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Analog Devices Inc. LT3475IFE#PBF
- Part No.:
- LT3475IFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3475IFE#PBF.pdf
- Description:
- IC LED DRV RGLTR PWM 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,119
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Product details
Overview
LT3475IFE#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, designed for high-brightness LED lighting systems requiring precise 1.5A per channel current regulation. It features high-side current sensing for grounded-cathode LED configuration, 3000:1 true-color PWM dimming, and operates from 4V to 36V input across –40°C to 125°C industrial temperature range.
For engineers reviewing the LT3475IFE#PBF datasheet, LT3475IFE#PBF pinout, LT3475IFE#PBF application, or LT3475IFE#PBF equivalent, this page delivers verified technical context, validated pin functions, confirmed thermal and switching specifications, and two rigorously cross-checked alternative parts for automotive lighting, architectural backlighting, and industrial display systems.
Technical Context
The LT3475IFE#PBF implements a dual independent current-mode PWM architecture with master-slave oscillator synchronization, enabling anti-phase switching to reduce input ripple. Each channel uses an internal 0.067Ω sense resistor and gm amplifier servo loop to regulate LED current via VADJ–REF voltage ratio, supporting adjustable output from 50mA to 1.5A.
It integrates open-LED protection (clamping LED pin to 14V), frequency foldback during overload, thermal shutdown, and undervoltage lockout with programmable SHDN threshold. The BOOST pins supply gate drive voltage >VIN to saturate internal bipolar switches, requiring external Schottky diode and capacitor per channel.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 36V operating; supports 12V/24V automotive and industrial rails without pre-regulation. |
| Max Output Current per Channel | 1.5A constant current; maintained over full temperature range with ±3% accuracy at 1.5A. |
| Switching Frequency Range | 200kHz to 2MHz via RT resistor; 600kHz typical with 24.3kΩ enables compact 3.3μH inductors. |
| Dimming Ratio | 3000:1 true-color PWM; preserves white LED chromaticity by avoiding analog current reduction. |
| Operating Temperature | –40°C to +125°C junction; qualified for under-hood automotive and high-ambient industrial use. |
| Package Thermal Resistance | θJC = 8°C/W; exposed pad (Pin 21) must be soldered to PCB ground plane for thermal integrity. |
| LED Pin Voltage Rating | 15V max (LT3475 variant); supports single or two-series white LEDs up to ~9.6V total VF. |
Pinout & Package
LT3475IFE#PBF is housed in a thermally enhanced 20-lead plastic TSSOP package with exposed ground pad (Pin 21). The package requires soldering of the exposed pad to a large PCB ground plane with thermal vias for reliable operation at full load and elevated ambient temperatures.
| 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. |
| LED1, LED2 (Pins 2, 9) | Current sense resistor output / LED anode node | Direct connection point for LED anodes; enables grounded-cathode topology. |
| VIN (Pins 5, 6) | Main power input | Dual VIN pins reduce trace resistance and improve current sharing; bypass with ≥4.7μF ceramic. |
| SW1, SW2 (Pins 4, 7) | Internal switch collector output | Drives external inductor and catch diode; high dv/dt node requiring tight layout. |
| BOOST1, BOOST2 (Pins 3, 8) | Bootstrap gate drive supply | Must be ≥1.8V above respective SW pin; requires external Schottky + capacitor per channel. |
| GND (Pins 15, 21) | Signal and power ground | Pin 21 is exposed thermal pad - electrically and thermally connected to PCB ground plane. |
| RT (Pin 14) | Oscillator timing input | Resistor to GND sets switching frequency; 24.3kΩ yields 600kHz for optimal size/efficiency tradeoff. |
| SHDN (Pin 16) | Enable/disable control | 2.6V threshold enables UVLO functionality; pull <0.3V to shut down bias circuits and regulators. |
| REF (Pin 17) | 1.25V buffered reference output | Used with VADJ to set LED current; tie to VADJ for fixed 1.5A output per channel. |
| VADJ1, VADJ2 (Pins 19, 12) | Current programming input | Voltage determines LED current via ILED = 1.5A × VADJ/1.25V; supports 50mA–1.5A range. |
| PWM1, PWM2 (Pins 20, 11) | Digital dimming control | Active-low input disconnects VC loop; enables linear 3000:1 PWM dimming without color shift. |
| VC1, VC2 (Pins 18, 13) | Error amplifier output | Controls peak switch current; used for loop compensation with external RC network. |
Key Features
| Feature | Design Value |
|---|---|
| True-color PWM dimming | 3000:1 ratio achieved by digital VC pin disconnection - preserves LED spectral output across entire range. |
| High-side current sensing | Enables grounded-cathode LED strings, simplifying thermal management and eliminating high-voltage cathode routing. |
| Anti-phase switching | 180° phase shift between channels reduces input ripple amplitude and eases input capacitor sizing. |
| Integrated open-LED protection | Clamps LED pin to 14V and forces low-frequency operation during open-circuit fault - prevents overvoltage damage. |
| Programmable switching frequency | 200kHz–2MHz via single RT resistor - allows optimization for efficiency (low f) or component size (high f). |
Applications
| Automotive Headlamp Control | Architectural Accent Lighting |
|---|---|
|
Use Scenario: Driving dual high-intensity white LED strings in adaptive front-lighting systems (AFS) with dynamic beam shaping. IC Role / Device Role / Timing Role: Dual-channel constant-current source regulating 1.5A per string; synchronized anti-phase switching minimizes EMI in safety-critical vehicle subsystems. Use Value: Maintains precise luminous flux and CCT stability across –40°C to 125°C engine bay temperatures while meeting CISPR-25 Class 5 EMC limits. |
Use Scenario: Powering RGBW LED modules in museum-grade wall washers and façade lighting with smooth dimming transitions. IC Role / Device Role / Timing Role: Independent current regulation per color channel; PWM inputs accept 100Hz–25kHz control signals for flicker-free dimming. Use Value: 3000:1 true-color dimming preserves CRI >90 and avoids green/magenta shift during low-level illumination. |
| Industrial Display Backlighting | Medical Imaging Panel Illumination |
|
Use Scenario: Uniform backlight for 10.1"–15.6" TFT-LCD panels in factory HMIs and ruggedized tablets. IC Role / Device Role / Timing Role: Drives two parallel LED strings (each 1.5A) with matched current accuracy (<±3%) to eliminate vertical brightness bands. Use Value: High-side sensing eliminates need for floating return paths - simplifies mechanical design and improves long-term current matching. |
Use Scenario: Constant-current excitation of high-CRI phosphor-converted LEDs in surgical display calibration light sources. IC Role / Device Role / Timing Role: Precision 1.5A current source with <0.1% line regulation; REF/VADJ interface enables closed-loop feedback from photodiode monitor. Use Value: 1.25V reference with 0.05%/V line regulation ensures stable optical output despite 24V rail fluctuations in hospital-grade PSUs. |
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 |
|---|---|---|---|
| LT3475EFE#PBF | Same silicon, rated for –40°C to 85°C ambient; lower max junction temperature (125°C vs 150°C derated). | Suitable for commercial indoor lighting but not under-hood automotive or high-ambient industrial enclosures. | Select LT3475IFE#PBF when operation above 85°C ambient is required; no PCB changes needed. |
| LT3475IFE-1#PBF | Same package and temperature grade, but supports up to 25V LED string voltage (vs 15V); lacks open-LED protection. | Required for driving three-series white LEDs (~21V VF) where open-circuit fault detection is handled externally. | Choose LT3475IFE-1#PBF only when higher LED string voltage is mandatory and external OV protection is implemented. |
Compared with LT3475EFE#PBF, the LT3475IFE#PBF provides extended thermal margin for continuous 1.5A operation in high-ambient environments; compared with LT3475IFE-1#PBF, it retains integrated open-LED clamping critical for fail-safe lighting in unattended systems.
Availability
LT3475IFE#PBF is available at Aetrix Electronics and suitable for automotive headlamp control, architectural accent lighting, and industrial display backlighting requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT3475IFE#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) designs high-performance analog, mixed-signal, and power management ICs for demanding industrial, automotive, and communications applications.
The LT3475IFE#PBF belongs to Linear's precision LED driver product line, engineered specifically for high-reliability, high-current solid-state lighting systems requiring true-color dimming and robust fault protection.
FAQ
What is the maximum LED string voltage supported by LT3475IFE#PBF?
The LT3475IFE#PBF supports up to 15V on its LED1 and LED2 pins, as specified in the Absolute Maximum Ratings table. This accommodates two-series white LEDs (typical VF ≈ 6.8V–7.2V) or three-series low-VF LEDs. Exceeding 15V risks permanent damage; for higher string voltages, consider the LT3475IFE-1#PBF variant rated to 25V.
How does LT3475IFE#PBF achieve 3000:1 true-color PWM dimming?
The LT3475IFE#PBF achieves 3000:1 true-color PWM dimming by digitally disconnecting the VC error amplifier output during PWM low periods using internal NMOS switches. This preserves the compensation capacitor voltage and inductor current state, enabling linear light output vs. duty cycle without altering LED forward current magnitude - preventing chromaticity shift.
Can LT3475IFE#PBF operate with a single 12V input supplying two 1.5A LED strings?
Yes - the LT3475IFE#PBF is explicitly characterized for 12V input driving two series-connected 1.5A white LEDs (TA01b efficiency plot confirms >85% efficiency). Its 4V–36V input range, dual-channel architecture, and anti-phase switching make it ideal for this configuration without external pre-regulation.
What is the role of the exposed pad (Pin 21) on LT3475IFE#PBF?
The exposed pad (Pin 21) on LT3475IFE#PBF serves as both electrical ground and primary thermal path. It must be soldered to a large PCB ground plane with ≥4 thermal vias (0.3mm diameter) to achieve θJC = 8°C/W. Failure to connect it results in thermal shutdown at ≤1A/channel and violates Absolute Maximum Junction Temperature ratings.
Does LT3475IFE#PBF include open-LED protection, and how does it work?
Yes - the LT3475IFE#PBF includes integrated open-LED protection. When an LED string opens, the IC clamps the LED pin voltage to 14V (typical) and reduces switching frequency to limit input current. This prevents destructive overvoltage on external components and is confirmed in the "Open Circuit Protection" section of the datasheet.
LT3475IFE#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 ~ 125°C (TA)
- Grade:
- Automotive
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-TSSOP-EP
LT3475IFE#PBF FAQ
1.How can I place an order for LT3475IFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3475IFE#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 LT3475IFE#PBF reliable?
The price and inventory of LT3475IFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3475IFE#PBF is usually 5 days.
3.What payment methods are accepted for LT3475IFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3475IFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3475IFE#PBF?
LT3475IFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3475IFE#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 LT3475IFE#PBF?
For technical support, including LT3475IFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3475IFE#PBF requirements.
6.How does Aetrix verify that LT3475IFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3475IFE#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 LT3475IFE#PBF meets industry standards.
7.What is the process for return or replacement of LT3475IFE#PBF?
All LT3475IFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3475IFE#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 LT3475IFE#PBF part is unused and in its original packaging.
Return procedure for LT3475IFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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