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Analog Devices Inc. LT3791IFE#PBF
- Part No.:
- LT3791IFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 38-TFSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3791IFE#PBF.pdf
- Description:
- IC LED DRIVER CTRLR PWM 38TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,195
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Product details
Overview
LT3791IFE#PBF from Analog Devices is a 60V synchronous 4-switch buck-boost LED driver controller designed for constant-current regulation of LED strings up to 52V with input voltages from 4.7V to 60V. It supports seamless transitions between buck, boost, and buck-boost modes, delivers ±6% LED current accuracy across 0–52V LED voltage range, and operates at adjustable switching frequencies from 200kHz to 700kHz. It is used in automotive headlamps and industrial lighting systems requiring wide VIN/VOUT flexibility.
For engineers reviewing the LT3791IFE#PBF datasheet, LT3791IFE#PBF pinout, LT3791IFE#PBF application, or LT3791IFE#PBF equivalent, key selection criteria include its 38-lead TSSOP package with exposed pad, true color PWM™ dimming support, open/short LED fault protection, and ability to regulate LED current without top MOSFET refresh cycles in pure buck or boost operation.
Technical Context
The LT3791IFE#PBF implements a constant-frequency, forced-continuous conduction mode (FCCM) architecture with dual current-sense amplifiers - one for LED output current (ISP/ISN) and one for input current (IVINP/IVINN). Its control loop prioritizes the highest feedback signal among LED current, input current, and output voltage (FB), enabling automatic mode selection and stable regulation during VIN ≈ VOUT transitions.
It integrates high-side and low-side N-channel gate drivers (TG1/BG1/TG2/BG2) with programmable dead-time control, internal 5V INTVCC regulator, and dedicated fault monitoring pins (OPENLED, SHORTLED, OVLO). The VC pin serves as both error amplifier output and current threshold reference, while RT, SYNC, and CLKOUT enable frequency setting, external synchronization, and multi-phase expansion.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4.7V to 60V - supports 12V/24V/48V automotive and industrial rails without pre-regulation. |
| Output Voltage Capability | 0V to 60V (52V LED string max) - enables single-inductor operation across buck, boost, and buck-boost regions. |
| LED Current Accuracy | ±6% over 0V ≤ VLED < 52V - ensures consistent luminance in high-power lighting arrays. |
| Switching Frequency Range | 200kHz to 700kHz (RT-programmable) - balances efficiency, EMI, and inductor size for compact designs. |
| Package | 38-lead TSSOP with exposed pad - provides thermal performance suitable for ≥100W LED driver applications. |
| Operating Temperature | –40°C to +125°C junction - qualified for under-hood automotive and harsh industrial environments. |
| Efficiency | Up to 98.5% at 33.3V/3A (100W) - reduces thermal load and enables passive cooling in space-constrained fixtures. |
Pinout & Package
LT3791IFE#PBF is housed in a 38-lead plastic TSSOP package with exposed pad (Pin 39), which must be soldered to PCB ground for thermal and electrical integrity. Pin functions are validated per Linear Technology (now Analog Devices) datasheet Rev. 3791fc.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| CTRL (1) | Analog dimming threshold adjust | Sets LED current sense threshold from 6.5mV to 100mV via external voltage; 0–1.1V linear range, clamped at 100mV above 1.3V. |
| SS (2) | Soft-start & fault timer | Controls startup inrush current; also latches off on open/short LED faults when pulled to VREF via 500kΩ resistor. |
| PWM (3) | Digital dimming enable | Active-low signal halts switching and disconnects VC; PWMOUT mirrors this signal for external MOSFET control. |
| OPENLED (4) | Open-circuit fault indicator | Open-drain output asserts when FB > 1.15V and V(ISP−ISN) < 10mV - triggers external fault handling circuitry. |
| SHORTLED (5) | Short-circuit fault indicator | Open-drain output asserts when FB < 400mV - enables fast shutdown of LED string during short events. |
| VREF (6) | 2.00V precision reference | Stable 2V output (±2%) supplies bias for CTRL divider and supports temperature compensation networks. |
| ISMON (7) | LED current monitor | Outputs 10× V(ISP−ISN); 1V = 100mV sense voltage - simplifies current measurement and feedback loop design. |
| IVINMON (8) | Input current monitor | Outputs 20× V(IVINP−IVINN); 1V = 50mV sense voltage - enables input power limiting and diagnostics. |
| EN/UVLO (9) | Enable & undervoltage lockout | 1.2V falling threshold with 15mV hysteresis; sub-µA bias above threshold, 3µA pull-down below - ensures clean start/stop behavior. |
| IVINP/IVINN (10/11) | Input current sense inputs | Differential pair for 46.5–54mV threshold; common-mode range 3–60V - supports high-side or low-side input sensing. |
| VIN (12) | Main power input | Accepts 4.7–60V; requires local ceramic bypass to PGND - powers internal regulators and gate drivers. |
| INTVCC (13) | Internal 5V supply | Regulated 5.0V ±2% output; dropout <350mV at –10mA - powers logic, drivers, and analog circuits. |
| TG1/BG1 (14/18) | Channel 1 top/bottom gate drives | TG1: bootstrapped N-ch driver (2.6Ω pull-up); BG1: ground-referenced N-ch driver (3Ω pull-up) - controls M1/M2 switches. |
| BST1/SW1 (15/16) | Bootstrap supply & switch node | BST1 floats ~5V above SW1; SW1 swings from diode drop below GND to VIN - defines high-side drive capability. |
| PGND (17,20) | Power ground | Low-impedance return path for bottom MOSFET sources and high-current paths - must be connected near MOSFET source pads. |
| BG2/TG2 (19/24) | Channel 2 bottom/top gate drives | BG2: ground-referenced N-ch driver (3Ω pull-up); TG2: bootstrapped N-ch driver (2.6Ω pull-up) - controls M3/M4 switches. |
| SW2/BST2 (21/22) | Channel 2 switch node & bootstrap | SW2 swings from diode drop below GND to VOUT; BST2 floats ~5V above SW2 - enables high-side drive on output side. |
| ISP/ISN (25/26) | LED current sense inputs | Differential pair for 47.5–106mV threshold (VCTRL-dependent); common-mode range 0–60V - supports high-side LED current sensing. |
| SNSP/SNSN (27/28) | Current comparator inputs | Compare VC-derived threshold against sensed inductor current slope - core of FCCM current-mode control. |
| TEST1 (29)/SGND (30) | Test pin & signal ground | TEST1 must connect to SGND; SGND is isolated small-signal reference - connects to PGND at single point for noise immunity. |
| PWMOUT (31) | Buffered PWM output | INTVCC-rail-to-rail buffered copy of PWM pin - drives external N-MOSFET for LED string disconnect. |
| TEST2 (32) | Test pin | Must connect to INTVCC (Pin 13) for normal operation - internal test function disabled otherwise. |
| CLKOUT (33) | Master clock output | Provides in-phase oscillator signal at fSW - synchronizes multiple LT3791 devices for parallel LED driver scaling. |
| SYNC (34) | External sync input | Accepts 200–700kHz external clock; internal 90kΩ pull-down - enables system-level timing coordination. |
| RT (35) | Frequency set resistor | Resistor to SGND sets fSW: 147kΩ → 200kHz, 59kΩ → 400kHz, 29.1kΩ → 700kHz - enables EMI optimization. |
| VC (36) | Error amplifier output & threshold | 0.7–1.9V control voltage sets current limit; also serves as compensation node for loop stability. |
| FB (37) | Output voltage feedback | Regulates to 1.2V (±1.5%); detects open LED (>1.15V) or short LED (<400mV) - primary safety and protection interface. |
| OVLO (38) | Overvoltage lockout | Shuts down if >3.15V (rising); 75mV hysteresis - protects downstream components from overvoltage transients. |
| Exposed Pad (39) | Signal ground (SGND) | Thermally and electrically critical; must be soldered to solid PCB ground plane - improves thermal resistance by ~28°C/W. |
Key Features
| Feature | Design Value |
|---|---|
| 4-switch single-inductor topology | Enables VIN above, below, or equal to VOUT without topology change - eliminates need for separate buck/boost stages. |
| True Color PWM™ dimming | Delivers flicker-free, high-contrast LED dimming with no color shift - critical for automotive adaptive lighting and display backlighting. |
| No top MOSFET refresh cycle | Eliminates unnecessary switching loss in pure buck/boost modes - improves efficiency by 1–2% vs conventional controllers. |
| VOUT disconnected from VIN during shutdown | Prevents backfeed into input rail when disabled - enhances system safety and meets automotive ISO 16750-2 requirements. |
| Integrated open/short LED fault protection | Dedicated OPENLED/SHORTLED pins provide immediate, latchable fault signaling - reduces BOM count and firmware complexity. |
| 100W+ per IC capability | Validated 100W (33.3V/3A) operation with 98.5% efficiency - supports high-lumen LED modules in compact form factors. |
Applications
| Automotive Head Lamps | Industrial High-Bay Lighting |
|---|---|
Use Scenario: Adaptive driving beam (ADB) systems requiring dynamic LED current control across varying battery voltage (9–16V) and LED forward voltage (20–52V). IC Role / Device Role / Timing Role: Primary LED current controller managing four-quadrant power conversion with seamless buck-boost transitions during beam pattern changes. Use Value: Maintains ±6% LED current accuracy despite 7:1 VIN/VOUT ratio variation - ensures consistent photometric output and compliance with ECE R123. | Use Scenario: 100–200W LED fixtures powered from 24–48V DC industrial rails, operating in ambient temperatures up to 70°C. IC Role / Device Role / Timing Role: Constant-current LED driver with integrated input current limiting and thermal derating via CTRL pin. Use Value: Delivers 98.5% peak efficiency and 125°C junction rating - enables fanless operation and extends fixture lifetime in enclosed enclosures. |
| Emergency Vehicle Warning Lights | Portable Battery-Powered Lighting |
Use Scenario: Flashing red/blue LED arrays powered from 12V vehicle batteries with rapid on/off cycling and ESD-prone environments. IC Role / Device Role / Timing Role: High-reliability LED controller with robust fault detection (open/short LED, OVLO) and true color PWM dimming for strobe control. Use Value: OPENLED/SHORTLED outputs trigger immediate fault isolation; PWMOUT drives external MOSFET to disconnect LED string - prevents thermal runaway during flash duty cycles. | Use Scenario: Rechargeable 12–24V Li-ion powered work lights delivering 3A LED current with runtime optimization. IC Role / Device Role / Timing Role: Wide-input buck-boost LED driver supporting battery discharge from 24V down to 9V while maintaining constant LED brightness. Use Value: 4.7V minimum VIN enables full utilization of battery capacity; 1µA shutdown IQ preserves charge during standby - extends usable runtime by >15%. |
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 higher 80V rating, improved 99% efficiency, integrated boost diode, and enhanced spread-spectrum EMI reduction. | Targets next-gen automotive and industrial designs where higher voltage margin and lower EMI are required. | Select LT8391EFE#PBF for new designs needing extended voltage range, better thermal performance, or stricter EMC compliance. |
| LTC3789EGN#PBF | 4-switch buck-boost controller without integrated LED-specific features: no OPENLED/SHORTLED pins, no ISMON/IVINMON monitors, no True Color PWM™. | Used in general-purpose DC/DC conversion (e.g., 12V–48V telecom supplies), not optimized for LED current regulation. | Choose LTC3789EGN#PBF only when LED-specific protection, dimming, and monitoring are unnecessary and cost is primary concern. |
Compared with LT3791IFE#PBF, the LT8391EFE#PBF offers higher voltage tolerance and EMI performance but requires layout revision; the LTC3789EGN#PBF lacks LED-specific safety and dimming features, making it unsuitable for lighting applications requiring certified fault response or flicker-free dimming.
Availability
LT3791IFE#PBF is available at Aetrix Electronics and suitable for automotive headlamps, industrial high-bay lighting, emergency warning systems, and portable battery-powered LED fixtures requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT3791IFE#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 (formerly Linear Technology) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving automotive, industrial, communications, and healthcare markets.
The LT3791 product line was developed specifically for high-efficiency, wide-input-range LED driver applications requiring seamless buck-boost operation, precise current regulation, and robust fault protection in demanding environments.
FAQ
What is the maximum LED string voltage supported by the LT3791IFE#PBF?
The LT3791IFE#PBF supports LED string voltages up to 52V, as specified in its absolute maximum ratings and electrical characteristics. This is distinct from its 60V output capability - the 52V limit applies specifically to the LED forward voltage range over which ±6% current accuracy is guaranteed. Operation beyond 52V may compromise regulation accuracy and is not recommended for production designs using LT3791IFE#PBF.
Does the LT3791IFE#PBF require external Schottky diodes for synchronous rectification?
No, the LT3791IFE#PBF does not require external Schottky diodes for synchronous rectification. Its gate drivers are designed to fully control all four N-channel MOSFETs in the 4-switch buck-boost topology. However, adding Schottky diodes across M2 and M4 can improve peak efficiency by 1–2% at 500kHz by reducing dead-time conduction losses - this is optional and application-dependent, not mandatory for LT3791IFE#PBF functionality.
How does the LT3791IFE#PBF handle transitions between buck, boost, and buck-boost operating modes?
The LT3791IFE#PBF handles mode transitions seamlessly using its proprietary control architecture and dual current-sense amplifiers. It continuously monitors ISP-ISN (LED current), IVINP-IVINN (input current), and FB (output voltage), selecting the dominant feedback signal to determine operating mode. No external intervention or mode-select pins are needed - transitions occur automatically within a single switching cycle as VIN approaches VOUT, ensuring stable regulation without output disturbance during LT3791IFE#PBF operation.
Can the LT3791IFE#PBF be synchronized to an external clock source?
Yes, the LT3791IFE#PBF supports external synchronization via its SYNC pin (Pin 34), which accepts clock signals from 200kHz to 700kHz. The internal 90kΩ pull-down resistor allows direct connection to CMOS/TTL clock sources. When synchronized, the LT3791IFE#PBF aligns its rising edge to the external SYNC signal, enabling EMI reduction through frequency dithering or multi-phase interleaving with other LT3791IFE#PBF devices using CLKOUT.
What thermal management considerations apply to the LT3791IFE#PBF in 100W LED driver designs?
For 100W LED driver designs, the LT3791IFE#PBF requires proper thermal management via its exposed pad (Pin 39), which must be soldered to a large PCB copper area connected to system ground. With θJA = 28°C/W, maintaining junction temperature ≤125°C demands ≤2.8W dissipation - achievable with ≥4 cm² of 2-oz copper and thermal vias. The LT3791IFE#PBF's internal overtemperature protection activates at 150°C, but continuous operation above 125°C degrades reliability; thermal design must ensure safe derating per Analog Devices' application notes.
LT3791IFE#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
LT3791IFE#PBF FAQ
1.How can I place an order for LT3791IFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3791IFE#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 LT3791IFE#PBF reliable?
The price and inventory of LT3791IFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3791IFE#PBF is usually 5 days.
3.What payment methods are accepted for LT3791IFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3791IFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3791IFE#PBF?
LT3791IFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3791IFE#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 LT3791IFE#PBF?
For technical support, including LT3791IFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3791IFE#PBF requirements.
6.How does Aetrix verify that LT3791IFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3791IFE#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 LT3791IFE#PBF meets industry standards.
7.What is the process for return or replacement of LT3791IFE#PBF?
All LT3791IFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3791IFE#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 LT3791IFE#PBF part is unused and in its original packaging.
Return procedure for LT3791IFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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