Datasheet

14
MSL2021 [DATASHEET]
42062A–LED–02/2013
8. Typical Application Circuit
MSL2021 controlling the output of an isolated PFC controller; a linear current sink regulates the white LED string current
and a floating buck converter regulates the color LED string current.
Figure 8-1. Typical application circuit
9. Detailed Description
The MSL2021 drives two LED strings, the main string and the color-adjust string. The main string LEDs are typically
white and used to provide accurate light intensity control.The color-adjust string LEDs are used to control the color
temperature. The combined light output is a blended high CRI light, for example, than what white LEDs can alone
produce. The main string is directly controlled by a Pulse Width Modulated (PWM) constant current controller (current
sink to ground). An Efficiency Optimizer (EO) output controls the main string voltage, via feed-back to the LED string
power supply, to minimize the voltage across the LED current controller, minimizing power loss.
The color-adjust string is regulated by a floating buck controller. The buck controller converts the voltage of the main
string’s supply to a voltage appropriate for the color-adjust LEDs. Additionally, the MSL2021 has a programmable 8-bit
registers that allows adjustment of the current by changing the source feedback reference voltages (see“Block Diagram”
on page 11).
G
DRV
AVIN12V
AGND
AC-DC
ISOLATED
With PFC
SDA SCL
CONFIGURATION INTERFACE
MSL2021
LED DRIVER
REXT
CS
PWM
PWM
+
-
0.56Ω
THM
ERT-
J0EG103FA
FLTB
FAULT
FBO
EN
EN
WHITE
LEDS
COLOR
LEDS
PGND
VAC
R
TOP
R
BOTTOM
820μH
D
PVIN
VCC
VDD
TOFF
S
(OPTIONAL)
46.4kΩ
45.3kΩ
10μF
10uF
1μF
1μF
0.56Ω
100kΩ
1μF
1.50kΩ
Q1
Q2
D1