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Analog Devices Inc. LT3478IFE
- Part No.:
- LT3478IFE
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3478IFE.pdf
- Description:
- IC LED DRV RGLTR PWM 16TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,260
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Product details
Overview
LT3478IFE from Analog Devices (formerly Linear Technology) is a 4.5A monolithic step-up DC/DC LED driver IC with true-color PWM dimming, designed for constant-current driving of high-power LED strings in boost, buck-boost, or buck topologies. It features a 42V internal NPN switch, 2.8V–36V input range, and operates across –40°C to 125°C junction temperature. Used in automotive TFT LCD backlights and heads-up displays requiring stable 700mA LED current at 15W output.
For engineers reviewing the LT3478IFE datasheet, LT3478IFE pinout, LT3478IFE application, or LT3478IFE equivalent, key selection criteria include its 3000:1 PWM dimming range with color fidelity, integrated inductor current sensing, programmable OVP via OVPSET, thermal derating capability via CTRL2, and compatibility with external RSENSE for sub-100mV current sense accuracy.
Technical Context
The LT3478IFE implements current-mode control using LED current-not output voltage-as the primary feedback signal. Its transconductance error amplifier (VC pin) regulates peak switch current to maintain programmed LED current, with slope compensation ensuring loop stability across wide duty cycles.
It supports three operating modes (boost/buck-buck-boost) via external component configuration, uses an external RT resistor to set switching frequency from 200kHz to 2.25MHz, and integrates inrush current protection, open-LED detection, and micropower shutdown with 3µA quiescent current when SHDN = 0V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.8V to 36V - supports 12V automotive systems and wide-range industrial supplies without pre-regulation. |
| Max Output Current | 1050mA (LT3478IFE-1 variant); LT3478IFE uses external RSENSE for scalable current programming down to 100mA with ±3% accuracy. |
| Internal Switch Rating | 42V VCE(SAT), 4.5A continuous - enables direct drive of multi-LED strings up to ~42V without external MOSFETs. |
| PWM Dimming Range | 3000:1 (0.033%–100% duty cycle at 100Hz) - preserves consistent LED chromaticity across full brightness range. |
| Operating Temp Range | –40°C to +125°C junction - qualified for under-hood automotive lighting and industrial ambient environments. |
| Switching Frequency | 200kHz–2.25MHz (RT-programmable) - allows trade-off between inductor size (higher f) and efficiency (lower f). |
| OVP Threshold | Programmable 12.3V–41V via OVPSET pin (OVP = OVPSET × 41) - protects against open-LED fault conditions. |
Pinout & Package
LT3478IFE is housed in a 16-lead thermally enhanced TSSOP package with exposed pad (Pin 17) that must be soldered to PCB ground plane for thermal management (θJA = 35°C/W). The exposed pad is PGND and serves as primary thermal path.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SW (Pins 1, 2) | Switch Collector Node | Connects to inductor and Schottky diode anode; fused internally; requires minimal trace area to reduce EMI. |
| VIN (Pin 3) | Main Input Supply | Supplies bias and base drive for internal NPN; must be locally bypassed with ceramic capacitor. |
| VS (Pin 4) | Inductor Supply Input | Separate supply for inductor current sensing; can be shorted to VIN if single-rail system. |
| L (Pin 5) | Inductor Current Sense | Internal resistor between VS and L monitors inrush; exceeding 6A triggers immediate shutdown. |
| VOUT (Pin 6) | Boost Output Voltage | Monitored for open-LED protection; connects to output capacitor and LED string anode. |
| LED (Pin 7) | LED String Return | Current-sense node: internal 0.1Ω resistor (LT3478IFE-1) or external RSENSE (LT3478IFE) between VOUT and LED. |
| OVPSET (Pin 8) | OVP Programming Input | Sets overvoltage threshold: OVP = OVPSET × 41V; 0.3V–1V input yields 12.3V–41V clamp. |
| VC (Pin 9) | Error Amplifier Output | Transconductance amplifier output; used for loop compensation and peak current control. |
| VREF (Pin 10) | 1.24V Bandgap Reference | Stable 1.24V source (±2.2% over temp); supplies ≤100µA; used to bias CTRL1/CTRL2/OVPSET dividers. |
| SHDN (Pin 11) | Shutdown Control | 1.4V UVLO threshold; 10µA hysteresis enables programmable undervoltage lockout with resistor divider. |
| CTRL1 (Pin 12) | Max LED Current Set | Voltage input (0.1V–1.05V) programs max LED current linearly; 0.7V = 700mA (LT3478IFE-1). |
| CTRL2 (Pin 13) | Thermal Derating Input | Accepts negative-temp-coefficient voltage to reduce LED current above breakpoint temperature. |
| PWM (Pin 14) | PWM Dimming Enable | 1V threshold; controls external MOSFET in LED cathode path for true-color dimming without color shift. |
| RT (Pin 15) | Frequency Set Resistor | Resistor to GND sets fSW: 9.09kΩ = 2.25MHz, 31.6kΩ = 1.12MHz, 200kΩ = 200kHz. |
| SS (Pin 16) | Soft-Start Timing | Capacitor to GND sets startup ramp time; discharges on fault to latch shutdown until reset. |
| Exposed Pad (Pin 17) | Power Ground / Thermal Path | Must be soldered to solid copper ground plane; primary thermal conduction path (TJMAX = 125°C). |
Key Features
| Feature | Design Value |
|---|---|
| True Color PWM™ Dimming | 3000:1 dimming ratio with constant LED chromaticity-enables precise brightness control in HUDs and instrument clusters without color drift. |
| Integrated Inductor Current Sensing | Internal resistor between VS and L pins detects inrush; eliminates need for external current-sense resistor and associated layout complexity. |
| Programmable Thermal Derating | CTRL2 pin accepts NTC-based voltage divider to automatically scale LED current vs. temperature-maximizes lumen output while preventing LED thermal runaway. |
| Wide Input Voltage Range | 2.8V–36V operation accommodates cold-crank (6V) to load-dump (36V) transients in automotive 12V systems without external protection. |
| Open LED Protection | OVPSET pin enables user-defined overvoltage clamp (12.3V–41V); prevents damage during LED string open-circuit faults. |
| Micropower Shutdown | 3µA shutdown current (SHDN = 0V) meets automotive "always-on" low-power requirements for courtesy lighting and memory retention. |
Applications
| Automotive TFT LCD Backlight | Automotive Heads-Up Display (HUD) |
|---|---|
Use Scenario: Driving 6× white Luxeon III LEDs in series from 8V–16V vehicle battery for high-brightness LCD panel illumination. IC Role / Device Role / Timing Role: Constant-current boost controller regulating 700mA LED string current with 3000:1 PWM dimming synchronized to display frame rate. Use Value: Maintains uniform luminance and color point across full dimming range-critical for daytime/nighttime auto-brightness adaptation in infotainment systems. |
Use Scenario: Powering green/cyan/blue Luxeon V emitters in projection-based HUD optics requiring precise current stability under vibration and thermal cycling. IC Role / Device Role / Timing Role: Buck-boost LED driver with thermal derating (via CTRL2) to sustain 1000mA peak current while limiting junction temperature in confined optical housing. Use Value: Enables maximum lumen output without LED degradation-extending projector lifetime and maintaining image contrast in sunlight-readable HUDs. |
| Automotive Courtesy Lighting | Industrial High-Bay LED Fixture |
Use Scenario: Controlling warm-white LED strips in door sills and footwells with smooth fade-in/fade-out via PWM dimming. IC Role / Device Role / Timing Role: Boost-mode LED driver with soft-start (SS pin) and programmable UVLO (SHDN pin) for seamless entry/exit lighting sequences. Use Value: Eliminates turn-on pop-in and ensures reliable operation during low-battery conditions (down to 2.8V VIN), improving user experience and system robustness. |
Use Scenario: Driving 12–24 high-power white LEDs in series from 24VDC industrial power rail in warehouse lighting fixtures. IC Role / Device Role / Timing Role: High-efficiency boost converter with 2.25MHz switching (RT = 9.09kΩ) to minimize inductor size in space-constrained metal housings. Use Value: Reduces magnetic component volume by >50% vs. 500kHz design-enabling compact, thermally optimized fixture architecture with 95% peak efficiency. |
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 | Integrates 0.1Ω LED current sense resistor; fixed 100mA–1050mA range; no external RSENSE required. | Better suited for cost-sensitive designs where 1% current accuracy at mid-range currents suffices; less flexible for <100mA or >1A needs. | Select LT3478IFE-1 when minimizing BOM count and board space is prioritized over ultra-low-current precision or extended range. |
| LM3409QMY/NOPB | 4A buck LED controller (external MOSFET); 4.5V–42V input; analog/PWM dimming; no integrated switch. | Requires external high-side N-channel MOSFET and gate driver; supports higher output power (>30W) and wider thermal margin in forced-air systems. | Choose LM3409QMY/NOPB for >30W applications or where discrete FET selection enables optimized thermal/power trade-offs beyond monolithic limits. |
Compared with LT3478IFE-1, the LT3478IFE offers superior current programming resolution below 100mA and higher accuracy above 1A via external RSENSE; versus LM3409QMY/NOPB, it delivers lower system-level component count and faster time-to-light but trades off ultimate power scalability and thermal headroom.
Availability
LT3478IFE is available at Aetrix Electronics and suitable for automotive TFT LCD backlights, heads-up displays, and industrial high-bay LED fixtures requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT3478IFE 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 legacy Linear parts including the LT3478 family.
The LT3478IFE belongs to Linear's high-power LED driver product line, engineered specifically for automotive and industrial lighting systems demanding wide-input operation, precise current regulation, and robust fault protection without external sensing components.
FAQ
What is the guaranteed operating temperature range for the LT3478IFE?
The LT3478IFE is guaranteed over the full –40°C to +125°C junction temperature range, as explicitly stated in the datasheet's ordering information section. This exceeds the 0°C to +125°C spec of the EFE grade and qualifies the LT3478IFE for under-hood automotive use and industrial environments with extreme thermal cycling.
How does the LT3478IFE differ from the LT3478IFE-1 variant?
The LT3478IFE uses an external RSENSE resistor for LED current sensing, enabling programmable current from 100mA to >1A with higher accuracy at low currents. In contrast, the LT3478IFE-1 integrates a 0.1Ω sense resistor, fixing the current range to 100mA–1050mA and eliminating one external component-but sacrificing flexibility and sub-100mV sense resolution.
Can the LT3478IFE drive LEDs in buck configuration?
Yes-the LT3478IFE supports buck, boost, and buck-boost topologies via external component configuration. In buck mode, the LED string connects between VOUT and ground, with the inductor placed between VIN and SW. The datasheet Figure 10 provides a verified buck-mode schematic with component values for 700mA operation.
What is the purpose of the VS and L pins on the LT3478IFE?
The VS (inductor supply) and L (inductor) pins enable separate routing of inductor power and current sensing. An internal resistor between them monitors inductor current for inrush protection. If only one supply is available, VS may be shorted to VIN; alternatively, connecting the inductor directly to L (and leaving VS open) disables input current monitoring-requiring local bypass on L.
How is overvoltage protection configured on the LT3478IFE?
OVP is configured using the OVPSET pin: applying a voltage from 0.3V to 1.0V sets the VOUT overvoltage clamp to OVP = OVPSET × 41V (e.g., 0.5V → 20.5V). This protects against open-LED faults without external comparators or Zener diodes-reducing BOM count and improving reliability in automotive lighting modules.
LT3478IFE Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- True Color PWM™
- Package/Case:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tube
- Product Status:
- Obsolete
- 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 FAQ
1.How can I place an order for LT3478IFE through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3478IFE 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 reliable?
The price and inventory of LT3478IFE are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3478IFE is usually 5 days.
3.What payment methods are accepted for LT3478IFE?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3478IFE transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3478IFE?
LT3478IFE orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3478IFE 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?
For technical support, including LT3478IFE datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3478IFE requirements.
6.How does Aetrix verify that LT3478IFE is sourced from the original manufacturer or authorized distributors?
All LT3478IFE 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 meets industry standards.
7.What is the process for return or replacement of LT3478IFE?
All LT3478IFE units undergo pre-shipment inspection (PSI). If there is an issue with LT3478IFE, 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 part is unused and in its original packaging.
Return procedure for LT3478IFE:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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