A humanoid robot with 30–40 joints draws 2–5 kW peak power from a 48V lithium-ion battery pack. The BMS/power management PCB manages battery monitoring, cell balancing, power distribution to servo drivers, and system-level power sequencing — all while fitting within the robot's torso alongside compute and sensor boards. This article covers the PCB design for robot power systems, with a focus on TI's BMS solutions.

Battery Architecture

• Pack voltage: 48V nominal (13S or 14S Li-ion configuration). 36–58.8V operating range. Capacity: 1–3 kWh (20–60 Ah) for 1–2 hours of operation

• Cell type: 18650 or 21700 cylindrical Li-ion (NCA/NMC). High discharge rate: 10–20A per cell continuous. 13S × 4P = 52 cells for a 2 kWh pack

• BMS topology: Centralized (single BMS PCB) for packs with <20 series cells is simpler than distributed master-slave. For humanoid robots with 13S–14S, centralized is adequate

TI Battery Monitoring Solutions

• BQ76952 (3–16S): Integrated battery monitor, protector, and cell balancer. Supports up to 16 series cells directly. 16-bit ΔΣ ADC for cell voltage measurement ±5 mV accuracy. Integrated high-side FET drivers for charge/discharge protection. Passive balancing: 300 mA per cell

• BQ34Z100-G1: Fuel gauge (coulomb counter + voltage-based SOC estimation). Uses Impedance Track algorithm for ±1% SOC accuracy. Communicates battery state (%SOC, time-to-empty, SOH) to the main controller via I²C

• BQ25756: Buck-boost battery charger controller. 4.2–65V input, 1–14S battery. Integrated FET drivers for synchronous rectification. The robot's external charger connects to this controller

Power Distribution Network (PDN)

• Total peak power: 30 joints × 100W peak per joint = 3 kW peak. Continuous: 500–1,000W during walking

• 48V bus distribution: Star topology from the central power PCB to each servo driver. 14–16 AWG silicone-jacketed wires with XT30/XT60 connectors. Each servo has a local 48V → 5V/3.3V buck converter

• PDN impedance: Target <50 mΩ from battery terminals to the furthest servo. At 60A peak total current, 50 mΩ = 3V drop on a 48V bus — acceptable. IR drop minimized through heavy copper: 3–4 oz on power planes, 2 oz minimum on distribution layers

• Bulk capacitance: 4,700–10,000 μF (polymer electrolytic, 63V) at the central power PCB to handle load transients. Additional 100–470 μF at each servo driver for local decoupling

Hot-Swap and Protection

• Hot-swap controller: The main battery connector is hot-swappable — the robot's battery can be swapped without powering down (with a backup supercapacitor maintaining compute state). Hot-swap controller (e.g., TI TPS2492) limits inrush current to <20A over 5 ms

• Protection: Overcurrent (100A fuse or eFuse), overvoltage (58.8V clamp), undervoltage lockout (36V cutoff to prevent cell over-discharge), reverse polarity protection (P-channel MOSFET or ideal diode)

• Emergency stop: A dedicated emergency power-off (EPO) MOSFET or contactor disconnects all servo power within 10 ms of an E-stop trigger. Independent of the main MCU — hardwired logic

PCB Design

• Layer count: 6–8 layers. Heavy copper on power layers (3–4 oz). L2: GND (solid), L5: 48V distribution

• Thermal: Charge/discharge MOSFETs dissipate 2–5W each. Copper pours with thermal vias to both sides. Mounted near board edge for heatsink attachment to chassis

• Safety: Creepage 3.2 mm between 48V and SELV domains. Fused outputs for each servo power channel. Conformal coating for condensation resistance