - prevents core saturation in forward transformer designs by hardware-limited timing logic. |
| 5V Reference Accuracy | ±1% over temperature - provides stable bias for external circuitry and feedback dividers without additional regulation. |
| VCC UVLO Threshold | 8.4V (falling), 14.5V (rising) - ensures reliable start-up and brownout recovery in high-voltage input rails. |
| Bootstrap Supply (VBST) | Up to 90V referenced to BSTREF - supports high-side N-MOSFETs in boost-referenced primary switches. |
| Current Sense Threshold | 150mV ±10mV - sets precise peak-current limit across sense resistor for consistent overcurrent protection. |
| Soft-Start Current | –10µA typical - linearly ramps VC voltage to control inrush current and minimize output overshoot during startup. |
Pinout & Package
LT3781IG#TRPBF is housed in a 20-lead plastic SSOP package (0.154" wide, 0.025" pitch), thermally enhanced for high-power controller operation in compact quarter-brick layouts.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SHDN (1) | Shutdown Enable Input | Logic-high >1.25V enables operation; 150mV hysteresis prevents chatter during sequencing or brownout. |
| OVLO (2) | Input Overvoltage Fault Sense | Resistor-divider monitoring of VIN triggers shutdown if >1.25V, protecting downstream circuitry from transients. |
| THERM (3) | Thermal Fault Sense | Accepts thermistor divider signal; >1.25V disables switching and resets soft-start for graceful thermal recovery. |
| SGND (4) | Signal Ground Reference | Separate low-noise ground for error amp, reference, and sense circuits-must be isolated from power ground paths. |
| 5VREF (5) | 5V Precision Reference Output | Supplies up to 20mA; short-circuit protected to ~45mA; used for biasing optocouplers and feedback networks. |
| FSET (6) | Oscillator Timing Input | RC network (RFSET + CFSET) programs switching frequency; internal 2.5V/1.5V hysteresis defines charge/discharge thresholds. |
| SYNC (7) | External Clock Synchronization Input | TTL-compatible; locks internal oscillator phase and frequency to external source up to 350kHz. |
| SS (8) | Soft-Start Control | 10µA sink charges external capacitor; voltage ramp controls current limit rise time to suppress startup overshoot. |
| VFB (9) | Error Amplifier Inverting Input | Receives feedback from output divider; referenced to internal 1.25V; open-circuit bias current ~50nA. |
| VC (10) | Error Amplifier Output | Inverting gain stage drives compensation network; sources/sinks up to 25mA/1mA for optocoupler bias integration. |
| SENSE (11) | Current Sense Input | Non-inverting input for ground-referenced sense resistor; adaptive blanking active while BG < 5V. |
| SG (12) | Synchronous Switch Driver Output | Drives bottom-side sync FET; leads BG by ~150ns to ensure proper dead-time sequencing. |
| VCC (13) | Main IC Power Supply Input | 9–18V operating range; 18V shunt clamp active in shutdown; UVLO disables all functions below 8.4V. |
| PWRGND (14) | Power Ground Reference | High-current return path for BG/SG/TG drivers; must connect directly to VIN decoupling capacitor. |
| BG (15) | Bottom-Side Primary Switch Driver | Drives low-side primary FET; lags TG turn-on and leads TG turn-off to concentrate switching losses on bottom FET. |
| BSTREF (18) | Bootstrap Reference Node | Connected to source of topside FET; defines reference for VBST supply and enables high-side gate drive. |
| TG (19) | Top-Side Primary Switch Driver | Drives high-side primary FET; gated by VBST–BSTREF UVLO (>7.0V required for enable). |
| VBST (20) | Bootstrap Supply Input | Charged via external Schottky diode from VCC; supports up to 90V referenced to BSTREF for high-VDS applications. |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous Forward Topology Support | Hardware-enforced ≤50% duty cycle and dedicated SG/BG/TG drivers simplify design of isolated 36–72V-to-5V/7A forward converters. |
| Programmable & Synchronizable Oscillator | RC-set frequency up to 350kHz with phase-locked SYNC input enables multi-controller interleaving and EMI reduction. |
| Integrated Fault Protection Suite | Dedicated OVLO, THERM, VCC UVLO, and 5VREF overcurrent detection with automatic soft-start reset ensures robust system-level reliability. |
| Adaptive Current Sense Blanking | Blanking triggered by BG voltage >5V eliminates false current-limit trips during FET turn-on transitions across wide gate capacitance ranges. |
| Bootstrap Gate Drive Architecture | VBST up to 90V with BSTREF-referenced operation enables efficient high-side N-MOSFET use without floating supplies or level shifters. |
| Optocoupler-Friendly Error Amplifier | Voltage-output VC pin with 25mA sourcing capability simplifies secondary-side feedback integration using standard PC817-class optocouplers. |
Applications
| Telecom Power Supplies | Industrial DC/DC Converters |
|---|---|
Use Scenario: 48V telecom rectifier output stepped down to 5V/7A for line card power in NEBS-compliant equipment. IC Role / Device Role / Timing Role: Primary-side synchronous forward controller managing dual N-MOSFETs, transformer reset, and isolation feedback via optocoupler. Use Value: High-voltage input tolerance (72V max), tight 5VREF accuracy (±1%), and robust fault handling meet stringent telecom reliability requirements. | Use Scenario: Distributed 24–72V bus powering PLC I/O modules requiring isolated 5V/3A with thermal derating. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller driving external MOSFETs in nonisolated forward configuration with sequencing support. Use Value: Programmable soft-start, SHDN-controlled power sequencing, and THERM-based thermal foldback ensure safe operation in harsh industrial environments. |
| Lead-Acid Battery Backup Systems | Automotive Heavy-Duty Power |
Use Scenario: 36–60V battery-backed UPS converting to regulated 5V for critical control electronics during grid failure. IC Role / Device Role / Timing Role: High-input-voltage forward controller with undervoltage lockout hysteresis (6V) and trickle-start VCC clamp for battery longevity. Use Value: Wide VCC operating range (9–18V) and self-biased startup enable reliable operation across deep battery discharge profiles. | Use Scenario: 24V vehicle electrical system powering 5V infotainment subsystems with transient immunity up to 72V load dump. IC Role / Device Role / Timing Role: Synchronized forward controller with OVLO protection and adaptive blanking to withstand automotive ISO 7637-2 pulses. Use Value: Input overvoltage shutdown (<1.25V threshold) and fast fault response (<650ns disable) protect against load-dump-induced damage. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar synchronous forward controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UCC28950RTJT | Phase-shifted full-bridge controller with integrated SR control; no bootstrap driver; requires external VDD bias. | Targets higher-efficiency full-bridge topologies; lacks native forward topology support and VBST architecture. | Select UCC28950RTJT only when migrating to phase-shifted bridge with synchronous rectification and lower EMI requirements. |
| LM5045MTX/NOPB | Current-mode forward controller with integrated high-side driver but no VBST rail; max VIN = 100V, no SYNC input. | Supports higher input voltage but lacks synchronization, soft-start programmability, and dedicated SG driver for synchronous FETs. | Choose LM5045MTX/NOPB for cost-sensitive forward designs where phase control and multi-controller sync are unnecessary. |
Compared with UCC28950RTJT and LM5045MTX/NOPB, the LT3781IG#TRPBF uniquely combines bootstrap-referenced high-side drive, dedicated synchronous switch timing, and full fault protection in a forward-optimized package-making it the preferred choice for quarter-brick telecom and industrial forward converters requiring precise sequencing and robustness.
Availability
LT3781IG#TRPBF is available at Aetrix Electronics and suitable for telecom power supplies, industrial DC/DC converters, and lead-acid battery backup systems requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.
Supply support for LT3781IG#TRPBF 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
Analog Devices, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors.
The LT3781IG#TRPBF belongs to Linear's high-voltage power controller product line, designed specifically for isolated and nonisolated synchronous forward converters in telecom, industrial, and automotive applications demanding reliability, precision, and fault resilience.
FAQ
What is the maximum input voltage supported by the LT3781IG#TRPBF?
The LT3781IG#TRPBF supports an absolute maximum input voltage of 72V on its VIN-related pins (VCC, OVLO, SHDN). Its VCC supply operates from 9V to 18V, with undervoltage lockout engaging below 8.4V and releasing above 14.5V. The VBST pin tolerates up to 90V referenced to BSTREF, enabling high-side gate drive in demanding forward topologies. This makes the LT3781IG#TRPBF suitable for 48V telecom and 24–72V industrial bus applications.
Does the LT3781IG#TRPBF support synchronization with external clock sources?
Yes, the LT3781IG#TRPBF supports synchronization via its TTL-compatible SYNC pin (Pin 7). It accepts external clock signals up to 350kHz and uses internal frequency doubling to phase-lock its oscillator. During synchronized operation, the controller also aligns switch phase across multiple units-critical for interleaved multi-converter systems. The LT3781IG#TRPBF does not require external components for SYNC interface and maintains ≤50% duty cycle enforcement even under synchronization.
How does the LT3781IG#TRPBF implement current sensing and blanking?
The LT3781IG#TRPBF senses current through the SENSE pin (Pin 11), comparing the voltage across an external ground-referenced sense resistor to an internal 150mV threshold. It features adaptive blanking: the current comparator is disabled while the BG pin voltage remains below 5V, eliminating false triggering during FET turn-on transients. This blanking is fully internal and requires no external timing components-ensuring reliable operation across diverse MOSFET gate charge profiles in the LT3781IG#TRPBF design.
What protection features are integrated into the LT3781IG#TRPBF?
The LT3781IG#TRPBF integrates five independent protection mechanisms: (1) VCC undervoltage lockout (8.4V/14.5V hysteresis), (2) input overvoltage shutdown via OVLO pin (1.25V threshold), (3) thermal shutdown via THERM pin (1.25V threshold), (4) 5VREF overcurrent shutdown (~45mA limit), and (5) VBST–BSTREF undervoltage lockout (7.0V threshold). All faults trigger a General Fault Condition (GFC), discharging the soft-start capacitor and forcing controlled restart-ensuring robust behavior in the LT3781IG#TRPBF under abnormal conditions.
Can the LT3781IG#TRPBF drive both high-side and low-side N-channel MOSFETs in a forward converter?
Yes, the LT3781IG#TRPBF is explicitly designed to drive dual N-channel MOSFETs in synchronous forward topologies. It provides three dedicated gate drivers: TG (top-side, bootstrap-referenced), BG (bottom-side primary), and SG (synchronous rectifier). The VBST pin supports up to 90V referenced to BSTREF, enabling robust high-side N-MOSFET drive without external level shifters. The LT3781IG#TRPBF's timing logic ensures correct dead-time sequencing between TG, BG, and SG outputs to prevent shoot-through.
LT3781IG#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-SSOP (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Up/Step-Down
- Output Configuration:
- Positive, Isolation Capable
- Topology:
- Forward Converter
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 9V ~ 18V
- Frequency - Switching:
- 700kHz
- Duty Cycle (Max):
- -
- Synchronous Rectifier:
- No
- Clock Sync:
- Yes
- Serial Interfaces:
- -
- Control Features:
- Enable, Soft Start
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SSOP
LT3781IG#TRPBF FAQ
1.How can I place an order for LT3781IG#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3781IG#TRPBF 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 LT3781IG#TRPBF reliable?
The price and inventory of LT3781IG#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3781IG#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3781IG#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3781IG#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3781IG#TRPBF?
LT3781IG#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3781IG#TRPBF 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 LT3781IG#TRPBF?
For technical support, including LT3781IG#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3781IG#TRPBF requirements.
6.How does Aetrix verify that LT3781IG#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3781IG#TRPBF 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 LT3781IG#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3781IG#TRPBF?
All LT3781IG#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3781IG#TRPBF, 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 LT3781IG#TRPBF part is unused and in its original packaging.
Return procedure for LT3781IG#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LT3781IG#TRPBF Tags
-
UCC28C45DR
Texas Instruments
-
UCC28C40DR
Texas Instruments
-
UCC28C43DR
Texas Instruments
-
ZXSC410E6TA
Diodes Incorporated
-
LM3524DMX/NOPB
Texas Instruments
-
LM3489MMX/NOPB
Texas Instruments
-
MIC2102YML-TR
Microchip Technology
-
LM5148RGYR
Texas Instruments
-
TL598CDR
Texas Instruments
-
LM5155DSSR
Texas Instruments
-
LM25085MYX/NOPB
Texas Instruments
-
UCC2813DTR-0
Texas Instruments
Tech Hub
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…
Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…
An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…
Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…
Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…
