Datasheet

15Atmel LED Driver-MSL3162
Efficiency Optimizer
The Efficiency Optimizer improves power efficiency by adjusting each external LED power supply output voltage to the
minimum required by the connected LED strings. It does this by injecting a current from the FBO output into the external
LED power source voltage divider (Figure 5), thus lowering the LED supply voltage. The power supply's feedback
voltage (internal reference voltage) must be 1.4V or less, and the voltage setting feedback network divider must be
accessible. Use a Schottky diode (CMPSH-3 or similar) as shown to protect the power source against reverse current
flow into the FBO pin, should the power supply circuit be powered before the MSL3162.
Figure 5. Atmel LED Driver-MSL3162
FBO_Connection to Power Supply Voltage Divider
Connecting an LED String Power Supply to an Efficiency Optimizer
An LED string power supply uses a voltage divider (R
TOP
and R
BOTTOM
in Figure 6) to set its output voltage. The maximum
output voltage is set by the voltage divider ratio and the power supply feedback regulation voltage per the equation:
BOTTOMTOP
BOTTOM
MAXOUTFB
RR
R
VV
+
= *
)(
or
BOTTOM
BOTTOMTOP
FBMAXOUT
R
RR
VV
+
= *
)(
V
OUT(MAX)
must exceed the maximum LED string voltage to ensure regulation, but ensure that V
OUT(MAX)
is always under
the 40V maximum rating of the MSL3162’s LED string outputs, STR0 to STR15.
The Efficiency Optimizer modifies the feedback network by injecting a current, I
FBO
, in the range of 0 to 45µA from the
FBO output into the measurement node, FB. The minimum power supply output voltage is determined by the equation:
( )
TOPMAXBOxFMAXOUTMINOUT
RIVV
*
)()()(
−=
where I
FBOx(MAX)
is the 45µA maximum output current from the Efficiency Optimizer output.
From these equations, the equations to calculate the feedback resistors are:
)(
*
MAXFBO
MINMAX
FBTOP
I
VV
VR
−
=
and
FBOUT
FB
TOPBOTTOM
VV
V
RR
−
= *
Atmel LED Driver-MSL3162
16-string, RGB and White LED Drivers with Adaptive
Power Control and 1MHz I
2
C/SMBus Serial Interface