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EPC9148 – 48 V Three-Level Synchronous Buck Converter

Part Number: EPC9148

Summary:

The EPC9148 demonstration board is an ultra-Thin, three-level DC-DC synchronous buck converter for high performance computing systems with 60V maximum input voltage, 12.5A maximum output current, 19V output voltage, measuring only 3.5 mm component height (5 mm height total including the printed circuit board) achieving a power density of 400 W/in³. It

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Digital Control Stage:

The default control system of the EPC9153 power module is a conventional average current mode control loop, consisting of an outer voltage loop providing the reference to an inner current loop based on the detected voltage error. The inner current loop then regulates the inductor current to correct the power delivered to the output, compensating the deviation of the voltage error. The current feedback is derived from a MCP6C02 shunt amplifier, sensing the voltage drop across a shunt amplifier located at the output of the converter. As the discrete current loop is based on selective sampling, the current feedback loop can track the effective average inductor current despite the fact that the feedback signal itself is not precisely synchronous to the real inductor current but phase-shifted and with damped peaks.

For proper operation, this three-level topology relies on a symmetrical, accurately balanced flying capacitor voltage. This is achieved by tying in an additional capacitor balancing control loop compensating for shifts of the capacitor voltage. This is especially important when the duty ratio is not in a 50/50 range.

Converter Design:

The EPC9148 features the high-performance dsPIC33CK32MP102 Digital Signal Controller (DSC). This 100 MIPS single-core device is equipped with dedicated peripherals for Switched-Mode Power Supply (SMPS) applications, such as a feature-rich 4-channel (8x output), 250ps resolution pulse-width modulation (PWM) logic, three 3.5 Msps Analog-To-Digital Converters (ADC), three 15 ns propagation delay analog comparators with integrated Digital-To-Analog Converters (DAC) supporting ramp signal generation, three operational amplifiers as well as Digital Signal Processing (DSP) core with tightly coupled data paths for high-performance real-time control applications. The dsPIC33CK device is used to drive and control the converter in a fully digital fashion where the feedback loops are implemented and executed in software.

It also features one EPC2053 GaN FET, three EPC2055 FETs in the power stage, and three EPC2038 GaN FETs for the synchronous bootstrap gate drive circuits with the uPI Semiconductor uP1966A gate drivers. The board also includes on-board housekeeping power supply, digital controller, current and voltage sensing, and output filter. Kelvin sensing test points of the input and output voltages are provided for accurate efficiency measurement.

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EPC9148 – 48 V Three-level Synchronous Buck Converter
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Product Features

    Product Features

    o Input Voltage: 44-60 V DC
    o Output Voltage: 5-20 V DC (programmable)
    o Output Current: 12.5 A (max.)
    o Peak efficiency of 98%
    o 3.5mm component height (5mm total incl printed circuit board)
    o Industry standard footprint and pinout
    o Constant switching frequency:400 kHz

    Applications:

    o High Performance Computing – computers, displays, thin consumer electronics

Summary

The EPC9148 demonstration board is an ultra-Thin, three-level DC-DC synchronous buck converter for high performance computing systems with 60V maximum input voltage, 12.5A maximum output current, 19V output voltage, measuring only 3.5 mm component height (5 mm height total including the printed circuit board) achieving a power density of 400 W/in³. It features the high-performance dsPIC33CK Digital Signal Controller (DSC), 40 V EPC2055 and the 100 V EPC2053 and EPC2038 GaN FETs.

This reference design, uses a flying capacitor at the input side to half the input voltage, increasing the dynamic bandwidth of the converter while still using a simple, non-isolated topology. For this purpose, the classical half-bridge drive has been split into an upper and lower half-bridge sections allowing to flip the flying capacitor voltage in every switching cycle. This approach allows the usage of switching devices with lower voltage ratings which have lower on-resistance and are overall faster than their higher voltage-rating counterparts. As a result, the slightly increased losses accumulated during the charge periods of the flying capacitor are compensated by the lower commutation losses of the switch stage ending up at an equal to slightly higher total efficiency. Biasing the buck topology from the flying capacitor directly instead of the input also doubles the inductor ripple frequency and lowers the ripple current peak value. This allows using lower inductance and smaller output capacitance, which further minimizes the size and increases the power density in comparison to a conventional buck converter topology (see EPC9153 for comparison).

This driving scheme works best with low voltage Gallium-Nitride switches due to their high switching speed and very low internal capacitance. The digital control stage is key to apply the delicate switching pattern and runtime balancing of the flying capacitor voltage.

For more information on hardware related documentation, design files and purchasing information, please visit EPC’s product website:
EPC9148 – 48 V Three-level Synchronous Buck Converter