21V fixed boost for backlight strings
The LM3501TLX-21/NOPB is a fixed-output step-up DC-DC regulator from Texas Instruments, purpose-built for backlight applications. It delivers a regulated 21V from an input supply ranging from 2.7V to 7V, with an integrated switch rated at 640mA.
1 MHz switching — inductor and footprint trade-offs
Switching at 1 MHz lets you use a physically smaller inductor — think 2.2 to 4.7 µH range — which helps when board space is tight. The trade-off is that switching losses are higher than a 500 kHz part, so thermal management in the 8-WFBGA package matters at the upper end of the load. The 8-DSBGA (8-WFBGA) package is a 0.50 mm pitch wafer-level ball grid array. No lab, no bench — this is a hot-air rework part. The exposed die face is the top; orientation is marked by a corner ball pattern, not a pin 1 dot you can see after reflow. Stencil aperture design and a proper reflow profile are non-negotiable.
Wide temperature range covers outdoor and engine-bay backlights
The 21V output is typical for driving two to six white LEDs in series, depending on LED Vf and current set by the external resistor.