Dell Vostro 3660 3669 Owner's Manual Linear Triple LED Driver in 4mm × 5mm QFN - Supports LCD Backlights in Buck, Boost or Buck-Boost Modes, and Delivers 3000 Lumens with a 1:1 PWM Dimming Ratio Design Note No. 449 Hua (Walker) Bai

Triple LED Driver in 4mm × 5mm QFN Supports LCD Backlights in Buck, Boost or Buck-Boost Modes and Delivers 3000:1 PWM Dimming Ratio Design Note 449 Hua (Walker) Bai Introduction Integrated PMOS Drivers Improve PWM Dimming

By integrating three independent LED drivers, the LT®3496 Ratio to 3000:1

offers a highly effi cient, compact and cost-effective A high PWM dimming ratio is critical in many display solution to drive multiple LED strings. All three drivers applications, especially in high end LCD panels. Beware, have independent on/off and PWM dimming control, and though, the defi nition of dimming ratio varies among can drive different numbers or types of LEDs. High side suppliers. When comparing dimming ratios, pay close current sensing and built-in gate drivers for PMOS LED attention to the PWM dimming frequency and linearity disconnect allow the LT3496 to operate in buck, boost, of the LED average current at different PWM duty cycles. SEPIC or buck-boost modes with up to 3000:1 True Color For instance, the LT3496’s high 3000:1 PWM dimming PWM™ dimming ratio. ratio can be achieved at a 100Hz PWM frequency—high

enough to keep the display fl icker-free over the entire

The LT3496 is offered in a single 4mm × 5mm QFN or

dimming range.

FE28 package. The effi ciency of each driver can exceed

L, LT, LTC and LTM are registered trademarks and True Color PWM is a trademark of

Linear Technology Corporation. All other trademarks are the property of their respective owners.

PVIN 12V

C1 TO C3

42V MAX CAP1

CAP2 CAP3 1μF

LED1 LED2 LED3 C2 CAP1 C3 CAP2 C4 CAP3

TG1 TG2 TG3 0.5Ω 0.5Ω 0.5Ω

LED1 LED2 LED3

0.5A 0.5A 0.5A TG1 M1 TG2 M2 TG3 M3

7 LEDs 200m A 7 LEDs 200m A 7 LEDs 200m A

L1 L2 L3 OVP3

OVP1 OVP2

SW1 SW2 SW3 TG1-3

SW1 SW2 SW3 TG1-3

CAP1-3 OVP1-3

VIN CAP1-3 OVP1-3

3.3V OR 5V LED1-3 VC1-3

LT3496 3.3V OR 5V LED1-3 VC1-3

LT3496

VIN VREF 22k

VIN VREF 18.2k

PWM1-3 PWM1-3 FADJ

PWM1-3 PWM1-3 FADJ

SHDN SHDN GND CTRL1-3 470p F 1n F

SHDN SHDN GND CTRL1-3

C5 DN449 F02

DN449 F01

1μF C1-C3, C7: MURATA GRM31MR71H105KA88 L1-L3: TAIYO YUDEN NP04SZB 100M 6.3V C1: TAIYO YUDEN UMK325BJ105MH L1-L3: SUMIDA CDRH3D14/HP-150 C4-C6: MURATA GRM188R71C474KA88 M1-M3: ZETEX ZXMP6A13F C2-C4: MURATA GRM21BR71H105K M1-M3: ZETEX ZXMP6A13F D1-D3: DIODES DFLS160 D1-D3: ROHM RB160M-60

Figure 1. Triple Buck Mode Can Drive 3x 500m A LED Strings Figure 2. Triple Boost Mode Can Drive 200m A LEDs