DC-DC reference board design for e-mobility

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EPC, in collaboration with MPS, has announced EPC9165, a 48-14V two-phase two-phase converter that operates at 97% peak efficiency at a small size. This solution is suitable for 48V batteries with high density and high power, such as those used in e-mobility market. According to the EPC, the system is scalable; for 4 kW two converters can be parallel, for 6 kW – three converters; or for 1 kW only one phase can be used. The output voltage in this program, which was reported in a press release, is 14 volts. The architecture, however, can be modified to support a wide range of input voltages from 12 to 36 volts because it is a rigid switching topology with adjustable output. The compatible controller module (EPC9528) includes a 16-bit Microchip dsPIC33CK256MP503 digital controller. Most analog controls are incompatible with GaN FETs, which requires additional circuits to match the shutter driver behavior. Digital solutions offer a simple and effective way to implement advanced power and temperature protection features in particular. In addition, digital control, such as dSPIC33CK, makes it easy to dynamically adjust downtime and extend designs from single-phase to multiphase.

Cecilia Contenti

Cecilia Contenti, vice president of strategic marketing at EPC, said bi-directional converters 48-12V or boost or boost are common to e-mobility, micro EV, lightweight mobile devices where the power is 2-2.5 kW. and soft hybrid cars with power up to 4 kW. One example is the “city car” which has 2 kW of power. Compared to the Si MOSFET solution limited to 100 kHz, the GaN solution can run at 500 kHz, while allowing more power per phase (due to less inductance and more current in the same inductance form factor). Overall, the solution is 58% smaller and lighter, the efficiency is> 97% peak versus 95% Si MOSFET (with the same type of inductor), and, thanks to the excellent thermal and GaN efficiency, water cooling is not required, “said Content.

Features of the board

The EPC9165 reference design board consists of an EPC2302 GaN FET in a QFN enclosure that uses the latest generation EPC 100 V GaN technology. The device provides approximately 101 A DC and 408 A Pulse. The package offers a radiator thermal resistance of 0.2 degrees C / W, a typical RDS (on) 1.4 mО and a typical QG of 23 nKl.

Thermoregulation is crucial to ensure proper and consistent operation. Even with the radiator installed, sufficient cooling is required for this module to operate in the entire specified output current range. According to the EPC, an installed radiator is needed to adequately dissipate the heat generated to the environment. As shown in the manual, the Wakefield 567-94AB heatsink can accommodate a 1 mm high SMD threaded M2 spacer board, leaving a 0.3 mm gap between the FET and the heatsink. Thermal conductivity is high. Strong thermal conductivity through a gap of 0.3 mm provides T-Global A1780 TIM 0.5 mm thick. The pre-installed heatsink and TIM materials (Figure 5) provide adequate cooling for testing (Figure 2).

View of the board from above and below
Figure 1: Top and bottom board view (Source: EPC)

The EPC9165 reference design also consists of a new MPS MPQ1918 100V half-bridge driver designed specifically for use with GaN FET. The MPQ1918 is available in a 3Q3 mm FCQFN enclosure with a 1.6 A peak current and a 0.2 ohm / 1.2 ohm pull-up / pull-up resistor to enable powerful FETs.

3d circuit board model
Figure 2: TIM and radiator installation shown (Source: EPC)
Overview of the functional flowchart
Figure 3: Overview of the functional block diagram of the EPC9165 board (Source: EPC)

To optimize performance, the driver must be optimized GaN devices and many companies offer drivers optimized for GaN. Optimization includes: 5 V gate drive voltage, high load voltage “clamp” to avoid overcharging the charging capacitor to more than 6 V, pin phase node with a negative voltage of about -3 V, low voltage lock set to 3.6V for disconnection and 4.0 V for switching on, high power dv / dt for switching unit:> 100 V / ns typical, up to 200 V / ns may be desirable; dead time control is ideally less than 10 ns, ”Contenti said. In addition, according to the EPC, the use of the MPS 100 V gate driver not only provides increased power density, but also simplifies design in critical conditions such as electronic mobility.

The EPC9165 includes 5V and 3.3V logic power supplies. It also provides power to the controller card via an extreme connector. The output current of the inductor and the input current are measured using a 0.2 mО resistor and a 50 V / V amplifier. Thus, the sense gain current is 0.01 V / A. Input and output voltages are measured using divider network resistors (100 k and 5.36 k), the gain is 0.05087.

“A shunt is located between the inductance of the main filter and the low voltage terminal. Due to the high current, a very low resistance of only 200 μО is used, which allows to keep the losses as low as possible without compromising the signal-to-noise ratio. The shunt voltage is amplified by a high-voltage shunt amplifier (65 V) that maintains a low number of components, takes up the smallest area, and has sufficient bandwidth for the converter. Due to the high switching frequency, the shunt inductance becomes an important factor in the design, primarily the reverse current path. Additional attention was paid to minimizing this inductance in the layout, and it was further compensated by using passive integration techniques to eliminate this inductance in a manner similar to DCR current sensing techniques. The complete combination provides a high-performance current sensing system, which in combination with a digital controller can easily exceed the 8 kHz control band, ”concluded Contenti.

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DC-DC reference board design for e-mobility

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