White LED Driver in Tiny SC70 Package (LT1937 Design Note 315)
Design note for the LT1937 white LED driver, featuring a 1.2MHz switching frequency, high efficiency, and constant current architecture for portable backlighting applications.
Overview
This design document details the LT1937, a step-up white LED driver optimized for Li-Ion powered applications such as cellular phones and digital cameras. The device uses a constant current architecture to ensure uniform LED brightness and color regardless of forward voltage variations. Key features include a 36V internal switch capable of driving up to eight LEDs in series, a 1.2MHz constant switching frequency to minimize component size, and a low 95mV feedback voltage to reduce power loss. The document provides a schematic for a 15mA three-LED driver, efficiency curves peaking at 84%, and various dimming control methods including PWM, DC voltage, and logic signal step-adjustment.
Use Cases
- Cellular phone backlight display
- PDA display backlighting
- Digital camera LCD backlighting
- Small battery-powered portable devices
Topics
Referenced Parts
LT1937
Linear Technology
The LT1937 step-up white LED driver is an ideal solution for small battery-powered portable devices such as cellular phones, PDAs and digital cameras.
LQH3C-220
Murata
L1: MURATA LQH3C-220 OR EQUIVALENT
| CMDSH-3 | Central Semiconductor | D1: CENTRAL SEMICONDUCTOR CMDSH-3 |
| LT1937 | Linear Technology | The LT1937 step-up white LED driver is an ideal solution for small battery-powered portable devices such as cellular phones, PDAs and digital cameras. |
| LQH3C-220 | Murata | L1: MURATA LQH3C-220 OR EQUIVALENT |