Project Owners: Mostafa Hussein Rayyan Mahmood

Requirements:

• Can take 6S voltage

• Can handle 50 A continuous

• Create block diagram

  • Show the high-level process of how the motor controller works from receiving a battery voltage to controlling the phases of the motor

• Create table for engineering decisions and tradeoffs for the following components:

  • MCU

    • We ordered an MCU that was to be used for the 4S ESC that was being designed, can potentially use this chip: https://www.digikey.ca/en/products/detail/stmicroelectronics/STM32L412KBT6/9656219

  • Gate driver IC

    • Does it have field-oriented control?

    • Does it have built in current sense? That would be extremely useful so that we don’t have to waste board space using a current sense amplifier and shunt

  • Power MOSFETs

  • Buck converter for MCU

  • Battery input connection type

  • PWM connection type

  • Programming pins connection type

Component Selection

Buck:

Buck Selection:

Re-evaluating the decision of going with the MAX5033DASA+ chip for the buck converter, mainly to reduce form factor while maintaining high efficiency.

Current Issue:

To optimize the circuit for the MAX5033DASA+ chip, specific requirements need to be considered for the output capacitor. The datasheet provides a specific range of frequencies for the zeros of the buck’s power stage which is controlled by the output capacitance and ESR. Furthermore, to optimize the capacitor selection for the proposed use case - 6S ESC, handing 6S lipo input, outputting 3.3V at 0.5 Amps - a tantalum or electrolytic capacitor is needed.

Additionally, operating at a fixed switching frequency, this chip forces a high inductance inductor to be used. The higher the inductance the larger the inductor.
Overall, the MAX5033DASA+ chip requires a large footprint to operate “optimally” for the restrictions desired.

Comparison Chart:

Note 1: All these chips have adjustable outputs using a feedback pin connected to a voltage divider.

Note 2: These (new) chips were selected for ease of use and available resources on their usage.

Decision Matrix:

Summary of Decision Matrix:

Each entry was given a max rating out of 5 to denote how “good” a chip using a score. Summing up all the scores for each chip, the one with the highest score would then be considered the “best” of this set of chips.

The logic behind scoring:

Vin Range (V): All components have a sufficient input range for a 6s Lipo battery (18 - 25.2 V)

Vout Range (V): All components have a sufficient output range for the desired application (3.3 V)

Iout Max (A): All the components satisfy the required output current (0.5 A).

Iq - Quiescent Current (mA): This is the current the buck draws when no load is applied / during idle. So here components were given a score, with the best score going to the chip with the lowest value.

Switching Frequency (kHz): This is the buck’s switching frequency. Having a higher frequency is good since it decreases the size of the inductor, however, that comes at the expense of switching losses. So here the components with a higher frequency have a higher score; especially those with a range of possible frequencies.

Electrolytic/ Tantalum Caps needed (Y/N): This is whether the buck will need a capacitor with a higher ESR value such that it can optimize the closed-loop stability of the power stage. Here all the chips that do not need such caps are given a 5 (all the newly selected ones) and those that need such caps are given a 1.

Number of pins: Not really a very big deal, but just the number of pins each chip has. Chips with fewer pins are considered better under the assumption that they are “simpler” but circuits for all of these chips are similar (same idea overall).

Price: Ranked the chips best on price, giving the MAX5033 a 5 since it is in the bay already.

Conclusion:

Given the current issues with the MAX5033 and evaluating it against other (similar) buck converter chips, it is evident that despite the advantage of already having the MAX5033, other bucks convert chips can satisfy the proposed requirements for the 6S ESC project while minimizing the buck converter circuit’s footprint on the PCB. Moreover, given the results from the Decision Matrix, the recommendation for the new buck chip is the TPS62932.

Plots used for buck selection:

MCU:

Current Sense:

Gate Driver:

MOSFET:
Calculations for decision matrix:

 MY SELECTION: CSD17577Q5A, primarily for generally lower power losses.

Conduction Loss:

Gate Charge Loss:

Output Capacitance Loss:

Switching Transition Loss: