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Atmel LED Driver-MSL3082

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

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

by a resistor, R

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

ohms.

For example, a full-scale LED current of 500mA

returns R

individually reduced from the full-scale resistor set value

with 6-bit resolution using ISTR

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