Datasheet

11Atmel LED Driver-MSL3082
The device interfaces to an MCU via the I
2
C/SMBus
interface. The robust 1MHz I
2
C/SMBus interface
supports up to sixteen devices on the bus, and is fast
enough to support area dimming for 16 interconnected
devices. While typically the LED drive PWM signal is
internally generated by the PWM engine, the device
also accepts an external direct PWM drive signal
applied to the PWM input to set the frequency and
duty cycle of the LED drive signals. When using the
PWM engine, the MSL3082 allows phase spreading of
the LED drive signals, which helps reduce the transient
load on the LED power supply. Phase spreading is not
supported for direct PWM drive.
The PWM frequency of the drivers is easily synchronized
to an external video signal applied to PHI. Typically, the
VSYNC signal from the video system is used as the PHI
input. A frame-rate multiplier (1x to 16x) processes
this signal for use by the PWM engine. The on-time of
each string is individually programmed via the device
registers, providing a peak resolution of 10 bits when
using the on-chip PWM generator. The actual resolution
of the PWM frequency depends on the ratio of the
GSC frequency (typically provided by a systems
HSYNC signal) to the PHI frequency because the on
time of a string is programmed as a function (8-bit
count) of the number of GSC cycles. This count can be
further scaled by a 6-bit global intensity register, when
enabled. The GSC clock is also used to precisely set
each string’s phase delay to be synchronized with its
physical position relative to the video frame. Additionally,
the MSL3082 features programmable temperature
compensation, which throttles back the PWM on time of
all strings when the temperature of the LEDs exceeds a
programmable threshold.
The Efficiency Optimizers control a wide range of
different external DC-DC and AC-DC converter
architectures. Multiple drivers in a system communicate
in real time among themselves to select an optimized
operating voltage for the LEDs. This allows design of the
power supply for the worst case forward voltage (V
f
)
of the LEDs without concern about excessive power
dissipation issues. During the start-up sequence, the
MSL3082 automatically reduces the power supply
voltage to the minimum voltage required to keep the
LEDs in current regulation. The devices are configured
to periodically perform this optimization to compensate
for changes in LED forward voltage, and to assure
continued optimum power savings.
Internal Regulators and Enable Input
The MSL3082 includes an internal linear regulator
powered from VIN that provides 2.5V, VDD, to power
the internal circuitry. Bypass VDD to GND with a 10µF
or greater capacitor.
The enable input, EN, turns the VDD regulator on and off.
To turn on the MSL3082 force EN high with a 5V logic
level, and force EN low to turn it off. When EN is low,
the MSL3082 enters low-power mode, and the serial
interface is ignored. Toggling EN low also clears all fault
registers and releases FLTB. Faults re-establish if the
conditions that generated them persist.
Setting LED String Currents
The maximum string current, I
LED
, for each string is set
by a resistor, R
Sn
, connected to ground from the source
terminal of the external string drive MOSFET. The
feedback threshold is 500mV. Determine the resistor
value using:
LED
Sn
I
R
5.0
=
, where I
LED
is in amperes and R
Sn
is in
ohms.
For example, a full-scale LED current of 500mA
returns R
Sn
= 1.00Ω. The current for the LED strings is
individually reduced from the full-scale resistor set value
with 6-bit resolution using ISTR
n
, the string current
control registers 0x10 through 0x1F.
Atmel LED Driver-MSL3082
8-string, High-power, White or RGB LED Driver for TV,
Blacklighting, or Intelligent Solid-state Lighting