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Analog Devices Inc. LT3909HDD#PBF
- Part No.:
- LT3909HDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 12-WFDFN Exposed Pad
- Datasheet:
-
LT3909HDD#PBF.pdf
- Description:
- IC LED DRVR RGLTR PWM 50MA 12DFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,030
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Product details
Overview
LT3909HDD#PBF 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 peak 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#PBF datasheet, LT3909HDD#PBF pinout, LT3909HDD#PBF application, or LT3909HDD#PBF equivalent, key selection criteria include its 12-pin 3mm×3mm DFN package with exposed thermal pad, programmable LED current (10–60mA/string via single ISET resistor), fault flag signaling open-LED or LED-short-to-GND, and internal thermal regulation protecting junction temperature up to 170°C.
Technical Context
The LT3909HDD#PBF integrates a peak-current-mode 2MHz 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 loop dynamically adjusts VOUT to the minimum required for string regulation-reducing power loss-while the GM2 loop activates during PWM off-time or fault conditions to regulate VOUT to a user-programmable OVP level via FB divider.
It features cycle-by-cycle 1.1A switch current limiting, internal soft-start with frequency ramp-up, and dual protection architecture: open-LED detection triggers when VOUT–VLEDx falls below 0.4V, while LED-short-to-GND is flagged when VLEDx drops below ~25% of VOUT. Fault status is latched only during PWM/CTRL high states, ensuring stable reporting during dimming transitions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.9V to 40V - enables direct operation from 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), supporting high-brightness white LED strings |
| Current Matching Accuracy | ±2% (typ ±0.3%) - ensures consistent luminance across dual displays or symmetric lighting zones |
| PWM Dimming Ratio | 40,000:1 at 100Hz - achieves deep black-level control in high-contrast automotive clusters with 250ns minimum on-time |
| Switching Frequency | 2MHz (±6%) - allows use of small 3.3–10µH inductors and minimizes EMI in space-constrained PCB layouts |
| Integrated Power Switch | 400mΩ, 40V, 1A N-channel DMOS - eliminates external MOSFET, reducing BOM count and layout complexity |
| Thermal Regulation | Junction temperature foldback above 170°C - autonomously derates LED current to prevent permanent die damage during sustained overload |
Pinout & Package
LT3909HDD#PBF is housed in a thermally enhanced 12-pin (3mm × 3mm) plastic DFN package with exposed ground pad (Pin 13) requiring soldering to PCB copper for thermal management (θJC = 5.5°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| INTVCC (1) | Internal 3.0V regulator output | Supplies gate driver and control circuits; must be bypassed with ≥1µF ceramic capacitor; max 100µA external load |
| VIN (2) | Main input supply | Accepts 2.9V–40V; requires local ceramic bypass capacitor to suppress high-frequency ripple |
| EN/UVLO (3) | Enable and input undervoltage lockout | Shuts down device below 0.4V; UVLO threshold programmable via resistor divider (1.215V falling threshold) |
| ISET (4) | LED current programming input | Single resistor to GND sets identical current for both strings (10–60mA); ILED = 1000 / RISET (mA) |
| CTRL (5) | 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 |
| FB (6) | OVP regulation feedback | Resistor divider from VOUT programs maximum regulated output voltage (e.g., 36V) for open-LED protection |
| PWM (7) | Digital dimming control | Active-low signal disables both high-side current sources; internal pull-up if unused |
| FAULT (8) | Open-LED/short-to-GND flag | Open-drain active-low output; pulled low during fault; requires external pull-up resistor (to VIN, INTVCC, or VOUT) |
| LED1 / LED2 (9,10) | High-side LED current outputs | Each drives one LED string anode; can be paralleled for >60mA total; cathodes connect to GND |
| VOUT (11) | Boost converter output | Connects to output capacitor; regulated to minimum voltage needed for LED string compliance |
| SW (12) | Internal switch drain node | Connects to inductor; also anode of internal Schottky diode; minimize trace area to reduce EMI |
| Exposed Pad (13) | Thermal ground | Must be soldered to solid PCB ground plane; primary path for heat dissipation (θJA = 43°C/W) |
Key Features
| Feature | Design Value |
|---|---|
| Adaptive VOUT regulation | Maintains only the voltage needed to bias LED strings - reduces power loss and improves efficiency across VF variation |
| Independent string fault handling | One string failure (open or short) does not disrupt regulation of the other string - critical for safety-critical dual-display systems |
| Internal Schottky diode | Eliminates external diode footprint and losses - simplifies layout and improves reliability in compact automotive modules |
| Programmable OVP via FB | Prevents overvoltage damage when LED strings reconnect after open-circuit fault - configurable to match system LED stack voltage |
| VOUT regulation during PWM off-time | Prevents droop from Schottky leakage - ensures instant LED current recovery at PWM rising edge for flicker-free dimming |
| Accurate EN/UVLO threshold | Enables precise system-level brown-out protection with 30mV hysteresis - avoids erratic startup/shutdown in noisy vehicle electrical environments |
Applications
| Automotive Instrument Clusters | High-Brightness GPS Displays |
|---|---|
Use Scenario: Dual-zone backlighting for TFT LCD cluster with speedometer and tachometer segments requiring matched luminance. IC Role / Device Role / Timing Role: Dual high-side constant-current source driving parallel white LED strings; regulates VOUT dynamically per string VF. Use Value: ±2% current matching ensures uniform brightness across zones; 40,000:1 PWM dimming enables seamless day/night transition without visible steps. |
Use Scenario: Sunlight-readable GPS receiver display in portable automotive navigation units. IC Role / Device Role / Timing Role: Boost LED driver powering 10-white-LED strings per side; operates from 12V vehicle supply with cold-crank tolerance down to 2.9V. Use Value: 2MHz switching enables compact 3.3µH inductor; integrated 400mΩ switch and Schottky reduce component count and thermal stress in sealed enclosures. |
| Industrial HMI Panels | Avionics Status Indicators |
Use Scenario: Ruggedized human-machine interface panel in construction equipment with wide ambient temperature range (−40°C to +125°C). IC Role / Device Role / Timing Role: LED driver with thermal foldback and fault flag; monitors LED health and reports failures to host MCU via FAULT pin. Use Value: Internal thermal regulation protects against overheating in sealed cabinets; open-LED detection prevents single-point failure from disabling entire display. |
Use Scenario: Red/green status indicator lighting in certified avionics cockpit displays requiring high reliability and fault containment. IC Role / Device Role / Timing Role: Dual-string driver with independent fault reporting; FAULT pin signals open or short condition without affecting second string. Use Value: Independent string operation meets redundancy requirements; programmable OVP prevents overvoltage transients during hot-swap events. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar LED driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3909EMSE#PBF | Same silicon, 12-lead MSOP package (5mm × 4mm); higher θJA (40°C/W) but no exposed pad requirement | Better suited for prototyping or low-volume designs where thermal pad soldering is impractical | Select when board assembly process cannot reliably solder exposed DFN pads or when manual rework is required |
| LT3909IDD#PBF | Identical DFN package and pinout; rated for same −40°C to +125°C junction temperature range | No functional difference; differs only in manufacturing lot traceability and screening for industrial-grade reliability | Choose for industrial applications requiring extended qualification testing or longer production lifecycle commitments |
Compared with LT3909EMSE#PBF, the LT3909HDD#PBF offers superior thermal performance (θJC = 5.5°C/W vs. ~7°C/W for MSOP) and smaller footprint, while LT3909IDD#PBF provides identical electrical behavior with enhanced process controls for mission-critical deployments - making LT3909HDD#PBF optimal for volume automotive production where thermal density and PCB area are constrained.
Availability
LT3909HDD#PBF is available at Aetrix Electronics and suitable for automotive instrument clusters, high-brightness GPS receivers, industrial HMI panels, and avionics status indicators requiring stable component supply, long-term manufacturability, and AEC-Q200-aligned reliability.
Supply support for LT3909HDD#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 healthcare markets.
The LT3909 belongs to Linear's precision LED driver product line, engineered specifically for dual-string automotive and industrial displays demanding tight current matching, robust fault handling, and wide-input-voltage operation without external compensation components.
FAQ
What is the maximum LED string voltage supported by the LT3909HDD#PBF?
The LT3909HDD#PBF supports up to 36V of total LED forward voltage per string, enabled by its 40V-rated internal switch and Schottky diode. The output voltage (VOUT) adapts dynamically to the lowest level required to maintain regulation - minimizing power loss - and is clamped to a user-programmable maximum via the FB pin resistor divider to protect against overvoltage during open-LED faults.
How does the LT3909HDD#PBF achieve 40,000:1 PWM dimming without VOUT droop?
The LT3909HDD#PBF samples the FB voltage at the PWM falling edge and holds that reference to regulate VOUT during the off-time using its GM2 loop. This active regulation compensates for leakage through the internal Schottky diode and other paths, preventing VOUT sag and enabling immediate LED current recovery at the next PWM rising edge - achieving stable 40,000:1 dimming at 100Hz with 250ns minimum on-time.
Can the LT3909HDD#PBF drive a single LED string at 120mA?
Yes - the LT3909HDD#PBF allows paralleling of LED1 and LED2 pins to combine both 60mA high-side current sources into a single 120mA output. To do so, connect both LED pins together to the anode of one LED string, tie the cathode to ground, and program ISET for 60mA per string (e.g., 16.7kΩ), resulting in 120mA total. Thermal design must account for doubled power dissipation in the IC.
What protection features does the LT3909HDD#PBF provide for LED string faults?
The LT3909HDD#PBF provides open-LED detection (VOUT–VLEDx < 0.4V), LED-short-to-GND detection (VLEDx < 25% of VOUT), and overtemperature foldback (junction > 170°C). Faults trigger the open-drain FAULT pin low, and crucially, only the affected string shuts down - the other remains fully regulated. Programmable OVP via FB further protects LEDs during reconnection after open-circuit events.
Is external compensation required for the LT3909HDD#PBF boost converter?
No - the LT3909HDD#PBF includes fully internal compensation for both the boost converter (GM1 loop) and OVP regulation (GM2 loop). No external compensation components are needed, simplifying design and improving consistency across production units. The internal slope compensation ensures stability at duty cycles above 50%, and the fixed 2MHz oscillator eliminates timing component variability.
LT3909HDD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 12-WFDFN Exposed Pad
- Packaging:
- Tube
- 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#PBF FAQ
1.How can I place an order for LT3909HDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3909HDD#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 LT3909HDD#PBF reliable?
The price and inventory of LT3909HDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3909HDD#PBF is usually 5 days.
3.What payment methods are accepted for LT3909HDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3909HDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3909HDD#PBF?
LT3909HDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3909HDD#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 LT3909HDD#PBF?
For technical support, including LT3909HDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3909HDD#PBF requirements.
6.How does Aetrix verify that LT3909HDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3909HDD#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 LT3909HDD#PBF meets industry standards.
7.What is the process for return or replacement of LT3909HDD#PBF?
All LT3909HDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3909HDD#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 LT3909HDD#PBF part is unused and in its original packaging.
Return procedure for LT3909HDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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