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Analog Devices Inc. LT3478EFE#PBF
- Part No.:
- LT3478EFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3478EFE#PBF.pdf
- Description:
- IC LED DRV RGLTR PWM 16TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,058
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Product details
Overview
LT3478EFE#PBF from Analog Devices (formerly Linear Technology) is a 4.5A monolithic step-up DC/DC LED driver IC with True Color PWM™ dimming, 2.8V–36V input range, 42V internal switch, and programmable 100mA–1050mA LED current. It operates in boost, buck-boost, or buck topologies and targets high-brightness automotive lighting systems requiring stable current regulation across temperature and input variation.
For engineers reviewing the LT3478EFE#PBF datasheet, LT3478EFE#PBF pinout, LT3478EFE#PBF application, or LT3478EFE#PBF equivalent, key selection criteria include its 3000:1 PWM dimming range with constant color fidelity, integrated inductor current sensing, programmable OVP via OVPSET pin, thermal derating capability via dual CTRL pins, and 16-pin thermally enhanced TSSOP package with exposed pad for thermal management.
Technical Context
The LT3478EFE#PBF implements current-mode control using LED current-not output voltage-as the primary feedback signal, enabling precise constant-current regulation independent of forward voltage drift. Its transconductance error amplifier (VC pin) directly modulates peak switch current to maintain programmed LED current.
True Color PWM™ dimming is achieved by synchronizing external MOSFET gate drive with the internal oscillator while preserving VC loop stability-enabling 0.033% minimum duty cycle at 100Hz without color shift. The dual CTRL pins support independent programming: CTRL1 sets maximum LED current (linear 0.1V–0.95V range), while CTRL2 implements temperature-dependent current derating using an NTC-based resistor divider.
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) conditions |
| Max Switch Current | 4.5A - enables driving high-power LED strings up to 15W (e.g., 6× white Luxeon III at 700mA) |
| LED Current Range | 100mA to 1050mA - programmable via CTRL1 voltage or external RSENSE (LT3478 variant) |
| PWM Dimming Range | 3000:1 - maintains constant LED chromaticity across full dimming range without color shift |
| Switching Frequency | 200kHz to 2.25MHz - set by RT pin resistor; higher frequencies reduce inductor size but increase switching losses |
| OVP Threshold | Programmable 12.3V to 41V - via OVPSET pin (OVP = OVPSET × 41V); protects against open-LED fault |
| Operating Temp | –40°C to 125°C - qualified for under-hood automotive applications with junction temperature monitoring |
Pinout & Package
LT3478EFE#PBF is housed in a 16-pin thermally enhanced TSSOP package (FE) with exposed pad (Pin 17) that must be soldered to PCB ground plane for thermal dissipation (θJA = 35°C/W). The exposed pad is PGND and forms the primary thermal path.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SW (1,2) | Switch Collector | Internal 42V/4.5A NPN power switch output; connects to inductor and Schottky diode anode |
| VIN (3) | Main Input Supply | Primary power input (2.8V–36V); supplies base current to internal switch; requires local 10µF bypass |
| VS (4) | Inductor Supply | Dedicated supply for inductor current sensing; can be shorted to VIN if single supply used |
| L (5) | Inductor Sense | Monitors inductor current via internal resistor; triggers inrush protection at >6A |
| VOUT (6) | Boost Output | Regulated output node; monitored for open-LED OVP; requires 4.7µF–10µF low-ESR ceramic cap |
| LED (7) | LED Cathode Return | Current-sense node for LED string; connects to external RSENSE (LT3478) or internal 0.1Ω (LT3478-1) |
| OVPSET (8) | OVP Programming | Sets VOUT overvoltage threshold: OVP = OVPSET × 41V (range 0.3V–1V → 12.3V–41V) |
| VC (9) | Error Amplifier Output | Transconductance amplifier output; controls peak switch current; used for loop compensation |
| VREF (10) | Bandgap Reference | 1.24V ±2.2% reference; supplies up to 100µA; used to bias CTRL1/CTRL2/OVPSET dividers |
| SHDN (11) | Shutdown Control | 1.4V UVLO threshold; 10µA hysteresis enables programmable undervoltage lockout |
| CTRL1 (12) | Max LED Current Set | Linear programming of LED current: 0.1V–0.95V → 100mA–1050mA (LT3478-1) or 10mV–105mV/RSENSE |
| CTRL2 (13) | Temp Derating Control | Accepts NTC-based voltage with negative tempco to reduce LED current above breakpoint temperature |
| PWM (14) | PWM Dimming Input | 1V threshold; drives external NMOS in LED cathode path for True Color PWM dimming |
| RT (15) | Freq Programming | Resistor-to-ground sets fSW: 9.09kΩ = 2.25MHz, 31.6kΩ = 1.12MHz, 200kΩ = 0.2MHz |
| SS (16) | Soft-Start Timing | Capacitor-to-ground programs startup ramp; discharges on fault (OVP, overcurrent, UVLO) |
| PGND (17) | Power Ground | Exposed pad; mandatory solder connection to PCB ground plane for thermal and electrical integrity |
Key Features
| Feature | Design Value |
|---|---|
| True Color PWM™ Dimming | 3000:1 range with zero color shift-achieved by maintaining VC loop stability during PWM blanking |
| Dual-Mode LED Current Programming | CTRL1 sets max current; CTRL2 adds temperature-dependent derating to extend LED lifetime |
| Integrated Inductor Current Sensing | Internal resistor between VS and L pins enables inrush protection without external sense components |
| Programmable Open-LED Protection | OVPSET pin allows precise 12.3V–41V overvoltage threshold to detect open-circuit LED faults |
| Separate VS and L Pins | Enables independent inductor supply routing to minimize noise coupling into current-sense path |
Applications
| Automotive TFT LCD Backlight | Automotive Head-Up Display (HUD) |
|---|---|
Use Scenario: Driving 6× white Luxeon III LEDs (700mA, 15W total) from 8V–16V vehicle battery with PWM dimming for ambient light adaptation. IC Role / Device Role / Timing Role: Constant-current boost controller with True Color PWM dimming and thermal derating to prevent LED degradation at dashboard temperatures. Use Value: Maintains consistent white point across 3000:1 dimming range while reducing thermal stress via CTRL2-programmed current roll-off above 75°C. | Use Scenario: Powering high-luminance green/cyan LED array in HUD projector module requiring stable brightness under engine bay thermal cycling. IC Role / Device Role / Timing Role: Buck-boost LED driver with programmable OVP and inrush protection to handle transient load-dump events (36V/100ms). Use Value: Delivers 100% rated LED current at –40°C startup and automatically reduces current above 85°C to preserve luminous flux and lifetime. |
| Automotive Courtesy Lighting | Automotive Heads-Up Display (HUD) Illumination |
Use Scenario: Controlling multi-color RGB LED strips in door panels and footwells with synchronized PWM dimming for mood lighting. IC Role / Device Role / Timing Role: High-efficiency boost driver supporting multiple topologies; uses separate VS/L pins to isolate inductor noise from sensitive analog control paths. Use Value: Enables compact layout with minimal EMI due to integrated current sensing and optimized SW pin routing (dual-pin fused output). | Use Scenario: Driving high-brightness royal blue LEDs in HUD combiner illumination system where color accuracy is critical for symbology clarity. IC Role / Device Role / Timing Role: Precision current regulator with 1.24V bandgap reference (±2.2%) and <12mV VREF load regulation for stable current setpoint. Use Value: Ensures <±3% LED current accuracy over temperature and line variations-critical for consistent photometric output in safety-critical HUDs. |
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#PBF | Extended temperature grade (–40°C to 125°C guaranteed vs. 0°C to 125°C for E-grade) | Required for under-hood applications with full-spec thermal validation across full range | Select LT3478IFE#PBF when full –40°C to 125°C operation must be guaranteed per datasheet limits |
| LT3478-1EFE#PBF | Integrated 0.1Ω LED current sense resistor; eliminates external RSENSE but caps max current at 1050mA | Reduces BOM count for fixed-current designs; not suitable when <100mA or >1050mA or ultra-high accuracy needed | Choose LT3478-1EFE#PBF to simplify layout and lower cost in production designs with 100–1050mA requirements |
Compared with LT3478EFE#PBF, LT3478IFE#PBF provides guaranteed performance across the full automotive temperature range, while LT3478-1EFE#PBF trades external RSENSE flexibility for reduced component count and tighter low-current accuracy-making each alternative optimal for distinct design constraints: thermal validation rigor versus production cost and simplicity.
Availability
LT3478EFE#PBF is available at Aetrix Electronics and suitable for automotive TFT LCD backlights, heads-up displays, and courtesy lighting requiring stable component supply with traceable sourcing and long-term lifecycle support.
Supply support for LT3478EFE#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 LT3478 product line was designed specifically for high-reliability, high-power LED driver applications in automotive environments-emphasizing thermal robustness, wide input range, precision current regulation, and advanced dimming fidelity.
FAQ
What is the maximum LED current supported by the LT3478EFE#PBF?
The LT3478EFE#PBF supports LED currents from 100mA to 1050mA, programmable via the CTRL1 pin voltage (0.1V–0.95V range) when CTRL2 is tied to VREF. For the LT3478 variant (not -1), current is set by external RSENSE using the formula ILED = VCTRL1/RSENSE × 10, enabling scaling beyond 1050mA with appropriate RSENSE selection. The LT3478EFE#PBF itself does not integrate RSENSE.
How does True Color PWM™ dimming work in the LT3478EFE#PBF?
True Color PWM™ dimming in the LT3478EFE#PBF maintains constant LED color by preserving the VC error amplifier's regulated state during PWM blanking intervals. Unlike conventional PWM that disrupts the control loop, the LT3478EFE#PBF holds VC voltage steady while disabling switching-ensuring identical LED forward voltage and spectral output at all dimming levels, achieving up to 3000:1 range without chromaticity shift.
Can the LT3478EFE#PBF drive LEDs in buck configuration?
Yes, the LT3478EFE#PBF supports buck, boost, and buck-boost topologies. In buck mode, the LED string is connected between VOUT and ground, with the inductor placed between VIN and SW. The IC regulates LED current by controlling switch duty cycle to maintain the programmed current through the external sense resistor (RSENSE) connected between LED and ground. Proper layout and component selection per the datasheet's Applications Information section are required.
What is the purpose of the VS and L pins on the LT3478EFE#PBF?
The VS (inductor supply) and L (inductor sense) pins on the LT3478EFE#PBF provide separate paths for powering the inductor and sensing inductor current. This separation minimizes noise coupling from high di/dt inductor current into the current-sense path. An internal resistor between VS and L monitors inductor current for inrush protection-triggering immediate shutdown if current exceeds 6A. VS can be shorted to VIN if only one supply is available.
How is overvoltage protection configured on the LT3478EFE#PBF?
Overvoltage protection (OVP) on the LT3478EFE#PBF is configured using the OVPSET pin: OVP threshold = OVPSET × 41V. Applying 0.3V to OVPSET sets OVP to 12.3V; 1.0V sets it to 41V. This protects against open-LED faults by disabling switching when VOUT exceeds the programmed threshold. The OVP circuit is internal and requires no external components-only a precision voltage applied to OVPSET via resistor divider from VREF.
LT3478EFE#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
LT3478EFE#PBF FAQ
1.How can I place an order for LT3478EFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3478EFE#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 LT3478EFE#PBF reliable?
The price and inventory of LT3478EFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3478EFE#PBF is usually 5 days.
3.What payment methods are accepted for LT3478EFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3478EFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3478EFE#PBF?
LT3478EFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3478EFE#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 LT3478EFE#PBF?
For technical support, including LT3478EFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3478EFE#PBF requirements.
6.How does Aetrix verify that LT3478EFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3478EFE#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 LT3478EFE#PBF meets industry standards.
7.What is the process for return or replacement of LT3478EFE#PBF?
All LT3478EFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3478EFE#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 LT3478EFE#PBF part is unused and in its original packaging.
Return procedure for LT3478EFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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