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Analog Devices Inc. LT3475EFE#TRPBF
- Part No.:
- LT3475EFE#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3475EFE#TRPBF.pdf
- Description:
- IC LED DRV RGLTR PWM 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:3,409
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Product details
Overview
LT3475EFE#TRPBF from Analog Devices (formerly Linear Technology) is a dual-channel, constant-current step-down DC/DC LED driver IC with integrated 1.5A bipolar NPN power switches. It delivers precise 50mA–1.5A LED current per channel using high-side current sensing, supports 3000:1 PWM dimming without color shift, and operates from 4V to 36V input across automotive lighting and display backlighting systems.
For engineers reviewing the LT3475EFE#TRPBF datasheet, LT3475EFE#TRPBF pinout, LT3475EFE#TRPBF application, or LT3475EFE#TRPBF equivalent, this page provides verified technical context, validated pin functions, confirmed thermal and electrical specifications, and two rigorously cross-checked alternative parts for constant-current LED driver selection.
Technical Context
The LT3475EFE#TRPBF implements a current-mode PWM architecture with dual independent oscillators operating anti-phase at 200kHz–2MHz (set via RT pin), enabling reduced input ripple and stable regulation under fast transients. Each channel features cycle-by-cycle current limiting, frequency foldback during overload, and internal open-circuit protection clamping LED pins to 14V (LT3475 variant only).
It uses high-side current sensing through an internal 0.067Ω sense resistor, allowing grounded-cathode LED configurations. The VC pin serves as error amplifier output controlling peak switch current, while VADJ sets LED current via ILED = 1.5A × VADJ/1.25V - supporting accurate analog dimming alongside true-color PWM dimming.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 36V operating; 40V absolute max - supports wide-range industrial and automotive supplies without external pre-regulation. |
| LED Output Current | 50mA to 1.5A per channel, adjustable via VADJ - enables single-part support for diverse LED string configurations. |
| Dimming Ratio | 3000:1 PWM dimming with constant color fidelity - eliminates chromatic shift in architectural and display lighting. |
| Switching Frequency | 200kHz to 2MHz, set by RT resistor - allows optimization of inductor size vs. efficiency (e.g., 600kHz typical with 24.3kΩ). |
| Current Sense Accuracy | ±3% over –40°C to 85°C - ensures stable brightness control across temperature in embedded lighting systems. |
| Thermal Protection | Thermal shutdown at 125°C junction - prevents latch-up during sustained overloads or poor PCB heatsinking. |
| Package | 20-lead TSSOP with exposed thermal pad - requires soldered ground pad for θJA = 30°C/W and reliable 1.5A operation. |
Pinout & Package
LT3475EFE#TRPBF is housed in a thermally enhanced 20-lead plastic TSSOP package (FE grade) with exposed ground pad (Pin 21). The package measures 6.5mm × 4.4mm × 1.1mm and requires mandatory soldering of the exposed pad to a large PCB ground plane with thermal vias for thermal performance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| OUT1, OUT2 (Pins 1, 10) | Current sense resistor input | Connects to inductor and output capacitor; forms high-side current sense node with LED pin. |
| LED1, LED2 (Pins 2, 9) | Current sense resistor output / LED anode connection | Direct anode tie point; enables grounded-cathode LED topology; clamped to 14V during open-circuit fault (LT3475). |
| VIN (Pins 5, 6) | Main power input | Dual pins reduce trace resistance and inductance; must be locally bypassed with ≥4.7μF ceramic capacitor. |
| SW1, SW2 (Pins 4, 7) | Internal switch collector output | Drives external inductor and Schottky diode; voltage swings from GND to VIN + VBOOST–VF. |
| BOOST1, BOOST2 (Pins 3, 8) | Charge pump drive voltage | Provides >VIN voltage to saturate internal NPN switches; requires external boost capacitor and Schottky diode. |
| GND (Pins 15, 21) | Power and signal reference | Pin 15 is signal ground; Pin 21 (exposed pad) is thermal & electrical ground - must be soldered to PCB ground plane. |
| RT (Pin 14) | Oscillator timing input | Resistor-to-ground sets switching frequency (e.g., 24.3kΩ → 600kHz); determines inductor size and ripple trade-off. |
| SHDN (Pin 16) | Enable/disable control | 2.6V threshold enables regulator; <0.3V shuts down bias circuits - usable as precision undervoltage lockout. |
| REF (Pin 17) | 1.25V buffered reference output | Source for VADJ divider; ties directly to VADJ for 1.5A full-scale LED current. |
| VADJ1, VADJ2 (Pins 19, 12) | Analog current programming input | Sets LED current via ILED = 1.5A × VADJ/1.25V - enables precise analog dimming or current scaling. |
| PWM1, PWM2 (Pins 20, 11) | Digital dimming control | Low-active disconnects VC pin; preserves compensation state for linear 3000:1 PWM dimming without color shift. |
| VC1, VC2 (Pins 18, 13) | Error amplifier output | Controls peak switch current; voltage range 0.8V–1.8V; used for loop compensation and external monitoring. |
Key Features
| Feature | Design Value |
|---|---|
| True-color PWM dimming | 3000:1 ratio with no perceptible LED color shift - achieved by preserving VC state during PWM off-time. |
| High-side current sensing | Enables grounded-cathode LED configuration - simplifies thermal management and improves system safety. |
| Anti-phase switching | Reduces input ripple current by up to 50% - lowers RMS stress on input capacitors and EMI filter requirements. |
| Integrated open-circuit protection | Clamps LED pins to 14V and reduces switching frequency - prevents overvoltage damage when LEDs are disconnected. |
| Adjustable 200kHz–2MHz frequency | Single RT resistor selects optimal trade-off between inductor size (smaller at higher f) and conduction losses (lower at lower f). |
| Thermally enhanced TSSOP | Exposed pad (Pin 21) tied to PCB ground plane achieves θJA = 30°C/W - sustains 1.5A/channel continuous operation. |
Applications
| Automotive Headlight Modules | Architectural Accent Lighting |
|---|---|
|
Use Scenario: Driving dual white LED strings in adaptive front-lighting systems with dynamic beam shaping. IC Role / Device Role / Timing Role: Dual-channel constant-current source regulating 1.5A per string; high-side sensing enables common-cathode layout with shared heat sink. Use Value: 3000:1 PWM dimming maintains consistent correlated color temperature (CCT) across all brightness levels - critical for regulatory-compliant glare control. |
Use Scenario: Illuminating façade elements and interior trim with tunable intensity and uniform spectral output. IC Role / Device Role / Timing Role: Dual independent current regulators powering parallel LED strips; anti-phase switching minimizes conducted EMI in sensitive building environments. Use Value: ±3% current accuracy over –40°C to 85°C ensures consistent lumen output despite ambient temperature swings in unconditioned spaces. |
| Industrial Display Backlighting | Medical Instrument Panel Lighting |
|
Use Scenario: Powering edge-lit LCD backlights in rugged HMIs requiring wide input voltage tolerance and low EMI. IC Role / Device Role / Timing Role: Dual buck controller delivering 1.5A to separate top/bottom LED banks; RT-programmable frequency avoids AM radio band interference. Use Value: 4V–36V input range accepts 12V/24V industrial rails and battery-backed supplies without external converters - reducing BOM count. |
Use Scenario: Providing flicker-free, precisely calibrated illumination for surgical displays and diagnostic device indicators. IC Role / Device Role / Timing Role: Constant-current source with analog + PWM dimming; VADJ and PWM pins enable dual-control interface for clinical brightness adjustment. Use Value: Internal open-circuit protection prevents hazardous overvoltage on disconnected LED traces - meeting IEC 60601-1 insulation and fault-safety requirements. |
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#TRPBF | Higher 3A per channel, synchronous buck architecture, no internal open-circuit protection; requires external MOSFETs. | Better suited for high-power (>2A) LED arrays; lacks integrated bipolar switches - increases component count but improves efficiency above 1.5A. | Select when >1.5A/channel is required and board space permits discrete FET layout; not drop-in due to different pinout and gate drive needs. |
| MAX16820ATP+ | Single-channel 1.5A driver; 4.5V–65V input; includes thermal foldback but no anti-phase switching or 3000:1 PWM. | Requires two units for dual-channel operation; supports higher input voltage but offers narrower dimming range (1000:1). | Choose for ultra-wide input (up to 65V) in single-string designs where cost-per-channel is prioritized over integration density. |
Compared with LTC3783EFE#TRPBF and MAX16820ATP+, the LT3475EFE#TRPBF uniquely integrates bipolar switches, anti-phase operation, and true-color 3000:1 PWM in a single 20-pin TSSOP - optimizing space, EMI, and color fidelity for mid-power dual-LED systems.
Availability
LT3475EFE#TRPBF 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 guaranteed parametric compliance over –40°C to 85°C.
Supply support for LT3475EFE#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and healthcare markets.
The LT3475 product line was designed specifically for high-accuracy, high-dimming-ratio LED driving in space-constrained applications - emphasizing thermal robustness, integrated protection, and simplified layout for lighting engineers.
FAQ
What is the maximum LED string voltage supported by the LT3475EFE#TRPBF?
The LT3475EFE#TRPBF (LT3475 variant) supports up to 14V on its LED pins due to internal open-circuit clamping. This corresponds to approximately four series-connected white LEDs (3.5V each) at nominal forward voltage. Exceeding this voltage risks triggering clamping action and reduced efficiency - verify string VF sum stays below 14V under all operating conditions for LT3475EFE#TRPBF.
Does the LT3475EFE#TRPBF require external MOSFETs or bipolar transistors?
No, the LT3475EFE#TRPBF integrates two bipolar NPN power switches capable of 1.5A continuous output per channel. External components required are inductors, Schottky diodes, boost capacitors, input/output ceramics, and the RT timing resistor - no external switching transistors are needed for standard operation of LT3475EFE#TRPBF.
How does the LT3475EFE#TRPBF achieve 3000:1 PWM dimming without color shift?
The LT3475EFE#TRPBF preserves the VC pin voltage state during PWM off-time by disconnecting the VC node from internal circuitry. This maintains the exact current-regulation setpoint across dimming cycles, preventing transient current overshoot/undershoot that causes chromatic variation - a design feature confirmed in the LT3475EFE#TRPBF datasheet Figure 1 and Applications section.
What is the role of the exposed pad (Pin 21) on the LT3475EFE#TRPBF package?
The exposed pad (Pin 21) on the LT3475EFE#TRPBF is electrically and thermally connected to GND. It must be soldered to a large PCB ground plane with multiple thermal vias to achieve θJA = 30°C/W. Failure to connect it results in excessive junction temperature, thermal shutdown, and potential reliability failure - a requirement explicitly stated in the LT3475EFE#TRPBF FE package documentation.
Can the LT3475EFE#TRPBF drive LED strings with different forward voltages on each channel?
Yes, the LT3475EFE#TRPBF supports independent LED string configurations per channel. OUT1/LED1 and OUT2/LED2 operate autonomously - each with its own VADJ, PWM, VC, and BOOST nodes. This allows one channel to drive a 10V string while the other drives a 6V string, provided both remain within the 14V LED pin clamp limit and input voltage constraints of LT3475EFE#TRPBF.
LT3475EFE#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-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:
- 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#TRPBF FAQ
1.How can I place an order for LT3475EFE#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3475EFE#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 LT3475EFE#TRPBF reliable?
The price and inventory of LT3475EFE#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3475EFE#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3475EFE#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3475EFE#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3475EFE#TRPBF?
LT3475EFE#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3475EFE#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 LT3475EFE#TRPBF?
For technical support, including LT3475EFE#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3475EFE#TRPBF requirements.
6.How does Aetrix verify that LT3475EFE#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3475EFE#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 LT3475EFE#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3475EFE#TRPBF?
All LT3475EFE#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3475EFE#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 LT3475EFE#TRPBF part is unused and in its original packaging.
Return procedure for LT3475EFE#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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