15Atmel LED Driver-MSLB9082
On/Off (EN) Control Input
The on/off control input, pin 9 of input connector J2,
turns on/off the LED driver. Drive it high (between 2.3
and 5V) to turn on the LED driver, and drive it low (0 to
0.8V) to turn it off. The on/off control input is internally
pulled up by a 100kΩ resistor. For automatic start-up,
leave EN unconnected.
External PWM Control Input
The MSL3162 operates in one of three modes: internal
PWM mode, external PWM mode, or gated PWM mode.
Internal PWM mode dims the LEDs with a frequency
and phase set by the MSL3162, and the state of
the PWM input is ignored and has no effect on LED
brightness. In this case, each string can have a different
PWM set by the MSL3162’s PWMn register setting. To
control the brightness of all LEDs simultaneously, set the
GINT register between 0 and 3F.
External PWM and gated PWM modes use the duty
cycle of the signal applied to the PWM input; connector
J2, pin 10. The PWM input is pulled high through a
100kΩ resistor. If not used, leave PWM unconnected
or drive it high. The MSL3162 digitizes the PWM input
signal and determines the duty cycle of that signal. This
value replaces the GINT register value to control the
global brightness (of all LEDs simultaneously). In this
case, individual string brightness is controlled through
the PWMn register.
Gated PWM mode turns on all LEDs when PWM is
driven high, and turns them off when PWM is driven
low. By programming the PWMn registers and GINT for
100% duty cycle, the LEDs are directly PWM dimmed
by the signal applied to the PWM input.
Fault Indicator Output
The MSL3162 includes fault detection circuitry that
detects and open-circuited LED string, and an LED string
with one or more short-circuited LEDs. If any fault is
detected, the output is driven low. Use this output as an
alert signal to a system controller. Once the controller
gets the alert signal, it determines which LED is faulty
by reading the STATUS, OCSTATUS, and SCSTATUS
registers through the I2C serial interface.
Connecting the LEDs to the Atmel LED Driver-
MSL9082 LED Driver
The MSLB9082 driver board drives LED arrays with
up to eight parallel strings of up to 12 series LEDs each
through the output connector, J3. Eight connections for
LED cathode connections allow the use of separate LED
strings or common-anode-connected LED strings.
Driving LEDs with Greater than 80mA
LED Current
The MSL3162 is capable of driving up to 80mA per
LED string. The MSLB9082 board has two string
drivers connected to each driver connection (STRA-
STRH), with one disabled. This allows driving up to
180mA per LED string by enabling the two drivers and
setting the same PWM duty ratios and phasing for both
MSL3162 driver inputs (dual-string mode). See the
MSL3162 datasheet for more details on programming
the MSL3162.
Table 8 shows the switch settings and the full-scale,
per-string LED current for each setting when operating
in parallel mode.
Atmel LED Driver-MSLB9082
LED Backlight Driver Module
Compact, 8-channel, 20W LED Driver Board with I2C Interface