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Analog Devices Inc. LT3909IDD#PBF
- Part No.:
- LT3909IDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- LED Drivers
- Package:
- 12-WFDFN Exposed Pad
- Datasheet:
-
LT3909IDD#PBF.pdf
- Description:
- IC LED DRVR RGLTR PWM 50MA 12DFN
- Quantity:
- Payment:
- Shipping:
Inventory:1,411
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Product details
Overview
LT3909IDD#PBF from Analog Devices (formerly Linear Technology) is a 2-string, 60mA high-side LED driver IC with integrated 2MHz step-up DC/DC converter, ±2% current matching, and programmable output voltage regulation up to 36V. It delivers precise constant-current drive for automotive instrument clusters and high-contrast displays requiring stable brightness control across wide input (2.9V–40V) and temperature (–40°C to 125°C) ranges.
For engineers reviewing the LT3909IDD#PBF datasheet, LT3909IDD#PBF pinout, LT3909IDD#PBF application, or LT3909IDD#PBF equivalent, key selection criteria include its dual-string ±0.3% typical current matching, 40,000:1 PWM dimming at 100Hz, internal 400mΩ/40V/1A switch, integrated Schottky diode, and fault-flag–enabled open-LED/short-to-GND protection with independent string regulation.
Technical Context
The LT3909IDD#PBF integrates a fixed-frequency (2MHz), peak-current-mode boost controller with two independent high-side current sources. Each source regulates LED current via feedback from VOUT–LEDx differential voltage, dynamically adapting output voltage to minimum required headroom (1.3V typical) for optimal efficiency.
It features dual-loop regulation: GM1 loop maintains VOUT–LEDx at 1.3V during normal operation; GM2 loop regulates FB to 1.215V for programmable overvoltage protection (OVP) during fault conditions or PWM off-time, preventing VOUT droop from Schottky leakage and enabling fast LED current recovery.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.9V to 40V - supports direct connection to automotive battery (9V–16V nominal) and industrial 24V rails without pre-regulation. |
| Max LED Current per String | 60mA - set by single ISET resistor (16.7kΩ); enables driving 10 white LEDs/string at full brightness with thermal margin. |
| Current Matching Accuracy | ±2% (typ ±0.3%) - ensures consistent luminance between strings in dual-display or stereo backlight applications. |
| PWM Dimming Ratio | Up to 40,000:1 at 100Hz - achieved via OVP hold during PWM off-time, eliminating brightness flicker and enabling ultra-low-light UI modes. |
| Switching Frequency | 2MHz (±6%) - allows use of compact 3.3µH–10µH inductors and minimizes EMI in space-constrained portable and automotive modules. |
| Integrated Power Switch | 400mΩ, 40V, 1A N-channel DMOS - eliminates external MOSFET, reduces BOM count, and supports up to 36V LED stack (e.g., 10×3.6V white LEDs). |
| Thermal Protection | Internal junction temperature regulation - derates LED current above 125°C to prevent permanent degradation in sealed enclosures. |
Pinout & Package
LT3909IDD#PBF is housed in a thermally enhanced 12-lead (3mm × 3mm) plastic DFN package with exposed pad (Pin 13) soldered to PCB ground for low θJA (43°C/W). The exposed pad is electrically GND and mandatory for thermal performance and reliability.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 INTVCC | Internal 3.0V regulator output | Bypass with ≥1µF ceramic capacitor; powers gate driver and control circuits; max 100µA external load allowed. |
| 2 VIN | Main input supply | Accepts 2.9V–40V; requires local ceramic bypass capacitor; supplies boost converter and INTVCC regulator. |
| 3 EN/UVLO | Enable and undervoltage lockout input | 0.4V shutdown / 1.215V falling enable threshold; supports programmable UVLO with resistor divider from VIN. |
| 4 ISET | LED current programming node | Single resistor to GND sets both string currents (10–60mA); 16.7kΩ yields 60mA per string. |
| 5 CTRL | Analog dimming and latch-off control | Voltage ≤80mV disables LED current; 0.1V–1.0V enables 10:1 analog dimming; used with NTC for thermal derating. |
| 6 FB | Output voltage regulation feedback | Resistor divider from VOUT to GND programs OVP level (1.215V reference); enables fault-mode VOUT clamping. |
| 7 PWM | Digital dimming control | Active-high signal; controls synchronous on/off of both high-side current sources; supports 250ns minimum on-time. |
| 8 FAULT | Open-LED/short-to-GND flag | Active-low open-drain output; asserts when VOUT–LEDx <0.3V (open) or VLEDx <6.0V (short); other string remains regulated. |
| 9 LED1 / 10 LED2 | High-side LED current outputs | Each drives one LED string anode; cathodes connect to GND; pins may be paralleled for >60mA total current. |
| 11 VOUT | Boost converter output | Connects to LED string cathodes via capacitor; regulated to minimum headroom (1.3V) for efficiency; max 40V rating. |
| 12 SW | Internal switch drain | Drain of integrated 1A/400mΩ MOSFET and anode of internal Schottky; connects to inductor; minimize trace area for EMI. |
| 13 (Exposed Pad) | Thermal and electrical ground | Mandatory solder connection to large PCB copper pour; provides primary thermal path and reduces die temperature rise. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated Schottky diode | Eliminates external diode, saves 2–3mm² PCB area, and reduces component count in space-critical handheld and automotive modules. |
| Programmable VOUT OVP | User-defined overvoltage protection via FB resistor divider prevents LED overvoltage damage when strings reconnect after open-circuit faults. |
| Independent string fault tolerance | When one LED string fails open or shorted, the other remains fully regulated-critical for safety-critical instrument cluster redundancy. |
| Internal compensation & soft-start | Reduces external components; soft-start ramps inductor current and switching frequency to limit inrush and EMI during power-up. |
| Accurate EN/UVLO threshold | ±15mV enable hysteresis and 2.0µA pin current enable robust, repeatable system-level undervoltage lockout design. |
Applications
| Automotive Instrument Clusters | High-Contrast Industrial Displays |
|---|---|
|
Use Scenario: Driving dual-row LED backlights for TFT LCD gauges in vehicles operating across –40°C to 125°C under battery transients. IC Role / Device Role / Timing Role: Dual high-side current source regulating 60mA per string with ±0.3% matching to eliminate luminance asymmetry between left/right display zones. Use Value: Maintains consistent color and brightness despite wide temperature swings and input voltage dips to 6V during cranking. |
Use Scenario: Backlighting medical or test equipment displays requiring flicker-free dimming down to 0.0025% brightness for low-light environments. IC Role / Device Role / Timing Role: 2MHz boost controller with 40,000:1 PWM dimming and OVP hold during off-time to prevent VOUT droop and ensure instant LED turn-on. Use Value: Enables diagnostic-grade grayscale fidelity without visible PWM artifacts or brightness lag during rapid UI transitions. |
| Portable GPS Receivers | PDA & Handheld Computers |
|
Use Scenario: Powering monochrome or color LED backlights in outdoor GPS units powered by single-cell Li-ion (3.0V–4.2V) or alkaline batteries. IC Role / Device Role / Timing Role: Wide-input (2.9V–40V) boost converter with adaptive VOUT regulation to maintain 60mA drive even as battery discharges below LED forward voltage. Use Value: Extends usable battery life by minimizing conversion losses and avoiding dropout at end-of-life cell voltages. |
Use Scenario: Compact backlight solution for legacy PDAs with tight board area budgets and no dedicated PMIC. IC Role / Device Role / Timing Role: Integrated 1A switch, Schottky diode, and internal compensation reduce external parts to only inductor, ISET resistor, and two capacitors. Use Value: Cuts BOM cost and layout time while meeting stringent EMI limits via 2MHz switching and minimized high-di/dt loop area. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar LED driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3220EUD#PBF | Charge-pump architecture (no inductor); max 40mA per string; 1.2MHz; no integrated Schottky; no OVP programming. | Suitable only for low-voltage LED stacks (<12V); limited to space-constrained USB-powered devices where inductors are prohibited. | Select LTC3220EUD#PBF only if inductor-free design is mandatory and LED VF sum is ≤12V; not suitable for automotive or 36V LED strings. |
| MAX16822ATP+T | Boost + linear hybrid; 60mA per string; 500kHz; external MOSFET required; no integrated Schottky; ±3% matching. | Requires external high-voltage switch and diode; larger solution size; lower switching frequency increases inductor size and EMI filtering burden. | Choose MAX16822ATP+T only if higher thermal dissipation margin is needed via external FET, or if 500kHz EMI profile better fits system constraints. |
Compared with LTC3220EUD#PBF and MAX16822ATP+T, the LT3909IDD#PBF uniquely combines inductor-based 2MHz efficiency, integrated Schottky, programmable OVP, and sub-1% current matching-making it the only option supporting 36V LED strings with automotive-grade fault resilience and ultra-deep PWM dimming in a 3mm × 3mm DFN.
Availability
LT3909IDD#PBF is available at Aetrix Electronics and suitable for automotive instrument clusters, high-contrast industrial displays, and portable GPS receivers requiring stable component supply across extended temperature and long product lifecycles.
Supply support for LT3909IDD#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 for precision instrumentation, automotive, and industrial systems.
The LT3909IDD#PBF belongs to Linear's high-reliability LED driver product line, designed specifically for demanding backlighting applications where luminance consistency, fault tolerance, and wide-input operation are critical.
FAQ
What is the maximum LED string voltage supported by the LT3909IDD#PBF?
The LT3909IDD#PBF supports up to 36V of LEDs per string, enabled by its 40V-rated internal switch and VOUT pin. This accommodates configurations such as ten 3.6V white LEDs in series. Absolute maximum ratings specify VOUT and LED1/LED2 pins at 40V, providing 4V design margin for transient spikes and layout parasitics.
How does the LT3909IDD#PBF achieve 40,000:1 PWM dimming without brightness droop?
The LT3909IDD#PBF samples the FB pin voltage at the PWM falling edge to capture the optimum VOUT level required for LED regulation, then actively regulates VOUT to that stored value during PWM off-time using the GM2 loop. This prevents droop from Schottky diode leakage or capacitor discharge, ensuring immediate LED current recovery at the next PWM rising edge.
Can the LT3909IDD#PBF drive a single LED string at 120mA?
Yes - the LT3909IDD#PBF allows paralleling of LED1 and LED2 pins to combine both high-side current sources. With ISET set for 60mA per string (16.7kΩ), paralleling yields 120mA total into one string. Thermal design must account for doubled power dissipation in the IC's exposed pad and PCB copper area.
What protection features does the LT3909IDD#PBF provide against LED faults?
The LT3909IDD#PBF provides open-LED detection (VOUT–LEDx < 0.3V) and LED-short-to-GND detection (VLEDx < 6.0V), both triggering the active-low FAULT pin. Critically, fault detection is per-string: if LED2 shorts, LED1 remains fully regulated. Programmable OVP via FB further protects LEDs during reconnection after open faults.
Is the LT3909IDD#PBF pin-compatible with other variants in the LT3909 family?
Yes - the LT3909IDD#PBF shares identical pinout and footprint with LT3909EDD#PBF, LT3909EMSE#PBF, and LT3909IMSE#PBF. All use the same 12-lead DFN or MSOP packages with identical pin numbering and functions. Only temperature grade (E = 0°C–125°C, I = –40°C–125°C) and package type differ; the IDD grade specifies –40°C to 125°C operation in DFN.
LT3909IDD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 12-WFDFN 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-DFN (3x3)
LT3909IDD#PBF FAQ
1.How can I place an order for LT3909IDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3909IDD#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 LT3909IDD#PBF reliable?
The price and inventory of LT3909IDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3909IDD#PBF is usually 5 days.
3.What payment methods are accepted for LT3909IDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3909IDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3909IDD#PBF?
LT3909IDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3909IDD#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 LT3909IDD#PBF?
For technical support, including LT3909IDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3909IDD#PBF requirements.
6.How does Aetrix verify that LT3909IDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3909IDD#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 LT3909IDD#PBF meets industry standards.
7.What is the process for return or replacement of LT3909IDD#PBF?
All LT3909IDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3909IDD#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 LT3909IDD#PBF part is unused and in its original packaging.
Return procedure for LT3909IDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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