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Analog Devices Inc. LT3477EUF#PBF
- Part No.:
- LT3477EUF#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 20-WFQFN Exposed Pad
- Datasheet:
-
LT3477EUF#PBF.pdf
- Description:
- IC LED DRIVER RGLTR PWM 3A 20QFN
- Quantity:
- Payment:
- Shipping:
Inventory:1,442
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Product details
Overview
LT3477EUF#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 2.5V–25V input, operates from 200kHz to 3.5MHz via external RT resistor, and enables constant-current/constant-voltage regulation for high-power LED drivers in boost, buck-boost, or inverting topologies.
For engineers reviewing the LT3477EUF#PBF datasheet, LT3477EUF#PBF pinout, LT3477EUF#PBF application, or LT3477EUF#PBF equivalent, key selection criteria include dual 100mV current sense thresholds, programmable soft-start, ± output voltage capability (boost/inverting/SEPIC/flyback), thermal performance of the 4mm × 4mm QFN package, and compatibility with PWM dimming circuits for LED brightness control.
Technical Context
The LT3477EUF#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 adjustable via IADJ1/IADJ2 pins. Its error amplifier outputs drive a PWM comparator whose threshold is set by the VC pin voltage and oscillator ramp sum.
It integrates a 3A/42V NPN switch with 0.3V VCE(SAT) at 2.5A, supports both positive and negative output configurations through externally accessible error amplifier inputs, and uses an external RC network on VC for loop compensation-enabling stable operation across boost, inverting, SEPIC, and flyback topologies.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.5V to 25V - supports wide industrial and automotive supply rails without pre-regulation. |
| Switch Current Limit | 3A nominal - ensures robust overcurrent protection for inductor and external diode selection. |
| Current Sense Threshold | 100mV per channel - enables precise, low-loss current sensing with standard 0.1Ω–1Ω shunts. |
| Switching Frequency Range | 200kHz to 3.5MHz - allows trade-off between EMI, inductor size, and efficiency via RT resistor. |
| Reference Voltage | 1.235V (E grade) - sets output voltage accuracy and stability in constant-voltage mode. |
| Soft-Start Control | External capacitor on SS pin - limits inrush current and prevents output overshoot during startup. |
| Operating Temperature | –40°C to +85°C - qualified for commercial and industrial ambient environments. |
| Package Thermal Resistance | θJA = 37°C/W - enables higher power dissipation than TSSOP variant due to exposed PGND pad. |
Pinout & Package
LT3477EUF#PBF is housed in a thermally enhanced 20-lead (4mm × 4mm) plastic QFN package with exposed power ground (PGND) pad (Pin 21), requiring soldering to PCB for electrical continuity and thermal performance. Pin numbering follows standard QFN top-view convention.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pin 3) | Input Supply | Powers internal circuitry; must be locally bypassed with low-ESR ceramic capacitor. |
| RT (Pin 4) | Frequency Set | Connects external resistor to GND to program switching frequency from 200kHz–3.5MHz. |
| 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 | Controls ramp rate of VC voltage; external capacitor sets startup time and peak inductor current limit. |
| VC (Pin 7) | Compensation | Output of error amplifier; connects external RC network to stabilize voltage/current loop response. |
| FBN (Pin 8) | Inverting Feedback Input | Used for positive-output configurations; connects to resistive divider tap for CV regulation. |
| FBP (Pin 9) | Noninverting Feedback Input | Used for negative-output configurations; connects to GND or external divider for CV regulation. |
| VREF (Pin 10) | Bandgap Reference | 1.235V reference source; supplies current to feedback dividers and can be bypassed with 100pF. |
| IADJ1 (Pin 11) | Current Sense 1 Adjust | Adjusts first current sense threshold linearly below 625mV; >650mV defaults to 100mV. |
| IADJ2 (Pin 12) | Current Sense 2 Adjust | Adjusts second current sense threshold linearly below 625mV; >650mV defaults to 100mV. |
| ISP2 / ISN2 (Pins 13–14) | Current Sense 2 Inputs | Differential inputs for second rail-to-rail current amplifier; used for dual-output or input-current limiting. |
| ISP1 / ISN1 (Pins 15–16) | Current Sense 1 Inputs | Differential inputs for primary current amplifier; commonly used for LED string or battery charge current. |
| GND (Pin 17) | Analog Ground | Reference for internal circuitry; connect directly to local ground plane with low-inductance path. |
| SW (Pins 18–19) | Switch Collector | Connects to inductor and diode; minimize trace area to reduce EMI and switching losses. |
| Exposed Pad (Pin 21) | Power Ground (PGND) | Mandatory solder connection to PCB ground for thermal dissipation and low-noise return path. |
Key Features
| Feature | Design Value |
|---|---|
| Dual 100mV rail-to-rail current sense | Enables simultaneous regulation of two independent current paths (e.g., dual LED strings or input/output current limiting) without external op-amps. |
| Programmable switching frequency (200kHz–3.5MHz) | Allows optimization of magnetic component size, EMI filtering, and efficiency for specific board space and noise constraints. |
| ± output voltage capability | Supports boost, inverting, SEPIC, and flyback topologies using same IC-reducing BOM count across multiple power architectures. |
| Internal 3A/42V NPN switch with 0.3V VCE(SAT) | Reduces conduction loss and simplifies layout vs. external switch solutions; eliminates gate-drive complexity. |
| Independent IADJ1/IADJ2 pins | Permits dynamic adjustment of current thresholds (e.g., analog dimming or adaptive charging) without changing sense resistors. |
| Thermally enhanced 4mm × 4mm QFN | Delivers lower θJA (37°C/W) vs. TSSOP (40°C/W), enabling higher continuous output power in compact designs. |
Applications
| High-Power LED Driver | DSL Modem Power Supply |
|---|---|
|
Use Scenario: Driving 4–6 white LEDs in automotive interior lighting or industrial signage with 300mA constant current and PWM dimming up to 500:1 ratio. IC Role / Device Role / Timing Role: Acts as constant-current boost controller with dual-sense capability for redundant current monitoring and open-LED fault detection. Use Value: Achieves >80% efficiency at 5V input → 16V LED string, maintains chromaticity via PWM dimming, and supports thermal derating down to 200:1 dimming at 85°C. |
Use Scenario: Generating isolated ±12V and +5V rails from a single 3.3V or 5V supply in DSL line card power management. IC Role / Device Role / Timing Role: Functions as inverting and SEPIC controller to produce negative bias for line drivers and positive auxiliary voltages. Use Value: Eliminates need for multiple converters; leverages dual current sense for input current limiting during surge events and output short-circuit protection. |
| Distributed Power System | Constant-Voltage/Constant-Current Source |
|
Use Scenario: Local DC/DC conversion in telecom base station sub-units where 12V or 24V backplane supplies feed point-of-load regulators. IC Role / Device Role / Timing Role: Serves as flexible intermediate bus converter supporting boost (for higher voltage rails) or buck-boost (for variable input conditions). Use Value: Wide 2.5V–25V input accommodates brownout and hot-swap transients; programmable frequency avoids sensitive RF bands in dense RF environments. |
Use Scenario: Precision current source for battery charging or sensor excitation where both voltage compliance and current accuracy are critical. IC Role / Device Role / Timing Role: Operates in hybrid CV/CC mode-switching seamlessly between voltage regulation and current regulation based on load demand. Use Value: Dual 100mV sense channels allow independent programming of charge current and termination voltage thresholds, improving safety and cycle life. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar DC/DC converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3780EUF#PBF | 4-switch synchronous buck-boost controller (no integrated switch); requires external MOSFETs and supports 4V–36V input. | Designed for higher-efficiency, higher-power (>5A), bidirectional buck-boost applications-not suitable for simple boost or inverting topologies. | Select when >95% efficiency, >5A output, or bidirectional power flow is required; not a drop-in replacement for LT3477EUF#PBF. |
| LT3957EFE#PBF | 3A boost/SEPIC/inverting converter with 60V switch; includes spread-spectrum frequency modulation and improved EMI performance. | Targets high-voltage LED drivers and industrial systems needing >42V output or stricter EMI compliance (CISPR 25 Class 5). | Choose for 60V-rated switch, integrated spread-spectrum, or automotive-grade EMI robustness-requires layout changes due to different pinout and compensation. |
Compared with LTC3780EUF#PBF and LT3957EFE#PBF, the LT3477EUF#PBF offers integrated switching, simpler design for ≤3A boost/inverting applications, and lower BOM cost-but lacks synchronous rectification and advanced EMI features found in newer generations.
Availability
LT3477EUF#PBF is available at Aetrix Electronics and suitable for high-power LED driver, DSL modem power, distributed power system, and constant-current source applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.
Supply support for LT3477EUF#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 medical markets.
The LT3477 belongs to Linear's legacy high-voltage DC/DC converter family, designed specifically for constant-current LED driving and flexible topology power conversion in space-constrained, thermally demanding applications.
FAQ
What is the maximum output voltage achievable with the LT3477EUF#PBF?
The LT3477EUF#PBF does not impose a hard limit on output voltage-the maximum is determined by external components and topology. In boost mode, output can exceed 42V if the external diode and capacitor ratings support it; however, the internal 42V switch limits safe operation to ≤42V at the SW node. For higher outputs, inverting or SEPIC topologies with appropriately rated external switches are recommended. Always verify voltage stress on ISP/ISN pins (max 42V) and FBP/FBN (max 6V).
Can the LT3477EUF#PBF operate in buck mode?
Yes-the LT3477EUF#PBF supports buck-mode operation when configured with an external PMOS or NMOS high-side switch and appropriate feedback routing. Figure 8a in the datasheet shows a validated 32V-to-6-LED buck implementation using a PMOS switch and dual NMOS PWM control. The IC regulates current through the LED string while the external switch handles high-side conduction; the internal switch remains unused in this configuration.
How do I configure the LT3477EUF#PBF for negative output voltage generation?
To generate a negative output, connect FBN to GND and route the feedback divider from the negative output rail to FBP. Use the equation VOUT = –1.235V × (1 + R3/R4), where R3 connects to output and R4 connects to GND. Ensure the ISP/ISN pins are referenced to the negative rail or use level-shifting networks if sensing current on the negative side. The LT3477EUF#PBF's dual error amplifier inputs enable stable regulation regardless of polarity.
What is the purpose of the exposed pad (Pin 21) on the LT3477EUF#PBF QFN package?
The exposed pad (Pin 21) on the LT3477EUF#PBF is designated PGND (power ground) and must be soldered to a solid PCB ground plane. It serves two critical functions: (1) provides the primary thermal path to dissipate heat from the internal 3A switch, lowering junction temperature by ~10°C versus floating pad; and (2) establishes a low-inductance return path for high-frequency switch currents, reducing EMI and improving stability. Failure to solder this pad degrades both thermal performance and electrical behavior.
Does the LT3477EUF#PBF support PWM dimming for LED applications?
Yes-the LT3477EUF#PBF is explicitly optimized for PWM dimming in LED drivers. By adding two external NMOS transistors controlled by a logic-level PWM signal (as shown in Figure 7a), the IC achieves a 500:1 dimming ratio at 100Hz. The internal current sense architecture ensures fast LED current rise/fall times, preserving color consistency. Dimming range decreases above 100Hz and drops to ~200:1 at 85°C due to Schottky diode leakage.
LT3477EUF#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 ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-QFN (4x4)
LT3477EUF#PBF FAQ
1.How can I place an order for LT3477EUF#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3477EUF#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 LT3477EUF#PBF reliable?
The price and inventory of LT3477EUF#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3477EUF#PBF is usually 5 days.
3.What payment methods are accepted for LT3477EUF#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3477EUF#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3477EUF#PBF?
LT3477EUF#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3477EUF#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 LT3477EUF#PBF?
For technical support, including LT3477EUF#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3477EUF#PBF requirements.
6.How does Aetrix verify that LT3477EUF#PBF is sourced from the original manufacturer or authorized distributors?
All LT3477EUF#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 LT3477EUF#PBF meets industry standards.
7.What is the process for return or replacement of LT3477EUF#PBF?
All LT3477EUF#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3477EUF#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 LT3477EUF#PBF part is unused and in its original packaging.
Return procedure for LT3477EUF#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LT3477EUF#PBF Tags
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