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Analog Devices Inc. LT3955IUHE#TRPBF
- Part No.:
- LT3955IUHE#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 36-WFQFN, 28 Leads, Exposed Pad
- Datasheet:
-
LT3955IUHE#TRPBF.pdf
- Description:
- IC LED DRVR RGLTR PWM 3.5A 36QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,168
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Product details
Overview
LT3955IUHE#TRPBF from Analog Devices (formerly Linear Technology) is a 60V-input, constant-current/constant-voltage DC/DC converter with integrated 80V/3.5A N-channel MOSFET, designed for high-power LED driving in boost, SEPIC, buck-boost, and flyback topologies. It delivers ±3% current regulation and ±2% voltage regulation, supports 3000:1 True Color PWM™ dimming, and operates from –40°C to 125°C junction temperature.
For engineers reviewing the LT3955IUHE#TRPBF datasheet, LT3955IUHE#TRPBF pinout, LT3955IUHE#TRPBF application, or LT3955IUHE#TRPBF equivalent, this page provides verified technical context, validated pin functions, confirmed thermal and electrical specifications, and real-world application mappings - all derived from the official Linear Technology/LT3955 datasheet and product documentation.
Technical Context
The LT3955IUHE#TRPBF implements a fixed-frequency, current-mode control architecture with internal slope compensation, enabling stable operation across wide input (4.5V–60V) and output voltage ranges. Its dual-loop capability allows simultaneous or selective regulation of LED current (via ISP/ISN differential sensing) and output voltage (via FB feedback), with seamless mode transition signaled by VMODE.
It integrates a programmable PWM dimming signal generator (170Hz–390Hz), analog dimming via CTRL (0–1V linear threshold adjustment), and protection features including open-LED detection (FB–50mV + ISP–ISN <25mV), overcurrent shutdown (ISP–ISN ≥600mV), and FB overvoltage latch-off (FB ≥ VFB+60mV). The INTVCC LDO (7.85V, 36mA) powers internal drivers and supports external gate drive.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4.5V to 60V - supports automotive battery, industrial 24V/48V rails, and wide-range off-line inputs without pre-regulation. |
| Switch Rating | 80V drain-source, 3.5A continuous - enables direct high-brightness LED string driving up to ~65V in boost configuration. |
| Current Regulation Accuracy | ±3% - ensures consistent LED brightness across temperature and line/load variations without external calibration. |
| PWM Dimming Ratio | 3000:1 True Color PWM™ - preserves color fidelity at ultra-low duty cycles for architectural and display lighting. |
| Switching Frequency Range | 100kHz to 1MHz - adjustable via RT resistor to balance efficiency, EMI, and magnetics size (e.g., 350kHz typical in 20W designs). |
| Junction Temperature Range | –40°C to 125°C - qualified for under-hood automotive, outdoor signage, and industrial LED driver applications. |
| Package Thermal Resistance | θJC = 3°C/W - low junction-to-case resistance enables high-power dissipation when exposed pad is soldered to PCB copper. |
Pinout & Package
LT3955IUHE#TRPBF is housed in a thermally enhanced 36-lead (5mm × 6mm) plastic QFN package with two exposed pads: Pin 37 (GND) and Pin 38 (SW), both requiring direct solder connection to respective PCB planes for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| GND (Pins 4, 24, 37) | Signal and Power Ground Reference | Primary ground return for analog circuitry; exposed pad (Pin 37) must be soldered to large GND plane for thermal management and noise immunity. |
| SW (Pins 8, 9, 20, 21, 38) | Drain of Internal N-Channel MOSFET | High dv/dt switching node; exposed pad (Pin 38) must connect directly to SW copper pour to minimize loop inductance and EMI. |
| ISP / ISN | High-Side or Low-Side Current Sense Inputs | Differential pair measuring LED current; supports rail-to-rail common-mode range (0V–80V); bias currents vary with CTRL voltage and sensing polarity. |
| FB | Voltage Feedback Input | Regulates output voltage to 1.25V reference; enables open-LED detection and FB overvoltage protection (latches PWMOUT low if FB ≥ VFB+60mV). |
| CTRL | Analog Dimming & Current Threshold Control | Adjusts ISP–ISN current sense threshold from 21mV (10% scale) to 258mV (full scale); 0–1V linear range, clamped above 1.2V. |
| PWM / PWMOUT | Digital Dimming Interface & Buffered Output | PWM accepts logic-level signals for 3000:1 dimming; PWMOUT drives external NMOS disconnect FET or level-shifts for isolated control. |
| VMODE | Open-LED / CV Mode Indicator | Open-drain output pulled low when FB ≥ VFB–50mV AND ISP–ISN ≤25mV - signals transition from CC to CV regulation or open-circuit fault. |
| DIM/SS | Soft-Start & PWM Generator Programming | Internal 12µA pull-up sets soft-start time and PWM frequency/duty via external capacitor; resets on UVLO, overcurrent, or thermal fault. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 80V/3.5A Power Switch | Eliminates external high-voltage MOSFET, reducing BOM count and layout complexity in boost/SEPIC LED drivers up to 20W. |
| True Color PWM™ Dimming | 3000:1 ratio with no color shift - achieved via precise internal PWM generator and synchronized VC loop hold during off-time. |
| Rail-to-Rail Current Sense Range | 0V to 80V common-mode - enables flexible high-side or low-side sensing in any topology without level-shifting circuitry. |
| Output Short-Circuit Protected Boost | Automatic shutdown when ISP–ISN ≥600mV - protects switch and inductor during LED string short or wiring fault. |
| C/10 Charging Indication | VMODE assertion at ISP–ISN ≤25mV - provides end-of-charge signal for battery/supercapacitor charging applications. |
| Thermally Enhanced QFN | θJC = 3°C/W with soldered exposed pads - sustains full 3.5A switch current at 125°C junction temperature with proper PCB copper area. |
Applications
| Automotive Headlamp Driver | Industrial High-Bay LED Lighting |
|---|---|
Use Scenario: Driving 4–6 series white LEDs (60–72V total Vf) from 12V/24V vehicle battery with EMI-constrained layout. IC Role / Device Role / Timing Role: Constant-current controller in boost configuration; regulates LED current while rejecting battery ripple and cold-crank transients. Use Value: ±3% current accuracy maintains consistent lumen output; 3000:1 PWM dimming enables adaptive driving beam control without color shift. |
Use Scenario: 100W LED fixture powered from 48V DC distribution bus in warehouse or factory environment. IC Role / Device Role / Timing Role: Constant-current SEPIC regulator supporting wide input variation and output short-circuit tolerance. Use Value: Rail-to-rail ISP/ISN sensing allows direct high-side current measurement; open-LED reporting via VMODE enables predictive maintenance alerts. |
| Battery & Supercapacitor Charger | UV-C LED Disinfection System |
Use Scenario: Charging 12V LiFePO₄ battery or 25V supercapacitor bank from 24V industrial supply with C/10 termination. IC Role / Device Role / Timing Role: Constant-voltage/constant-current charger using FB for voltage regulation and ISP/ISN for current limiting. Use Value: C/10 indication via VMODE provides precise end-of-charge signal; ±2% voltage regulation ensures safe battery float voltage. |
Use Scenario: Pulsed operation of high-power 275nm UV-C LEDs requiring precise current control and thermal derating. IC Role / Device Role / Timing Role: Constant-current buck-boost driver with analog dimming (CTRL) for intensity control and thermal foldback. Use Value: 0–1V CTRL input enables closed-loop thermal compensation; 125°C max junction rating supports compact heatsink designs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar LED driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3756IUH#TRPBF | Higher 100V input rating, 5A switch, but no integrated PWM generator; requires external oscillator for dimming. | Better suited for >60V input systems (e.g., 72V telecom) and higher current (>3.5A) LED arrays; lacks self-oscillating dimming. | Select LT3756IUH#TRPBF when input exceeds 60V or peak current >3.5A is required; accept added external components for dimming control. |
| LM3409QMH/NOPB | 48V max input, 5A switch, analog/digital dimming, but no integrated PWM generator or VMODE reporting. | Cost-optimized for automotive interior lighting; lacks open-LED status signaling and C/10 charge indication. | Choose LM3409QMH/NOPB for lower-voltage (<48V), cost-sensitive designs where VMODE and C/10 features are not required. |
Compared with LT3955IUHE#TRPBF, LT3756IUH#TRPBF extends input voltage and current capability at the expense of integrated dimming logic, while LM3409QMH/NOPB reduces cost and voltage rating but omits critical diagnostics like VMODE and C/10 reporting - making LT3955IUHE#TRPBF optimal for feature-rich, mid-range LED and charging applications.
Availability
LT3955IUHE#TRPBF is available at Aetrix Electronics and suitable for automotive headlamp systems, industrial high-bay lighting, and battery/supercapacitor charging applications requiring stable component supply, extended temperature operation, and robust protection features.
Supply support for LT3955IUHE#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 its high-performance analog IC portfolio, emphasizing precision power management, signal conditioning, and reliability for demanding industrial and automotive markets.
The LT3955IUHE#TRPBF belongs to Linear's LED driver product line, engineered specifically for high-efficiency, high-reliability constant-current LED power conversion with integrated protection and multi-topology flexibility.
FAQ
What is the maximum LED string voltage supported by the LT3955IUHE#TRPBF in boost configuration?
The LT3955IUHE#TRPBF supports LED string voltages up to ~65V in boost mode, constrained by its 80V-rated internal MOSFET and practical design margins. At VIN = 24V and ILED = 0.3A, typical application circuits achieve 65V output with 94% efficiency. Exceeding 65V risks violating the 80V SW pin absolute maximum rating under transient conditions, so derating is recommended for long-term reliability.
Does the LT3955IUHE#TRPBF support both high-side and low-side current sensing?
Yes, the LT3955IUHE#TRPBF supports both configurations via its ISP and ISN pins, with rail-to-rail input common-mode range (0V to 80V). High-side sensing connects ISP to LED anode and ISN to sense resistor top; low-side places the resistor between LED cathode and PGND. Bias currents differ per configuration and depend on CTRL voltage, as documented in the Electrical Characteristics table.
How does the VMODE pin function in LED open-circuit detection?
The VMODE pin asserts low when two conditions occur simultaneously: FB ≥ (VFB – 50mV) and (ISP – ISN) ≤ 25mV (C/10 threshold). This indicates loss of LED current while output voltage remains regulated - confirming an open LED string. The pin is open-drain and requires an external pull-up (typically to INTVCC); it only updates when PWM is high, latching status during idle periods.
Can the LT3955IUHE#TRPBF be used in SEPIC or flyback topologies?
Yes, the LT3955IUHE#TRPBF is explicitly designed for multiple topologies including SEPIC, flyback, buck-boost, CUK, and buck modes - as stated in its Features list and confirmed in application schematics. Its current-mode control, wide ISP/ISN common-mode range, and independent FB loop enable stable operation in isolated and non-inverting configurations with appropriate transformer or coupled inductor design.
What is the purpose of the DIM/SS pin beyond soft-start?
Beyond soft-start timing, the DIM/SS pin programs the internal PWM dimming signal generator: its charging current (set by internal 12µA pull-up plus optional external current) determines both PWMOUT frequency and duty ratio. As shown in Figure 3955 G16, DIM/SS current directly scales PWM duty from ~4% to 96%, enabling analog-programmed dimming without external clock sources or microcontroller intervention.
LT3955IUHE#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 36-WFQFN, 28 Leads, 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):
- 4.5V
- Voltage - Supply (Max):
- 60V
- Voltage - Output:
- -
- Current - Output / Channel:
- 3.5A (Switch)
- Frequency:
- 100kHz ~ 1MHz
- Dimming:
- Analog, PWM
- Applications:
- -
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 36-QFN (5x6)
LT3955IUHE#TRPBF FAQ
1.How can I place an order for LT3955IUHE#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3955IUHE#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 LT3955IUHE#TRPBF reliable?
The price and inventory of LT3955IUHE#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3955IUHE#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3955IUHE#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3955IUHE#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3955IUHE#TRPBF?
LT3955IUHE#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3955IUHE#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 LT3955IUHE#TRPBF?
For technical support, including LT3955IUHE#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3955IUHE#TRPBF requirements.
6.How does Aetrix verify that LT3955IUHE#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3955IUHE#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 LT3955IUHE#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3955IUHE#TRPBF?
All LT3955IUHE#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3955IUHE#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 LT3955IUHE#TRPBF part is unused and in its original packaging.
Return procedure for LT3955IUHE#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LT3955IUHE#TRPBF Tags
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BCR402RE6327HTSA1
Infineon Technologies
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BCR430UXTSA2
Infineon Technologies
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BCR420UE6433HTMA1
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BCR420UE6327HTSA1
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BCR421UE6327HTSA1
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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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