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Analog Devices Inc. LT3478IFE#PBF
- Part No.:
- LT3478IFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3478IFE#PBF.pdf
- Description:
- IC LED DRV RGLTR PWM 16TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:150
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Product details
Overview
LT3478IFE#PBF from Analog Devices (formerly Linear Technology) is a 4.5A monolithic boost LED driver IC with True Color PWM dimming, designed for high-power constant-current LED applications. It operates from 2.8V to 36V input, delivers up to 1050mA LED current (via external sense resistor), supports 200kHz–2.25MHz programmable switching frequency, and integrates inrush protection, open-LED OVP, and temperature-de-rated current control. It is used in automotive TFT LCD backlights driving six white Luxeon III LEDs at 700mA.
For engineers reviewing the LT3478IFE#PBF datasheet, LT3478IFE#PBF pinout, LT3478IFE#PBF application, or LT3478IFE#PBF equivalent, key selection considerations include its 42V/4.5A internal NPN switch, 3000:1 PWM dimming range with color stability, dual CTRL pins for LED current and thermal derating programming, and thermally enhanced 16-pin TSSOP package with exposed pad.
Technical Context
The LT3478IFE#PBF implements a current-mode boost topology where LED current-not output voltage-serves as the primary feedback signal. Its transconductance error amplifier (VC pin) regulates peak switch current to maintain precise constant current across varying LED forward voltages and input conditions.
It features dual independent control paths: CTRL1 sets maximum LED current linearly (100mA–1050mA), while CTRL2 enables negative-temperature-coefficient derating via external resistor networks. The integrated 1.24V bandgap reference (VREF) supplies bias for all analog control functions and supports resistor-divider programming of UVLO, OVP, and current thresholds.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.8V to 36V - supports wide automotive battery range including cold-crank (6V) and load-dump (36V) transients. |
| Max LED Current | 1050mA - set via external RSENSE and CTRL1 voltage; enables high-brightness multi-LED strings without external current amplifiers. |
| Internal Switch | 42V VCE(SAT), 4.5A rating - eliminates need for external high-voltage/high-current transistor; 270mV saturation reduces conduction loss at full load. |
| Switching Frequency | 200kHz to 2.25MHz - adjustable via RT pin resistor; higher frequencies shrink inductor size but trade off efficiency due to switching losses. |
| PWM Dimming Range | 3000:1 - maintains constant LED chromaticity across full dimming range using dedicated PWM pin and external MOSFET gate control. |
| OVP Threshold | Programmable 12.3V to 41V - set by OVPSET pin voltage (0.3V–1V); protects against open-LED fault by clamping VOUT before overvoltage damages LEDs or capacitors. |
| Junction Temp Range | –40°C to +125°C - fully specified and guaranteed; enables deployment in under-hood automotive environments and industrial lighting enclosures. |
Pinout & Package
LT3478IFE#PBF is housed in a 16-pin thermally enhanced TSSOP package with an exposed pad (Pin 17) that must be soldered to PCB ground for thermal performance (θJA = 35°C/W). The package supports high-power dissipation in compact automotive and industrial LED driver layouts.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SW (Pins 1,2) | Collector of internal NPN power switch | Fused internally; connects to inductor and Schottky diode anode; requires minimal trace area to reduce EMI radiation. |
| VIN (Pin 3) | Main input supply rail | Supplies base drive current to internal NPN; must be locally bypassed with low-ESR capacitor to minimize noise and voltage droop. |
| VS (Pin 4) | Inductor supply input | Separate supply path for inductor; can be shorted to VIN if single-rail system; enables optimized inrush current limiting. |
| L (Pin 5) | Inductor current sensing node | Internal resistor between VS and L monitors inductor current; triggers immediate shutdown if >6A peak detected. |
| VOUT (Pin 6) | Boost converter output | Connected to LED string anode via output capacitor; monitored internally for open-LED OVP detection. |
| LED (Pin 7) | LED string cathode connection | Current-sense node for LED string; interfaces with external RSENSE (LT3478) or internal 0.1Ω resistor (LT3478-1). |
| OVPSET (Pin 8) | OVP threshold programming input | Voltage sets OVP level as OVP = OVPSET × 41V; 0.3V–1V range yields 12.3V–41V clamping window. |
| VC (Pin 9) | Error amplifier output & compensation node | Transconductance amplifier output; used for loop compensation and slope compensation injection in current-mode control. |
| VREF (Pin 10) | 1.24V precision bandgap reference | Stable 1.24V source (±2.2% over temp); supplies bias for CTRL1/CTRL2/OVPSET dividers and loads up to 100µA. |
| SHDN (Pin 11) | Enable/disable control with UVLO hysteresis | 1.4V threshold; 10µA hysteresis current enables programmable undervoltage lockout with external resistor divider. |
| CTRL1 (Pin 12) | Maximum LED current programming | Voltage (0.1V–1.05V) sets max LED current linearly; 0.7V = 700mA for LT3478 with 0.1Ω RSENSE. |
| CTRL2 (Pin 13) | Temperature-dependent LED current derating | Accepts NTC-based voltage with negative tempco; overrides CTRL1 above breakpoint temperature to prevent LED thermal overstress. |
| PWM (Pin 14) | True Color PWM dimming input | 1V threshold; drives external NMOS gate in series with LED cathode; enables 3000:1 dimming without color shift. |
| RT (Pin 15) | Switching frequency programming | Resistor to ground sets fSW; 31.6kΩ = 1.12MHz typical; supports layout-optimized frequency selection. |
| SS (Pin 16) | Soft-start timing capacitor node | Capacitor value sets ramp time; discharges during fault to latch shutdown; recharges at 12µA after fault clearance. |
| Exposed Pad (Pin 17) | Power ground & thermal path | Must be soldered to solid copper plane; primary heat extraction path; reduces junction-to-ambient thermal resistance by >50%. |
Key Features
| Feature | Design Value |
|---|---|
| True Color PWM™ Dimming | 3000:1 dimming ratio with constant LED chromaticity achieved by synchronizing PWM gate drive with converter switching cycle. |
| Integrated Inductor Current Sensing | Internal resistor between VS and L pins detects inrush current; triggers immediate shutdown at >6A peak, eliminating need for external current-sense IC. |
| Dual Independent Current Programming | CTRL1 sets baseline LED current; CTRL2 injects temperature-dependent reduction-enabling full-rated LED current at room temp while preventing thermal runaway at 125°C. |
| Programmable Open-LED Protection | OVPSET pin allows precise setting of VOUT clamp voltage (12.3V–41V); prevents capacitor overvoltage and LED string damage during open-circuit faults. |
| Separate VS and L Pins | Enables independent routing of inductor supply and current-sense paths-reducing noise coupling into sensitive analog control circuitry. |
| Thermally Enhanced TSSOP | 16-pin TSSOP with exposed pad achieves θJA = 35°C/W; supports 4.5A continuous operation without heatsink in standard 2-layer PCB layouts. |
Applications
| Automotive TFT LCD Backlight | High-Brightness Courtesy Lighting |
|---|---|
Use Scenario: Driving six-series white Luxeon III LEDs (3.2V each) from 12V automotive battery in instrument cluster display. IC Role / Device Role / Timing Role: Constant-current boost controller regulating 700mA LED string; uses PWM pin for dashboard brightness adjustment synchronized to vehicle CAN bus commands. Use Value: Maintains consistent white point across 0.033%–100% dimming range; withstands 36V load-dump transients without latch-up or LED overcurrent. | Use Scenario: Illuminating entryway footwells and door sills in luxury vehicles using high-CRI amber LEDs. IC Role / Device Role / Timing Role: Buck-boost LED driver powering 4–8 LEDs from variable 9–16V battery; leverages wide VIN range and programmable OVP for robustness. Use Value: Delivers stable 1050mA output even at cold-crank 6V input; thermal derating via CTRL2 extends LED lifetime beyond 50,000 hours. |
| Heads-Up Display (HUD) Illumination | Industrial Machine Vision Lighting |
Use Scenario: Powering green/cyan LED array in automotive HUD projector requiring flicker-free, high-intensity illumination. IC Role / Device Role / Timing Role: High-frequency (2.25MHz) boost driver minimizing inductor size; uses SS pin for controlled startup to avoid optical flash artifacts. Use Value: 2.25MHz operation enables <10mm³ inductor volume; 3000:1 PWM dimming ensures seamless brightness transitions during HUD symbology updates. | Use Scenario: Driving high-power blue LEDs in automated optical inspection systems requiring precise intensity control and thermal stability. IC Role / Device Role / Timing Role: Constant-current source with dual CTRL pins enabling factory-set current limits and on-the-fly thermal compensation during extended runtime. Use Value: Prevents LED wavelength drift during 24/7 operation; programmable soft-start avoids camera sensor saturation at power-on. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar high-power LED driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3478IFE-1#PBF | Integrates 0.1Ω LED current sense resistor; max LED current limited to 1050mA; no external RSENSE required. | Simplifies BOM and layout for fixed-current designs; less flexible for low-current (<100mA) or ultra-high-accuracy applications. | Select LT3478IFE-1#PBF when design uses fixed 700mA–1050mA LED current and seeks lowest component count. |
| LM3409QMY/NOPB | 42V, 5A buck LED controller with external MOSFET; requires external current-sense amp and gate driver; no integrated switch. | Better suited for high-efficiency buck topologies where input > LED string VF; lacks True Color PWM and integrated OVP. | Select LM3409QMY/NOPB when system requires >95% efficiency at >2A and input voltage exceeds total LED forward voltage. |
Compared with LT3478IFE-1#PBF, the LT3478IFE#PBF offers greater LED current flexibility (down to 100mA) and higher accuracy via external RSENSE, while LM3409QMY/NOPB provides higher peak current and buck-only efficiency but demands more external components and lacks integrated thermal derating.
Availability
LT3478IFE#PBF is available at Aetrix Electronics and suitable for automotive TFT LCD backlights, high-brightness courtesy lighting, and heads-up display illumination requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT3478IFE#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving automotive, industrial, communications, and healthcare markets.
The LT3478IFE#PBF belongs to Linear's high-power LED driver product line, engineered specifically for automotive-grade constant-current LED control with emphasis on thermal resilience, wide input range, and color-stable dimming in safety-critical lighting systems.
FAQ
What is the maximum LED current supported by the LT3478IFE#PBF?
The LT3478IFE#PBF supports up to 1050mA LED current when used with an external 0.1Ω sense resistor and CTRL1 set to 1.05V. Its current-sense architecture scales linearly: 0.7V on CTRL1 yields 700mA, and 0.1V yields 100mA. This range is confirmed in the Electrical Characteristics table (page 3) and Figure G01 of the LT3478/LT3478-1 datasheet.
Does the LT3478IFE#PBF require an external current-sense resistor?
Yes, the LT3478IFE#PBF requires an external current-sense resistor (RSENSE) between the LED and VOUT pins to set LED current. Unlike the LT3478-1 variant, it does not integrate the sense resistor. Typical values are 0.1Ω for 1050mA full scale, yielding 105mV drop-matching the device's 10mV–105mV VSENSE range per the datasheet specification.
How does the LT3478IFE#PBF implement True Color PWM dimming?
The LT3478IFE#PBF implements True Color PWM dimming by using its dedicated PWM pin to gate an external NMOS transistor in series with the LED cathode. This keeps the LED string continuously biased while modulating current flow-preserving forward voltage and junction temperature stability. As confirmed in the Features section and Figure G03, this achieves 3000:1 dimming without chromaticity shift.
What is the purpose of the VS and L pins on the LT3478IFE#PBF?
The VS pin supplies power to the inductor, while the L pin connects to the inductor's other terminal and hosts an internal current-sensing resistor. This separation allows independent routing to minimize noise coupling. When VS and L are shorted, inrush current protection is disabled; when separated, the internal resistor monitors inductor current and shuts down the switch if >6A is detected-protecting against startup surges.
Can the LT3478IFE#PBF operate in buck mode?
Yes, the LT3478IFE#PBF supports buck, boost, and buck-boost configurations as stated in the Features section. In buck mode, the LED string connects between VIN and the LED pin, with SW grounded. This requires external Schottky diode and inductor placement per the Applications Information section (page 9), enabling efficient step-down operation when input voltage exceeds LED string forward voltage.
LT3478IFE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Type:
- DC DC Regulator
- Topology:
- Step-Down (Buck), Step-Up (Boost)
- Internal Switch(s):
- Yes
- Number of Outputs:
- 1
- Voltage - Supply (Min):
- 2.8V
- Voltage - Supply (Max):
- 36V
- Voltage - Output:
- 42V
- Current - Output / Channel:
- 4.5A (Switch)
- Frequency:
- 200kHz ~ 2.25MHz
- Dimming:
- PWM
- Applications:
- Backlight
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-TSSOP-EP
LT3478IFE#PBF FAQ
1.How can I place an order for LT3478IFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3478IFE#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 LT3478IFE#PBF reliable?
The price and inventory of LT3478IFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3478IFE#PBF is usually 5 days.
3.What payment methods are accepted for LT3478IFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3478IFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3478IFE#PBF?
LT3478IFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3478IFE#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 LT3478IFE#PBF?
For technical support, including LT3478IFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3478IFE#PBF requirements.
6.How does Aetrix verify that LT3478IFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3478IFE#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 LT3478IFE#PBF meets industry standards.
7.What is the process for return or replacement of LT3478IFE#PBF?
All LT3478IFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3478IFE#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 LT3478IFE#PBF part is unused and in its original packaging.
Return procedure for LT3478IFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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