Texas Instruments LM3500TLX-21/NOPB

Overview

LM3500TLX-21/NOPB from Texas Instruments is a synchronous step-up DC/DC converter optimized for white LED backlighting, featuring 20.5 V internal overvoltage protection (OVP), 1 MHz fixed switching frequency, and 2.7 V to 7 V input range. It drives 4–5 series white LEDs with integrated NMOS/PMOS switches, no external Schottky diode required, and delivers up to 670 mA switch current limit (typ.) at 3 V input.

For engineers reviewing the LM3500TLX-21/NOPB datasheet, LM3500TLX-21/NOPB pinout, LM3500TLX-21/NOPB application, or LM3500TLX-21/NOPB equivalent, key selection criteria include OVP threshold accuracy (20.5 V), shutdown isolation (<0.1 µA), feedback voltage precision (0.5 V ±30 mV), and DSBGA-8 thermal performance (θ_JA = 75°C/W) in space-constrained portable lighting designs.

Technical Context

The LM3500TLX-21/NOPB implements current-mode PWM control with internal compensation, eliminating external loop components. Its synchronous rectification uses an integrated NMOS (R_DS(on) = 0.43 Ω) and PMOS (R_DS(on) = 1.1–2.3 Ω) pair, enabling high efficiency without external diodes.

Protection architecture includes dedicated comparators for input undervoltage lockout (UVP: 2.4–2.6 V), output overvoltage (OVP: 20–21 V), and thermal shutdown (trip: ~150°C, hysteresis: ~35°C), all operating independently of external circuitry.

Key Specifications

Pinout & Package

LM3500TLX-21/NOPB uses an 8-bump thin DSBGA package (1.5 mm × 1.5 mm, 0.5 mm pitch) with exposed thermal pad. Pin assignment follows TI's standard DSBGA layout: A1=AGND, B1=VIN, C1=VOUT, C2=VSW, C3=GND, B3=FB, A3=NC, A2=SHDN.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-up LED driver applications.

Compared with TPS61061DRVR and MAX1910EUT+T, LM3500TLX-21/NOPB offers superior integration (no external diode or compensation), tighter OVP accuracy (±0.5 V), and lower shutdown current (0.1 µA vs. 1 µA), making it optimal for space- and battery-limited 4–5 LED portable backlighting.

Availability

LM3500TLX-21/NOPB is available at Aetrix Electronics and suitable for LCD bias supplies, white LED backlighting, handheld devices, digital cameras, and portable applications requiring stable component supply with guaranteed long-term sourcing.

Supply support for LM3500TLX-21/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 and embedded processing technologies, with decades of expertise in power management ICs for portable and industrial systems.

The LM3500 product line was designed specifically for high-efficiency, small-footprint white LED backlighting in battery-powered consumer electronics, emphasizing integration, thermal robustness, and fault protection.

FAQ

What is the exact overvoltage protection threshold for LM3500TLX-21/NOPB?

The LM3500TLX-21/NOPB features a precisely trimmed internal OVP comparator with a typical turn-on threshold of 20.5 V and hysteresis of 1 V (turn-off at ~19.5 V). This is confirmed in the Electrical Characteristics table (OVP ON Threshold: 20 V min / 20.5 V typ / 21 V max) and applies exclusively to the -21 variant-distinct from the -16 version's 15.5 V threshold.

Can LM3500TLX-21/NOPB drive more than five white LEDs in series?

LM3500TLX-21/NOPB can drive more than five white LEDs only if their combined forward voltage remains below 20 V (accounting for 0.53 V FB pin drop and OVP margin). Per TI's Application Information, six LEDs require ≤3.24 V each and seven require ≤2.78 V each-feasible only with low-V_F GaN or advanced phosphor LEDs, not standard InGaN types.

What is the recommended inductor value for LM3500TLX-21/NOPB in a 4-LED, 20-mA design?

For a 4-LED, 20-mA design with 3.3 V input and 15 V output, TI recommends ≥22 µH per the datasheet's inductor selection guidance. Equation (4) yields ~18 µH minimum, but bench validation confirms 22 µH (e.g., TDK VLP4612T-220MR34) ensures stable operation across temperature and load, avoiding subharmonic oscillation.

Does LM3500TLX-21/NOPB require external compensation components?

No, LM3500TLX-21/NOPB uses internal compensation-confirmed in the Operation section ("internally compensated thus eliminating the need for any external compensation components"). This reduces BOM count and layout sensitivity, distinguishing it from controllers like TPS61061 that require external RC networks.

How does the shutdown function of LM3500TLX-21/NOPB isolate input from output?

LM3500TLX-21/NOPB achieves true shutdown isolation by disabling both NMOS and PMOS power switches and disconnecting the FB pin bias path. As verified in the Shutdown section, this results in <0.1 µA supply current and zero DC current flow from VIN to VOUT-critical for preserving battery charge in always-on portable devices.