Solution Description
This 75 W digitally controlled constant current LED driver consists of a PFC stage and two parallel DC-DC converters designed to work in transition mode (TM) to achieve optimized efficiency. The LED driver can dim the LEDs down to 0.5% of the maximum brightness level through both analog and digital approaches. The operation is flicker free across the entire dimming range using either of the dimming techniques.
The 32-bit STM32F071CB microcontroller implements digital power controls for both the PFC and DC-DC conversion stages, which is highly advantageous in terms of cost and flexibility compared with the standard design based on analog ICs.
A N-Channel 600 V MDmesh™ M2 Power MOSFET used in the PFC and DC-DC converters is a key design choice as it is tailored for optimal performance under light load conditions, which is desirable in dimming applications.
The PM8841 is the high frequency single channel low-side MOSFET driver employed in the PFC boost converter. The driver is specifically designed to work with digital power conversion microcontrollers such as the STM32 family. The PM8841 output can sink 1 A and source 0.8 A, which is well suited for the application.
The buck converter MOSFET is driven by the L6395 gate driver, whose high-side (floating) section is designed to withstand a voltage rail up to 600 V. The logic inputs are CMOS/TTL compatible down to 3.3 V for easy microcontroller/DSP interfacing.
The inverse/modified buck converter is driven by the flexible, high-frequency dual low-side PM8834 driver, specifically designed to work with high capacitive MOSFETs and IGBTs. Both PM8834 outputs can sink and source 4 A independently. The second channel of PM8834 is used for 0-10V dimming function.
The microcontroller and the gate driver section are supplied through a VIPer012LS 60 kHz high voltage off-line converter, which manages the auxiliary SMPS in flyback topology.
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Key Product Benefits
STM32F071CB - High performance MCU
The STM32F071 microcontroller incorporates the high-performance Arm®Cortex®-M0 32-bit RISC core operating at up to 48 MHz frequency, high-speed embedded memories (up to 128 Kbytes of Flash memory and 16 Kbytes of SRAM), and an extensive range of enhanced peripherals and I/Os. This device offers standard communication interfaces (two I2Cs, two SPI/one I2S, one HDMI CEC and four USARTs), one 12-bit ADC, one 12-bit DAC with two channels, seven 16-bit timers, one 32-bit timer and an advanced-control PWM timer. Thanks to advanced timer, the solution implements LED dimming down to 0.5% level of the maximum brightness.
PM8841 - High efficiency low-side driver
The PM8841 is a high frequency single channel low-side MOSFET driver specifically designed to work with digital power conversion microcontrollers. The PM8841 output can sink 1 A and source 0.8A. The input levels of the driver are derived by the voltage present at the IN_TH pin (between 2 V and 5.5 V). This pin is typically connected at the same voltage of the microcontroller supply voltage. The PM8841 device includes both input and output pull-down resistors. UVLO circuitry for input and output stages prevent the IC from driving the external MOSFET in unsafe conditions. The device is available in SOT23-5 small package.
L6395 - High Voltage gate diver
The L6395 is a high voltage device manufactured with the BCD™ “offline” technology. It is a single chip high and low-side gate driver for N-channel power MOSFETs or IGBTs. The high-side (floating) section is designed to withstand a voltage rail up to 600 V. The logic inputs are CMOS/TTL compatible down to 3.3 V for easy microcontroller/DSP interfacing.
PM8834 - Dual low side driver
The PM8834 is a flexible, high-frequency dual low-side driver specifically designed to work with high capacitive MOSFETs and IGBTs. Both PM8834 outputs can sink and source 4 A independently. A higher driving current can be obtained by connecting the two PWM outputs in parallel. The PM8834 provides two enable pins which can be used to enable the operation of one or both the output lines. Both lines are used in this specific solution, one to drive the low-side MOSFET of the inverse buck, and one for the 0-10V dimming operation. The PM8834 works with a CMOS/TTL-compatible PWM signal. The device is available in an SO8 or an MSOP8 package with an exposed pad
VIPer012LS - High voltage converter
o The VIPer012 is a high voltage converter smartly integrating an 800 V avalanche-rugged power MOSFET with PWM current mode control. The power MOSFET with 800 V breakdown voltage allows the extended input voltage range to be applied, as well as the size of the DRAIN snubber circuit to be reduced. This IC meets the most stringent energy-saving standards as it has very low consumption and operates in pulse frequency modulation under light load. The design of flyback, buck and buck boost converters is supported. The integrated HV startup, sense-FET, error amplifier and oscillator with jitter allow a complete application to be designed with the minimum number of components.
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All Features
- Wide input voltage range 85 – 265 VAC
- Transition Mode PFC
- Two constant current outputs working in transition mode based on different topologies:
- Buck topology
- Inverse buck topology
- Output current: 500 mA ±2.5%
- Number of LEDs connected at output: 16 – 24 white LEDs (3.3 V each)
- PFC > 0.97 and THD < 20% at full load with input voltage 85-265 VAC
- Peak Efficiency at maximum load ≅ 91%
- Comprehensive safety protections:
- Open/no-load circuit protection
- Short-/overload circuit protection
- Soft start implementation
- LED dimming range: 0.5% to 100%
- Analog dimming
- Digital dimming
- Dimming control options:
- Push button
- 0-10 V input
- Meets IEC55022 Class B EMI Standard
