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Analog Devices Inc. LT3751IUFD#PBF
- Part No.:
- LT3751IUFD#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- Power Management - Specialized
- Package:
- 20-WFQFN Exposed Pad
- Datasheet:
-
LT3751IUFD#PBF.pdf
- Description:
- IC CTRLR CAP CHRGR 4.75V 20-QFN
- Quantity:
- Payment:
- Shipping:
Inventory:1,568
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Product details
Overview
LT3751IUFD#PBF from Analog Devices (formerly Linear Technology) is a high-input-voltage flyback controller designed for rapid high-voltage capacitor charging and regulated high-voltage supply generation. It features integrated 2A rail-to-rail MOSFET gate drivers, 106mV current-sense threshold, user-programmable over/undervoltage lockouts on VCC and VTRANS, and supports charging a 1000µF capacitor to 500V in under one second. Its primary circuit role is controlling energy transfer in isolated flyback topologies for precision high-voltage DC output.
For engineers reviewing the LT3751IUFD#PBF datasheet, LT3751IUFD#PBF pinout, LT3751IUFD#PBF application, or LT3751IUFD#PBF equivalent, this page delivers verified technical context, exact package mapping (20-pin 4mm × 5mm QFN), confirmed pin functions, real-world timing and regulation behavior, and two validated alternative parts with documented functional differences.
Technical Context
The LT3751IUFD#PBF implements boundary-mode (discontinuous conduction mode) flyback control with dual DCM thresholds-startup (VTH1) and normal operation (VTH2)-to prevent primary current runaway during low-output-voltage conditions. Its internal 26kHz one-shot clock and auxiliary current comparator dynamically adjust switching intervals during startup.
It operates in three FB-pin-defined modes: charge-only (FB < 1.16V), low-noise regulation (1.16V ≤ FB ≤ 1.34V), and no-load (FB > 1.34V). Regulation uses peak-current limiting (106mV/RSENSE) combined with duty-cycle modulation, while voltage feedback is implemented via resistive divider to the FB pin referenced to 1.22V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.75V to 24V - enables direct compatibility with industrial 12V/24V rails without external regulators. |
| Current Sense Threshold | 106mV - sets precise peak switch current limit with ±6mV tolerance over temperature, critical for consistent energy per cycle. |
| FB Reference Voltage | 1.22V ±30mV - defines regulation setpoint; used with external resistor divider to scale output voltage accurately. |
| Gate Drive Capability | 2A peak pull-up/pull-down - drives large external NMOS gates efficiently, supporting fast turn-on/turn-off even at low VCC (≤8V with LVGATE). |
| UVLO/OVLO Thresholds | 1.225V ±30mV per pin - user-configurable via external resistors to protect against input supply faults on both VCC and VTRANS rails. |
| Operating Temperature | –40°C to +125°C - qualified for harsh industrial and automotive under-hood environments. |
| Package | 20-pin QFN (4mm × 5mm, exposed pad) - provides low thermal resistance (θJA = 43°C/W) and compact layout for high-voltage isolation. |
Pinout & Package
LT3751IUFD#PBF is housed in a 20-pin plastic QFN package (4mm × 5mm) with an exposed thermal pad (Pin 21) that must be soldered to PCB ground for thermal and electrical integrity. The package supports reflow-compatible lead-free finish and operates up to 125°C junction temperature.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| RVTRANS (Pin 1 / Pin 19) | Transformer supply sense input | Connects to VTRANS via resistor to enable undervoltage/overvoltage detection; minimum operating VTRANS = 4.75V. |
| UVLO1 (Pin 2 / Pin 20) | VTRANS undervoltage lockout input | Senses VTRANS drop below 1.225V + 50µA·RUVLO1; triggers FAULT latch and halts switching until CHARGE pin toggled. |
| OVLO1 (Pin 3 / Pin 1) | VTRANS overvoltage lockout input | Senses VTRANS rise above 1.225V + 50µA·ROVLO1; disables switching and asserts FAULT until VTRANS falls and CHARGE is toggled. |
| FAULT (Pin 6 / Pin 4) | Open-collector fault indicator | Active-low signal indicating UVLO/OVLO violation or internal fault; requires external pull-up for logic-level interfacing. |
| DONE (Pin 7 / Pin 5) | Open-collector charge-complete indicator | Asserts low when target output voltage is reached or FAULT occurs; signals end of charging cycle to host controller. |
| CHARGE (Pin 8 / Pin 6) | Charge initiation and ON/OFF control | Rising edge >1.5V starts new charge cycle; falling edge <0.3V forces shutdown; ramp rate must be 10ns–10ms to avoid initialization failure. |
| CLAMP (Pin 9 / Pin 7) | Internal gate driver clamp selection | Tie to GND for 10.5V HVGATE clamp; tie to VCC for 5.6V clamp - selects optimal gate drive voltage based on VCC level. |
| FB (Pin 10 / Pin 8) | Feedback regulation input | Internally regulated to 1.22V; connects to output divider to enable low-noise voltage regulation mode (1.16V–1.34V range). |
| CSP / CSN (Pins 12/11 / Pins 10/9) | Positive/negative current sense inputs | Measure NMOS source voltage drop across RSENSE; define 106mV current limit in charge mode, down to 11mV in regulation mode. |
| HVGATE / LVGATE (Pins 15/14 / Pins 13/12) | High/low-voltage gate drive outputs | HVGATE drives NMOS gate to VCC – 2V; LVGATE active only when VCC ≤ 8V and tied to NMOS gate directly for rail-to-rail drive. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 2A rail-to-rail gate driver | Enables efficient drive of large external NMOS switches across full 4.75V–24V VCC range, eliminating need for external driver stages. |
| User-selectable 5.6V or 10.5V gate clamp | Prevents gate oxide overstress on NMOS devices by limiting HVGATE swing - selected via CLAMP pin connection, not fixed. |
| Programmable VCC/VTRANS UVLO/OVLO | Four independent comparator inputs allow custom fault thresholds for both power rails, enabling robust system-level protection without external comparators. |
| Two-stage DCM detection with hysteresis | Startup (VTH1) and boundary-mode (VTH2) thresholds prevent oscillation and current runaway during low-output-voltage conditions. |
| Three-mode FB pin control (charge/regulation/no-load) | Automatically transitions from rapid capacitor charging to precision low-noise regulation as output voltage rises, optimizing speed and stability. |
Applications
| Professional Photoflash Systems | Emergency Strobe Lights |
|---|---|
|
Use Scenario: Charging high-energy storage capacitors (e.g., 1000µF @ 300–500V) for xenon flash tubes in studio lighting and medical imaging equipment. IC Role / Device Role / Timing Role: Primary flyback controller managing transformer energy transfer, peak current limiting, and precise voltage termination via DONE signal. Use Value: Achieves sub-second charge time with ±1% output voltage accuracy and automatic transition from charge to regulation mode to minimize ripple during flash trigger. |
Use Scenario: Powering high-intensity LED or xenon strobes in fire alarms, aircraft warning lights, and emergency vehicle beacons requiring rapid, repeatable high-voltage pulses. IC Role / Device Role / Timing Role: High-voltage capacitor charger with programmable UVLO/OVLO ensuring reliable operation despite battery voltage sag or surge in 12V/24V vehicle systems. Use Value: Delivers stable 400–600V output with fault-protected restart logic (via CHARGE pin toggle) after brownout or overvoltage events. |
| Security/Inventory Control Systems | Detonator Firing Circuits |
|
Use Scenario: Generating controlled high-voltage pulses for electro-mechanical locks, RFID interrogators, and laser-based perimeter sensors in access control hardware. IC Role / Device Role / Timing Role: Precision HV supply controller with DONE and FAULT pins providing deterministic status signaling to microcontroller-based safety logic. Use Value: Enables safe, repeatable 200–450V output with built-in overvoltage lockout preventing accidental discharge during firmware updates or sensor calibration. |
Use Scenario: Charging low-capacitance, high-voltage firing capacitors (e.g., 1–10µF @ 1–2kV) in explosive initiation systems where reliability and predictable timing are mission-critical. IC Role / Device Role / Timing Role: Isolated high-voltage charger with dual-rail monitoring (VCC + VTRANS) and hardware-enforced shutdown on any supply anomaly. Use Value: Guarantees single-shot operation with CHARGE pin edge-triggered start and FAULT-latched inhibition - no software dependency for safety-critical arming. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar high-voltage capacitor charger controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3895EFE#PBF | Fixed 105V VIN max, no VTRANS sensing, no DCM detection; integrates synchronous rectifier driver. | Targeted at high-current DC/DC conversion, not capacitor charging; lacks DONE/FAULT signaling and programmable UVLO/OVLO on secondary rail. | Select only if designing non-isolated high-voltage buck-derived supplies with lower output voltage (<105V) and no need for transformer-based isolation or charge-cycle signaling. |
| MAX17596ATP+T | Wide 4.5V–60V input, no integrated gate driver, requires external high-side driver; no dedicated CHARGE/DONE/FAULT pins. | Designed for industrial isolated flyback with digital interface (I²C); lacks analog charge-control logic and hardware fault latching. | Choose when system requires programmable soft-start, fault logging via I²C, or multi-rail sequencing - but expect added BOM cost and firmware complexity versus LT3751IUFD#PBF's analog simplicity. |
Compared with LTC3895EFE#PBF and MAX17596ATP+T, the LT3751IUFD#PBF uniquely combines dedicated charge-cycle control (CHARGE/DONE/FAULT), dual-rail UVLO/OVLO, and boundary-mode DCM detection - making it irreplaceable for safety-critical, rapid high-voltage capacitor charging where deterministic analog timing and hardware fault response are mandatory.
Availability
LT3751IUFD#PBF is available at Aetrix Electronics and suitable for professional photoflash systems, emergency strobe lighting, and security/industrial detonator circuits requiring stable component supply, long-term lifecycle support, and guaranteed −40°C to +125°C operation.
Supply support for LT3751IUFD#PBF 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 acquired Linear Technology in 2017 and maintains full product support, datasheets, and application engineering for all Linear ICs including the LT3751 family.
The LT3751IUFD#PBF belongs to Linear's high-voltage power controller product line, engineered specifically for isolated flyback-based capacitor charging and regulated high-voltage DC supplies in safety-critical industrial and defense applications.
FAQ
What is the function of the CLAMP pin on the LT3751IUFD#PBF?
The CLAMP pin on the LT3751IUFD#PBF selects the internal gate driver voltage clamp: tying it to GND enables a 10.5V clamp on HVGATE, while tying it to VCC activates a 5.6V clamp. This prevents NMOS gate overvoltage during switching transients and must be configured before power-up. The LT3751IUFD#PBF does not auto-detect VCC level - correct CLAMP configuration is required for reliable gate drive across the full 4.75V–24V VCC range.
How does the LT3751IUFD#PBF distinguish between charge mode and regulation mode?
The LT3751IUFD#PBF determines operating mode solely from the FB pin voltage: below 1.16V triggers charge-only mode (rapid capacitor charging), 1.16V–1.34V enables low-noise regulation mode (peak-current + duty-cycle control), and above 1.34V enters no-load mode. The LT3751IUFD#PBF automatically transitions between modes without external intervention - no mode-select pins or register writes are needed.
Can the LT3751IUFD#PBF be used with a primary-side or secondary-side output voltage sense configuration?
Yes, the LT3751IUFD#PBF supports both configurations. For secondary-side sensing, connect RVOUT to the output capacitor and use the internal 0.98V reference with RBG to scale feedback. For primary-side sensing, tie RVOUT to VTRANS and use transformer turns ratio to derive output voltage - eliminating optocoupler latency and improving transient response. Both methods are explicitly supported in the LT3751IUFD#PBF datasheet and typical application schematics.
What is the purpose of the dual DCM thresholds (VTH1 and VTH2) in the LT3751IUFD#PBF?
The LT3751IUFD#PBF uses two DCM thresholds to ensure reliable startup and stable boundary-mode operation: VTH1 (startup threshold) prevents primary current runaway when output voltage is near zero, while VTH2 (normal threshold) enables efficient energy transfer once regulation begins. The mode latch switches between them automatically after the first DCM one-shot - a hardware-implemented hysteresis that eliminates need for external timing components or firmware tuning.
Does the LT3751IUFD#PBF require external components for VCC and VTRANS overvoltage/undervoltage protection?
No - the LT3751IUFD#PBF integrates four dedicated comparator inputs (UVLO1, OVLO1, UVLO2, OVLO2) that accept external resistor dividers to set custom trip points for both VTRANS and VCC rails. Each pin has a 1.225V internal reference and 50µA bias current, so trip voltage = 1.225V + 50µA × RSET. No external comparators, references, or logic are required - all protection logic is self-contained within the LT3751IUFD#PBF.
LT3751IUFD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-WFQFN Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Applications:
- Photoflash Capacitor Charger
- Current - Supply:
- 5.5mA
- Voltage - Supply:
- 4.75V ~ 24V
- Operating Temperature:
- -40°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-QFN (4x5)
LT3751IUFD#PBF FAQ
1.How can I place an order for LT3751IUFD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3751IUFD#PBF 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 LT3751IUFD#PBF reliable?
The price and inventory of LT3751IUFD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3751IUFD#PBF is usually 5 days.
3.What payment methods are accepted for LT3751IUFD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3751IUFD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3751IUFD#PBF?
LT3751IUFD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3751IUFD#PBF 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 LT3751IUFD#PBF?
For technical support, including LT3751IUFD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3751IUFD#PBF requirements.
6.How does Aetrix verify that LT3751IUFD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3751IUFD#PBF 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 LT3751IUFD#PBF meets industry standards.
7.What is the process for return or replacement of LT3751IUFD#PBF?
All LT3751IUFD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3751IUFD#PBF, 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 LT3751IUFD#PBF part is unused and in its original packaging.
Return procedure for LT3751IUFD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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