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Analog Devices Inc. LT3909HDD#TRPBF
- Part No.:
- LT3909HDD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 12-WFDFN Exposed Pad
- Datasheet:
-
LT3909HDD#TRPBF.pdf
- Description:
- IC LED DRVR RGLTR PWM 50MA 12DFN
- Quantity:
- Payment:
- Shipping:
Inventory:3,528
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Product details
Overview
LT3909HDD#TRPBF from Analog Devices (formerly Linear Technology) is a 2-string, 60mA high-side LED driver IC with integrated 40V/1A switch and Schottky diode, operating at fixed 2MHz boost switching frequency. It delivers ±2% current matching between strings, adapts VOUT to LED forward voltage for optimal efficiency, and supports analog dimming (10:1) and ultra-high-ratio PWM dimming (40,000:1 at 100Hz). It is used in automotive instrument clusters requiring precise dual-string brightness control under wide input (2.9V–40V) conditions.
For engineers reviewing the LT3909HDD#TRPBF datasheet, LT3909HDD#TRPBF pinout, LT3909HDD#TRPBF application, or LT3909HDD#TRPBF equivalent, key selection criteria include its ±0.3% typical current matching, programmable 10–60mA per string via single ISET resistor, fault-flag–enabled open-LED/short-to-GND protection per string, thermal regulation loop, and 3mm × 3mm 12-pin DFN package with exposed ground pad.
Technical Context
The LT3909HDD#TRPBF integrates a peak-current-mode 2MHz boost converter with two independent high-side current sources, each regulated by a dedicated feedback path monitoring VOUT–LEDx differential. Its GM1 loop maintains 1.3V across each current source for adaptive output voltage control, while the GM2 loop regulates FB to 1.215V for programmable overvoltage protection during fault conditions.
It features internal soft-start, 400mΩ switch RDS(ON), integrated Schottky diode, and dual-dimming capability: CTRL pin enables analog dimming down to 80mV latch-off threshold, while PWM pin controls digital dimming with 250ns minimum on-time and leakage-independent regulation - critical for maintaining stable VOUT during off periods.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.9V to 40V - supports direct connection to automotive battery (cold-crank to load-dump) without pre-regulation. |
| Max LED Current per String | 60mA - set precisely via single external resistor (16.7kΩ for 60mA), enabling scalable design across brightness tiers. |
| Current Matching Accuracy | ±2% (typ ±0.3%) - ensures consistent luminance between dual LED strings in displays and clusters. |
| PWM Dimming Ratio | 40,000:1 at 100Hz - enables ultra-fine grayscale control in high-contrast instrumentation without visible flicker. |
| Switching Frequency | 2MHz (±6%) - allows use of compact 3.3–10µH inductors and reduces EMI filtering requirements. |
| Fault Protection | Independent open-LED (VOUT–VLEDx < 0.4V) and LED-short-to-GND (VLEDx < 6.0V) detection per string - FAULT pin asserts low while unaffected string remains regulated. |
| Thermal Regulation | Internal junction temperature foldback - automatically derates LED current above ~170°C to prevent thermal runaway. |
Pinout & Package
LT3909HDD#TRPBF is housed in a thermally enhanced 12-pin (3mm × 3mm) plastic DFN package with exposed ground pad (Pin 13), optimized for high-power LED driving in space-constrained automotive and industrial applications. The exposed pad must be soldered to a continuous PCB ground plane for effective thermal dissipation (θJA = 43°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 INTVCC | Internal 3.0V regulator bypass | Supplies gate driver and control circuits; requires ≥1µF X7R ceramic capacitor to GND; max 100µA external load. |
| 2 VIN | Main input supply | Accepts 2.9V–40V; must be locally bypassed with low-ESR ceramic capacitor for transient current handling. |
| 3 EN/UVLO | Enable and undervoltage lockout input | 0.4V shutdown / 1.215V falling enable threshold; supports programmable UVLO hysteresis via resistor divider from VIN. |
| 4 ISET | LED current programming | Single resistor to GND sets identical current (10–60mA) for both strings using ILEDx = 1000/RISET (in kΩ). |
| 5 CTRL | Analog dimming and thermal derating control | Voltage below 1V linearly scales LED current; <80mV latches off current - enables NTC-based ambient temperature compensation. |
| 6 FB | Output voltage regulation feedback | Resistor divider from VOUT to GND programs OVP level (regulated to 1.215V); also sampled during PWM off-time to hold VOUT steady. |
| 7 PWM | Digital dimming control | Active-low signal disables both high-side current sources; internal pull-up not provided - requires external pull-up. |
| 8 FAULT | Open/short fault flag output | Open-drain, active-low; pulled low if either LED string opens or shorts to GND; latched during PWM/CTRL low states. |
| 9 LED1 10 LED2 |
High-side LED current outputs | Each drives one LED string anode; constant-current sinks to GND; pins may be paralleled for >60mA total current. |
| 11 VOUT | Boost converter output | Regulated node supplying both LED strings; requires low-ESR ceramic capacitor (1µF for VOUT<20V, 2.2µF for VOUT>20V). |
| 12 SW | Power switch drain / Schottky anode | Connects to inductor; internal 40V/1A N-channel DMOS switch and Schottky diode - minimize trace area to reduce EMI. |
| 13 (Exposed Pad) | Ground reference and thermal path | Must be soldered to solid copper ground plane; primary thermal conduction path - critical for junction temperature management. |
Key Features
| Feature | Design Value |
|---|---|
| Adaptive VOUT regulation | Maintains only the minimum voltage needed across LED strings (via GM1 loop), reducing power loss and heat generation in variable-VF arrays. |
| Leakage-immune PWM dimming | VOUT is actively regulated during PWM off-time using stored FB sample - eliminates droop from Schottky leakage, enabling fast current recovery and stable 40,000:1 dimming. |
| Per-string fault isolation | Open-LED or short-to-GND on one string triggers FAULT but leaves the other string fully operational - essential for safety-critical dual-display systems. |
| Integrated thermal foldback | Automatically reduces LED current when junction temperature exceeds safe limit - protects device and LEDs without external sensors or circuitry. |
| Single-resistor current setting | One precision resistor (e.g., 16.7kΩ for 60mA) programs identical current in both strings - simplifies BOM, layout, and calibration vs. dual-trim solutions. |
| Programmable overvoltage protection | OVP threshold set by FB divider (1.215V reference) - prevents overvoltage damage when LED strings are reconnected after open-circuit faults. |
Applications
| Automotive Instrument Clusters | High-Contrast GPS Displays |
|---|---|
|
Use Scenario: Dual-row TFT backlight with independent brightness zones in vehicle dashboards. IC Role / Device Role / Timing Role: Dual high-side constant-current source regulating two parallel LED strings, adapting VOUT dynamically to aging and temperature-induced VF shifts. Use Value: Ensures uniform luminance across display zones despite varying LED forward voltages, meeting automotive AEC-Q100 Class 0 thermal requirements (–40°C to +125°C). |
Use Scenario: Outdoor navigation unit requiring daylight-readable contrast under 10,000+ cd/m² ambient light. IC Role / Device Role / Timing Role: 2MHz boost driver delivering 60mA per string with 40,000:1 PWM dimming to maintain visibility from full sun to nighttime. Use Value: Enables seamless grayscale transition without flicker or color shift, leveraging ultra-fast 250ns LED on-time and leakage-compensated VOUT hold. |
| Industrial HMI Panels | Avionics Status Indicators |
|
Use Scenario: Ruggedized touch-panel interface in factory environments with wide input voltage (9–36V DC). IC Role / Device Role / Timing Role: LED driver with EN/UVLO hysteresis and fault-flag reporting for system-level diagnostics and graceful degradation. Use Value: Supports brown-out immunity and real-time fault logging via FAULT pin, reducing field failure rates in unattended equipment. |
Use Scenario: Red/green status lighting in cockpit displays where reliability and fault containment are mission-critical. IC Role / Device Role / Timing Role: Dual-string driver with independent short/open detection and thermal derating to prevent single-point failure propagation. Use Value: Maintains partial functionality (one string) during LED failure, satisfying DO-160E lightning-induced transient and thermal stress requirements. |
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 |
|---|---|---|---|
| LT3965IMSE#TRPBF | 4-channel, 150mA/channel, 3MHz switching, no integrated Schottky, requires external MOSFETs | Higher channel count and current for multi-zone lighting; lacks integrated diode and single-resistor current setting | Choose for scalable multi-string designs needing >60mA or higher frequency; avoid if board space or BOM simplicity is prioritized. |
| TPS61165DRVR | Single-string, 40mA, 1.2MHz, no thermal regulation, no per-string fault flag | Limited to one LED string; no independent fault reporting or junction temperature protection | Choose only for cost-sensitive single-string applications without safety or redundancy requirements; not suitable for dual-string automotive use. |
Compared with LT3909HDD#TRPBF, LT3965IMSE#TRPBF offers greater channel scalability but increases layout complexity and component count, while TPS61165DRVR sacrifices fault isolation, thermal safety, and dual-string capability - making LT3909HDD#TRPBF uniquely suited for safety-aware dual-string automotive backlighting.
Availability
LT3909HDD#TRPBF is available at Aetrix Electronics and suitable for automotive instrument clusters, high-contrast GPS receivers, and industrial HMI panels requiring stable component supply, AEC-Q100-compliant operation, and long-term production continuity.
Supply support for LT3909HDD#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, 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 LT3909HDD#TRPBF belongs to Linear's high-reliability LED driver product line, engineered specifically for automotive-grade dual-string backlighting with emphasis on fault resilience, thermal robustness, and adaptive efficiency under wide-input-voltage conditions.
FAQ
What is the maximum LED forward voltage supported by the LT3909HDD#TRPBF?
The LT3909HDD#TRPBF supports up to 36V total LED forward voltage across both strings, enabled by its 40V-rated internal switch and Schottky diode. Its adaptive VOUT regulation ensures only the minimum required voltage is generated - for example, with two 18V LED strings, VOUT will regulate just above 18V plus the 1.3V current-source headroom, minimizing power loss and heat generation in the IC.
How does the LT3909HDD#TRPBF achieve 40,000:1 PWM dimming without VOUT droop?
The LT3909HDD#TRPBF samples the FB pin voltage at the PWM falling edge and holds that value to regulate VOUT during the off period - a technique that compensates for leakage from the internal Schottky diode or external components. This active regulation prevents VOUT sag, ensuring immediate LED current recovery at the next PWM rising edge and enabling stable 40,000:1 dimming even at 100Hz.
Can the LT3909HDD#TRPBF drive a single LED string at 120mA?
Yes - the LT3909HDD#TRPBF allows paralleling of LED1 and LED2 pins to combine both 60mA current sources into a single 120mA output. When doing so, program the ISET resistor for 30mA per source (e.g., 33.2kΩ) to achieve 120mA total. Ensure thermal design accounts for doubled power dissipation in the shared current path and verify PCB copper area supports the increased current.
What is the purpose of the exposed pad (Pin 13) on the LT3909HDD#TRPBF DFN package?
The exposed pad (Pin 13) on the LT3909HDD#TRPBF is a dedicated ground connection and primary thermal conduction path. It must be soldered to a continuous PCB ground plane to achieve θJA = 43°C/W and prevent junction temperature exceedance under full-load conditions. Leaving it unconnected or floating degrades thermal performance and risks thermal shutdown or reduced lifetime.
Does the LT3909HDD#TRPBF support analog dimming and PWM dimming simultaneously?
No - analog dimming (via CTRL pin) and PWM dimming (via PWM pin) are mutually exclusive control methods in the LT3909HDD#TRPBF. When PWM is asserted low, the CTRL pin is ignored and both LED strings are fully disabled. For combined control, external logic must ensure only one dimming method is active at a time - e.g., use CTRL for coarse adjustment and PWM for fine-grained frame-rate modulation.
LT3909HDD#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 12-WFDFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- 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 ~ 150°C (TJ)
- Grade:
- Automotive
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 12-DFN (3x3)
LT3909HDD#TRPBF FAQ
1.How can I place an order for LT3909HDD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3909HDD#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 LT3909HDD#TRPBF reliable?
The price and inventory of LT3909HDD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3909HDD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3909HDD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3909HDD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3909HDD#TRPBF?
LT3909HDD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3909HDD#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 LT3909HDD#TRPBF?
For technical support, including LT3909HDD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3909HDD#TRPBF requirements.
6.How does Aetrix verify that LT3909HDD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3909HDD#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 LT3909HDD#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3909HDD#TRPBF?
All LT3909HDD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3909HDD#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 LT3909HDD#TRPBF part is unused and in its original packaging.
Return procedure for LT3909HDD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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