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Analog Devices Inc. LT3474EFE#TRPBF
- Part No.:
- LT3474EFE#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3474EFE#TRPBF.pdf
- Description:
- IC LED DRVR RGLTR PWM 1A 16TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,552
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Product details
Overview
LT3474EFE#TRPBF from Analog Devices (formerly Linear Technology) is a fixed-frequency, current-mode step-down DC/DC converter optimized as a constant-current LED driver. It delivers up to 1 A output current with ±2% accuracy over 35 mA–1 A range, operates from 4 V to 36 V input, and integrates a boost diode and high-side current sense for grounded-cathode LED configurations. Used in automotive lighting and display backlighting where color-stable dimming is critical.
For engineers reviewing the LT3474EFE#TRPBF datasheet, LT3474EFE#TRPBF pinout, LT3474EFE#TRPBF application, or LT3474EFE#TRPBF equivalent, this page provides verified technical context, validated pin functions, confirmed thermal and protection features, and real-world dimming performance data - all specific to the LT3474EFE#TRPBF variant with –40°C to +85°C operation and 16-lead TSSOP package.
Technical Context
The LT3474EFE#TRPBF implements current-mode PWM control with internal NPN bipolar power switch, slope compensation, and cycle-by-cycle current limiting. Its oscillator supports adjustable frequency (200 kHz–2 MHz) via RT-to-GND resistor, and includes frequency foldback during overload or startup when VOUT < 2 V.
True Color PWM™ dimming achieves 400:1 ratio by disconnecting the VC pin during low-PWM periods, preserving capacitor charge state and eliminating color shift. High-side sensing enables cathode-grounded LED strings, while integrated boost diode and BIAS-to-OUT connection simplify layout and reduce external component count.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4 V to 36 V - supports 5 V logic rails, 12 V automotive, 24 V industrial, and unregulated wall adapters without external pre-regulation. |
| Max Output Current | 1 A - guaranteed across full temperature range (–40°C to +85°C), with ≤±2% regulation error from 35 mA to 1 A. |
| Switching Frequency | Adjustable 200 kHz–2 MHz - set by RT resistor; 500 kHz typical with 80.6 kΩ, enabling compact 3.3–4.7 μH inductors and ceramic output caps. |
| LED Dimming Ratio | 400:1 via True Color PWM™ - maintains consistent white LED chromaticity by preserving VC node voltage during PWM off-time. |
| Protection Features | Open-LED clamping (14.5 V max on LED pin), thermal shutdown, frequency foldback, and cycle-by-cycle current limit (1.6 A min at 25°C). |
| Reference Voltage | 1.25 V (±1.2%) - buffered REF pin enables precise VADJ-based current programming with <0.01%/V line regulation. |
| Package | 16-lead TSSOP with exposed thermal pad - θJA = 40°C/W, requires soldered GND pad for thermal integrity and EMI reduction. |
Pinout & Package
LT3474EFE#TRPBF uses a thermally enhanced 16-lead plastic TSSOP (FE package) with exposed GND pad (Pin 17). Pins 1 and 16 are DNC (do not connect); all GND pins (8, 15, and exposed pad) must be tied directly to PCB ground plane.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| OUT (Pin 2) | Current sense resistor input | Connects to inductor and output capacitor; forms high-side current sense node with LED pin. |
| LED (Pin 3) | Current sense resistor output | Drives LED anode directly; enables cathode-grounded topology and open-LED protection (clamped to 14.5 V). |
| VIN (Pin 4) | Main power input | Supplies internal bias and switch; requires local 2.2 μF X7R ceramic bypass to minimize input ripple and EMI. |
| SW (Pin 5) | Internal switch collector | Connects to inductor and Schottky catch diode; carries peak switch current up to 2.1 A (derated at temp). |
| BOOST (Pin 6) | Charge pump drive | Generates >VIN voltage via external capacitor to saturate internal NPN switch; ties to BIAS via integrated Schottky. |
| RT (Pin 9) | Oscillator timing | Sets switching frequency (200 kHz–2 MHz) with resistor to GND; 80.6 kΩ yields 500 kHz nominal. |
| SHDN (Pin 10) | Enable/disable control | 2.65 V threshold enables regulator; doubles as accurate UVLO when used with external resistor divider. |
| REF (Pin 11) | 1.25 V reference output | Buffered reference for VADJ programming; tie to VADJ for 1 A output or use divider for lower currents. |
| VC (Pin 12) | Error amplifier output | Controls peak switch current; used for loop compensation; clamped at 1.9 V to limit max LED current. |
| VADJ (Pin 13) | Current setpoint input | Accepts 0–1.25 V to program ILED = 1 A × (VADJ/1.25 V); bias current <400 nA minimizes divider error. |
| PWM (Pin 14) | Dimming control | Disconnects VC from internal circuitry when pulled low; preserves compensation state for linear 400:1 dimming. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated boost diode | Eliminates external Schottky for BOOST path, reducing BOM count and board area in space-constrained LED drivers. |
| High-side current sensing | Enables grounded-cathode LED configuration - simplifies thermal management and eliminates floating return paths in multi-string designs. |
| True Color PWM™ dimming | Maintains LED chromaticity across 400:1 dimming range by preserving VC node voltage during PWM off-cycles. |
| Frequency foldback | Reduces switching frequency to 20% of nominal under overload or short-circuit, limiting peak switch current and thermal stress. |
| Open-LED protection | Clamps LED pin voltage to 14.5 V and skips switching cycles to prevent overvoltage damage when LED string opens. |
Applications
| Automotive Headlamp Control | Architectural Accent Lighting |
|---|---|
Use Scenario: Driving single or dual-series high-brightness white LEDs in vehicle headlamps with strict EMC and thermal constraints. IC Role / Device Role / Timing Role: Constant-current buck controller with integrated boost diode and high-side sensing, delivering stable 1 A output despite 8–16 V battery variation and load dump transients. Use Value: Eliminates need for external current-sense resistor and boost diode, reducing solution size by >30% versus discrete alternatives while maintaining ±2% current accuracy. | Use Scenario: Powering RGBW LED strips in museum displays where color fidelity and smooth dimming are mandatory. IC Role / Device Role / Timing Role: Precision current source with 400:1 True Color PWM™ dimming, enabling flicker-free, chromatically stable light output across ambient light conditions. Use Value: Delivers consistent CCT (correlated color temperature) from 100% to 0.25% brightness without manual calibration or secondary feedback. |
| Industrial Display Backlight | Constant-Current Test Load |
Use Scenario: Driving edge-lit LCD backlights in ruggedized HMIs requiring wide input range and long-term current stability. IC Role / Device Role / Timing Role: Fixed-frequency current-mode regulator with 4 V–36 V input tolerance and <0.01%/V reference line regulation. Use Value: Maintains <±2% LED current accuracy over 10-year field life despite electrolytic capacitor aging and temperature cycling. | Use Scenario: Serving as programmable electronic load in automated test equipment for validating LED driver ICs and power supplies. IC Role / Device Role / Timing Role: Precision 35 mA–1 A current sink with fast transient response and cycle-by-cycle current limiting. Use Value: Replaces multiple fixed-resistor loads with single IC; VADJ interface allows software-controlled current ramping and fault injection testing. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar constant-current buck LED driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3474IFE#TRPBF | Same functionality and pinout; rated for –40°C to +125°C junction temperature vs. LT3474EFE#TRPBF's –40°C to +85°C. | Required for under-hood automotive or high-ambient industrial environments exceeding 85°C ambient. | Select LT3474IFE#TRPBF only if extended temperature operation is needed; otherwise LT3474EFE#TRPBF offers identical performance at lower cost. |
| LT3474EFE-1#TRPBF | Same package and temperature grade, but supports up to 26 V LED string voltage (vs. 15 V for LT3474EFE#TRPBF) and omits open-LED protection. | Used for longer LED strings (e.g., 6–8 white LEDs in series) where open-circuit voltage exceeds 15 V and external protection is implemented. | Choose LT3474EFE-1#TRPBF only when driving >15 V LED strings; LT3474EFE#TRPBF is preferred for general-purpose 1–4 LED strings with built-in safety. |
Compared with LT3474IFE#TRPBF, the LT3474EFE#TRPBF trades extended temperature capability for cost efficiency in commercial-grade lighting; compared with LT3474EFE-1#TRPBF, it provides integrated open-LED clamping at the expense of lower maximum LED voltage - making it safer and simpler for standard 12 V systems.
Availability
LT3474EFE#TRPBF is available at Aetrix Electronics and suitable for automotive lighting, architectural accent lighting, and industrial display backlighting requiring stable component supply, long-term manufacturability, and RoHS-compliant packaging.
Supply support for LT3474EFE#TRPBF 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 design tools for the LT3474 family.
The LT3474 product line was designed specifically for high-accuracy, high-dimming-ratio LED current regulation in space-constrained, thermally demanding applications - emphasizing integration, thermal robustness, and color-stable dimming.
FAQ
What is the maximum LED string voltage supported by the LT3474EFE#TRPBF?
The LT3474EFE#TRPBF supports up to 14.5 V on the LED pin, as specified by its absolute maximum rating and open-LED clamp voltage. This limits practical use to 3–4 series-connected white LEDs (typ. 3.2–3.6 V each) at room temperature. Exceeding this voltage risks latch-up or permanent damage, and the LT3474EFE-1#TRPBF variant must be used for higher-voltage strings.
Does the LT3474EFE#TRPBF require an external Schottky diode?
No, the LT3474EFE#TRPBF integrates a Schottky diode between the BIAS and BOOST pins, eliminating the need for an external boost diode. However, an external Schottky catch diode (e.g., 1N5819) is still required between SW and OUT to complete the buck power path - the internal diode does not replace this function.
How is LED current programmed on the LT3474EFE#TRPBF?
LED current is programmed via the VADJ pin using the formula ILED = 1 A × (VADJ/1.25 V). Tie REF to VADJ for 1 A output; for lower currents, use a resistor divider from REF to GND. VADJ bias current is ≤400 nA, so divider resistors can be large (e.g., 100 kΩ/100 kΩ for 0.5 A) without significant error.
What thermal management is required for the LT3474EFE#TRPBF in 1 A operation?
The LT3474EFE#TRPBF requires soldering of its exposed thermal pad (Pin 17) to a minimum 100 mm² copper pour on the PCB to achieve θJA = 40°C/W. At 1 A output and 12 V input, typical power dissipation is ~0.8 W; without proper pad soldering, junction temperature may exceed 125°C even at 25°C ambient, triggering thermal shutdown.
Can the LT3474EFE#TRPBF drive multiple parallel LED strings?
No - the LT3474EFE#TRPBF is a single-channel constant-current source intended for one LED string. Driving parallel strings causes current imbalance due to VF mismatch, risking overcurrent in one string. For multi-string applications, use one LT3474EFE#TRPBF per string or select a multi-channel IC like the LT3466.
LT3474EFE#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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#TRPBF FAQ
1.How can I place an order for LT3474EFE#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3474EFE#TRPBF 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#TRPBF reliable?
The price and inventory of LT3474EFE#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3474EFE#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3474EFE#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3474EFE#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3474EFE#TRPBF?
LT3474EFE#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3474EFE#TRPBF 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#TRPBF?
For technical support, including LT3474EFE#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3474EFE#TRPBF requirements.
6.How does Aetrix verify that LT3474EFE#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3474EFE#TRPBF 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#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3474EFE#TRPBF?
All LT3474EFE#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3474EFE#TRPBF, 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#TRPBF part is unused and in its original packaging.
Return procedure for LT3474EFE#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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