MSL2042GU Atmel, MSL2042GU Datasheet - Page 12

• Manufacturer Part Number: MSL2042GU
• Description: LED Lighting Drivers 4Str RGB or White LED Driver lighting
• Manufacturer: Atmel

Specifications of MSL2042GU

• Rohs: yes
• Input Voltage: 10.8 V to 13.2 V
• Maximum Supply Current: 31.5 mA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SOP-32
• Minimum Operating Temperature: - 40 C
• Power Dissipation: 1576 mW
• Factory Pack Quantity: 1000

Detailed Description
The MSL2041 and MSL2042 are highly integrated,
flexible, four-string LED drivers that use external
MOSFETs to allow high string currents, and include
power supply control to maximize efficiency of up
to two external string power supplies. Optimized for
stand-alone operation they require only external PWM
signal(s), a few external components (including the
string drive N-Channel MOSFETs) and an external string
power supply. The MSL2041/2s four MOSFET gate
drive outputs, G0 - G3, are optimized to drive FETs with
a maximum gate voltage threshold of 3V.
The MSL2041/2 LED drivers provide simple control
of LED brightness through both peak current and
external PWM drive controls. Peak current control, set
by external FET source resisters, offers excellent color
consistency, while pulse width control allows simple
brightness management. Multiple devices easily connect
together to drive more than four LED strings while
maintaining optimum system efficiency. An active low
fault output activates when either a string open circuit
or an LED short circuit condition is detected and verified.
The MSL2041/2 are intended for stand-alone operation
but offer additional string control and monitoring through
a 1MHz I
the serial interface is not required for operation.
The MSL2041 offers four PWM inputs that directly
control the four string drive outputs, while the MSL2042
requires only a single PWM input signal and features
automatic, progressive phase spreading of the four
string drive signals. With phase spreading a ¼ PWM
frame time delay is calculated and applied progressively
to the string drive signals. Phase spreading helps reduce
both the transient load on the LED power supply, and
the power supply output capacitor size requirement.
The Adaptive SourcePower Efficiency Optimizer (EO)
outputs control a wide range of different architectures of
external DC/DC and AC/DC converters. Multiple drivers
in a system communicate with each other in real time to
select an optimized operating voltage for the LEDs. The
EO allows design of the power supply for the worst case
Forward Voltage (V
about excessive power dissipation issues, while ensuring
that the LED drive system is operating at optimum
12
2
C/SMBus compatible serial interface. Use of
f
) of the LEDs without worrying
efficiency. During start-up the EO automatically reduces
the string power supply voltage to the minimum value
required to keep the LEDs in current regulation. The EO
periodically performs re-optimization to compensate for
changes of the LED’s forward voltage, and to assure
continued optimum power savings. Additionally, all string
drivers are continually monitored for proper operation,
and if any of the LED strings become starved for current
the Efficiency Optimizer automatically increases the
string power supply voltage to bring the string back in
to current regulation.
Setting the Maximum LED String Current with
the FET Source Resistor R
The maximum string current, I
is set by a shunt resistor, R
from the source terminal of the string drive MOSFET
(Figure 1, page 6). Determine the resistor value using
(where 127 is the default value of ISTR, String Current
Control register 0x0E). For example, a full-scale LED
current of 350mA returns R
1% resistor value).
LED String Fault Response
The MSL2041/2 monitor the LED strings to detect LED
short-circuit and string open-circuit faults (Figure 3).
When verified, all string faults force the open drain fault
output FLTB low.
After power-up, when shorted LEDs are verified in a
string the string is disabled and no longer monitored
by the Efficiency Optimizer. The short circuit threshold
is 6V (typical) and the additive voltage drop lost from
the shorted LEDs, plus the headroom required for the
external FET, must be equal to or greater than the 6V
threshold to generate a fault. Typically, two LEDs in a
string must be shorted to cause a short circuit fault,
R
S
=



127
255

∗ 


 

. 0
50196
I
LED
S
, connected to ground
S

 

= 0.715Ω (to the nearest
Ω
LED
S
Atmel LED Drivers-MSL2041/2042
, for each string