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Analog Devices Inc. LT3477EFE#PBF
- Part No.:
- LT3477EFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT3477EFE#PBF.pdf
- Description:
- IC LED DRVR RGLTR PWM 3A 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:769
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Product details
Overview
LT3477EFE#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 for constant-current/constant-voltage LED driver and inverting power supply applications.
For engineers reviewing the LT3477EFE#PBF datasheet, LT3477EFE#PBF pinout, LT3477EFE#PBF application, or LT3477EFE#PBF equivalent, key selection factors include dual 100mV current sense thresholds, ±40°C to +85°C operating junction range, thermally enhanced 20-lead TSSOP package with exposed PGND pad, and independent IADJ1/IADJ2 pins for adjustable current regulation.
Technical Context
The LT3477EFE#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), 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 topologies including boost, inverting, SEPIC, and flyback.
Switching frequency is set by an external resistor on RT (200kHz–3.5MHz), soft-start is controlled by capacitor on SS pin (9µA charge current), and current limit is fixed at 3A with 0.3V VCE(SAT) at 2.5A. The device integrates dual rail-to-rail current sense amplifiers with 100mV default threshold, adjustable down to ~60mV via IADJ1/IADJ2 pins.
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 - limits peak inductor current to protect internal NPN switch and external magnetics during fault or startup. |
| Current Sense Threshold | 100mV (default) - sets regulated current as IOUT = 100mV / RSENSE; adjustable via IADJ1/IADJ2 pins. |
| Switching Frequency Range | 200kHz to 3.5MHz - enables optimization of size (higher fSW) vs. efficiency (lower fSW) using single RT resistor. |
| Reference Voltage | 1.235V (typ) - stable bandgap reference used for output voltage setting and feedback accuracy. |
| Operating Temperature | –40°C to +85°C (E grade) - qualified for commercial and industrial ambient environments. |
| Efficiency | Up to 93% - achieved in typical boost LED driver configurations, reducing thermal load and system power loss. |
Pinout & Package
LT3477EFE#PBF is housed in a thermally enhanced 20-lead plastic TSSOP package (4.4mm × 6.5mm) with exposed power ground pad (Pin 21) that must be soldered to PCB for electrical integrity and thermal performance (θJA = 40°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pin 3) | Input Supply | Primary power input for internal circuitry; requires local ceramic bypass capacitance. |
| RT (Pin 4) | Frequency Set | Connects external resistor to GND to program switching frequency from 200kHz to 3.5MHz. |
| SHDN (Pin 5) | Enable Control | Active-high shutdown: ≥2V enables operation; ≤0.3V disables switch and reduces quiescent current to 0.1µA. |
| SS (Pin 6) | Soft-Start | Controls ramp rate of VC voltage during startup; 9µA internal current charges external capacitor. |
| VC (Pin 7) | Error Amplifier Output | Compensation node for voltage/current loop stability; connects RC network to GND for pole-zero tuning. |
| FBN (Pin 8) | Inverting Feedback Input | Connects to resistive divider tap for positive-output voltage regulation (e.g., boost mode). |
| FBP (Pin 9) | Noninverting Feedback Input | Connects to resistive divider tap for negative-output voltage regulation (e.g., inverting mode). |
| VREF (Pin 10) | Bandgap Reference | 1.235V precision reference; supplies current to feedback dividers and can be bypassed with 100pF. |
| IADJ1 (Pin 11) | Current Sense 1 Adjust | Sets first current sense threshold linearly when <625mV; >650mV defaults to 100mV. |
| IADJ2 (Pin 12) | Current Sense 2 Adjust | Sets second current sense threshold independently; identical behavior to IADJ1. |
| ISP1/ISN1 (Pins 15/16) | Current Sense 1 Inputs | Differential pair sensing voltage across external RSENSE for first constant-current channel. |
| ISP2/ISN2 (Pins 13/14) | Current Sense 2 Inputs | Differential pair for second independent current regulation path (e.g., dual LED strings). |
| GND (Pin 17) | Analog Ground | Signal reference for internal amplifiers; separate from PGND (exposed pad) to minimize noise coupling. |
| SW (Pins 18,19) | Switch Collector | High-current output node connecting to inductor/diode; requires minimal trace area to reduce EMI. |
| Exposed Pad (Pin 21) | Power Ground (PGND) | Mandatory solder connection to PCB ground plane for thermal dissipation and low-impedance return path. |
Key Features
| Feature | Design Value |
|---|---|
| Dual rail-to-rail current sense amplifiers | Enables simultaneous regulation of two independent current paths (e.g., dual LED strings or input/output current limiting) with 100mV threshold and pin-adjustable scaling. |
| Programmable switching frequency (200kHz–3.5MHz) | Allows trade-off between magnetic component size and conversion efficiency using a single external resistor on RT pin. |
| Positive/negative output capability | Supports boost, buck-boost, inverting, and flyback topologies via externally accessible FBP/FBN amplifier inputs and flexible feedback configuration. |
| 3A, 42V internal NPN switch with 0.3V VCE(SAT) | Reduces conduction losses and thermal stress in high-current DC/DC stages without requiring external MOSFET drivers. |
| Independent IADJ1/IADJ2 pins | Permits dynamic adjustment of each current sense threshold (down to ~60mV) without changing sense resistor values-ideal for analog dimming or adaptive current control. |
Applications
| High-Power LED Driver | DSL Modem Power Supply |
|---|---|
|
Use Scenario: Driving 4 white LEDs (12–16V total VF) from 5V USB input in telecom equipment with PWM dimming. IC Role / Device Role / Timing Role: Constant-current boost controller regulating LED string current at 300mA while maintaining 93% efficiency and 500:1 dimming ratio. Use Value: Eliminates need for external current-sense op-amps and discrete switch; integrated dual current sense enables redundant monitoring or multi-string control. |
Use Scenario: Generating –12V and +12V rails from single 3.3V supply in DSL line card with tight space constraints. IC Role / Device Role / Timing Role: Inverting DC/DC converter with FBP tied to GND and FBN connected to voltage divider, delivering ±12V at 300mA per rail. Use Value: Single-chip solution replaces dual converters; rail-to-rail current sense allows precise input current limiting during surge events. |
| Distributed Power System | Input/Output Current Limited Converter |
|
Use Scenario: Local 24V-to-48V boost stage powering remote PHY modules in industrial Ethernet infrastructure. IC Role / Device Role / Timing Role: High-efficiency (91%) step-up regulator with programmable 1MHz switching frequency and soft-start to limit inrush into long cable runs. Use Value: Exposed PGND pad ensures thermal reliability at 3A continuous load; dual current sense supports input overcurrent and output short-circuit protection. |
Use Scenario: SEPIC converter with input current limiting for battery-powered test equipment requiring stable 5V output despite varying 3–4.2V Li-ion input. IC Role / Device Role / Timing Role: Constant-current loop regulates average input current to 1.5A while voltage loop maintains 5V output under load transients. Use Value: Prevents battery sag during startup; dual feedback architecture avoids instability common in single-loop current-limited designs. |
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. | Used where higher efficiency (>95%), bidirectional power flow, or wider output voltage range is required; lacks dual current sense. | Select LTC3780EFE#PBF when designing high-power (>10W), high-efficiency systems needing synchronous rectification and flexible topology support. |
| LT3958EFE#PBF | 40V, 5A monolithic boost/SEPIC/inverting converter; single current sense amplifier; 100mV threshold; 100kHz–1MHz frequency range. | Optimized for high-current LED drivers and industrial boost applications; no dual current sense or negative output flexibility. | Choose LT3958EFE#PBF for simpler single-string LED drivers or higher-current (5A) boost-only designs where dual current regulation is unnecessary. |
Compared with LTC3780EFE#PBF and LT3958EFE#PBF, the LT3477EFE#PBF uniquely provides dual independent current sense channels in a monolithic 3A boost solution, enabling true constant-current/constant-voltage dual-mode operation without external amplifiers-critical for multi-string LED or input/output current-limited topologies.
Availability
LT3477EFE#PBF is available at Aetrix Electronics and suitable for high-reliability LED driver, DSL modem power, distributed power, and current-limited DC/DC converter applications requiring stable component supply across industrial temperature ranges.
Supply support for LT3477EFE#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 ICs, serving industrial, automotive, communications, and medical markets.
The LT3477 belongs to Linear's high-voltage monolithic DC/DC converter product line, designed specifically for constant-current/constant-voltage applications such as LED lighting, telecom power, and isolated/non-isolated current-limited supplies.
FAQ
What is the maximum input voltage supported by the LT3477EFE#PBF?
The LT3477EFE#PBF supports a maximum input voltage of 25V on the VIN and SHDN pins, as specified in its Absolute Maximum Ratings. Operation beyond this level risks permanent damage. The device is rated for continuous operation from 2.5V to 25V, making it suitable for 12V and 24V industrial bus systems with transient margin.
How does the dual current sense feature of the LT3477EFE#PBF enable unique applications?
The LT3477EFE#PBF integrates two independent rail-to-rail current sense amplifiers (ISP1/ISN1 and ISP2/ISN2), each with adjustable 100mV threshold via IADJ1/IADJ2. This allows simultaneous regulation of two current paths-such as dual LED strings, input current limiting + output current regulation, or redundant safety monitoring-without external op-amps or additional ICs.
Can the LT3477EFE#PBF generate negative output voltages, and how is it configured?
Yes, the LT3477EFE#PBF supports negative output voltages using inverting, SEPIC, or flyback topologies. For inverting operation, FBN is tied to GND and FBP connects to a resistive divider from the negative output. The internal error amplifier's fully differential inputs and externally accessible nodes allow stable regulation of negative rails without polarity-reversal circuitry.
What is the role of the exposed pad (Pin 21) on the LT3477EFE#PBF TSSOP package?
The exposed pad (Pin 21) on the LT3477EFE#PBF is designated as Power Ground (PGND) and must be soldered to the PCB ground plane. It serves dual functions: providing a low-impedance return path for high-current switch node currents and enabling effective thermal dissipation (θJA = 40°C/W). Failure to solder this pad degrades both electrical performance and thermal reliability.
How is switching frequency programmed on the LT3477EFE#PBF, and what is the recommended resistor range?
Switching frequency on the LT3477EFE#PBF is set by connecting a resistor between RT (Pin 4) and GND. The datasheet specifies RT values from 2.43kΩ (3.5MHz) to 107kΩ (200kHz). A 17.2kΩ resistor yields 1MHz operation. The RT pin must never be left floating; improper resistor selection may cause instability or excessive EMI.
LT3477EFE#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 ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-TSSOP-EP
LT3477EFE#PBF FAQ
1.How can I place an order for LT3477EFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3477EFE#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 LT3477EFE#PBF reliable?
The price and inventory of LT3477EFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3477EFE#PBF is usually 5 days.
3.What payment methods are accepted for LT3477EFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3477EFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3477EFE#PBF?
LT3477EFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3477EFE#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 LT3477EFE#PBF?
For technical support, including LT3477EFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3477EFE#PBF requirements.
6.How does Aetrix verify that LT3477EFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3477EFE#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 LT3477EFE#PBF meets industry standards.
7.What is the process for return or replacement of LT3477EFE#PBF?
All LT3477EFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3477EFE#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 LT3477EFE#PBF part is unused and in its original packaging.
Return procedure for LT3477EFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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