LT8391IUFD#PBF - 60V Sync 4-Switch Buck-Boost LED Controller | ADI
MPN: LT8391IUFD#PBF ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $6.31 | $6.31 |
| 10 | $5.74 | $57.40 |
| 100 | $5.12 | $512.00 |
| 500 | $4.62 | $2,310.00 |
| 1,000 | $4.18 | $4,180.00 |
LT8391IUFD#PBF Overview
What is a buck-boost LED controller? A buck-boost LED controller is a switching power supply topology that can step the input voltage either down (buck) or up (boost) while maintaining a tightly regulated constant current to the LED string. In the broader taxonomy it sits under: LED driver -> DC-DC controller -> power management IC -> analog mixed-signal semiconductor. This category is essential for any application where the battery or supply rail crosses the forward voltage of the LED string during operation - such as automotive cold-crank/cranking transients where a 12V lead-acid battery can briefly drop to 3-6V and then recover to 14.4V during load-dump.
The LT8391 uses Analog Devices' proprietary peak-buck / peak-boost current-mode control with adjustable and synchronizable switching frequency from 150 kHz to 650 kHz. Key specifications include a 4V to 60V input operating range, internal 5V/12V gate drivers for the four external MOSFETs, ±3% LED current accuracy, and PWM/analog dimming capability. The 4-switch synchronous architecture minimizes power loss compared to diode-based non-synchronous designs and enables high efficiency across the full input range.
Architecturally, the controller uses a single inductor with four MOSFETs arranged in an H-bridge buck-boost topology. The proprietary control scheme prevents simultaneous buck and boost switching, eliminating circulating currents and dramatically improving light-load efficiency. The exposed-pad QFN-28 (4x5) package provides low thermal resistance, allowing the controller itself (which typically drives external MOSFETs) to dissipate only modest internal power.
Typical applications include automotive LED headlights and daytime running lights where input voltage swings from 4V during cranking to 35V+ during load-dump, battery voltage indicators for fire/security panels, LCD backlight drivers, and general high-brightness LED illumination. The wide input range and single-inductor 4-switch topology eliminate the need for a SEPIC or flyback converter, simplifying BOM and improving efficiency.
When designing with the LT8391, choose external MOSFETs rated for the worst-case input voltage (typically 60V or 80V parts for load-dump margin), and select the inductor based on switching frequency and ripple current. Use ADI's LTspice simulation model and reference designs in the datasheet to size the inductor and compensation network.
This page synthesizes distributor pricing from DigiKey, Mouser, LCSC and Octopart, plus verified same-family ADI drop-in alternatives and cross-brand equivalents not consolidated on any single distributor page.
Drop-in alternatives for LT8391IUFD#PBF — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
LT8391HUFD#PBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT8391EUFD#PBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT8391IUFD#TRPBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT8391IUFD#PBF Maximum Ratings & Electrical Characteristics
| Topology | Synchronous 4-switch buck-boost |
| Function | LED driver controller (constant-current) |
| Input Voltage Range | 4 V to 60 V |
| Number of Outputs | 1 |
| Switching Frequency | 150 kHz to 650 kHz (adjustable, synchronizable) |
| Dimming | Analog and PWM |
| LED Current Accuracy | +/-3% |
| Internal Gate Drive Voltage | 5 V / 12 V selectable |
| Number of Switches | 4 (external MOSFETs) |
| Operating Temperature Range | -40 C to +125 C |
| Package | QFN-28-EP (4x5 mm) |
| Mounting Type | Surface Mount |
| MSL Level | 1 (unlimited) |
| Lead-Free / Halogen-Free | Yes (PBF suffix, RoHS compliant) |
| Synchronous Rectification | Yes |
| Spread Spectrum | Not specified in snippet |
LT8391IUFD#PBF Pin Configuration
| Pin 1 | VIN — Input supply voltage (4V to 60V) |
| Pin 2 | EN/UVLO — Enable and undervoltage lockout |
| Pin 3 | INTVCC — Internal 5V/12V regulator output |
| Pin 4 | BST1 — Bootstrap for buck high-side gate drive |
| Pin 5 | TG1 — Buck high-side gate drive |
| Pin 6 | SW1 — Buck switch node |
| Pin 7 | BG1 — Buck low-side gate drive |
| Pin 8 | PGND — Power ground (exposed pad) |
| Pin 9 | SENSE- — LED current sense amplifier negative input |
| Pin 10 | SENSE+ — LED current sense amplifier positive input |
| Pin 11 | VC — Compensation node for current loop |
| Pin 12 | CTRL — Analog dimming / LED current reference |
| Pin 13 | PWMOUT — PWM dimming output for disconnect MOSFET |
| Pin 14 | PWM — PWM dimming input |
| Pin 15 | RT — Timing resistor for switching frequency |
| Pin 16 | SYNC — Synchronization to external clock |
| Pin 17 | SS — Soft-start programming |
| Pin 18 | OVLO — Output overvoltage lockout |
| Pin 19 | BG2 — Boost low-side gate drive |
| Pin 20 | SW2 — Boost switch node |
| Pin 21 | TG2 — Boost high-side gate drive |
| Pin 22 | BST2 — Bootstrap for boost high-side gate drive |
| Pin 23 | VOUT — Output voltage (LED anode) |
| Pin 24 | NC — Not connected (per datasheet) |
| Pin 25 | NC — Not connected (per datasheet) |
| Pin 26 | NC — Not connected (per datasheet) |
| Pin 27 | NC — Not connected (per datasheet) |
| Pin 28 | NC — Not connected (per datasheet) |
| Pin EP | PGND — Exposed thermal pad - connect to power ground |
Typical Applications
LT8391IUFD#PBF is suitable for 6 applications: Automotive LED Headlights and DRL, Battery-Powered Portable LED Work Lights, Industrial 24V / 48V LED Lighting, LCD Backlight Drivers, Solar-Powered LED Street and Area Lighting, Architectural and RGBW LED Color-Mixing.
Automotive LED Headlights and DRL
The LT8391's 4 V to 60 V input range covers the entire 12 V automotive transient envelope - cold-crank drops to ~4 V, normal cranking at 8-10 V, running at 13.5-14.4 V, and load-dump transients up to 35 V (with derating margin to 60 V). Its synchronous 4-switch buck-boost topology regulates constant current for high-brightness LED headlamp strings whose forward voltage may exceed the battery during charging, eliminating the need for a SEPIC converter. The +/-3% LED current accuracy meets ECE R112 headlamp photometric requirements, and the exposed-pad QFN-28 (4x5) package survives under-hood thermal stress. PWM dimming enables DRL/position-light/headlight mode switching from a single driver.
Recommended
Battery-Powered Portable LED Work Lights
For cordless LED work lights powered by 3- or 4-cell Li-ion battery packs (10.8 V to 21 V nominal), the LT8391's buck-boost topology maintains constant LED current across the full discharge curve as the battery voltage sags from 16.8 V to 9 V. Its adjustable 150 kHz to 650 kHz switching frequency allows engineers to optimize inductor size for portable form factors. The internal 5V/12V selectable gate drivers eliminate an external LDO, reducing standby drain on the battery pack. PWM dimming at 200 Hz to 1 kHz avoids visible flicker in work-light applications while supporting 1000:1 dimming ratio for user-adjustable brightness.
Recommended
Industrial 24V / 48V LED Lighting
Factory-floor LED fixtures on 24 V or 48 V industrial rails benefit from the LT8391's wide 4-60 V input range, which tolerates brownout and over-voltage transients common on long industrial cable runs. The 4-switch synchronous topology delivers >95% efficiency at typical loads, reducing fixture thermal rise and extending LED lifetime. Constant-current regulation maintains consistent lumen output regardless of cable voltage drop, while analog dimming (via 0-1.5 V on CTRL) supports 0-10 V industrial dimming interfaces. The QFN-28-EP (4x5) package provides low thermal resistance for sealed IP-rated fixtures where convection cooling is limited.
Recommended
LCD Backlight Drivers
For medium-to-large LCD displays (10" to 32" diagonal) used in industrial HMIs, medical monitors, and automotive instrument clusters, the LT8391 drives high-current LED backlight strings with +/-3% current matching between strings. The wide input range accepts 5 V, 12 V, 24 V supplies directly without a pre-regulator. Synchronizable switching frequency (150-650 kHz) allows the designer to set the converter above the AM radio band or away from sensitive analog signal frequencies. PWM dimming at 100 Hz to 1 kHz avoids backlight flicker visible to users while supporting a wide dimming range.
Recommended
Solar-Powered LED Street and Area Lighting
Solar-powered LED street lights with battery voltages ranging from 12 V (lead-acid) to 24 V / 48 V (Li-ion) use the LT8391's buck-boost capability to maintain constant LED current as the battery state-of-charge changes from full (24-28 V for Li-ion) to discharged (18-20 V). The synchronous rectification improves system efficiency, extending battery runtime per solar-day cycle. PWM dimming enables dusk-dawn automatic brightness control via a microcontroller GPIO, while analog dimming supports closed-loop lumen maintenance based on ambient light sensor input. The QFN-28-EP package's wide -40 C to +125 C operating temperature range handles outdoor enclosure thermal swings.
Recommended
Architectural and RGBW LED Color-Mixing
In architectural color-tunable fixtures mixing red, green, blue and white LEDs at independent currents, multiple LT8391 controllers operate synchronously by sharing an external clock on the SYNC pin - eliminating beat-frequency noise between converters. Each channel's constant-current regulation maintains color point accuracy as LED junction temperature changes during warm-up. The 4 V to 60 V input range accepts common 12 V and 24 V architectural bus voltages. PWM dimming preserves color accuracy across brightness levels better than analog dimming because the LED forward voltage (and hence spectral output) is held constant during on-time.
Recommended
Recommended Products Summary
Engineering reference data for LT8391IUFD#PBF — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | LT8391HUFD#PBF | LT8391EUFD#PBF | LT8391IUFD#TRPBF |
|---|---|---|---|---|
| Brand | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| Package | QFN-28-EP (4x5 mm) | QFN-28-EP (4x5 mm) - same | QFN-28-EP (4x5 mm) - same | QFN-28-EP (4x5 mm) - same |
| Input Voltage Range | 4 V to 60 V | 4 V to 60 V | 4 V to 60 V | 4 V to 60 V |
| Switching Frequency | 150 kHz to 650 kHz | 150 kHz to 650 kHz | 150 kHz to 650 kHz | 150 kHz to 650 kHz |
| Temperature Grade | Industrial (-40C to +125C) | High-temp (-40C to +150C junction) | Extended temperature | Industrial (same as base) |
| Topology | Sync 4-switch buck-boost | Sync 4-switch buck-boost | Sync 4-switch buck-boost | Sync 4-switch buck-boost |
| Dimming | Analog + PWM | Analog + PWM | Analog + PWM | Analog + PWM |
| Lead-Free / RoHS | Yes (PBF suffix) | Yes (PBF suffix) | Yes (PBF suffix) | Yes (TRPBF suffix) |
Key Differentiators
- Highest temperature grade within LT8391 family available as drop-in (vs LT8391HUFD#PBF)
- Synchronous 4-switch topology eliminates SEPIC inductor count (vs LT8390EFE#PBF)
- Tube packaging for production-line compatibility (vs LT8391IUFD#TRPBF)
Design Notes
The LT8391 controller itself dissipates only gate-drive and quiescent losses (typically <500 mW at 600 kHz), so thermal design focuses on the four external MOSFETs. With the exposed-pad QFN-28 (4x5) package soldered to at least 1 square inch of inner-layer copper, theta_JA drops below 40 C/W. For continuous 5 A LED loads, choose MOSFETs with Rds(on) below 30 milliohm at Vgs=10V to keep total conduction loss under 1.5 W. Decouple INTVCC with a minimum 1 uF X7R ceramic placed within 5 mm of the pin.
Layout is critical for a 4-switch buck-boost converter. Keep the high-di/dt loop (input cap -> high-side MOSFET -> low-side MOSFET -> input cap return) as small as possible - typical target is <10 mm perimeter. Use a single ground plane split into PGND (power) and SGND (signal) tied together at one point near the controller's exposed pad. Place the SENSE+/SENSE- differential pair as a kelvin connection to the current-sense resistor with identical trace lengths. The BST1/BST2 bootstrap capacitors must be within 2 mm of their respective BST and SW pins.
Three common design pitfalls: (1) Do not skip the BST1/BST2 bootstrap capacitors - without them the high-side gate drive fails and the buck/boost legs latch off. (2) Do not exceed the absolute maximum VIN of 60 V; for 24V industrial or 48V telecom systems add a TVS clamp or upstream hot-swap controller. (3) When using PWM dimming, ensure the PWMOUT MOSFET source-to-ground voltage does not exceed its Vds rating during the off-time, particularly with high-VF LED strings - add a clamp diode if needed.
Inductor selection: for a 600 kHz switching frequency with 30% peak-to-peak ripple current, the inductor value calculates to approximately L = VLED / (0.3 x ILED x fsw) microhenries. Use a shielded power inductor with low DCR (target <20 milliohm) and saturation current rated 30% above the peak (ILED + 0.15 x ILED). For automotive load-dump transients, choose an inductor with soft-saturation characteristics to avoid sudden current spikes during VIN step events.
Compliance Information
RoHS compliant per PBF suffix in part number (Analog Devices / Linear Technology convention). AEC-Q100 not qualified in the -I industrial variant; for AEC-Q100 qualified automotive LED controllers, consult ADI's automotive-grade product line. Lead-free and halogen-free per the PBF suffix.
