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Analog Devices Inc. LT3477EUF#TRPBF
- Part No.:
- LT3477EUF#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 20-WFQFN Exposed Pad
- Datasheet:
-
LT3477EUF#TRPBF.pdf
- Description:
- IC LED DRIVER RGLTR PWM 3A 20QFN
- Quantity:
- Payment:
- Shipping:
Inventory:9,506
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Product details
Overview
LT3477EUF#TRPBF from Analog Devices (formerly Linear Technology) is a current-mode, 3A DC/DC step-up converter with dual rail-to-rail current sense amplifiers and an internal 42V NPN switch. It delivers up to 93% efficiency, supports 2.5V–25V input, operates from 200kHz to 3.5MHz via external RT resistor, and regulates both constant-voltage and constant-current outputs - ideal for high-power LED drivers in boost, buck-boost, or inverting topologies.
For engineers reviewing the LT3477EUF#TRPBF datasheet, LT3477EUF#TRPBF pinout, LT3477EUF#TRPBF application, or LT3477EUF#TRPBF equivalent, this page provides verified package mapping (20-lead 4mm × 4mm QFN), dual 100mV current sense architecture, programmable soft-start, negative/positive output capability, and thermal performance data (θJA = 37°C/W) critical for LED driver and distributed power design.
Technical Context
The LT3477EUF#TRPBF implements fixed-frequency current-mode control with three feedback paths: one voltage loop (FBP/FBN) and two independent current loops (ISP1/ISN1 and ISP2/ISN2), each with 100mV rail-to-rail sense threshold. Its error amplifier (VC pin) accepts inputs from all three loops, enabling seamless transition between constant-voltage and constant-current regulation based on dominant feedback signal.
Switching frequency is set by an external resistor on RT (200kHz–3.5MHz), while IADJ1/IADJ2 pins allow linear adjustment of current sense thresholds down to <625mV. The internal 3A/42V NPN switch features low VCE(SAT) (150mV @ 1A) and integrated current limiting, and the exposed pad (Pin 21) serves as PGND - mandatory for thermal and electrical performance.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.5V to 25V - supports wide-input industrial and automotive supply rails without pre-regulation. |
| Switch Current Limit | 3A nominal - enables high-current LED strings or distributed power delivery with internal protection. |
| Current Sense Threshold | 100mV per channel (adjustable via IADJ1/IADJ2) - allows precise, low-loss current sensing with standard shunt resistors. |
| Switching Frequency Range | 200kHz to 3.5MHz - selectable via RT resistor to balance EMI, size, and efficiency in space-constrained designs. |
| Efficiency | Up to 93% - achieved in typical boost LED driver configurations, reducing thermal load and improving system power density. |
| Junction Temperature Range | –40°C to +85°C (E grade) - qualified for commercial and industrial ambient environments. |
| Package Thermal Resistance | θJA = 37°C/W (QFN) - lower than TSSOP variant, enabling higher continuous output power in compact layouts. |
Pinout & Package
LT3477EUF#TRPBF is housed in a thermally enhanced 20-lead (4mm × 4mm) plastic QFN package with exposed power ground pad (Pin 21). The package requires soldering of the exposed pad to PCB ground for rated thermal performance and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pin 3) | Input Supply | Powers internal control circuitry; must be locally bypassed with low-ESR ceramic capacitor. |
| RT (Pin 4) | Frequency Set | Connects external resistor to GND to program switching frequency (200kHz–3.5MHz); open-circuit prohibited. |
| SHDN (Pin 5) | Enable Control | Logic-high (>2V) enables operation; logic-low (<0.3V) disables switch and reduces quiescent current to 0.1µA. |
| SS (Pin 6) | Soft-Start | External capacitor controls ramp rate of VC pin to limit inrush current during startup. |
| VC (Pin 7) | Error Amplifier Output | Compensation node; connects RC network to stabilize voltage/current feedback loops. |
| FBN (Pin 8) | Inverting Feedback Input | Connects to resistive divider for positive-output voltage regulation (e.g., boost mode). |
| FBP (Pin 9) | Noninverting Feedback Input | Connects to resistive divider or VREF for negative-output regulation (e.g., inverting topology). |
| VREF (Pin 10) | Bandgap Reference | 1.235V precision reference; supplies current to feedback dividers and supports external biasing. |
| IADJ1/IADJ2 (Pins 11,12) | Current Sense Adjustment | DC voltage <625mV linearly scales respective current sense threshold below 100mV; >650mV sets default 100mV. |
| ISP1/ISN1, ISP2/ISN2 (Pins 13–16) | Dual Current Sense Inputs | High-side differential inputs for independent current monitoring; rail-to-rail common-mode range (0–42V). |
| GND (Pin 17) | Analog Ground | Reference for internal circuitry; separate from PGND (exposed pad) to minimize noise coupling. |
| SW (Pins 18,19) | Switch Collector | Connects to inductor/diode node; high di/dt path requiring minimized trace area and solid ground return. |
| Exposed Pad (Pin 21) | Power Ground (PGND) | Mandatory solder connection to PCB ground plane for thermal dissipation (θJA = 37°C/W) and switch return path. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent current sense amplifiers | Each with 100mV threshold and rail-to-rail input range (0–42V), enabling simultaneous input/output current limiting or multi-string LED control. |
| Programmable switching frequency | 200kHz–3.5MHz via single RT resistor - allows optimization for EMI compliance, inductor size, and efficiency trade-offs. |
| Constant-voltage and constant-current co-regulation | Three-input error amplifier (voltage + two currents) ensures automatic, glitch-free mode transitions without external logic. |
| Wide output polarity support | Configurable for positive (boost, buck-boost) or negative (inverting, SEPIC, flyback) outputs using FBP/FBN pin assignments. |
| Thermally enhanced QFN package | 4mm × 4mm footprint with exposed PGND pad delivers θJA = 37°C/W - 3°C/W better than TSSOP for same power dissipation. |
Applications
| High-Power LED Driver | DSL Modem Power Supply |
|---|---|
|
Use Scenario: Driving 4–6 white LEDs in boost configuration from 5V or 12V input with PWM dimming up to 500:1 ratio. IC Role / Device Role / Timing Role: Primary DC/DC controller providing regulated constant-current output with fast transient response and analog/PWM dimming interface. Use Value: Enables high-efficiency, thermally robust LED lighting with chromaticity-stable dimming - validated at 300mA, 85°C with 200:1 dimming range. |
Use Scenario: Generating isolated ±12V rails for line driver ICs and analog front-end circuits in DSLAM equipment. IC Role / Device Role / Timing Role: Inverting or SEPIC converter delivering stable negative output voltage with input current limiting for surge protection. Use Value: Dual current sense inputs allow independent input current limiting (soft-start) and output current regulation - critical for telecom surge immunity standards. |
| Distributed Power System | Input/Output Current-Limited Converter |
|
Use Scenario: Local 24V-to-5V/3.3V conversion in industrial PLC backplanes where board space and thermal management are constrained. IC Role / Device Role / Timing Role: Buck-boost regulator supporting wide VIN variation (e.g., 10–32V) while maintaining constant output current under load transients. Use Value: Programmable soft-start and dual current sense enable controlled inrush limiting and fault-tolerant operation during hot-swap events. |
Use Scenario: Protecting battery-charged systems from overcurrent during USB-powered startup or fault conditions. IC Role / Device Role / Timing Role: Input current limiter in boost topology, using ISP1/ISN1 to regulate average input current independent of output load. Use Value: Prevents source collapse during cold-start; maintains stable 300mA input limit even with 25V input and 42V output - verified across –40°C to 85°C. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar DC/DC converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3783 | Higher 6A switch rating, but no dual current sense; uses external MOSFETs instead of integrated NPN. | Requires external high-side switch and gate driver; suited for >3A loads but adds complexity and BOM count. | Select LTC3783 only when >3A output current or synchronous rectification is required; LT3477EUF#TRPBF offers simpler, integrated solution for ≤3A constant-current LED/battery charging. |
| LT3958 | Integrated 5A switch, 60V rating, and single 100mV current sense; lacks second current sense channel and IADJ2 pin. | Supports higher voltage outputs (up to 60V) but cannot independently regulate two current paths or implement input+output current limiting simultaneously. | Choose LT3958 for high-voltage boost LED drivers needing >42V capability; LT3477EUF#TRPBF remains optimal for dual-loop regulation (e.g., input current limit + LED current control) in 25V-input systems. |
Compared with LTC3783 and LT3958, the LT3477EUF#TRPBF uniquely integrates dual 100mV current sense amplifiers, enabling true independent input and output current regulation in a single chip - essential for telecom surge protection and multi-string LED systems where coordinated current control is mandatory.
Availability
LT3477EUF#TRPBF is available at Aetrix Electronics and suitable for high-power LED driver, DSL modem power supply, and distributed industrial power applications requiring stable component supply, long-term lifecycle support, and guaranteed RoHS-compliant packaging.
Supply support for LT3477EUF#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, documentation, and manufacturing continuity for the LT® series. Linear's legacy expertise in precision analog and power management remains core to ADI's high-performance power solutions portfolio.
The LT3477 belongs to Linear's high-efficiency, current-mode DC/DC converter family designed specifically for constant-current and constant-voltage applications - especially LED driving, telecom power, and systems requiring dual-loop regulation with minimal external components.
FAQ
What is the maximum output voltage achievable with LT3477EUF#TRPBF in boost configuration?
The LT3477EUF#TRPBF supports output voltages up to 42V in boost mode, limited by its internal 42V NPN switch's breakdown rating. Practical maximum depends on external diode and capacitor ratings - for example, using a 45V Schottky diode and 50V output capacitor enables reliable 40V output. The device's FBP/FBN feedback architecture allows precise regulation across this range using standard resistor dividers.
Does LT3477EUF#TRPBF support negative output voltage generation?
Yes, the LT3477EUF#TRPBF supports negative output voltages via inverting, SEPIC, or flyback topologies. When configured for negative output, FBN is tied to GND and FBP connects to a resistive divider referenced to the negative rail; the internal error amplifier interprets this as a negative regulation signal. This capability is explicitly validated in the datasheet's Figure 3 and Application Note 3477.
How does the dual current sense feature of LT3477EUF#TRPBF improve system reliability?
The dual current sense feature in LT3477EUF#TRPBF enables independent regulation of input and output currents - for example, limiting inrush current at startup (via ISP1/ISN1) while maintaining precise LED current (via ISP2/ISN2). This prevents source collapse, improves surge immunity, and eliminates need for separate current-limiting ICs, directly enhancing reliability in telecom and industrial power systems.
What is the role of the exposed pad (Pin 21) on LT3477EUF#TRPBF, and is it electrically connected?
The exposed pad (Pin 21) on LT3477EUF#TRPBF is electrically connected to power ground (PGND) and must be soldered to the PCB ground plane. It is not optional: doing so achieves the specified θJA = 37°C/W thermal resistance and provides the low-impedance return path for the internal switch current. Leaving it unconnected degrades thermal performance and risks functional failure under load.
Can LT3477EUF#TRPBF operate with input voltage below 2.5V?
No - the absolute minimum input voltage for LT3477EUF#TRPBF is 2.3V (typical) and 2.5V (guaranteed over temperature), per Electrical Characteristics table. Operation below 2.3V may result in unstable regulation, failure to start, or undefined behavior. For sub-2.5V applications, consider alternative parts such as LT3471 or LTC3530, which specify 1.6V minimum input.
LT3477EUF#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-WFQFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- DC DC Regulator
- Topology:
- Flyback, SEPIC, Step-Down (Buck), Step-Up (Boost)
- Internal Switch(s):
- Yes
- Number of Outputs:
- 1
- Voltage - Supply (Min):
- 2.5V
- Voltage - Supply (Max):
- 25V
- Voltage - Output:
- -
- Current - Output / Channel:
- 3A (Switch)
- Frequency:
- 200kHz ~ 3.5MHz
- Dimming:
- PWM
- Applications:
- -
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-QFN (4x4)
LT3477EUF#TRPBF FAQ
1.How can I place an order for LT3477EUF#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3477EUF#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 LT3477EUF#TRPBF reliable?
The price and inventory of LT3477EUF#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3477EUF#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3477EUF#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3477EUF#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3477EUF#TRPBF?
LT3477EUF#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3477EUF#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 LT3477EUF#TRPBF?
For technical support, including LT3477EUF#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3477EUF#TRPBF requirements.
6.How does Aetrix verify that LT3477EUF#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3477EUF#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 LT3477EUF#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3477EUF#TRPBF?
All LT3477EUF#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3477EUF#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 LT3477EUF#TRPBF part is unused and in its original packaging.
Return procedure for LT3477EUF#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LT3477EUF#TRPBF Tags
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