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Analog Devices Inc. LT3477IFE#PBF
- Part No.:
- LT3477IFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3477IFE#PBF.pdf
- Description:
- IC LED DRVR RGLTR PWM 3A 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:496
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Product details
Overview
LT3477IFE#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 internal 42V NPN switch. It delivers up to 93% efficiency, supports 200kHz–3.5MHz programmable switching frequency via RT pin, and operates across 2.5V–25V input range-enabling high-power LED drivers in boost, buck-boost, or inverting configurations.
For engineers reviewing the LT3477IFE#PBF datasheet, LT3477IFE#PBF pinout, LT3477IFE#PBF application, or LT3477IFE#PBF equivalent, key selection considerations include dual 100mV current sense thresholds, independent IADJ1/IADJ2 voltage-adjustable current regulation, thermally enhanced 20-lead TSSOP package rated for –40°C to 125°C, and support for constant-current/constant-voltage operation in positive/negative output topologies.
Technical Context
The LT3477IFE#PBF implements fixed-frequency current-mode control with three feedback paths: one voltage loop (via FBP/FBN) and two independent current loops (via ISP1/ISN1 and ISP2/ISN2), each with 100mV default sense threshold. Its error amplifier (VC pin) accepts external RC compensation, and soft-start is controlled by SS pin current (9µA sink).
It integrates a 3A/42V NPN switch with 0.3V VCE(SAT) at 2.5A, supports both positive and negative output voltages (boost, inverting, SEPIC, flyback), and features shutdown (SHDN) with 0.3V–1.5V threshold and 0.1–60µA leakage current across temperature.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.5V to 25V - enables direct operation from single-cell Li-ion to industrial 24V rails. |
| Switch Current Limit | 3A nominal - protects internal NPN transistor and external inductor during overload or short-circuit. |
| Current Sense Threshold | 100mV per channel (adjustable via IADJ1/IADJ2) - sets precise LED or battery charge current without changing sense resistor. |
| Switching Frequency Range | 200kHz to 3.5MHz - selected by RT resistor; higher frequencies reduce output ripple but trade off efficiency. |
| Reference Voltage | 1.235V (I-grade, –40°C to 125°C) - stable bandgap reference for accurate output voltage regulation. |
| Efficiency | Up to 93% - achieved in typical boost LED driver applications with optimized layout and component selection. |
| Operating Temperature | –40°C to +125°C junction - qualified for automotive under-hood and industrial high-temp environments. |
Pinout & Package
LT3477IFE#PBF is housed in a thermally enhanced 20-lead plastic TSSOP package (4.4mm × 6.5mm × 1.1mm) with exposed pad (Pin 21) soldered to PCB ground for electrical integrity and thermal dissipation (θJA = 40°C/W). Pin 1 is located at bottom-left corner when notch faces upward.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pin 3) | Input supply rail | Power source for internal circuitry; requires local ceramic bypass (≥3.3µF) near pin. |
| RT (Pin 4) | Frequency programming node | Connects to GND via resistor (e.g., 17.2kΩ for 1MHz); open-circuit disables switching. |
| SHDN (Pin 5) | Enable/disable control | Logic-high ≥2V enables converter; ≤0.3V forces shutdown 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. |
| VC (Pin 7) | Error amplifier output | External RC compensation point (e.g., 1kΩ + 4.7nF) for loop stability in all topologies. |
| FBN (Pin 8) | Inverting voltage feedback input | Connects to resistive divider tap for positive-output regulation (e.g., VOUT = 1.235V × (1+R1/R2)). |
| FBP (Pin 9) | Noninverting voltage feedback input | Used for negative-output configurations; ties to GND or external divider depending on topology. |
| VREF (Pin 10) | Internal 1.235V reference | Provides bias for feedback networks; supplies up to 100µA; bypass with 100pF recommended. |
| IADJ1/IADJ2 (Pins 11–12) | Current sense threshold adjust | DC voltage <625mV linearly scales sense threshold from 100mV down; >650mV restores default. |
| ISP1/ISN1, ISP2/ISN2 (Pins 13–16) | Dual current sense inputs | Each pair measures differential voltage across external sense resistor; rail-to-rail input common-mode range. |
| GND (Pin 17) | Analog ground reference | Low-impedance return path for feedback and sense circuits; separate from power ground (exposed pad). |
| SW (Pins 18–19) | Switch collector node | Connects to inductor and diode; high dv/dt node requiring minimal trace area and tight layout. |
| Exposed Pad (Pin 21) | Power ground (PGND) | Mandatory solder connection to PCB ground plane for thermal performance and EMI reduction. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent current sense amplifiers | Each provides 100mV threshold with rail-to-rail input common-mode range up to 42V - enables simultaneous input and output current limiting in SEPIC or dual-LED string control. |
| Programmable switching frequency | 200kHz–3.5MHz via single RT resistor - allows optimization of size (higher fSW) vs. efficiency (lower fSW) without changing IC. |
| Constant-current/constant-voltage dual-mode operation | Automatic seamless transition between modes using shared VC node - ideal for LED drivers with open-circuit protection and battery chargers with CC/CV profiles. |
| Thermally enhanced TSSOP package | 20-lead TSSOP with exposed PGND pad - achieves θJA = 40°C/W and supports continuous 3A output in industrial ambient temperatures. |
| Wide-input, high-voltage switch | 2.5V–25V input range with integrated 42V/3A NPN switch - eliminates need for external high-voltage transistor in boost/inverting designs up to 40V output. |
Applications
| High-Power LED Driver | DSL Modem Power Supply |
|---|---|
|
Use Scenario: Driving 4 white LEDs (12V total VF) from 5V USB input in portable lighting or display backlight. IC Role / Device Role / Timing Role: Acts as constant-current boost controller with PWM dimming interface; regulates LED current at 300mA via 0.33Ω sense resistor. Use Value: Achieves 500:1 dimming ratio at 100Hz PWM while maintaining chromaticity and >80% efficiency - superior to analog dimming. |
Use Scenario: Generating ±12V rails from 3.3V or 5V motherboard supply in DSL line card power management. IC Role / Device Role / Timing Role: Configured in inverting mode to produce negative output; uses FBP tied to GND and FBN connected to divider for regulation. Use Value: Eliminates need for isolated transformer or dual converters; supports fast transient response required for ADSL2+ burst-mode signaling. |
| Distributed Power System | Input/Output Current-Limited Converter |
|
Use Scenario: Local 24V-to-36V boost for remote sensor nodes in industrial IoT gateways with strict EMI limits. IC Role / Device Role / Timing Role: Operates in boost mode with 1MHz switching (RT = 17.2kΩ); SW node tightly routed to minimize radiated emissions. Use Value: Delivers stable 3A output with <10mVpp ripple using ceramic output caps; exposed pad ensures thermal reliability at 70°C ambient. |
Use Scenario: Protecting upstream 5V/2A supply while powering a 12V/1.5A load in battery-powered test equipment. IC Role / Device Role / Timing Role: Uses ISP1/ISN1 to monitor input current and ISP2/ISN2 to regulate output current - dual-loop enforcement. Use Value: Prevents input overcurrent tripping during cold start while guaranteeing safe 1.5A output even under short-circuit conditions. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar DC/DC converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3780EFE#PBF | 4-switch synchronous buck-boost controller (external MOSFETs); no integrated switch; supports 4–36V input, ±40V output. | Requires external power stage; better suited for >5A, high-efficiency (>95%) applications where thermal headroom is constrained. | Choose LTC3780EFE#PBF when higher output current, synchronous rectification, or wider output voltage range is required - not a drop-in replacement. |
| LT3757AEMSE#TRPBF | Current-mode flyback/boost controller with 65V switch; single current sense; no dual-rail-to-rail sensing; 100kHz–1MHz frequency range. | Optimized for isolated flyback and high-VOUT boost; lacks independent dual-current regulation capability. | Choose LT3757AEMSE#TRPBF for cost-sensitive, single-string LED or AC/DC adapter designs where dual current loops are unnecessary. |
Compared with LTC3780EFE#PBF and LT3757AEMSE#TRPBF, LT3477IFE#PBF uniquely integrates dual 100mV current sense amplifiers and a 3A/42V switch in a compact TSSOP, enabling self-contained constant-current/constant-voltage operation without external MOSFETs or complex compensation - ideal for space-constrained LED and distributed power systems.
Availability
LT3477IFE#PBF is available at Aetrix Electronics and suitable for high-reliability LED driver, DSL modem power, and industrial distributed power applications requiring stable component supply, extended temperature operation (–40°C to 125°C), and long-term lifecycle continuity.
Supply support for LT3477IFE#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, 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 LT3477 product line was designed specifically for high-current, multi-loop DC/DC conversion in LED lighting, telecom power, and precision current-source applications - emphasizing dual current sensing, wide input range, and robust thermal packaging.
FAQ
What is the maximum output voltage achievable with LT3477IFE#PBF in boost configuration?
The LT3477IFE#PBF supports output voltages up to 40V in boost mode, limited by its 42V internal switch rating and practical layout constraints. With proper Schottky diode selection (e.g., 45V+ reverse voltage) and low-ESR output capacitors, stable 36V output at 3A is demonstrated in typical applications. Exceeding 40V risks switch breakdown and is not recommended.
Does LT3477IFE#PBF support true negative output voltage generation?
Yes, LT3477IFE#PBF natively supports negative output voltages via inverting, SEPIC, or flyback topologies. In inverting mode, FBN is tied to GND and FBP connects to a resistive divider referenced to the negative rail - enabling regulated –5V, –12V, or –24V outputs with full current-mode control and soft-start functionality.
How does the dual current sense feature of LT3477IFE#PBF improve system safety?
The dual current sense amplifiers in LT3477IFE#PBF allow independent monitoring of input and output currents - for example, enforcing 2A input limit while delivering 3A output in a SEPIC converter. This prevents upstream supply overload during startup or fault conditions, providing hardware-level protection that complements software-based system monitoring.
Can LT3477IFE#PBF be used in buck mode, and what are the key layout requirements?
Yes, LT3477IFE#PBF operates in buck mode when configured with external PMOS/NMOS switches (as shown in Figure 8a). Critical layout requirements include minimizing SW node loop area, placing the high-side PMOS close to SW/GND pins, using Kelvin connections for current sense resistors, and routing VC compensation components directly adjacent to the IC to maintain loop stability.
What is the purpose of the exposed pad (Pin 21) on LT3477IFE#PBF, and how must it be connected?
The exposed pad (Pin 21) on LT3477IFE#PBF is power ground (PGND), not signal ground. It must be soldered to a solid PCB ground plane using ≥4 thermal vias (0.3mm diameter) to achieve rated thermal performance (θJA = 40°C/W) and ensure electromagnetic compatibility. Leaving it unconnected degrades efficiency, increases junction temperature, and may cause premature failure.
LT3477IFE#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:
- 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-TSSOP-EP
LT3477IFE#PBF FAQ
1.How can I place an order for LT3477IFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3477IFE#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 LT3477IFE#PBF reliable?
The price and inventory of LT3477IFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3477IFE#PBF is usually 5 days.
3.What payment methods are accepted for LT3477IFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3477IFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3477IFE#PBF?
LT3477IFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3477IFE#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 LT3477IFE#PBF?
For technical support, including LT3477IFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3477IFE#PBF requirements.
6.How does Aetrix verify that LT3477IFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3477IFE#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 LT3477IFE#PBF meets industry standards.
7.What is the process for return or replacement of LT3477IFE#PBF?
All LT3477IFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3477IFE#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 LT3477IFE#PBF part is unused and in its original packaging.
Return procedure for LT3477IFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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