Project Owners: Mena Azab Mostafa Hussein Rayyan Mahmood
Requirements:
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Component Selection
Buck:
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Part Number | Price | Comments | |
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MAX5033DASA+ | Already in the bay TPS62932DRLR | $1.09 | Buck IC |
RC0805FRRC0603FR-071ML0716KL | $0.1615 | R1R7(1MΩ16kΩ) - Upper Lower resistor in Feedback voltage divider; by Vin | |
RC0805FRRC0603FR-07130KL0749K9L | $0.1615 | R2R6(130KΩ49.9KΩ) - Lower Upper resistor in Feedback voltage divider; by Vin | |
CL10B104KB8NNNCGCM188R71H333KA55D | $0.15 | CVD & CBST - 0.1µF x2 | |
TYS8040151M-10 | $1 | L1 (150µF) - Inductor | |
GRM21BR61H106KE43L | $0.44 | Cin(10µF) - Ceramic Cap , 50V | |
TR3D476K016C0100 | $2.14 | Cout(47uf @ 100mOhm ESR) - Tantalum | |
B240A-FDITR-ND | $0.63 | D1 - B240/A recommended by datasheet | |
RC0805FR-1324KL | $0.16 | R3(24kΩ) - Upper resistor in feedback voltage divider | |
RC0805FR-0714KL | $0.16 | R4(14kΩ) - Lower resistor in feedback voltage divider37 | Css (Soft-start Cap) - 33nF |
GCM188R71H104KA57J | $0.26 (x2) | CBST & Filtering Cap (0.1uF - 50V) | |
GCM32EC71H106KA03K | $1.22 (x2) | Cin(10µF) x 2 (since it is around 6.1µF at 25.3 Volts due to DC Bias) - Ceramic Cap , 50V (size 1210) | |
RC0603FR-0720KL | $0.15 | R2 (20 KΩ) UVLO | |
RC0603FR-07280KL | $0.15 | R1 (280 KΩ) UVLO | |
SRP3212A-3R3M | $0.41 | L1 (3.3uH - 3.1A) | |
GRM21BR61A476ME15K | $0.91 | Cout (47UF - 10V) |
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:
LMR54406 | TPS54302 | TPS563300 | TPS62932 | MAX5033 | |
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Vin Range (V) | 4 - 36 | 4.5 - 28 | 3.8 - 28 | 3.8 - 30 | 7.5 - 76 |
Vout Range (V) | 1 - 28 | 0.6 -26 | 0.8 - 22 | 0.8 - 22 | 1.25 - 13.2 |
Iout Max (A) | 0.6 | 3 | 3 | 3 | 0.5 |
Switching Freq. (kHz) | 935 - 1264 | 400 | 500 | 200 - 2200 | 125 |
Electrolytic/Tantalum Caps needed? (Y/N) | Ceramic | Ceramic | Ceramic | Ceramic | Tantalum |
Package Size | 8.12 mm² | 8.12 mm² | 3.36 mm² | 3.36 mm² | - |
Price | $1.55 | $2.42 | $1.03 | $1.09 | In the bay ($6.40) |
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:
LMR54406 | TPS54302 | TPS563300 | TPS62932 | MAX5033 | Max | |
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Vin Range (V) | 5 | 5 | 5 | 5 | 5 | 5 |
Vout Range (V) | 5 | 5 | 5 | 5 | 5 | 5 |
Iout Max (A) | 5 | 5 | 5 | 5 | 5 | 5 |
Switching Freq. (kHz) | 4 | 2 | 2 | 5 | 1 | 5 |
Electrolytic/Tantalum Caps needed? (Y/N) | 5 | 5 | 5 | 5 | 1 | 5 |
Package Size | 3 | 3 | 5 | 5 | 3 | 5 |
Price | 3 | 2 | 5 | 5 | 5 | 5 |
Totals | 30 | 27 | 32 | 30 | 25 | 30 |
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:
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MCU:
Part Number | Price | Comments |
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STM32L412KBT6 | Already orderd && in the bay | same mcu as 4s esc with same passives |
Current Sense:
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Part Number | Price | Comments |
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Already orderd && in the bay | same current sense IC as 4s esc | |
WSR31L000FEAD1CSA2512MR001F-T3 | $2$1.4151 | 1mOhms, 3W 6W shunt resistor |
CL10B104KB8NNNC | $0.15 (x2) | Bypass Cap and filter caps, 0.1uF x2 |
RC0603FRRC0603JR-0710KL07160RL | $0.1615 | Filter resistor, 10kOhms160 Ohms, 1/10W |
Gate Driver:
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Part Number | Price | Comments |
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DRV8328BRUYR | already ordered | same gate driver as 4s esc |
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Gate Driver Pins Connecting to MCU Pins (GPIO Connections):
Pins 18-20 (INHC, INHB, INHA): Control output of high-side FETs
Pins 21-23(INLC, INLB, INLA): Control output of low-side FETs
Pin 24 (nFAULT): Fault indicator output
Pin 25 (nSLEEP): When pulled LOW, device will go to low-power sleep mode.
MOSFET:
Calculations for decision matrix:
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Part Number | Price | Vds | Rds on ( |
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max) | Continuous Current |
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Output Charge (nC)
Gate Charge (nC) | Rise time | Fall time | Max Operating Temperature | Switching Transition Loss | Switching Loss | Conduction Loss | Temperature Rise By… [Base 25°C] | Comments |
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5. |
77 |
40V |
0. |
45mOhm @ 50A, 10V | 60A |
2.2
30V
8mOhm @ 10V
55A
129 nC @ 10 V | 6ns | 14ns | 175°C | 4W | 0.722W | 1.125W | 204.36°C | ||||||
5.36 | 40V | 0.55mOhm @ 100A, 10V | 62A | 170 nC @ 10 V | 13ns | 26ns | 175°C | 7.8W | N/A [datasheet missing Coss] | 1.375W | 142.76°C | ||
2.25 | 30V | 0.47mOhm @ 20A, 10V | 85.9A | 180 nC @ 10 V | 11ns | 11ns | 150°C | 3.3W | 0.369W | 1.175W | 89.89°C | ||
4.71 | 40V | 0.44mOhm @ 88A, 10V | 175A | 169 nC @ 10 V | 12ns | 24ns | 175°C | 1.1W | 0.687W | 4.536W | 168.66°C | ||
4.06 | 30V | 0.57mOhm @ 20A, 10V | 87A | 230 nC @ 10 V | 10ns | 15ns | 150°C | 1.375W | 0.7347W | 3.15W | 94.67°C |
MY SELECTION: SIR500DP-T1-RE3
Primarily for generally lower power losses and lower temperature rise.
Conduction Loss:
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Gate Charge Loss:
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