Why the 5V Buck Design Matters
Flight controller power supply design is underappreciated. An unstable 5V rail causes MCU brown-outs during hard maneuvers when battery voltage sags. High-frequency switching noise couples into your SPI IMU lines and corrupts gyro readings. Poor layout creates ground loops that appear as unexplained OSD flickering.
The TPS563201 from Texas Instruments is a 3A synchronous buck converter specifically designed for compact, efficient power supplies in industrial and consumer electronics — making it a natural fit for FPV flight controllers running from 3S–6S LiPo batteries.
TPS563201 Key Specifications
| Parameter | Value | Notes |
|---|---|---|
| Input Voltage | 4.5V – 17V | Covers 3S–4S LiPo direct; 6S needs pre-regulator |
| Output Current | 3A continuous | Peak 4A; adequate for full FC stack |
| Switching Frequency | 570 kHz (fixed) | Above gyro noise band; below RF interference zone |
| Quiescent Current | 37 μA | Excellent for sleep/standby modes |
| Output Voltage | Adjustable (feedback) | Set with two resistors; typically 5.0V |
| Efficiency (peak) | 95% | Versus 40–60% for linear regulators |
| Package | SOT-23-6 | Tiny; hand-solderable |
| Enable Pin | Active high | For sequenced power-up |
Schematic Walkthrough: Standard 5V FC Application
A minimal TPS563201 5V rail requires just 6 external components:
- L1 (Inductor): 2.2 μH, 4A rated — see sizing below
- C_in: 10 μF / 25V ceramic X5R (2× in parallel for low ESR)
- C_out: 22 μF / 6.3V ceramic X5R (2× in parallel)
- R_top: 560 kΩ (feedback divider upper)
- R_bot: 180 kΩ (feedback divider lower for 5.0V output)
- C_boot: 100 nF (bootstrap capacitor; required)
The output voltage is set by: V_out = 0.8 × (1 + R_top/R_bot). For 5.0V output: R_top/R_bot = (5.0/0.8) – 1 = 5.25. Use 560 kΩ / 107 kΩ (use standard 110 kΩ for 4.96V) or 560 kΩ / 180 kΩ for slightly higher 5.04V.
Inductor Selection for Minimum Noise
The inductor is the single most important component for noise performance. Selection criteria for a 5V / 3A / 570 kHz design:
| Criterion | Calculation/Recommendation |
|---|---|
| Inductance | 2.2 μH (for ΔI_L = 30% at typical operating point) |
| Saturation current | ≥ 4.5A (1.5× max output; leave thermal margin) |
| DCR | < 50 mΩ (reduces conduction loss and heat) |
| Package | 3 × 3 mm shielded drum core (e.g., Würth 744043220) |
| Shielding | Shielded/semi-shielded only — open cores radiate switching noise into IMU |
Critical: Never use an unshielded inductor for this application. The magnetic field from an open drum core at 570 kHz will directly inject noise into nearby magnetometers and gyros. Use a molded-body shielded inductor like the Würth 744043220 or equivalent.
PCB Layout Rules for Minimum Noise
Layout has a larger impact on output noise than component selection. Follow these rules strictly:
- Hot loop minimization: C_in, Q1 (SW high-side), and the inductor form the primary switching loop. Keep this loop area as small as possible — target < 25 mm².
- Ground plane integrity: Use a continuous ground plane under the converter. Never cut the ground plane for routing. The switching return current creates a high-di/dt loop.
- Feedback network placement: Place R_top and R_bot close to the FB pin and route away from the SW node. Any coupling from the switching node to the feedback pin causes output voltage ripple.
- Isolation: If possible, place the converter in a separate zone from the IMU and MCU. Use ferrite beads in the 5V distribution trace if sensitive analog circuitry is present.
- Thermal via: Place 4–6 thermal vias under the SOT-23 exposed pad to the ground plane for heat spreading.
Alternative Buck ICs for FC Design
Several other buck converters are commonly used in FC designs, each with trade-offs:
| IC | Imax | Fsw | Vin Max | Notes |
|---|---|---|---|---|
| TPS563201 | 3A | 570 kHz | 17V | Best for 3S/4S; very compact |
| TPS5430 | 3A | 500 kHz | 45V | Suitable for 6S direct input |
| MP2307 | 3A | 340 kHz | 23V | Monolithic IC; popular in 4S builds |
| TPS54331 | 3A | 570 kHz | 28V | Higher voltage headroom vs TPS563201 |
Measured Output Noise Results
Using a Rigol DS1054Z with 100 MHz bandwidth and proper probe technique (ground lead minimized), a well-laid-out TPS563201 design typically achieves:
- Output ripple (peak-to-peak): 12–18 mV at 570 kHz switching frequency
- Transient response (0 to 2A step): < 80 mV overshoot, settling within 20 μs
- IMU gyro noise (measured via Betaflight blackbox): Equivalent to or better than linear regulator designs
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Submit RFQ Now →Frequently Asked Questions
No. The TPS563201 is rated for 4.5–17V input. For 6S applications (up to 25.2V fully charged), use the TPS5430 (45V rated) or TPS54331 (28V rated). Alternatively, add a 6S-rated primary buck to drop to ~12V, then a secondary TPS563201 stage for 5V.
Use a 100 MHz+ oscilloscope with the probe ground lead shortened to <2 cm (cut the standard ground lead and use a probe tip spring adapter). Measure at the output capacitor, not at the load. Check both AC-coupled peak-to-peak at the switching frequency and 100 MHz bandwidth broadband noise.
For the TPS563201, use ceramic X5R or X7R capacitors (not Y5V). Two 22 μF / 6.3V ceramics in parallel give effective capacitance with minimal ESR. Never use tantalum capacitors here — they can fail short-circuit under surge current conditions. A small 1 μF X7R in parallel reduces high-frequency impedance further.
Technically yes, but not recommended for performance builds. VTX transmit switching creates large current transients that couple back through the 5V rail into the FC. Use separate converters — one for the FC (MCU, receivers, IMU) and one for the video system. This significantly reduces OSD noise.
Suitable alternatives include: Coilcraft XAL4030-222, TDK SLF10145T-2R2N4R5-PF, Bourns SRR5028-2R2Y. Key specs to match: 2.2 μH inductance, ≥4A saturation current, ≤50 mΩ DCR, shielded/molded body, 3–4 mm footprint.