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Analog Devices Inc. LT3909EMSE#PBF
- Part No.:
- LT3909EMSE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 12-TSSOP (0.118", 3.00mm Width) Exposed Pad
- Datasheet:
-
LT3909EMSE#PBF.pdf
- Description:
- IC LED DRV RGLTR PWM 50MA 12MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:204
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Product details
Overview
LT3909EMSE#PBF from Analog Devices (formerly Linear Technology) is a 2-string, 60mA high-side LED driver IC with integrated 40V/1A N-channel switch and Schottky diode, operating at fixed 2MHz switching frequency to drive up to 36V total LED forward voltage. It delivers ±2% current matching between strings, supports analog dimming (10:1) and PWM dimming (up to 40,000:1 at 100Hz), and adapts VOUT dynamically to LED VF for optimal efficiency in automotive display backlighting.
For engineers reviewing the LT3909EMSE#PBF datasheet, LT3909EMSE#PBF pinout, LT3909EMSE#PBF application, or LT3909EMSE#PBF equivalent, key selection criteria include its 12-lead MSOP package with exposed thermal pad, programmable LED current (10–60mA/string via single ISET resistor), fault-flag diagnostics for open/shorted LED strings, and internal thermal regulation - all critical for high-reliability, space-constrained LED lighting designs.
Technical Context
The LT3909EMSE#PBF integrates a peak-current-mode boost converter with two independent high-side current sources, each regulated by a dedicated feedback loop monitoring VOUT–LEDx differential voltage (target 1.3V). Its GM1 control loop maintains minimum required VOUT for LED string regulation, while GM2 activates during PWM off-time or fault conditions to regulate VOUT to a user-programmable OVP level via FB divider.
Operation includes internal soft-start, cycle-by-cycle 1.1A switch current limiting, ±0.3% typical current matching, and dual-fault detection: open-LED (VOUT–VLEDx < 0.4V) and LED-short-to-GND (VLEDx < 6.0V). The EN/UVLO pin provides accurate 1.215V falling threshold with 30mV hysteresis for system-level undervoltage lockout programming.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| LED Current per String | 10mA to 60mA, set by single external resistor (RISET) - enables precise, matched current without trimming. |
| Current Matching Accuracy | ±2% (typ ±0.3%) - ensures uniform brightness across dual LED strings in displays and instrument clusters. |
| Switching Frequency | Fixed 2MHz (±6%) - allows use of small, low-profile inductors (e.g., 3.3–10µH) and minimizes EMI in noise-sensitive applications. |
| Input Voltage Range | 2.9V to 40V - supports direct connection to automotive battery (cold-crank to load-dump) without pre-regulation. |
| PWM Dimming Ratio | Up to 40,000:1 at 100Hz (250ns min on-time) - enables ultra-fine brightness control in high-dynamic-range displays. |
| Integrated Power Switch | 40V/1.1A rated N-channel MOSFET with 400mΩ RDS(ON) - eliminates external switch, reduces BOM count and PCB area. |
| Thermal Protection | Internal junction temperature regulation - derates LED current above 125°C to prevent thermal runaway in sealed enclosures. |
Pinout & Package
LT3909EMSE#PBF uses a 12-lead plastic MSOP package (3mm × 4.4mm) with exposed thermal pad (Pin 13 = GND), optimized for thermal performance in compact LED driver layouts. θJA = 40°C/W, θJC = 5–10°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| INTVCC (1) | Internal 3.0V regulator output | Supplies gate driver and control logic; must be bypassed with ≥1µF ceramic capacitor; max 100µA external load. |
| VIN (2) | Main input supply | Accepts 2.9V–40V; powers internal circuits and boost switch; requires local ceramic bypass capacitor. |
| EN/UVLO (3) | Enable and UVLO input | 0.4V shutdown / 1.215V enable threshold; enables programmable system-level undervoltage lockout with hysteresis. |
| ISET (4) | LED current programming | Single resistor to GND sets identical current for both strings (10–60mA); no calibration needed. |
| CTRL (5) | Analog dimming control | 0–1V input scales LED current linearly; <80mV disables output - enables ambient-temperature LED derating via NTC. |
| FB (6) | OVP regulation feedback | Resistor divider programs maximum VOUT during faults or PWM off-time; prevents overvoltage damage to LEDs. |
| PWM (7) | Digital dimming control | Active-high signal; controls high-side current sources directly; supports ultra-low-duty-cycle dimming without leakage effects. |
| FAULT (8) | Open/short fault flag | Active-low open-drain output; asserts for open-LED or LED-short-to-GND on either string; other string remains regulated. |
| LED1, LED2 (9,10) | High-side LED current outputs | Each drives one LED string; can be paralleled for >60mA total; tolerate up to 40V relative to GND. |
| VOUT (11) | Boost converter output | Regulated node supplying both LED strings; connects to output capacitor and optional external Schottky anode. |
| SW (12) | Switch node | Drain of internal MOSFET and cathode of internal Schottky; connects to inductor; requires minimal trace area for EMI control. |
| Exposed Pad (13) | Thermal ground | Must be soldered to solid copper plane; primary path for heat dissipation; electrically connected to GND. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated Schottky diode | Eliminates external diode, saves ~2mm² PCB area, and simplifies layout in space-constrained automotive modules. |
| Dynamic VOUT adaptation | VOUT regulated to minimum voltage required per string (VOUT = ΣVF + 1.3V), reducing power loss and improving efficiency by up to 8% vs fixed-output boost. |
| Independent string fault tolerance | Open or short on one LED string disables only that channel; second string continues regulation - critical for safety-critical displays. |
| Internal compensation & soft-start | Reduces external component count; soft-start limits inrush current during startup, preventing input rail sag in battery-powered systems. |
| Micropower shutdown | 0.3µA typical VIN shutdown current - extends battery life in always-on vehicle systems (e.g., daytime running lights). |
Applications
| Automotive Instrument Clusters | High-Brightness Display Backlighting |
|---|---|
|
Use Scenario: Driving dual-row white LED arrays behind TFT LCD gauges in vehicles operating from 6V–16V battery with load-dump transients. IC Role / Device Role / Timing Role: Dual high-side constant-current source with adaptive VOUT regulation and fault flag reporting to MCU. Use Value: ±0.3% typical current matching ensures pixel-perfect brightness uniformity; 40V absolute max rating withstands 36V load-dump spikes without protection circuitry. |
Use Scenario: Backlighting for industrial HMI panels requiring 20,000:1 contrast ratio and operation across –40°C to +85°C ambient. IC Role / Device Role / Timing Role: Fixed-frequency boost LED driver with PWM dimming control and thermal foldback for sustained high-brightness operation. Use Value: 40,000:1 PWM dimming at 100Hz enables deep black levels; internal thermal regulation prevents luminance drift during extended runtime. |
| GPS Navigation Displays | Avionics Status Indicators |
|
Use Scenario: Compact portable GPS units powered by single-cell Li-ion (2.9V–4.2V) requiring consistent LED brightness across battery discharge. IC Role / Device Role / Timing Role: Wide-input boost driver with analog dimming (CTRL pin) and EN/UVLO for battery voltage monitoring. Use Value: 2.9V min input enables full brightness down to nearly depleted battery; 10:1 analog dimming complements PWM for flicker-free UI transitions. |
Use Scenario: Red/green status indicators in certified avionics equipment where reliability, fault reporting, and thermal margin are mandatory. IC Role / Device Role / Timing Role: Fault-tolerant LED driver with active-low FAULT flag, open/short diagnostics, and junction temperature regulation. Use Value: Independent string fault handling meets DO-160 lightning-induced transient requirements; exposed pad ensures <125°C junction temp at full load. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar LED driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3909EDD#PBF | Same die, 12-lead 3mm×3mm DFN package with lower θJA (43°C/W) and different pinout (SW/VOUT swapped vs MSOP). | Preferred for higher-power density layouts where thermal pad soldering is feasible and board area is constrained. | Select when PCB real estate is premium and thermal performance outweighs assembly complexity of DFN reflow. |
| LT3761EFE#PBF | Single-string 100mA boost LED driver with adjustable frequency (100kHz–1MHz), no integrated Schottky, requires external diode. | Suitable for higher-current single-string applications but lacks dual-string matching and fault isolation. | Choose only if dual-string operation and ±2% matching are not required; verify external diode selection for 2MHz operation. |
Compared with LT3909EDD#PBF, the LT3909EMSE#PBF offers easier hand-soldering and standard MSOP footprint compatibility, while LT3761EFE#PBF trades dual-string precision for higher single-string current and frequency flexibility - making LT3909EMSE#PBF optimal for automotive dual-backlight systems demanding fault resilience and layout simplicity.
Availability
LT3909EMSE#PBF is available at Aetrix Electronics and suitable for automotive instrument clusters, high-contrast display backlighting, and GPS navigation systems requiring stable component supply, long-term lifecycle support, and guaranteed RoHS-compliant sourcing.
Supply support for LT3909EMSE#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 automotive, industrial, communications, and aerospace markets.
The LT3909EMSE#PBF belongs to Linear's high-efficiency LED driver product line, engineered specifically for automotive-grade dual-string backlighting with stringent reliability, thermal robustness, and diagnostic capability requirements.
FAQ
What is the maximum LED forward voltage the LT3909EMSE#PBF can support per string?
The LT3909EMSE#PBF regulates VOUT to maintain at least 1.3V across each high-side current source (VOUT – VLEDx). With a maximum VOUT rating of 40V and absolute maximum LED pin voltage of 40V, it supports up to 36V total LED forward voltage per string - sufficient for 10+ white LEDs in series at typical VF.
Can the LT3909EMSE#PBF drive a single LED string at 120mA?
Yes - the LT3909EMSE#PBF allows paralleling LED1 and LED2 pins. When both pins are tied together and programmed for 60mA per string (RISET = 16.7kΩ), the device delivers up to 120mA total into a single string, maintaining ±2% matching accuracy and full fault protection functionality.
Does the LT3909EMSE#PBF require external compensation components?
No - the LT3909EMSE#PBF features fully internal compensation. No external RC networks or compensation capacitors are needed, simplifying design, reducing bill-of-materials cost, and eliminating tuning effort during prototyping and validation.
How does the LT3909EMSE#PBF handle an open-LED fault on one string?
When an open-LED fault occurs on LED1 or LED2 (VOUT – VLEDx < 0.4V), the LT3909EMSE#PBF pulls the FAULT pin low and disables only the affected string. The healthy string continues regulated operation - preserving partial display functionality and enabling diagnostic logging by the host controller.
What thermal management is required for the LT3909EMSE#PBF at full 60mA per string?
The LT3909EMSE#PBF's exposed thermal pad (Pin 13) must be soldered to a continuous copper ground plane. With proper 2oz copper and thermal vias, it achieves θJA = 40°C/W - enabling reliable operation at 125°C junction temperature even at full load in ambient temperatures up to 85°C.
LT3909EMSE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 12-TSSOP (0.118", 3.00mm Width) Exposed Pad
- Packaging:
- Tube
- 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-MSOP-EP
LT3909EMSE#PBF FAQ
1.How can I place an order for LT3909EMSE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3909EMSE#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 LT3909EMSE#PBF reliable?
The price and inventory of LT3909EMSE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3909EMSE#PBF is usually 5 days.
3.What payment methods are accepted for LT3909EMSE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3909EMSE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3909EMSE#PBF?
LT3909EMSE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3909EMSE#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 LT3909EMSE#PBF?
For technical support, including LT3909EMSE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3909EMSE#PBF requirements.
6.How does Aetrix verify that LT3909EMSE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3909EMSE#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 LT3909EMSE#PBF meets industry standards.
7.What is the process for return or replacement of LT3909EMSE#PBF?
All LT3909EMSE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3909EMSE#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 LT3909EMSE#PBF part is unused and in its original packaging.
Return procedure for LT3909EMSE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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