Texas Instruments LM3509SDX/NOPB

Overview

LM3509SDX/NOPB from Texas Instruments is a dual-output, I²C-compatible white LED and OLED display bias supply IC featuring two independently configurable current sinks (MAIN and SUB/FB), 30 mA per string maximum output, 1.27 MHz fixed-frequency boost converter, and 2.7V–5.5V input range. It operates in portable LCD backlighting and OLED panel power applications with adaptive voltage regulation for >90% efficiency.

For engineers reviewing the LM3509SDX/NOPB datasheet, LM3509SDX/NOPB pinout, LM3509SDX/NOPB application, or LM3509SDX/NOPB equivalent, key selection considerations include dual-mode operation (LED+LED or LED+OLED), 0.15% current matching in unison mode, 21 V over-voltage protection, I²C brightness control with 32 exponential steps, and thermal shutdown at +140°C.

Technical Context

The LM3509SDX/NOPB integrates a current-mode PWM boost controller with dual regulated outputs: MAIN functions as a constant-current sink up to 30 mA, while SUB/FB is configurable either as a second current sink or as a 1.21 V feedback input for constant-voltage OLED bias up to 21 V. Adaptive regulation dynamically adjusts output voltage to maintain ≥500 mV headroom across both current sinks.

Control is implemented via an I²C-compatible interface (7-bit address 0x36) supporting independent or unison brightness control (32 exponential steps), programmable ramp rates, active-low hardware reset, and GPIO functionality. Internal soft-start limits inrush current, and over-voltage protection triggers at 21.2 V (min) with hysteresis down to 19.7 V.

Key Specifications

Pinout & Package

LM3509SDX/NOPB is housed in a thermally enhanced 10-pin WSON package (3 mm × 3 mm × 0.8 mm) with exposed DAP for improved heat dissipation. The package supports −40°C to +85°C ambient operation and achieves θ_JA = 54°C/W on a standard 4-layer FR-4 PCB.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-output display bias supply applications.

Compared with LM3508SDX/NOPB, the LM3509SDX/NOPB adds critical dual-string coordination and OLED compatibility; versus TPS61165DRVR, it delivers integrated I²C control, unison dimming, and adaptive regulation - making it the only option for compact, feature-rich hybrid display power architectures.

Availability

LM3509SDX/NOPB is available at Aetrix Electronics and suitable for smartphone backlighting, tablet hybrid displays, portable medical monitors, and industrial HMIs requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for LM3509SDX/NOPB 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and power management technologies, with decades of expertise in display power solutions and automotive-grade reliability validation.

The LM3509 product line was designed specifically for space-constrained portable electronics requiring high-efficiency, multi-mode display bias with minimal external components - targeting smartphones, wearables, and medical handhelds.

FAQ

What is the maximum number of white LEDs the LM3509SDX/NOPB can drive per string?

The LM3509SDX/NOPB supports up to 5 white LEDs in series per string when delivering 30 mA, based on its 21 V maximum output capability and typical white LED forward voltage of ~3.2 V. Driving 10 LEDs total (5+5) is confirmed in TI's SNVS495D datasheet Figure 3, and operation remains stable with proper inductor and capacitor selection per the recommended design guidelines.

Does the LM3509SDX/NOPB support true shutdown with zero LED leakage current?

Yes. The LM3509SDX/NOPB provides true shutdown isolation: when both ENM and ENS bits in the General Purpose register are cleared, MAIN and SUB/FB outputs enter high-impedance state with <100 nA leakage current. This is verified in the Electrical Characteristics table under "Shutdown Current" (3.6–5 µA total device current, dominated by internal circuitry).

How does the LM3509SDX/NOPB achieve 0.15% current matching between MAIN and SUB/FB outputs?

The LM3509SDX/NOPB achieves 0.15% typical current matching in unison mode (UNI bit = 1) by disabling independent BSUB register control and forcing both MAIN and SUB/FB current sinks to track the same BMAIN register value. This eliminates inter-channel gain variation and leverages matched internal current mirror architecture, as specified in the Electrical Characteristics table under "ILED-MATCH".

Can the LM3509SDX/NOPB drive an OLED panel while simultaneously powering a white LED string?

Yes. When configured in OLED mode (OLED bit = 1 in GP register), the LM3509SDX/NOPB uses SUB/FB as a 1.21 V feedback input to regulate a constant output voltage up to 21 V for OLED panels, while MAIN continues to deliver up to 30 mA to a white LED string - provided ≥300 mV headroom is maintained at MAIN, as confirmed in the OPERATION DESCRIPTION section of SNVS495D.

What is the function of the RESET/GPIO pin on the LM3509SDX/NOPB?

The RESET/GPIO pin on the LM3509SDX/NOPB serves dual roles: as an active-low hardware reset (default at power-up) that forces all registers to 0x00, or as a programmable general-purpose I/O. Its mode is controlled by the GPIO register; when configured as output, it operates open-drain with internal pull-down, requiring an external pull-up resistor for logic-high assertion.