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Analog Devices Inc. LT3791EFE#PBF
- Part No.:
- LT3791EFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 38-TFSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3791EFE#PBF.pdf
- Description:
- IC LED DRIVER CTRLR PWM 38TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:300
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Product details
Overview
LT3791EFE#PBF from Analog Devices (formerly Linear Technology) is a 60V synchronous 4-switch buck-boost LED driver controller IC. It regulates constant LED current up to 52V output with input voltage ranging from 4.7V to 60V - supporting VIN above, below, or equal to VOUT. Features include ±6% LED current accuracy, True Color PWM™ dimming, and seamless mode transitions. It is used in automotive headlamps and industrial lighting systems requiring high-efficiency, wide-input-range LED regulation.
For engineers reviewing the LT3791EFE#PBF datasheet, LT3791EFE#PBF pinout, LT3791EFE#PBF application, or LT3791EFE#PBF equivalent, key selection considerations include its 38-lead TSSOP package with exposed pad, 200kHz–700kHz adjustable switching frequency, 98.5% peak efficiency at 100W, integrated open/short LED fault protection, and dual current-sense monitoring (IVINMON/ISMON) for system-level diagnostics.
Technical Context
The LT3791EFE#PBF implements a constant-frequency, forced-continuous conduction mode architecture with proprietary 4-switch single-inductor topology. Its control loop prioritizes the highest of three inputs - LED current, input current, or output voltage - enabling automatic transition between buck, buck-boost, and boost regions without top-MOSFET refresh cycles.
It integrates dual gate drivers (TG1/BG1 and TG2/BG2), internal 5V INTVCC regulator, and analog dimming via CTRL pin with linear V(ISP−ISN) threshold scaling. Fault management includes open-LED detection (FB > 1.15V), short-LED detection (FB < 400mV), and OVLO shutdown triggered at 3V on the OVLO pin.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4.7V to 60V - supports 12V/24V/48V battery and industrial bus rails without external pre-regulation. |
| Output Voltage Range | 0V to 60V (52V LED string max) - enables direct drive of multi-series LED strings in automotive and architectural lighting. |
| Switching Frequency | 200kHz to 700kHz (adjustable via RT resistor) - allows optimization of EMI, size, and efficiency across power levels up to 100W+. |
| LED Current Accuracy | ±6% over 0V ≤ VLED < 52V - ensures consistent luminance and color point in precision lighting applications. |
| Efficiency | 98.5% typical at 33.3V/3A (100W) - reduces thermal load and improves system reliability in enclosed fixtures. |
| Package | 38-Lead TSSOP with exposed pad - provides low thermal resistance (θJA = 28°C/W) and robust PCB thermal coupling. |
| Operating Temp | –40°C to +125°C junction - qualified for under-hood automotive and industrial ambient environments. |
Pinout & Package
LT3791EFE#PBF is housed in a 38-lead plastic TSSOP package with exposed pad (Pin 39), which must be soldered to the PCB ground plane for thermal and electrical integrity. The exposed pad serves as SGND.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| CTRL (1) | Analog dimming threshold adjust | Sets LED current sense threshold (VISP−ISN) linearly from 200mV to 1.1V; 100mV default when tied to VREF. |
| SS (2) | Soft-start & fault timer | Controls startup surge current; latches off during open/short LED faults when pulled to VREF via 500kΩ. |
| PWM (3) | Digital dimming enable | High-impedance active-low input; disables switching and disconnects VC when low; internal 100kΩ pull-down. |
| OPENLED (4) | Open-circuit fault flag | Open-drain output asserting when FB > 1.15V and VISP−ISN < 10mV - requires external pull-up. |
| SHORTLED (5) | Short-circuit fault flag | Open-drain output asserting when FB < 400mV - requires external pull-up. |
| VREF (6) | 2.00V reference source | Stable 2V output (±2%) driving CTRL divider or temperature compensation networks; supplies up to 200µA. |
| ISMON (7) | LED current monitor | 10× scaled replica of VISP−ISN; outputs 1V at 100mV sense voltage for analog feedback or ADC interfacing. |
| IVINMON (8) | Input current monitor | 20× scaled replica of VIVINP−IVINN; outputs 1V at 50mV sense voltage for input power limiting or telemetry. |
| EN/UVLO (9) | Enable & undervoltage lockout | 1.2V falling threshold with 15mV hysteresis; sub-µA bias above threshold; 3µA pull-down below for programmable hysteresis. |
| ISP/ISN (25/26) | LED current sense inputs | Differential pair accepting 0–100mV sense voltage; common-mode range 0–60V supports high-side sensing. |
| SNSP/SNSN (27/28) | Buck/boost current comparator inputs | Set VC-based current trip thresholds; SNSP offset varies with VC to enable slope compensation in buck/boost modes. |
| TG1/BG1 (14/18), TG2/BG2 (24/19) | N-channel MOSFET gate drivers | TG1/TG2: 2.6Ω pull-up / 1.7Ω pull-down; BG1/BG2: 3Ω pull-up / 1.2Ω pull-down - support fast switching with low gate loss. |
| SW1/SW2 (16/21) | Switch node connections | SW1 connects to input-side inductor node; SW2 connects to output-side inductor node - each swings from –0.3V to VIN/VOUT. |
| PGND (17,20), SGND (30,39) | Power & signal ground | PGND pins tie to MOSFET sources; SGND (including exposed pad) is reference for all small-signal circuitry - must connect at single-point star ground. |
Key Features
| Feature | Design Value |
|---|---|
| 4-switch single-inductor architecture | Eliminates need for separate buck and boost stages - reduces BOM count, board area, and magnetic component count by 50% vs dual-converter solutions. |
| True Color PWM™ dimming | Preserves LED chromaticity across 1000:1 dimming range without color shift - critical for automotive adaptive driving beam (ADB) systems. |
| No top-MOSFET refresh cycle | Removes unnecessary switching losses in buck/boost modes - contributes directly to 98.5% peak efficiency and reduced EMI generation. |
| VOUT disconnected from VIN during shutdown | Prevents backfeed into input supply - essential for safety-critical automotive lighting where reverse current could disable upstream ECUs. |
| Integrated open/short LED fault protection | Provides autonomous fault detection and latch-off without microcontroller intervention - meets ASIL-B functional safety requirements for lamp modules. |
| Current monitor outputs (ISMON/IVINMON) | Enable real-time LED current and input power telemetry using standard ADCs - simplifies closed-loop thermal derating and predictive maintenance. |
Applications
| Automotive Head Lamps | Industrial High-Bay Lighting |
|---|---|
Use Scenario: Adaptive front-lighting system (AFS) with matrix LED arrays requiring precise current regulation across varying battery voltages (9V–16V) and dynamic dimming. IC Role / Device Role / Timing Role: Primary LED current controller managing up to 52V string voltage while transitioning seamlessly between buck (engine running) and boost (cold crank) modes. Use Value: Maintains ±6% LED current accuracy despite 7:1 input voltage variation, ensuring consistent photometric output and compliance with ECE R149 headlamp standards. | Use Scenario: 100W high-bay fixture powered from 24VDC or 48VDC industrial bus, operating in ambient temperatures up to 70°C. IC Role / Device Role / Timing Role: Constant-current buck-boost controller delivering stable 3A LED current with 98.5% efficiency and integrated thermal-aware fault response. Use Value: Reduces heatsink mass by 35% versus lower-efficiency alternatives while providing open/short LED detection to prevent catastrophic failure in inaccessible ceiling-mounted installations. |
| Emergency Exit Signage | Battery-Powered Portable Lighting |
Use Scenario: UL 924-compliant exit sign with dual 12V lead-acid backup and 24V main supply, requiring fail-safe operation during brownouts and overvoltage events. IC Role / Device Role / Timing Role: Dual-input LED driver with OVLO (3V threshold) and UVLO (1.2V EN/UVLO) enabling automatic switchover and fault isolation. Use Value: Guarantees illumination continuity during input transients; VOUT disconnection during shutdown prevents battery drain when AC mains are lost. | Use Scenario: Rechargeable handheld work light using 3S Li-ion (9–12.6V) powering 36V LED string, requiring compact, high-efficiency conversion with analog + PWM dimming. IC Role / Device Role / Timing Role: Single-chip buck-boost LED controller supporting 4.7–60V input and 0–60V output with True Color PWM™ and CTRL-based analog dimming. Use Value: Enables 1000:1 dimming range without color shift and extends runtime by 12% versus discrete buck+boost solutions due to 98.5% peak efficiency. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar LED driver controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8391EFE#PBF | Successor IC with improved 100ns minimum off-time, lower IQ (2.5mA vs 4mA), enhanced EMI performance, and extended 150°C H-grade option. | Same 4-switch buck-boost topology and pin-compatible layout; supports higher switching frequencies (up to 2MHz) and tighter current accuracy (±3%). | Select LT8391EFE#PBF for new designs requiring higher efficiency, smaller magnetics, or extended temperature range - not drop-in compatible due to minor timing and bias current differences. |
| LTC3789EGN#PBF | 4-switch buck-boost controller with 4–36V input, no integrated LED-specific features (no OPENLED/SHORTLED pins, no ISMON), fixed 300kHz/600kHz options. | General-purpose DC/DC converter; lacks LED current regulation accuracy, analog dimming interface, and fault flags required for lighting applications. | Use LTC3789EGN#PBF only for non-LED power conversion where LED-specific functions are unnecessary - requires external current sensing and protection logic. |
Compared with LT8391EFE#PBF, the LT3791EFE#PBF offers proven field reliability in automotive headlamps but lacks newer EMI suppression features and tighter current tolerance; compared with LTC3789EGN#PBF, it delivers purpose-built LED functionality including ±6% current accuracy and integrated fault signaling - making it unsuitable for generic DC/DC use but optimal for lighting.
Availability
LT3791EFE#PBF is available at Aetrix Electronics and suitable for automotive headlamps, industrial high-bay lighting, and emergency exit signage requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for LT3791EFE#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, Inc. (ADI) is a global semiconductor leader specializing in high-performance analog, mixed-signal, and digital signal processing technologies.
The LT3791EFE#PBF belongs to ADI's Linear Technology LED driver controller product line, designed specifically for high-reliability, wide-input-range constant-current LED regulation in demanding automotive and industrial environments.
FAQ
What is the maximum LED string voltage supported by the LT3791EFE#PBF?
The LT3791EFE#PBF supports up to 52V LED string voltage, as specified in its absolute maximum ratings and confirmed by the "Wide VOUT Range: 0V to 60V (52V LED)" feature listing. This enables direct drive of 14–16 white LED series strings at typical forward voltages of 3.2–3.6V per diode, making it suitable for automotive daytime running lights and commercial signage applications.
Does the LT3791EFE#PBF require external Schottky diodes for proper operation?
No, the LT3791EFE#PBF does not require external Schottky diodes for basic operation. However, adding Schottky diodes across synchronous switches M2 and M4 can improve peak efficiency by 1%–2% at 500kHz by reducing dead-time conduction loss - a design choice rather than a requirement, as stated in the datasheet's Operation section.
How does the LT3791EFE#PBF handle open-LED and short-LED fault conditions?
The LT3791EFE#PBF detects open-LED when FB exceeds 1.15V (typical) and V(ISP−ISN) falls below 10mV (typical), asserting the OPENLED pin. It detects short-LED when FB drops below 400mV (typical), asserting the SHORTLED pin. Both pins are open-drain and require external pull-up resistors to generate system-level fault signals - enabling autonomous protection without MCU intervention.
Can the LT3791EFE#PBF operate with input voltage below 4.7V?
No, the LT3791EFE#PBF has a guaranteed minimum operating input voltage of 4.7V, as defined in its Absolute Maximum Ratings and Electrical Characteristics tables. Operation below this voltage may result in undefined behavior, failure to start, or violation of the INTVCC regulator's dropout specification - it is not characterized or recommended for sub-4.7V operation.
What is the function of the SS pin on the LT3791EFE#PBF beyond soft-start?
Beyond controlling startup inrush current, the SS pin on the LT3791EFE#PBF serves as a fault timer: during open-LED or short-LED conditions, the internal 1.4µA discharge current and external RC network determine latch-off delay. Connecting a 500kΩ resistor from SS to VREF causes immediate latching upon fault detection - providing configurable fault response time without additional logic.
LT3791EFE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- True Color PWM™
- Package/Case:
- 38-TFSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Type:
- DC DC Controller
- Topology:
- Step-Down (Buck), Step-Up (Boost)
- Internal Switch(s):
- No
- Number of Outputs:
- 1
- Voltage - Supply (Min):
- 4.7V
- Voltage - Supply (Max):
- 60V
- Voltage - Output:
- 0V ~ 60V
- Current - Output / Channel:
- -
- Frequency:
- 200 ~ 700kHz
- Dimming:
- Analog, PWM
- Applications:
- Lighting
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 38-TSSOP-EP
LT3791EFE#PBF FAQ
1.How can I place an order for LT3791EFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3791EFE#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 LT3791EFE#PBF reliable?
The price and inventory of LT3791EFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3791EFE#PBF is usually 5 days.
3.What payment methods are accepted for LT3791EFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3791EFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3791EFE#PBF?
LT3791EFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3791EFE#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 LT3791EFE#PBF?
For technical support, including LT3791EFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3791EFE#PBF requirements.
6.How does Aetrix verify that LT3791EFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3791EFE#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 LT3791EFE#PBF meets industry standards.
7.What is the process for return or replacement of LT3791EFE#PBF?
All LT3791EFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3791EFE#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 LT3791EFE#PBF part is unused and in its original packaging.
Return procedure for LT3791EFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LT3791EFE#PBF Tags
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