Datasheet

13Atmel LED Driver-MSL2100
Detailed Description
The MSL2100 is a highly integrated, flexible, multi-string
LED driver that uses external MOSFETs to allow high
LED string currents and includes power supply control
for three supplies to maximize efficiency. The driver
optionally connects to a video subsystem to offer easy
synchronization for use in LCD TV backlight applications.
Up to sixteen devices may be connected together to
drive a large number of LED strings in a system. The
drivers provide multiple methods of controlling LED
brightness through both peak current control and pulse
width control of the string drive signals. Peak current
control offers excellent color consistency, while pulse
width control allows brightness management. An on-chip
EEPROM holds all the default control register values. At
power-up, the data in the EEPROM are automatically
copied directly to the control registers, setting up the
device for operation. The factory programmed EEPROM
values are changeable through the serial interface if a
different power-up condition is desired.
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 duty cycle and the
frequency of the LED drive signals. When using the
PWM engine, the MSL2100 allows phase spreading of
the LED drive signals, which helps reduce the transient
load on the LED power supplies. 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 MSL2100 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 supplies for the worst case forward voltage
(V
f
) of the LEDs without concern about excessive
power dissipation issues. During the start-up sequence,
the MSL2100 automatically reduces the power supply
voltage to the minimum 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 MSL2100 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 MSL2100, force EN high with a 5V
logic level, and force EN low to turn it off. When EN is
low, the MSL2100 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.
Atmel LED Driver-MSL2100
8-string, High-power, White or RGB LED Drivers for TVs,
Monitors, or Intelligent Solid-state Lighting