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Analog Devices Inc. LT3909EDD#TRPBF
- Part No.:
- LT3909EDD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 12-WFDFN Exposed Pad
- Datasheet:
-
LT3909EDD#TRPBF.pdf
- Description:
- IC LED DRVR RGLTR PWM 50MA 12DFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,355
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Product details
Overview
LT3909EDD#TRPBF from Analog Devices (formerly Linear Technology) is a 2-string, 60mA LED driver IC with integrated 2MHz step-up DC/DC converter, ±2% current matching between strings, and internal 400mΩ/40V/1A power switch. It regulates LED current up to 36V total forward voltage and supports analog dimming (10:1) and PWM dimming (up to 40,000:1 at 100Hz). It is used in automotive instrument clusters requiring precise dual-string brightness control.
For engineers reviewing the LT3909EDD#TRPBF datasheet, LT3909EDD#TRPBF pinout, LT3909EDD#TRPBF application, or LT3909EDD#TRPBF equivalent, this page delivers verified technical context, real-world dimming performance data, thermal regulation behavior, fault flag logic, and package-specific layout guidance for DFN-12 (3mm × 3mm) assembly.
Technical Context
The LT3909EDD#TRPBF integrates a fixed-frequency (2MHz), current-mode boost controller with two independent high-side current sources. Each string features ±0.3% typical current matching and adapts VOUT to minimum required LED VF for peak efficiency - even when VIN exceeds VOUT. The internal 400mΩ N-channel DMOS switch and integrated Schottky diode enable compact, high-efficiency operation without external power components.
It implements dual-loop regulation: GM1 loop maintains 1.3V across each current source (VOUT–LEDx), while GM2 loop regulates FB to 1.215V for programmable OVP during open-LED or short-to-GND faults. Fault detection is latched only during PWM/CTRL high states, and thermal foldback derates LED current above 170°C junction temperature.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.9V to 40V - supports wide automotive battery range including cold-crank (6V) and load-dump (40V) transients. |
| Switching Frequency | 2MHz (±6%) - enables use of small 3.3–10µH inductors and minimizes EMI in space-constrained displays. |
| Max LED Current per String | 60mA (±2% matching) - set by single ISET resistor; allows precise dual-string brightness balancing in HUDs and clusters. |
| PWM Dimming Ratio | 40,000:1 at 100Hz (250ns on-time) - enables ultra-low-brightness control without visible flicker in night-mode instrumentation. |
| VOUT Regulation Accuracy | FB = 1.215V ±0.025V - ensures stable overvoltage protection threshold across temperature for reliable open-LED fault response. |
| Thermal Protection | Junction temperature foldback at 170°C - actively reduces LED current before permanent damage occurs, preserving display uptime. |
| Shutdown Current | 0.3µA at VIN = 12V - meets automotive micro-power requirements for always-on display subsystems. |
Pinout & Package
LT3909EDD#TRPBF uses a 12-pin (3mm × 3mm) plastic DFN package with exposed thermal pad (Pin 13 = GND). The exposed pad must be soldered to a continuous PCB ground plane for thermal management (θJC = 5.5°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 INTVCC | Internal 3.0V regulator output | Bypass with ≥1µF X7R ceramic; supplies gate driver and control circuits; max 100µA external load. |
| 2 VIN | Main input supply | Accepts 2.9–40V; requires local ceramic bypass capacitor; powers internal regulator and switch. |
| 3 EN/UVLO | Enable and undervoltage lockout input | 0.4V shutdown / 1.215V enable threshold; supports programmable UVLO with resistor divider. |
| 4 ISET | LED current programming input | Single resistor to GND sets both strings' current (10–60mA); 16.7kΩ yields 60mA per string. |
| 5 CTRL | Analog dimming and latch-off control | Voltage <80mV disables LEDs; 0.1–1.0V enables 10:1 analog dimming; connects to NTC for thermal derating. |
| 6 FB | Output voltage feedback | Sets programmable OVP level (1.215V reference); samples VOUT during PWM off-time to prevent droop. |
| 7 PWM | Digital dimming control | Active-high; controls high-side current sources; enables 40,000:1 PWM dimming independent of VOUT leakage. |
| 8 FAULT | Open-LED/short-to-GND flag | Active-low open-drain output; pulled low if either LED1 or LED2 detects fault; latched during PWM/CTRL high. |
| 9 LED1 10 LED2 |
High-side LED current outputs | Each drives one LED string (anode-connected); can be paralleled for >60mA total; tolerate up to 40V. |
| 11 VOUT | Boost converter output | Regulated node supplying both LED strings; connect ≥1µF (VOUT <20V) or ≥2.2µF (VOUT >20V) X7R ceramic. |
| 12 SW | Internal switch drain | Connects to inductor; anode of internal Schottky; minimize trace area to reduce EMI. |
| 13 (EP) | Exposed thermal pad | Must be soldered to solid GND plane; primary thermal path; not electrically isolated. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 400mΩ/40V/1A power switch | Eliminates external MOSFET and reduces BOM count; rated for full 60mA per string with margin. |
| ±0.3% typical current matching | Ensures consistent luminance across dual LED strings without calibration - critical for automotive cluster symmetry. |
| VOUT adaptive regulation | Maintains only the voltage needed to drive LEDs (not fixed rail), improving efficiency by up to 15% vs non-adaptive drivers. |
| Independent fault handling | One string remains regulated if the other experiences open-LED or short-to-GND; FAULT pin signals failure without shutdown. |
| Internal soft-start and compensation | Removes need for external compensation network; smooth startup prevents inrush current spikes in sensitive systems. |
| Thermal regulation loop | Derates LED current above 170°C junction temperature - protects die and extends lifetime in sealed enclosures. |
Applications
| Automotive Instrument Clusters | High-Contrast Automotive HUDs |
|---|---|
|
Use Scenario: Dual-string white LED backlighting for TFT LCD gauges with variable ambient light conditions. IC Role / Device Role / Timing Role: High-side current regulator with adaptive VOUT control and 2MHz switching for minimal EMI in CAN/FlexRay environments. Use Value: ±0.3% current matching ensures uniform brightness across speedometer/tachometer zones; 40,000:1 PWM dimming enables seamless transition from daylight to night mode. |
Use Scenario: Compact head-up display requiring ultra-low-light visibility and thermal stability behind windshield glass. IC Role / Device Role / Timing Role: Dual-string LED driver with thermal foldback and fault-isolated operation to maintain HUD integrity during LED failure. Use Value: Adaptive VOUT regulation maintains efficiency at elevated temperatures; FAULT pin alerts system controller without interrupting remaining string operation. |
| Industrial Panel Meters | Avionics Display Backlighting |
|
Use Scenario: Ruggedized front-panel meters operating across –40°C to +85°C with long-term luminance stability. IC Role / Device Role / Timing Role: Precision current source with programmable UVLO and shutdown current <1µA for battery-backed operation. Use Value: 0.3µA shutdown current extends backup battery life; ±2% matching preserves calibrated intensity over 10-year field deployment. |
Use Scenario: Safety-critical cockpit displays requiring redundancy, fault reporting, and DO-160 compliance. IC Role / Device Role / Timing Role: Dual-independent LED driver with latched FAULT flag and open-LED detection referenced to VOUT. Use Value: Independent string regulation satisfies dual-channel redundancy requirements; FAULT signal interfaces directly with flight control monitoring systems. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-string LED driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3909EMSE#TRPBF | Same die, MSOP-12 package (5.0mm × 4.0mm); θJA = 40°C/W vs DFN's 43°C/W; no exposed pad. | Lower power density; less effective thermal dissipation; suitable for lower-current or lower-ambient designs. | Select when board space permits larger footprint and thermal load is ≤400mW; avoid for high-temperature automotive under-hood use. |
| MAX16820ATP+ | 3-string, 100mA/channel; 600kHz switching; no integrated Schottky; external MOSFET required. | Higher channel count but lower frequency; requires more external components; lacks adaptive VOUT regulation. | Choose for multi-string (>2) applications where cost-per-channel matters more than size or efficiency; not drop-in compatible. |
Compared with LT3909EMSE#TRPBF, the LT3909EDD#TRPBF offers superior thermal performance via its exposed pad and smaller footprint - critical for dense automotive PCBs. Against MAX16820ATP+, it trades channel count for integration, eliminating external FETs and enabling higher-frequency operation with lower EMI.
Availability
LT3909EDD#TRPBF is available at Aetrix Electronics and suitable for automotive instrument clusters, avionics displays, and industrial panel meters requiring stable component supply, AEC-Q200-aligned reliability, and long-term production continuity.
Supply support for LT3909EDD#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 full product support, documentation, and manufacturing continuity for all Linear-branded ICs including the LT3909 series.
The LT3909 belongs to Linear's high-performance LED driver product line, designed specifically for automotive and industrial displays demanding precision current matching, robust fault protection, and adaptive efficiency optimization.
FAQ
What is the maximum total LED forward voltage supported by the LT3909EDD#TRPBF?
The LT3909EDD#TRPBF supports up to 36V total LED forward voltage across both strings. Its internal 40V-rated switch and integrated Schottky diode allow safe operation with VOUT up to 40V. The adaptive regulation loop dynamically adjusts VOUT to the minimum required voltage - typically VOUT = max(VF_LED1, VF_LED2) + 1.3V - ensuring optimal efficiency without overvoltage stress on LEDs.
How does the LT3909EDD#TRPBF handle an open-LED fault in one string?
When an open-LED fault occurs on LED1 or LED2, the LT3909EDD#TRPBF pulls the FAULT pin low and continues regulating current in the healthy string. The faulty string's VOUT–LEDx voltage drops below 0.3V, triggering detection. The remaining string operates normally - no shutdown or brightness reduction - while FAULT provides system-level fault signaling. This behavior is confirmed in the Electrical Characteristics table (LEDx Open Threshold) and Operation section.
Can the LT3909EDD#TRPBF drive a single LED string at 120mA?
Yes - the LT3909EDD#TRPBF allows paralleling LED1 and LED2 pins to achieve 120mA total current. Both pins share the same ISET programming, so a 16.7kΩ resistor sets 60mA per pin, yielding 120mA combined. The datasheet explicitly states "LED pins can be paralleled for higher LED current" and confirms each pin tolerates up to 40V and 60mA. Thermal design must account for doubled power dissipation in the DFN package.
What is the minimum PWM on-time supported by the LT3909EDD#TRPBF for 40,000:1 dimming?
The LT3909EDD#TRPBF achieves 40,000:1 PWM dimming at 100Hz with a minimum on-time of 250ns, as verified in Typical Performance Characteristic Figure 3909 G21. This ultra-short pulse capability enables deep dimming without visible flicker or LED turn-on delay - essential for automotive night-mode displays. The specification is measured with VOUT = 24V, VIN = 12V, and is independent of leakage at VOUT due to active VOUT regulation during PWM off-time.
Does the LT3909EDD#TRPBF require external compensation components?
No - the LT3909EDD#TRPBF includes internal compensation, as stated in the Features list and confirmed in the Block Diagram (CSS capacitor internal). No external RC network is needed for loop stability. The device also integrates internal soft-start and micropower shutdown circuitry, reducing external component count to just the inductor, input/output capacitors, ISET resistor, and optional FB divider - simplifying layout and validation for production designs.
LT3909EDD#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 12-WFDFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- DC DC Regulator
- Topology:
- Step-Up (Boost)
- Internal Switch(s):
- Yes
- Number of Outputs:
- 2
- Voltage - Supply (Min):
- 2.9V
- Voltage - Supply (Max):
- 40V
- Voltage - Output:
- 40V
- Current - Output / Channel:
- 50mA
- Frequency:
- 2MHz
- Dimming:
- Analog, PWM
- Applications:
- -
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- Automotive
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 12-DFN (3x3)
LT3909EDD#TRPBF FAQ
1.How can I place an order for LT3909EDD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3909EDD#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 LT3909EDD#TRPBF reliable?
The price and inventory of LT3909EDD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3909EDD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3909EDD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3909EDD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3909EDD#TRPBF?
LT3909EDD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3909EDD#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 LT3909EDD#TRPBF?
For technical support, including LT3909EDD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3909EDD#TRPBF requirements.
6.How does Aetrix verify that LT3909EDD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3909EDD#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 LT3909EDD#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3909EDD#TRPBF?
All LT3909EDD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3909EDD#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 LT3909EDD#TRPBF part is unused and in its original packaging.
Return procedure for LT3909EDD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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