Datasheet

16 Atmel LED Driver-MSL1060
The MSL1060 is an integrated boost regulator plus
LED driver solution for driving an array of LEDs with
up to 8W of power. The MSL1060 is especially suited
to drive up to 72 white LEDs for notebook computer
backlighting. It is also suitable for industrial lighting and
signage applications, and can for example drive a 6
string x 18 series LED array, totaling 108 red LEDs
(2.5V LED forward voltage drop).
The MSL1060 includes 6 current sinks (STR0 through
STR5) that each control the LED current of series
connected LEDs. A built-in step-up regulator supplies
power to the LEDs. The MSL1060 controls the output
voltage of the boost regulator such that all LED strings
have sufficient voltage to maintain regulated LED
current. This control loop operates automatically without
any user interaction.
LED Current Sinks
The LEDs are connected in both series and parallel
combinations. The MSL1060 powers up to six parallel
strings with each string having up to 12 series-connected
white LEDs. The MSL1060 internally controls the current
of each string to ensure that all LEDs operate at the same
current. The MSL1060 measures the voltage at each of
the current sink outputs, STR0 to STR5, and determines
which has the lowest voltage. It uses this voltage to
control the internal boost regulation voltage such that
all current sink voltages have sufficient headroom to
maintain high current accuracy and matching.
Use equal numbers of LEDs with the same part number
in each LED string to maintain the same nominal voltage
drop across each string. If the number or type of LEDs
on each string does not match, the MSL1060 adjusts
the LED voltage so that the largest-forward-voltage
string has enough voltage at its current sink for the
necessary current accuracy and matching. If there’s
excessive variation between the voltages at the STR0
to STR5 current sinks, the MSL1060 dissipates extra
power, thereby reducing power efficiency.
By matching LED string voltages, the voltage drop
across each string driver (the current sink outputs
STR0 to STR5) is also matched. This allows the LED
driver to adjust the boost regulator output voltage to
minimize voltage headroom and thus power dissipation.
Minimizing string driver dissipation optimizes efficiency.
Disable unused current sink outputs by connecting
them to GND. At startup, the MSL1060 checks each
current sink output, STR0 to STR5, to determine if the
respective LED string shorted to GND. If a current sink
output is connected to GND, the MSL1060 detects that
as an unused string and disables it.
PWM Brightness Control
The MSL1060 uses an external PWM signal whose
waveform (frequency and duty) directly controls the
current sink outputs, STR0 to STR5. The MSL1060
turns-on all active LED strings when the PWM input is
high, and turns them off when it is low. Transition the
external PWM signa between the 0.9V maximum logic
low level and the 2.0V minimum logic high level as
quickly as possible to allow the MSL1060 to produce
an accurate PWM dimming time without jitter. Also, the
14µs LED string output fall time and 3.2µs rise time limit
the external PWM to 230Hz for 8-bit (256:1) brightness
resolution at the lowest end of the PWM duty range.
Detailed Description