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Analog Devices Inc. LT3474EFE#PBF
- Part No.:
- LT3474EFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3474EFE#PBF.pdf
- Description:
- IC LED DRVR RGLTR PWM 1A 16TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:14,594
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Product details
Overview
LT3474EFE#PBF from Analog Devices (formerly Linear Technology) is a fixed-frequency, current-mode step-down DC/DC converter optimized as a constant-current LED driver with integrated bipolar NPN switch and boost diode. It delivers up to 1A output current with ±2% LED current accuracy over 35mA–1A range, operates from 4V–36V input, and supports 400:1 True Color PWM™ dimming for architectural lighting and display backlighting.
For engineers reviewing the LT3474EFE#PBF datasheet, LT3474EFE#PBF pinout, LT3474EFE#PBF application, or LT3474EFE#PBF equivalent, key selection criteria include its 16-lead TSSOP thermal package, internal 0.1Ω current sense resistor, open-LED protection (14V clamp), and adjustable 470kHz–540kHz switching frequency via RT pin-critical for minimizing inductor size while maintaining low output ripple in space-constrained LED systems.
Technical Context
The LT3474EFE#PBF implements current-mode PWM control with cycle-by-cycle peak current limiting and slope compensation, enabling fast transient response and stable operation across wide duty cycles (up to 98%). Its internal bipolar NPN power switch is driven by a charge-pump boosted gate voltage (via BOOST pin), allowing full saturation at high input voltages.
True Color PWM™ dimming is achieved by disconnecting the VC error amplifier during PWM low periods, preserving capacitor state and ensuring linear light-output vs. duty-cycle relationship. Open-circuit protection clamps the LED pin at 13.2–14.5V and initiates cycle skipping, while frequency foldback reduces oscillator frequency to 70kHz under overload to limit switch current.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 36V - supports direct connection to lead-acid batteries, unregulated wall adapters, and industrial 24V rails without pre-regulation. |
| Max Output Current | 1A - guaranteed minimum 0.98A at VADJ = VREF, enabling single-chip drive of high-brightness white LEDs. |
| LED Current Accuracy | ±2% over 35mA–1A - maintained by internal 0.1Ω sense resistor and precision 1.23–1.265V reference, eliminating external sensing errors. |
| Switching Frequency | 470kHz–540kHz (RT = 80.6kΩ) - enables use of ≤4.7μH inductors and ceramic output capacitors for compact, low-EMI designs. |
| Dimming Ratio | 400:1 via True Color PWM™ - preserves LED chromaticity across full intensity range by avoiding analog current reduction. |
| Open-LED Protection | 13.2–14.5V clamp on LED pin - prevents overvoltage damage during LED string failure or disconnection. |
| Thermal Range | –40°C to +85°C - specified performance over full industrial temperature range, validated for automotive lighting ambient conditions. |
Pinout & Package
LT3474EFE#PBF uses a 16-lead thermally enhanced TSSOP package (FE) with exposed pad (Pin 17) soldered to PCB ground for optimal thermal dissipation (θJA = 40°C/W). Pins 1 and 16 are DNC (do not connect); exposed pad must be electrically and thermally tied to system ground plane.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| OUT (2) | Current sense resistor input | Connects to inductor and output capacitor; forms high-side current sense node with LED pin. |
| LED (3) | Current sense resistor output / LED anode node | Direct connection point for LED string anode; clamped at 14V during open-circuit fault. |
| VIN (4) | Main power input | Supplies internal bias circuits and power switch; requires local 2.2μF ceramic bypass. |
| SW (5) | Internal switch collector | Drives external inductor; switches between VIN and GND; peak current limited to ≥1.6A. |
| BOOST (6) | Charge-pump voltage supply | Provides >VIN gate drive to internal NPN switch via integrated Schottky diode and external capacitor. |
| RT (9) | Oscillator timing input | Resistor-to-GND sets switching frequency (200kHz–2MHz); 80.6kΩ yields 500kHz nominal. |
| SHDN (10) | Enable/disable control | 2.65V threshold enables operation; <0.3V forces shutdown drawing only 0.01μA quiescent current. |
| REF (11) | 1.25V buffered reference output | Used to set VADJ for 1A output; ties directly to VADJ for full-scale current programming. |
| VC (12) | Error amplifier output | Controls peak switch current; 0.8V threshold activates switch; 1.9V clamp limits max output current. |
| VADJ (13) | Current programming input | Voltage divider input determining LED current: ILED = 1A × VADJ/1.25V. |
| PWM (14) | Digital dimming control | Low signal disconnects VC from internal circuitry, enabling lossless PWM dimming with no color shift. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated boost diode | Eliminates external Schottky diode, reducing BOM count and PCB area in boost-capacitor-based gate-drive circuits. |
| High-side current sensing | Enables grounded-cathode LED configuration - simplifies thermal management and eliminates high-side current-sense amplifier. |
| Adjustable switching frequency | 200kHz–2MHz via single RT resistor - balances inductor size, efficiency, and EMI for diverse LED array configurations. |
| True Color PWM™ dimming | 400:1 linear dimming without current modulation - maintains CCT and CRI across full brightness range in architectural lighting. |
| Open-LED fault protection | 14V clamp + cycle skipping - prevents destructive voltage rise and maintains system reliability during LED string failure. |
Applications
| Automotive Headlamp Control | Architectural Accent Lighting |
|---|---|
Use Scenario: Driving high-power white LED arrays in adaptive front-lighting systems (AFS) with dynamic beam shaping. IC Role / Device Role / Timing Role: Constant-current source regulating 700mA–1A per channel with synchronized PWM dimming for precise lumen control. Use Value: Maintains color consistency across 400:1 dimming range while surviving 36V load-dump transients and –40°C cold cranking. | Use Scenario: Illuminating façade elements and interior coves using long LED strings powered from 24V distributed supplies. IC Role / Device Role / Timing Role: Step-down LED driver with open-circuit protection, enabling reliable operation in inaccessible installations where LED failure is hard to service. Use Value: 14V LED-pin clamp and cycle-skipping prevent overvoltage damage to downstream optics and drivers during field failures. |
| Industrial Display Backlighting | Medical Instrument Indicators |
Use Scenario: Powering edge-lit LCD backlights in rugged HMIs requiring flicker-free dimming and EMI compliance. IC Role / Device Role / Timing Role: High-frequency (500kHz) current regulator minimizing inductor size and enabling ceramic-only output filtering for low-profile designs. Use Value: Low 50mVPP output ripple (with 10μF X7R) ensures no visible display artifacts during video playback or data visualization. | Use Scenario: Providing calibrated status illumination in diagnostic equipment where consistent luminance and spectral stability are critical. IC Role / Device Role / Timing Role: Precision current source delivering 100mA–1A with ±2% accuracy across temperature, referenced to internal 1.25V bandgap. Use Value: Eliminates need for external current-sense resistors and calibration, reducing component count and long-term drift in Class II medical devices. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar constant-current LED driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3783EFE#PBF | Higher 60V input rating; requires external MOSFET; no integrated boost diode; supports SEPIC/Cuk topologies. | Better suited for >36V inputs or multi-string configurations requiring independent current control. | Select when input exceeds 36V or when programmable topology flexibility outweighs BOM simplicity. |
| LM3409QMH/NOPB | Lower 40V max input; external N-channel MOSFET; no integrated boost diode; 100kHz–1MHz adjustable frequency. | Optimized for cost-sensitive automotive exterior lighting with AEC-Q100 Grade 1 qualification. | Choose for production automotive programs requiring AEC-Q100 certification and lower unit cost at volume. |
Compared with LTC3783EFE#PBF and LM3409QMH/NOPB, the LT3474EFE#PBF offers superior integration (internal switch + boost diode), tighter current accuracy (±2% vs ±5%), and simpler layout for single-string 1A applications below 36V - making it optimal for space-constrained industrial and architectural LED systems where reliability and design simplicity are prioritized over ultra-high input voltage or automotive qualification.
Availability
LT3474EFE#PBF is available at Aetrix Electronics and suitable for automotive headlamp control, architectural accent lighting, industrial display backlighting, and medical instrument indicators requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT3474EFE#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 and maintains full product support, datasheet documentation, and application engineering for legacy Linear parts including the LT3474 series.
The LT3474 product line was designed specifically for high-accuracy, high-reliability constant-current LED driving in demanding environments - emphasizing thermal robustness, fault protection, and color-stable dimming for professional lighting infrastructure.
FAQ
What is the maximum LED string voltage supported by the LT3474EFE#PBF?
The LT3474EFE#PBF supports LED string voltages up to 14.5V on the LED pin, as defined by its open-LED protection clamp. This allows driving one or two high-brightness white LEDs (typically 3.0–3.6V each) in series while maintaining safe operating margins. Exceeding this voltage risks triggering cycle skipping or potential damage during fault conditions.
How does the LT3474EFE#PBF achieve 400:1 dimming without color shift?
The LT3474EFE#PBF achieves 400:1 dimming without color shift using True Color PWM™: during PWM low periods, the VC error amplifier is disconnected from the control loop, preserving the compensation capacitor's voltage state. This ensures instantaneous, linear recovery of LED current upon PWM high transition - eliminating analog current modulation that causes chromaticity drift in white LEDs.
Can the LT3474EFE#PBF operate with input voltages below 4V?
No, the LT3474EFE#PBF has a minimum input voltage of 4V as specified in absolute maximum ratings and electrical characteristics. Below this threshold, undervoltage lockout disables switching operation, and the device draws only 2μA quiescent current. Attempting operation below 4V may result in unstable regulation or failure to start.
What thermal considerations apply to the LT3474EFE#PBF's exposed pad?
LT3474EFE#PBF's exposed pad (Pin 17) must be soldered to a dedicated PCB ground plane with ≥4 thermal vias to achieve θJA = 40°C/W. Failure to do so raises junction temperature beyond 125°C under 1A load at 85°C ambient, triggering thermal shutdown. The pad serves dual electrical (GND) and thermal functions - floating or improperly connected pads cause premature thermal limiting.
Is the LT3474EFE#PBF pin-compatible with the LT3474-1 variants?
No, the LT3474EFE#PBF is not pin-compatible with LT3474-1 variants. While both share identical pinouts, the LT3474-1 lacks open-LED protection and supports higher 26V LED pin voltage - requiring different fault-handling circuitry. Substituting LT3474EFE#PBF for LT3474EFE-1#PBF in a design risks overvoltage damage during LED open-circuit events.
LT3474EFE#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)
- Internal Switch(s):
- Yes
- Number of Outputs:
- 1
- Voltage - Supply (Min):
- 3.5V
- Voltage - Supply (Max):
- 36V
- Voltage - Output:
- -
- Current - Output / Channel:
- 1A
- Frequency:
- 200kHz ~ 2MHz
- Dimming:
- PWM
- Applications:
- Backlight
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- Automotive
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-TSSOP-EP
LT3474EFE#PBF FAQ
1.How can I place an order for LT3474EFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3474EFE#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 LT3474EFE#PBF reliable?
The price and inventory of LT3474EFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3474EFE#PBF is usually 5 days.
3.What payment methods are accepted for LT3474EFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3474EFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3474EFE#PBF?
LT3474EFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3474EFE#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 LT3474EFE#PBF?
For technical support, including LT3474EFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3474EFE#PBF requirements.
6.How does Aetrix verify that LT3474EFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3474EFE#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 LT3474EFE#PBF meets industry standards.
7.What is the process for return or replacement of LT3474EFE#PBF?
All LT3474EFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3474EFE#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 LT3474EFE#PBF part is unused and in its original packaging.
Return procedure for LT3474EFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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