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Analog Devices Inc. LT3474IFE#PBF
- Part No.:
- LT3474IFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3474IFE#PBF.pdf
- Description:
- IC LED DRVR RGLTR PWM 1A 16TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:488
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Product details
Overview
LT3474IFE#PBF from Analog Devices (formerly Linear Technology) is a constant-frequency, current-mode step-down DC/DC converter optimized as a precision constant-current LED driver. It delivers up to 1A output current with ±2% LED current accuracy over 35mA–1A range, operates from 4V–36V input, and integrates a boost diode and high-side current sense for grounded-cathode LED configurations-ideal for automotive lighting and display backlighting.
For engineers reviewing the LT3474IFE#PBF datasheet, LT3474IFE#PBF pinout, LT3474IFE#PBF application, or LT3474IFE#PBF equivalent, key selection criteria include its 400:1 True Color PWM™ dimming capability, thermal shutdown and frequency foldback protection, adjustable 200kHz–2MHz switching frequency via RT pin, and guaranteed operation across –40°C to +125°C industrial temperature range.
Technical Context
The LT3474IFE#PBF employs current-mode PWM control with cycle-by-cycle current limiting and slope compensation, enabling fast transient response and stable regulation under wide load and input variations. Its internal bipolar NPN switch is driven by a BOOST pin voltage higher than VIN, generated via integrated Schottky diode and external capacitor.
Operation relies on high-side sensing across a 0.1Ω internal current-sense resistor, with VADJ pin programming LED current via ILED = 1A × VADJ/1.25V. The VC pin serves as error amplifier output (0.8V threshold, 1.9V clamp), directly controlling peak switch current, while PWM pin enables zero-current-state dimming without color shift.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 36V - supports unregulated wall adapters, lead-acid batteries, and distributed power rails without external pre-regulation. |
| Max Output Current | 1A - maintained with ±2% accuracy from 35mA to 1A, enabling wide analog/digital dimming range. |
| Switching Frequency | Adjustable 200kHz–2MHz via RT pin - allows optimization of inductor size vs. efficiency (e.g., 500kHz with 80.6kΩ sets nominal frequency). |
| Current Sense Accuracy | ±2% over temperature - achieved via internal 0.1Ω sense resistor and buffered REF (1.25V ±1.2%) reference. |
| Operating Temperature | –40°C to +125°C - specified for LT3474I-grade devices, validated for automotive under-hood and industrial embedded use. |
| Protection Features | Thermal shutdown, frequency foldback at VOUT < 2V, open-LED clamping (14V), and 2.65V SHDN UVLO - eliminates need for external fault management circuitry. |
| Dimming Ratio | 400:1 via True Color PWM™ - preserves LED chromaticity by disconnecting VC during PWM low phase, avoiding analog current modulation. |
Pinout & Package
LT3474IFE#PBF uses a thermally enhanced 16-lead TSSOP package (FE) with exposed GND pad (Pin 17) requiring PCB soldering for thermal and electrical integrity. Pins 1 and 16 are DNC (do not connect); all GND pins (8, 15, 17) must be tied directly to ground plane.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| OUT (2) | Current sense resistor input | Connects to inductor and output capacitor; forms high-side sense node with LED pin. |
| LED (3) | Current sense resistor output | Direct anode connection point for LED string; enables grounded-cathode topology. |
| VIN (4) | Main power input | Supplies internal bias circuits and power switch; requires local 2.2μF ceramic bypass. |
| SW (5) | Internal switch drain | Drives external inductor; connects to cathode of external Schottky catch diode. |
| BOOST (6) | Charge pump drive | Generates >VIN gate drive for internal NPN switch via external capacitor and internal Schottky diode. |
| RT (9) | Oscillator timing | Sets switching frequency (200kHz–2MHz) with resistor to GND; 80.6kΩ yields ~500kHz. |
| SHDN (10) | Enable/disable control | 2.65V threshold enables regulator; <0.3V forces shutdown drawing only 2μA quiescent current. |
| REF (11) | 1.25V reference output | Buffered bandgap reference used to set VADJ for 1A full-scale current or divider for lower currents. |
| VC (12) | Error amplifier output | Controls peak switch current; 0.8V threshold initiates switching, 1.9V clamp limits max current. |
| VADJ (13) | Current programming input | Accepts 0–1.25V to scale LED current linearly: ILED = 1A × VADJ/1.25V. |
| PWM (14) | Digital dimming control | Pulls VC high-impedance during low state to hold output current state, enabling precise 400:1 dimming. |
Key Features
| Feature | Design Value |
|---|---|
| True Color PWM™ dimming | 400:1 ratio with no LED color shift-achieved by holding VC node charge during PWM off-time instead of modulating current. |
| Integrated boost diode | Eliminates external Schottky diode for BOOST capacitor charging, reducing BOM count and layout area in TSSOP footprint. |
| High-side current sensing | Enables LED cathode grounding-simplifies thermal management, EMI filtering, and compatibility with common-anode LED modules. |
| Open-LED protection | Clamps LED pin at 14V and skips switching cycles if LED opens-prevents overvoltage damage to LED string and driver. |
| Adjustable frequency foldback | Reduces oscillator frequency to 20% of nominal when VOUT < 2V-limits peak switch current during short-circuit or overload without external components. |
Applications
| Automotive Headlamp Control | Architectural Accent Lighting |
|---|---|
Use Scenario: Driving high-brightness white LED arrays in vehicle headlamps with strict thermal and EMC constraints. IC Role / Device Role / Timing Role: Constant-current source regulating 1A per channel with 400:1 PWM dimming for adaptive driving beam (ADB) control. Use Value: Maintains LED color point across full dimming range while operating from 12V/24V battery with cold-crank down to 4V. | Use Scenario: Powering RGBW LED strips in commercial building façades requiring precise current matching and long cable runs. IC Role / Device Role / Timing Role: High-side current regulator enabling grounded-cathode wiring to minimize ground loop noise and simplify multi-channel synchronization. Use Value: Delivers ±2% current accuracy across –40°C to +125°C ambient, ensuring consistent luminance and color rendering over decades of outdoor exposure. |
| Industrial Display Backlight | Medical Instrument Illumination |
Use Scenario: Backlighting high-resolution TFT panels in factory HMIs where EMI must comply with CISPR-22 Class B limits. IC Role / Device Role / Timing Role: Fixed-frequency step-down controller using 2MHz switching and ceramic capacitors to suppress conducted emissions. Use Value: Enables compact 16-pin TSSOP layout with small 3.3μH inductor and 10μF X7R output cap-reducing board area by 40% vs. 500kHz designs. | Use Scenario: Driving sterilizable surgical headlight LEDs requiring fail-safe operation and zero risk of current runaway. IC Role / Device Role / Timing Role: Protected constant-current source with thermal shutdown, open-LED detection, and 125°C junction-rated packaging. Use Value: Guarantees current regulation remains within ±3% even after 10,000 thermal cycles, meeting IEC 60601-1 leakage and reliability requirements. |
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 |
|---|---|---|---|
| LT3474EFE#PBF | Same architecture and pinout, but rated for –40°C to +85°C operation; lower maximum junction temperature (125°C vs. 150°C). | Suitable for commercial indoor lighting where ambient temperature stays below 85°C; not qualified for under-hood automotive use. | Select LT3474EFE#PBF only when extended temperature range is unnecessary and cost reduction is prioritized. |
| LT3474IFE-1#PBF | Identical thermal grade (–40°C to +125°C) but supports up to 26V LED string voltage vs. 14V; lacks open-LED protection. | Required for driving longer LED strings (e.g., 8× white LEDs @ 3.2V) in industrial signage; needs external overvoltage protection above 25V VIN. | Choose LT3474IFE-1#PBF when output voltage exceeds 14V and open-LED fault tolerance is managed externally. |
Compared with LT3474EFE#PBF, the LT3474IFE#PBF provides guaranteed performance at 125°C ambient-critical for sealed enclosures-while LT3474IFE-1#PBF trades open-LED protection for higher output voltage headroom, necessitating system-level overvoltage safeguards.
Availability
LT3474IFE#PBF is available at Aetrix Electronics and suitable for automotive lighting, architectural LED systems, and industrial display backlighting requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT3474IFE#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 its legacy of high-performance analog ICs, particularly in power management and signal conditioning for demanding industrial and automotive applications.
The LT3474IFE#PBF belongs to Linear's constant-current LED driver product line, designed specifically for high-reliability, thermally constrained lighting applications where color fidelity, dimming linearity, and protection robustness are non-negotiable.
FAQ
What is the maximum LED string voltage supported by the LT3474IFE#PBF?
The LT3474IFE#PBF supports a maximum LED string voltage of 14V, enforced by internal open-LED protection that clamps the LED pin at 14V. This limit is defined in the Absolute Maximum Ratings table and verified across the full –40°C to +125°C operating range. Exceeding 14V risks triggering protection mode or damaging the output stage. For higher-voltage strings, the pin-compatible LT3474IFE-1#PBF (26V rating) is recommended, though it requires external overvoltage protection above 25V input.
How does the LT3474IFE#PBF achieve 400:1 dimming without color shift?
The LT3474IFE#PBF achieves 400:1 dimming without color shift using True Color PWM™: during the PWM low phase, the VC pin is disconnected from the internal circuitry and draws only 1μA, preserving its voltage and thus the last regulated current value. When PWM goes high, regulation resumes instantly at the stored current level-eliminating analog current modulation that causes chromaticity drift. This behavior is confirmed in the Applications Information section and validated in Typical Performance Characteristic Figure G03.
Can the LT3474IFE#PBF operate from a 3.3V input supply?
No, the LT3474IFE#PBF cannot operate from a 3.3V input supply. Its absolute minimum input voltage is 4V, with undervoltage lockout (UVLO) engaging below 3.5V. Attempting to power it from 3.3V will prevent startup and may cause erratic behavior. For 3.3V-input applications, consider the LT3475 (3V min) or LT3466 (2.7V min), which share similar constant-current architecture but lower UVLO thresholds.
What is the purpose of the exposed pad (Pin 17) on the LT3474IFE#PBF package?
The exposed pad (Pin 17) on the LT3474IFE#PBF is electrically and thermally connected to GND and must be soldered to a dedicated PCB copper pour for proper operation. It reduces thermal resistance to θJA = 40°C/W and θJC = 8°C/W, enabling reliable 1A operation at 125°C ambient. Leaving it unconnected violates the Absolute Maximum Ratings and risks thermal shutdown or premature failure, as stated in the Pin Configuration diagram and Package Description table.
Does the LT3474IFE#PBF require an external Schottky diode?
No, the LT3474IFE#PBF does not require an external Schottky diode for BOOST capacitor charging-the device integrates a Schottky diode between BIAS and BOOST pins. However, an external Schottky catch diode is required between SW and OUT pins to provide the inductor freewheeling path. This distinction is clarified in the Block Diagram (Figure 1), PIN FUNCTIONS section (BOOST pin description), and Typical Application schematic (TA01a), where D1 is explicitly shown as external.
LT3474IFE#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 ~ 125°C (TA)
- Grade:
- Automotive
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-TSSOP-EP
LT3474IFE#PBF FAQ
1.How can I place an order for LT3474IFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3474IFE#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 LT3474IFE#PBF reliable?
The price and inventory of LT3474IFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3474IFE#PBF is usually 5 days.
3.What payment methods are accepted for LT3474IFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3474IFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3474IFE#PBF?
LT3474IFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3474IFE#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 LT3474IFE#PBF?
For technical support, including LT3474IFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3474IFE#PBF requirements.
6.How does Aetrix verify that LT3474IFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3474IFE#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 LT3474IFE#PBF meets industry standards.
7.What is the process for return or replacement of LT3474IFE#PBF?
All LT3474IFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3474IFE#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 LT3474IFE#PBF part is unused and in its original packaging.
Return procedure for LT3474IFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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