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Analog Devices Inc. LT3477IUF#PBF
- Part No.:
- LT3477IUF#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 20-WFQFN Exposed Pad
- Datasheet:
-
LT3477IUF#PBF.pdf
- Description:
- IC LED DRIVER RGLTR PWM 3A 20QFN
- Quantity:
- Payment:
- Shipping:
Inventory:1,483
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Product details
Overview
LT3477IUF#PBF 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 integrated 42V NPN switch. It delivers up to 93% efficiency, supports 2.5V–25V input, operates from –40°C to 125°C, and enables constant-current/constant-voltage regulation for high-power LED drivers in boost, buck-boost, or inverting topologies.
For engineers reviewing the LT3477IUF#PBF datasheet, LT3477IUF#PBF pinout, LT3477IUF#PBF application, or LT3477IUF#PBF equivalent, this page provides verified technical context, package-specific pin mapping, real-world design meaning of key specs, and two validated alternative parts for constant-current DC/DC converter selection in industrial and automotive lighting systems.
Technical Context
The LT3477IUF#PBF implements fixed-frequency current-mode control with independent voltage feedback (via FBP/FBN) and dual current feedback loops (via ISP1/ISN1 and ISP2/ISN2), enabling seamless transition between constant-voltage and constant-current modes. Its error amplifier features externally accessible inputs (FBP, FBN) and compensation node (VC), supporting both positive and negative output configurations (boost, inverting, SEPIC, flyback).
Switching frequency is set by an external resistor on RT (200kHz–3.5MHz), soft-start is programmable via SS pin (9µA current source), and current sense thresholds are independently adjustable via IADJ1/IADJ2 (default 100mV, linearly scalable down to ~88mV). The internal 3A/42V NPN switch exhibits 0.3V VCE(SAT) at 2.5A and is thermally optimized for the 4mm × 4mm QFN package with exposed PGND pad.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.5V to 25V - supports wide-input industrial rails and battery-backed systems without pre-regulation. |
| Switch Current Limit | 3A nominal - sets maximum peak inductor current; protects internal NPN switch and external magnetics during overload or short-circuit. |
| Current Sense Threshold | 100mV per channel (E/I grade: 97.5–103mV) - enables precise, low-loss current sensing with standard 0.1Ω–1Ω shunts. |
| Reference Voltage | 1.235V (I grade: 1.210–1.260V) - stable bandgap reference used for output voltage setting and feedback loop accuracy. |
| Switching Frequency Range | 200kHz to 3.5MHz - selectable via RT resistor; higher frequencies reduce inductor size but trade off efficiency and EMI. |
| Operating Junction Temp | –40°C to 125°C - qualified for under-hood automotive, industrial control, and high-ambient lighting applications. |
| Package Thermal Resistance | θJA = 37°C/W - enabled by 4mm × 4mm QFN with soldered exposed pad (Pin 21 = PGND), critical for 3A continuous operation. |
Pinout & Package
LT3477IUF#PBF 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 electrical integrity and thermal performance (θJA = 37°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pin 3) | Input supply rail | Powers internal circuitry; must be locally bypassed with low-ESR ceramic capacitor (≥3.3µF). |
| RT (Pin 4) | Frequency programming node | Connects external resistor to GND; sets switching frequency from 200kHz to 3.5MHz (e.g., 17.2kΩ = 1MHz). |
| SHDN (Pin 5) | Enable/disable control | Logic-high (>1.5V) enables converter; logic-low (<0.3V) disables with <1µA quiescent current. |
| SS (Pin 6) | Soft-start timing node | Sinks 9µA to charge external capacitor; controls VC ramp rate and limits inrush current at startup. |
| VC (Pin 7) | Error amplifier output / compensation node | External RC network (e.g., 1kΩ + 4.7nF) sets loop stability; directly limits peak switch current during transients. |
| FBN (Pin 8) | Inverting input of voltage feedback amplifier | Connected to resistive divider tap for positive-output regulation; referenced to VREF (1.235V). |
| FBP (Pin 9) | Noninverting input of voltage feedback amplifier | Connected to resistive divider tap for negative-output regulation; tied to GND for inverting topology. |
| VREF (Pin 10) | Internal bandgap reference output | 1.235V ±1.2%; supplies reference for feedback and can source up to 100µA for external biasing. |
| IADJ1 (Pin 11) | First current sense threshold adjust | DC voltage <625mV linearly scales ISP1/ISN1 sense threshold below 100mV; >650mV locks at default 100mV. |
| IADJ2 (Pin 12) | Second current sense threshold adjust | Same function as IADJ1 for ISP2/ISN2 channel; enables independent dual-current regulation (e.g., parallel LED strings). |
| ISP1 (Pin 13) | Noninverting input of first current sense amp | Connects to high-side of current sense resistor; used for output or input current monitoring in boost/buck-boost. |
| ISN1 (Pin 14) | Inverting input of first current sense amp | Connects to low-side of current sense resistor; differential input rejects common-mode noise up to 42V. |
| GND (Pin 17) | Analog ground reference | Must tie directly to local ground plane; separate from PGND (exposed pad) in layout for noise isolation. |
| SW (Pins 18,19) | Internal NPN switch collector | High-di/dt node; connects to inductor and diode; requires minimal trace area and solid ground return path. |
| Exposed Pad (Pin 21) | Power ground (PGND) | Mandatory solder connection to PCB ground plane; provides primary thermal path and low-inductance return for switch current. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent current sense amplifiers | Each provides rail-to-rail input common-mode range (0–42V), 100mV default threshold, and pin-adjustable scaling - enables simultaneous regulation of two LED strings or input/output current limiting. |
| Configurable output polarity | Supports boost (positive VOUT), inverting (negative VOUT), SEPIC, and flyback topologies via FBP/FBN pin routing - eliminates need for separate ICs in multi-rail systems. |
| Programmable soft-start | 9µA constant-current source on SS pin charges external capacitor to linearly ramp VC voltage - prevents inrush current and output overshoot during startup. |
| Thermally optimized QFN package | 4mm × 4mm footprint with soldered exposed PGND pad achieves θJA = 37°C/W - sustains 3A continuous output current in compact industrial and automotive layouts. |
| Wide switching frequency range | 200kHz–3.5MHz via single RT resistor - allows optimization of magnetic size (higher fSW) vs. efficiency/EMI (lower fSW) without changing IC. |
Applications
| High-Power LED Driver | DSL Modem Power Supply |
|---|---|
|
Use Scenario: Driving 4–6 white LEDs (12–24V total VF) from 5V or 12V input in automotive headlamps or industrial signage. IC Role / Device Role / Timing Role: Constant-current DC/DC controller regulating LED string current via ISP1/ISN1 sense; uses PWM dimming interface (NMOS gate drive) for 500:1 dimming ratio. Use Value: Eliminates need for external current regulators; 93% efficiency reduces thermal load; 125°C rating ensures reliability in sealed enclosures. |
Use Scenario: Generating isolated ±12V rails from 3.3V or 5V motherboard supply in DSL line cards with strict EMI limits. IC Role / Device Role / Timing Role: Inverting converter (FBN = GND, FBP = divider) generating negative output; RT resistor set to 1MHz for compact magnetics and reduced audible noise. Use Value: Single-chip solution replaces discrete charge-pump or transformer-based designs; rail-to-rail current sense enables precise input current limiting during surge events. |
| Distributed Power System | Constant-Voltage/Constant-Current Source |
|
Use Scenario: Local 24V boost converter feeding multiple point-of-load regulators in telecom base station backplanes. IC Role / Device Role / Timing Role: High-efficiency (≥90%) step-up regulator with programmable soft-start and remote ON/OFF (SHDN); configured for constant-voltage mode via FBP/FBN feedback. Use Value: 25V absolute max input withstands 24V rail transients; 3A capability supports >20W output; QFN package eases thermal management in dense layouts. |
Use Scenario: Lab-grade bench power supply module delivering 0–30V / 0–3A with automatic CV/CC crossover for battery charging or sensor biasing. IC Role / Device Role / Timing Role: Dual-loop controller using ISP1/ISN1 for CC mode (LED/battery) and FBP/FBN for CV mode (voltage regulation); IADJ1 adjusts current limit dynamically. Use Value: Seamless mode transition avoids output glitches; 100mV sense threshold enables accurate low-current regulation (e.g., 100mA with 1Ω shunt); 125°C rating supports unventilated enclosures. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar constant-current DC/DC converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3783EFE#PBF | 4-switch synchronous buck-boost controller (no integrated switch); supports 4–36V input, 0.8–36V output; requires external MOSFETs. | Better suited for high-efficiency, high-current (>5A) buck-boost where thermal budget is constrained; lacks integrated current sense amps. | Select when >3A output or >95% efficiency is required; avoid if board space or BOM count reduction is critical. |
| LM3478MM/NOPB | Adjustable 1A current-mode boost controller (no integrated switch); 2.97–40V input; no dual current sense or CV/CC auto-transition. | Lower cost for basic boost-only applications; requires external sense amp and op-amp for CC mode; limited to 1A switch current. | Select for cost-sensitive, lower-current (<1.5A) boost designs where dual-loop regulation is unnecessary. |
Compared with LTC3783EFE#PBF and LM3478MM/NOPB, the LT3477IUF#PBF uniquely integrates dual rail-to-rail current sense amplifiers and a 3A/42V switch in a thermally optimized QFN, enabling compact, self-contained constant-current LED drivers and CV/CC sources without external power devices or signal conditioning.
Availability
LT3477IUF#PBF is available at Aetrix Electronics and suitable for high-reliability LED driver, distributed power, and telecom power supply applications requiring stable component supply across extended temperature ranges.
Supply support for LT3477IUF#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and healthcare markets.
The LT3477 belongs to Linear's precision DC/DC converter product line, designed specifically for constant-current applications such as high-brightness LED driving, battery charging, and programmable current sources where dual-loop regulation and wide input range are essential.
FAQ
What is the maximum input voltage rating for the LT3477IUF#PBF?
The LT3477IUF#PBF has an absolute maximum VIN rating of 25V. Exceeding this voltage risks permanent damage. The device operates reliably across its full specified input range of 2.5V to 25V, making it suitable for 12V and 24V industrial systems with transient margin. Always verify input rail stability and include appropriate clamping or filtering per application requirements.
How does the LT3477IUF#PBF achieve constant-current and constant-voltage regulation simultaneously?
The LT3477IUF#PBF uses a dual-loop architecture: the voltage feedback loop (FBP/FBN) regulates output voltage, while two independent current feedback loops (ISP1/ISN1 and ISP2/ISN2) regulate current. Whichever loop demands lower peak switch current takes precedence, enabling automatic, glitch-free transition between CV and CC modes - a core feature confirmed in the LT3477IUF#PBF datasheet block diagram and operation section.
Can the LT3477IUF#PBF drive negative output voltages, and how is it configured?
Yes, the LT3477IUF#PBF supports negative outputs via inverting, SEPIC, or flyback topologies. For inverting operation, connect FBN to GND and route the output divider to FBP. This configuration leverages the LT3477IUF#PBF's fully differential error amplifier inputs and rail-to-rail current sense capability - explicitly detailed in the "Setting Negative Output Voltages" section of the official datasheet.
What is the purpose of the exposed pad (Pin 21) on the LT3477IUF#PBF QFN package?
The exposed pad (Pin 21) on the LT3477IUF#PBF is designated PGND (power ground) and must be soldered to the PCB ground plane. It serves two critical functions: (1) provides the primary low-inductance return path for the 3A switch current, and (2) establishes the main thermal conduction path, enabling the specified θJA = 37°C/W. Omitting this connection degrades both electrical performance and thermal reliability.
Does the LT3477IUF#PBF support PWM dimming for LED applications, and what is the achievable dimming ratio?
Yes, the LT3477IUF#PBF supports external PWM dimming with a typical 500:1 dimming ratio at 100Hz, as validated in the datasheet's Figure 7c and Application Information section. This is achieved by synchronously gating NMOS transistors in series with the LED string using a logic-level PWM signal - a method that preserves LED chromaticity and avoids analog current variation. Dimming range decreases at higher PWM frequencies due to switching limitations.
LT3477IUF#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-WFQFN Exposed Pad
- Packaging:
- Tube
- 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 ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-QFN (4x4)
LT3477IUF#PBF FAQ
1.How can I place an order for LT3477IUF#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3477IUF#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 LT3477IUF#PBF reliable?
The price and inventory of LT3477IUF#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3477IUF#PBF is usually 5 days.
3.What payment methods are accepted for LT3477IUF#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3477IUF#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3477IUF#PBF?
LT3477IUF#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3477IUF#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 LT3477IUF#PBF?
For technical support, including LT3477IUF#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3477IUF#PBF requirements.
6.How does Aetrix verify that LT3477IUF#PBF is sourced from the original manufacturer or authorized distributors?
All LT3477IUF#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 LT3477IUF#PBF meets industry standards.
7.What is the process for return or replacement of LT3477IUF#PBF?
All LT3477IUF#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3477IUF#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 LT3477IUF#PBF part is unused and in its original packaging.
Return procedure for LT3477IUF#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LT3477IUF#PBF Tags
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BCR402RE6327HTSA1
Infineon Technologies
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BCR430UXTSA2
Infineon Technologies
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BCR420UE6433HTMA1
Infineon Technologies
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BCR420UE6327HTSA1
Infineon Technologies
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BCR421UE6327HTSA1
Infineon Technologies
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LYT1604D-TL
Power Integrations
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HV9910CLG-G
Microchip Technology
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CL2N8-G
Microchip Technology
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BCR420UW6-7
Diodes Incorporated
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BCR421UW6-7
Diodes Incorporated
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BCR420UFD-7
Diodes Incorporated
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BCR421UFD-7
Diodes Incorporated
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