Complete guide to selecting buck converters and LDOs for drone power rails. TPS563201, TPS5430, MP2307, and LM3671 evaluated on efficiency, noise, and PCB footprint for 5V/3.3V FC rails.
Power Architecture on a Modern Flight Controller
A typical FPV FC takes 3S–6S LiPo input (12–25.2V) and regulates it to 5V for the FC MCU/IMU, 3.3V for sensors, and often 9–12V for video transmitters. Each rail has different noise and efficiency requirements.
5V Rail Design: TPS563201 Deep Dive
Texas Instruments' TPS563201 is the most popular single-IC solution for FC 5V rails in compact designs. At 3A output with a tiny 2×3 mm SOT-23-6 package, it fits on densely routed 30×30 mm FC boards.
| Spec | TPS563201 | TPS5430 | MP2307 |
|---|---|---|---|
| Input Range | 4.5–17V | 5.5–36V | 4.75–23V |
| Max Output Current | 3A | 3A | 3A |
| Switching Freq | 570 kHz | 500 kHz | 340 kHz |
| Efficiency (peak) | 95% | 93% | 92% |
| Package | SOT-23-6 | PowerPAD-8 | SOP-8 |
| Notes | Best for compact FC | Better for >4S input | Common in clones |
Inductor Selection for TPS563201
The datasheet recommends a 2.2–4.7 μH inductor. For RF-noise-sensitive FCs (IMU directly coupled to the same 5V rail), use a shielded ferrite inductor (e.g., TDK SLF6028T) to minimize EMI into the gyro noise floor.
3.3V LDO: The MCU Core Rail
Most FCs run a small LDO after the 5V buck to generate 3.3V for the MCU, avoiding switching noise on the digital core supply. The AP2112K-3.3V (600mA, SOT-23-5) is the standard choice — cheap, available, and adequately quiet.
Video TX Rail: TPS62110 and MP1584
The 9V or 12V video transmitter rail requires a higher-voltage buck. The TPS62110 handles 3S–6S input directly with adjustable output, while the MP1584 is commonly found on AIO FC boards due to its low BOM count.
Battery Voltage Sensing
For ADC-based battery voltage monitoring, use a simple resistor divider to the MCU ADC. Standard ratio: 10kΩ + 1kΩ gives a 3.3V ADC input at 36.3V max LiPo (6S charged). Add a 100nF bypass cap at the ADC pin for noise rejection.
Full Power Architecture for Modern Flight Controllers
A complete FC power supply system typically involves multiple stages:
- Stage 1: Battery to 12V — For 4S-6S builds, a first-stage buck provides regulated 12V for VTX and high-power peripherals
- Stage 2: 5V for FC and peripherals — The TPS563201 converts 12V or battery voltage to 5V for FC, receiver, camera, and OSD
- Stage 3: 3.3V for digital ICs — An LDO converts 5V to 3.3V for IMU, Flash chip, and other 3.3V digital logic
Common Power Rail Problems
Key failure modes and solutions:
- Brown-out resets under load: Check output capacitor ESR and bulk capacitance. Add 100 uF bulk cap near MCU VCC pin.
- Oscillation at light load: Add a minimum load resistor (1k-10k ohm) from output to ground, or select a buck IC with Eco-mode support.
- OSD noise: SPI bus noise from switching regulator. Add ferrite bead in series with 5V trace between VTX and FC power domains.
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