MSL3086-IU Atmel, MSL3086-IU Datasheet - Page 14

• Manufacturer Part Number: MSL3086-IU
• Description: LED Lighting Drivers 8-Str LED Driver Internal Boost Cntr
• Manufacturer: Atmel

Specifications of MSL3086-IU

• Rohs: yes
• Input Voltage: 5 V
• Operating Frequency: 200 Hz
• Maximum Supply Current: 18 mA
• Output Current: 350 uA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: VQFN-24
• Minimum Operating Temperature: - 40 C
• Power Dissipation: 1850 mW

8.5 Gate Driver
8.6 Soft-Start
8.7 Boost Fault Monitoring and Protection
8.8 LED Current Regulators and PWM Dimming Modes
8.9 Efficiency Optimizer (EO)
8.10 Fault Monitors
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 rectifier 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.
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-configured 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.
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 fixed threshold voltage across the current sense resistor, thus the current limit is set 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.
The MSL3086/88 include eight open-drain LED current regulators that regulate 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 control the Efficiency Optimizers which in turn controls the
boost regulator output voltage to minimize LED voltage while maintaining sufficient headroom for LED current regulators.
The LED regulation current is set by a single resistor from ILED to GND. LED dimming is by PWM, and is controlled by default through
an external signal(two signals in the case of the MSL3088), or optionally by internal registers accessed through the I
interface (for interface information see the MSL3040/50/60/80/86/87/88/89 Programming Guide). LED drive dimming signals are phase
shifted, where LED string on-times are successively delayed by 1/8th cycle from STR0 to STR7, reducing boost regulator transient
response and increasing the transient frequency of the boost regulator. The MSL3088 features synchronized dimming mode where
separate PWM and SYNC inputs control PWM dimming duty cycle and frequency.
The efficiency optimizer monitors LED strings and controls the boost regulator output voltage to minimize LED current regulator overhead
voltage while maintaining sufficient voltage for accurate current regulation. The efficiency optimizer injects a current into the boost
regulator FB input node to reduce the boost regulator output voltage.
The efficiency 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. The efficiency optimizer requires that strings have a minimum on-
time of 2µs for proper EO operations to maintain current regulation.
The MSL3086/88 include comprehensive fault monitoring and corrective action. They monitor the LED current regulators for LED string
open circuit and LED short circuit faults. They also monitor the boost regulator for output over-voltage. Strings with LED Short Circuit or
Open Circuit faults are turned off and ignored by the Efficiency 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
MSL3040/50/60/80/86/87/88/89 Programming Guide for information. For more information about string faults and automatic fault
handling see the section “Fault Monitoring and Automatic Fault Handling” beginning on page 15.
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
Atmel MSL3086/MSL3088 Datasheet
2
C compatible serial interface; see the
2
C compatible serial
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