Datasheet
15
Atmel MSL3080 Datasheet
8 String 60mA LED Driver with Integrated Boost Controller
8.4 Gate Driver
The gate driver drives the gate of the external boost regulator switching MOSFET. The drain of the switching MOSFET in turn drives the
boost inductor and rectier to boost the input voltage to the regulated output voltage. The gate driver sources and sinks up to 1A allowing
fast switching speed and allows the use of MOSFETs with high gate capacitance. The gate driver power is separated from the internal
circuitry power to reduce internal noise and to allow separate gate driver bypassing for optimal performance.
8.5 Soft-Start
The boost regulator includes a built in soft-start to prevent excessive input current overshoot at turn-on. The soft-start ramps the output
regulation voltage from 0V at turn-on to the as-congured regulation output voltage over 1.6ms. Note that the boost regulator only
controls output voltages greater than the input voltage; when the soft-start sets the regulation voltage below the input voltage, the actual
output voltage remains at approximately the input voltage.
8.6 Boost Fault Monitoring and Protection
The boost regulator includes fault monitoring and protection circuits to indicate faults and prevent damage to the boost regulator or other
circuitry. The boost regulator has cycle by cycle current limiting that prevents excessive current through the power MOSFET. The current
limit is has a xed threshold voltage across the current sense resistor, thus set the current limit by choosing the proper value current
sense resistor.
The boost regulator includes an output over-voltage fault monitor that indicates a fault when the voltage at FB exceeds the 2.8V over-
voltage protection (OVP) threshold. When an over-voltage fault occurs FLTB sinks current to GND to indicate that a fault has occurred.
OVP fault is non-latching, the fault clears when the over-voltage condition disappears.
8.7 LED Current Regulators and PWM Dimming Modes
The MSL3080 includes eight open-drain LED current regulators that sink LED current up to 60mA per channel and sustain up to 40V,
allowing them to drive up to 10 white LEDs each. The current regulators inform the Efciency Optimizers, which in turn control the boost
regulator output voltage to minimize LED voltage while maintaining sufcient headroom for the LED current regulators.
Set the LED regulation current using a single resistor from ILED to GND. LED dimming is by PWM, and is by default controlled through
an external signal, or optionally by internal registers accessed through the I2C compatible serial interface (for interface information see
the “MSL3040/50/60/80/86/87/88 Programming Guide”). The drivers feature synchronized dimming, where all PWM dimming outputs
sink current in unison.
8.8 Efciency Optimizer (EO)
The Efciency Optimizer monitors the LED string drivers and controls the boost regulator output voltage to minimize LED current
regulator overhead voltage while maintaining sufcient voltage for accurate current regulation. The Efciency Optimizer injects a current
into the boost regulator FB input node to reduce the boost regulator output voltage.
The Efciency Optimizer has two modes of operation, initial calibration and auto calibration. Initial calibration happens at turn-on and
optimizes boost regulator output voltage. Auto calibration happens once per second to re-optimize the boost output voltage in response
to changing LED forward voltage due to aging or temperature effects.
8.9 Fault Monitoring and Auto-handling
The MSL3080 includes comprehensive fault monitoring and corrective action. The LED current regulators are monitored for LED string
open circuit and LED short circuit faults. It also monitors the boost regulator for output over-voltage. Strings with LED Short Circuit or
Open Circuit faults are turned off and ignored by the Efciency Optimizer.
FLTB sinks current to GND when a fault is detected. The Boost Over-Voltage Fault does not latch, the fault goes away when the fault
condition no longer exists and FLTB is released; all other faults latch. Clear faults by toggling EN low and then high, or by cycling input
power off and on. Additionally, fault control is available through the I
2
C compatible serial interface; see the “MSL3040/50/60/80/86/87/88
Programming Guide” for information.