It integrates two outputs, each capable of driving LED strings, with a total internal switch current rating of 400 mA. The part operates as a step-up (boost) topology, taking a supply from 2.5 V to 5.5 V and delivering a regulated 16 V output to the LED load. Switching at 1 MHz keeps the external inductor small, which helps when board space is tight in a portable display or small-panel backlight.
Dimming and control — analog and PWM
This driver supports both analog and PWM dimming, giving the designer flexibility in brightness control. Analog dimming adjusts the LED current continuously, while PWM dimming switches the LEDs at a duty cycle for precise brightness levels without color shift. For a backlight in a handheld device or small LCD panel, having both options means you can trade off between simplicity (analog) and accuracy (PWM) depending on the system controller.
Package and mounting — hand-solderable with care
The LM3503SQ-16 comes in a 16-lead WFQFN with an exposed pad, measuring 4 mm x 4 mm. A hobbyist with a decent iron and some practice can hand-solder this — it's not a fine-pitch BGA — but the exposed pad does require a bit of technique to avoid cold joints. The 16-WQFN (4x4) supplier package code is the one to use for your PCB footprint.
Sourcing reality — obsolete and RoHS non-compliant
The LM3503SQ-16 is marked as obsolete by the manufacturer and is RoHS non-compliant. If you are qualifying a new design, look for a current, RoHS-compliant boost LED driver instead.