Datasheet

17Atmel LED Drivers-MSL1061/MSL1064
Boost Regulator Components
The boost regulator is internally compensated, includes
an internal high voltage power switch, and requires only
an inductor, rectifier, and bypass capacitors. The current-
mode boost regulator operates in either continuous
conduction mode (CCM) or discontinuous conduction
mode (DCM). In CCM, the inductor current does not fall
to zero when operating at full power, keeping inductor
ripple current low and switching noise at a minimum.
The boost regulator switching frequency is 1.1MHz set
by the 115kΩ resistor R4 from OSC pin to GND (Figure
6). Select the inductor, rectifier diode, and output
capacitors per the following guidelines.
To minimize losses in the rectifier, choose one with fast
switching and low forward voltage drop. Ensure that the
rectifier can withstand a reverse voltage equal to the
regulator output voltage. The average forward current
is equal to the total LED string current (for example 6
strings x 30mA = 180mA), while the peak current is
equal to the inductor peak current (2A).
The boost output capacitor holds the voltage at the
output of the boost regulator while the internal power
switch is on and the rectifier is not conducting. Use
ceramic capacitors for small size and high ripple current
capacity, and derate them for operating voltage because
of the voltage coefficient of capacitance which decreases
the effective capacitance with increased operating
voltage. Use two parallel-connected 1µF 100V X7R
ceramic capacitors and a 10µH inductor with a 1.7A
peak current rating.
Boost Supply Over-voltage Protection
(OVP) - R8 and R9
The OVP input sets the boost regulator’s output voltage
upper limit, and protects the boost regulator from an
open-circuit LED fault. Set the OVP voltage V
TRIP
by
resistors R8 and R9 (Figure 6):
9
)98(
R
RR
VV
OVPTRIP
+
=
where V
OVP
=1.28V, nominal.
Atmel LED Drivers-MSL1061/MSL1064
6-string PWM LED Driver with Digitally Compensated, 1.1MHz,
48V Boost Regulator, ±1.5% Current Balance, I
2
C Interface