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Analog Devices Inc. LT3475EFE-1#PBF
- Part No.:
- LT3475EFE-1#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3475EFE-1#PBF.pdf
- Description:
- IC LED DRV RGLTR PWM 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:441
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Product details
Overview
LT3475EFE-1#PBF from Analog Devices (formerly Linear Technology) is a dual-channel, constant-current step-down DC/DC LED driver IC with integrated bipolar NPN power switches. It delivers up to 1.5A per channel with ±3% LED current accuracy from 50mA to 1.5A, supports 4V–36V input, and enables grounded-cathode LED strings up to 25V using high-side current sensing. It is used in automotive lighting systems requiring precise dimming and thermal robustness.
For engineers reviewing the LT3475EFE-1#PBF datasheet, LT3475EFE-1#PBF pinout, LT3475EFE-1#PBF application, or LT3475EFE-1#PBF equivalent, key selection considerations include its 25V LED string voltage rating (LT3475-1 variant), anti-phase switching for ripple reduction, 3000:1 PWM dimming range without color shift, and TSSOP-20 thermally enhanced package with exposed ground pad.
Technical Context
The LT3475EFE-1#PBF implements a current-mode PWM architecture with dual independent control loops, each featuring an internal error amplifier (VC1/VC2), programmable oscillator (via RT pin), and cycle-by-cycle peak current limiting. Its master-slave oscillator configuration enables 180° anti-phase switching between channels to minimize input ripple.
It uses high-side current sensing via internal 0.067Ω sense resistors and external VADJ programming to set LED current (ILED = 1.5A × VADJ/1.25V). The device incorporates frequency foldback during overload, thermal shutdown, and undervoltage lockout (UVLO) with 3.7V minimum operating input and 40V absolute maximum VIN rating.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| LED Output Current | Up to 1.5A per channel, adjustable from 50mA to 1.5A via VADJ pin voltage; ±3% accuracy over temperature and line. |
| Input Voltage Range | 4V to 36V operating; 40V absolute maximum - supports 12V/24V automotive and industrial rails with transient tolerance. |
| LED String Voltage | Up to 25V (LT3475-1 variant); enables driving two or three white LEDs in series at full current. |
| Switching Frequency | 200kHz to 2MHz, set by RT resistor; 600kHz typical with 24.3kΩ - enables compact 3.3μH–4.7μH inductors and ceramic output caps. |
| Dimming Ratio | 3000:1 via PWM pin; maintains constant LED color across full range due to true-color PWM architecture. |
| Package | 20-lead TSSOP with exposed thermal pad (Pin 21 = GND); θJA = 30°C/W - requires PCB thermal vias for 125°C junction operation. |
| Operating Temperature | –40°C to +85°C (E-grade); validated for automotive cabin and exterior lighting ambient conditions. |
Pinout & Package
LT3475EFE-1#PBF is housed in a 20-lead plastic TSSOP package with exposed ground pad (Pin 21). The thermally enhanced design requires soldering the exposed pad directly to a large PCB ground plane with ≥6 thermal vias for reliable operation at full load.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| OUT1, OUT2 (Pins 1, 10) | Current sense resistor input | Connects to inductor and output capacitor; carries full channel output current; referenced to internal 0.067Ω sense element. |
| LED1, LED2 (Pins 2, 9) | Current sense resistor output / LED anode node | Drives LED string anode; supports grounded-cathode topology; max 25V rating for LT3475-1 variant. |
| VIN (Pins 5, 6) | Main power input | Supplies bias and switch drive; must be bypassed with ≥4.7μF X7R ceramic capacitor near pins. |
| SW1, SW2 (Pins 4, 7) | Internal NPN switch collector | Connects to inductor, Schottky diode, and BOOST capacitor; switches at programmed frequency with <500mV saturation voltage. |
| BOOST1, BOOST2 (Pins 3, 8) | Charge pump drive voltage | Provides >VIN gate drive to internal NPN switches; must exceed SW by ≥2.5V; max 60V rating. |
| GND (Pins 15, 21) | Signal and power ground | Pin 21 is exposed thermal pad - electrically and thermally connected to PCB ground plane; mandatory for thermal performance. |
| RT (Pin 14) | Oscillator timing input | Resistor-to-ground sets switching frequency (200kHz–2MHz); 24.3kΩ yields 600kHz typical. |
| SHDN (Pin 16) | Enable/disable control | 2.6V threshold; pulls device into ultra-low-IQ shutdown (<2μA) when <0.3V; doubles as accurate UVLO input. |
| PWM1, PWM2 (Pins 20, 11) | Digital dimming interface | Direct logic-level PWM input; disconnects VC loop during low pulse to preserve state and enable linear 3000:1 dimming. |
| VADJ1, VADJ2 (Pins 19, 12) | LED current programming input | Voltage-controlled current source input; ILED = 1.5A × VADJ/1.25V; 40nA bias current enables high-impedance divider use. |
Key Features
| Feature | Design Value |
|---|---|
| True-color PWM dimming | 3000:1 ratio with no perceptible LED color shift - achieved by preserving VC loop state during PWM off-time. |
| Anti-phase channel switching | 180° phase offset reduces input capacitor RMS current and EMI, enabling smaller bulk input capacitance. |
| High-side current sensing | Enables grounded-cathode LED configuration - simplifies thermal management and improves system safety in automotive applications. |
| Programmable 200kHz–2MHz switching | Single RT resistor selects frequency - balances inductor size vs. efficiency; 600kHz standard for optimal 3.3μH/4.7μH designs. |
| Integrated open-circuit protection (LT3475 only) | LT3475EFE-1#PBF omits this feature; requires external overvoltage clamp if LED string opens above 25V. |
Applications
| Automotive Exterior Lighting | Architectural Accent Lighting |
|---|---|
Use Scenario: Driving dual high-brightness white LED strings in headlamp or DRL modules under 12V/24V battery supply with wide temperature swing. IC Role / Device Role / Timing Role: Dual-channel constant-current regulator with independent PWM dimming and anti-phase switching for EMI control. Use Value: Enables precise 1.5A per channel current matching across temperature, eliminating visible brightness mismatch between left/right lamps. |
Use Scenario: Illuminating façade elements or signage with tunable white LED arrays requiring smooth 3000:1 dimming without hue shift. IC Role / Device Role / Timing Role: Constant-current source with true-color PWM dimming and 25V LED string support for multi-LED series configurations. Use Value: Maintains consistent CCT across full dimming range - critical for premium architectural lighting where color fidelity is specified. |
| Industrial Display Backlighting | Avionic Panel Lighting |
Use Scenario: Powering edge-lit LCD backlights in rugged HMI displays operating from 24V DC industrial power rails. IC Role / Device Role / Timing Role: Dual synchronous buck controller with high-side sensing and thermal shutdown for reliability in sealed enclosures. Use Value: Delivers stable 1.5A per channel with <±3% current accuracy - ensures uniform luminance across display area despite ambient temperature drift. |
Use Scenario: Providing fault-tolerant backlighting for cockpit instrumentation with strict DO-160 lightning surge and thermal requirements. IC Role / Device Role / Timing Role: Dual LED driver with UVLO, frequency foldback, and thermal shutdown - meets avionics safety-critical power sequencing needs. Use Value: Withstands 40V transients and operates from –40°C to +85°C - eliminates need for external protection circuitry in certified avionics designs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-channel constant-current LED driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3783EFE#PBF | Single-channel, higher 3A output; no integrated switches; requires external MOSFETs; supports SEPIC/buck-boost topologies. | Suitable for single high-power LED strings or non-grounded-cathode configurations; lacks dual-channel integration. | Select when >1.5A/channel or topology flexibility (e.g., buck-boost) is required; not a drop-in replacement. |
| MAX16820ATP+T | Single-channel, 1.2A max; integrated MOSFET; 4.5V–28V input; no anti-phase capability; lower dimming ratio (1000:1). | Better suited for space-constrained single-LED applications; lacks dual-channel synchronization and thermal grade. | Consider for cost-sensitive, single-string designs where 25V LED voltage and 3000:1 dimming are not required. |
Compared with LTC3783EFE#PBF and MAX16820ATP+T, the LT3475EFE-1#PBF uniquely integrates dual 1.5A channels with anti-phase switching, 25V LED compliance, and true-color 3000:1 PWM - making it optimal for compact, thermally demanding dual-string automotive and architectural lighting.
Availability
LT3475EFE-1#PBF is available at Aetrix Electronics and suitable for automotive lighting, architectural accent lighting, and industrial display backlighting requiring stable component supply, long-term lifecycle support, and AEC-Q200-aligned reliability.
Supply support for LT3475EFE-1#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 technical and manufacturing continuity for all Linear IC products, including precision power management solutions.
The LT3475EFE-1#PBF belongs to Linear's high-reliability LED driver product line, designed specifically for automotive, avionic, and industrial lighting systems demanding accurate constant-current regulation, wide input range, and robust thermal performance.
FAQ
What is the maximum LED string voltage supported by LT3475EFE-1#PBF?
The LT3475EFE-1#PBF supports LED string voltages up to 25V on its LED1 and LED2 pins, as specified in the Absolute Maximum Ratings table. This distinguishes it from the base LT3475 (15V max) and enables driving longer white LED strings - e.g., three 8V LEDs in series - without external boost circuitry. Always verify that the actual LED forward voltage sum remains within this limit at operating temperature.
Does LT3475EFE-1#PBF include open-circuit LED protection?
No, the LT3475EFE-1#PBF does not include internal open-circuit protection. Unlike the LT3475 variant (which clamps LED pin voltage at 14V), the LT3475-1 family relies on external overvoltage protection - such as the Zener clamp circuit shown in Figure 1 of the datasheet - especially when VIN exceeds 25V. Failure to implement this may risk exceeding the 25V ABSMAX rating on LED1/LED2 pins.
How is LED current adjusted on LT3475EFE-1#PBF?
LED current on LT3475EFE-1#PBF is set via the VADJ1 and VADJ2 pins using the formula ILED = 1.5A × VADJ/1.25V. Tie VADJ to the REF pin (1.25V) for full 1.5A output; use a resistor divider from REF to GND to scale downward. The VADJ pin draws only 40nA, enabling high-impedance dividers with minimal error. Each channel is independently programmable.
What thermal design practices are required for LT3475EFE-1#PBF?
The LT3475EFE-1#PBF requires soldering its exposed thermal pad (Pin 21) directly to a solid PCB ground plane with ≥6 thermal vias (0.3mm diameter, spaced ≤2mm apart) to achieve θJA = 30°C/W. Without proper thermal relief, junction temperature can exceed 125°C under 1.5A/channel continuous load at 85°C ambient. Use 2oz copper and minimize trace length between VIN/OUT/GND pins and bulk capacitors.
Can LT3475EFE-1#PBF operate with a single 12V input driving two 1.5A LED strings?
Yes - the LT3475EFE-1#PBF supports 4V–36V input and delivers up to 1.5A per channel continuously. With 12V input and two 3V white LED strings (total 6V), duty cycle remains ~55%, well within the 98% maximum limit. Efficiency exceeds 85% per channel (see Fig. 3475 TA01b), and anti-phase switching minimizes input ripple. Ensure inductors are rated for ≥2.2A saturation current.
LT3475EFE-1#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-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:
- 2
- Voltage - Supply (Min):
- 3.7V
- Voltage - Supply (Max):
- 36V
- Voltage - Output:
- -
- Current - Output / Channel:
- 1.5A
- Frequency:
- 200kHz ~ 2MHz
- Dimming:
- PWM
- Applications:
- Backlight, Lighting
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- Automotive
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-TSSOP-EP
LT3475EFE-1#PBF FAQ
1.How can I place an order for LT3475EFE-1#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3475EFE-1#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 LT3475EFE-1#PBF reliable?
The price and inventory of LT3475EFE-1#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3475EFE-1#PBF is usually 5 days.
3.What payment methods are accepted for LT3475EFE-1#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3475EFE-1#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3475EFE-1#PBF?
LT3475EFE-1#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3475EFE-1#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 LT3475EFE-1#PBF?
For technical support, including LT3475EFE-1#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3475EFE-1#PBF requirements.
6.How does Aetrix verify that LT3475EFE-1#PBF is sourced from the original manufacturer or authorized distributors?
All LT3475EFE-1#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 LT3475EFE-1#PBF meets industry standards.
7.What is the process for return or replacement of LT3475EFE-1#PBF?
All LT3475EFE-1#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3475EFE-1#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 LT3475EFE-1#PBF part is unused and in its original packaging.
Return procedure for LT3475EFE-1#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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