Senior/Staff Firmware Engineer - Battery Charger

1X Technologies AS•San Carlos, CA

About The Position

We are looking for a cross-functional Firmware / Embedded Engineer to develop and maintain the firmware for the battery charging system of a production humanoid robot. In this role, you will own the embedded software that controls AC-DC power conversion, charge profile management, and the interface between the charger and the battery management system. You will work closely with hardware architects, electrical engineers, systems engineers, and test engineers to ensure firmware reliably bridges hardware capabilities and higher-level system requirements across prototype and production platforms. The charger is a consumer-facing subsystem that must meet regulatory emissions requirements, operate safely in household environments, and manage the charge cycle for a high-energy lithium-ion pack that experiences demanding discharge profiles between charges. Charging behavior directly affects battery longevity, system availability, and user safety. The ideal candidate understands power conversion from magnetics and control loop fundamentals, writes firmware that is robust under component variation and fault conditions, and can reason about the interactions between charger behavior, battery chemistry, and EMC performance.

Requirements

Bachelor’s or Master’s degree in Electrical Engineering, Computer Engineering, or a related field
7+ years of industry experience with embedded systems and real-time firmware development
Proficiency in C and C++ for embedded targets
Production charger or power converter firmware experience — the candidate has developed or substantially modified firmware controlling an AC-DC or DC-DC power converter in a shipped product. Experience should include closed-loop regulation, protection logic, and charge profile implementation, not solely integration of a digital power controller evaluation board.
Power conversion fundamentals — working understanding of switched-mode power supply operation: common AC-DC topologies (flyback, LLC, phase-shifted full bridge), power factor correction stages, transformer isolation, and how firmware-controlled parameters (switching frequency, duty cycle, phase shift) affect converter behavior
Battery charging knowledge — understanding of lithium-ion charge protocols (CC-CV, multi-stage), the relationship between charge rate and cell degradation, and how temperature and cell age affect charge termination criteria
Embedded bus fluency — hands-on CAN implementation for charger-to-BMS coordination, plus additional embedded interfaces (SPI, I²C, UART) for communication with power controller ICs, monitoring devices, and auxiliary circuits
Hardware debug at the firmware boundary — experience using oscilloscopes, current probes, and power analyzers to diagnose problems that span firmware control behavior, converter waveform quality, and thermal performance
Schematic literacy — ability to read power stage schematics (switching FETs, gate drivers, magnetics, snubbers, feedback networks) and understand how firmware interacts with the physical circuit
Comfortable debugging firmware on real hardware using standard lab tools
Ability to collaborate closely across hardware, systems, and software teams

Nice To Haves

First-principles problem solving — a track record of approaching power conversion and charging problems from circuit and control theory fundamentals rather than relying solely on vendor reference designs or digital power controller auto-tuning tools
EMC and regulatory compliance — direct experience with charger or power supply products that required FCC Class B, CE, or equivalent emissions certification. Understanding of how firmware decisions (switching frequency selection, spread- spectrum modulation, burst mode behavior) affect compliance test results.
EV charging or high-power battery chargers — experience at automotive charger suppliers, EVSE manufacturers, or industrial battery charger companies where charge power exceeds 500W and regulatory, thermal, and reliability requirements are demanding
Consumer electronics power systems — experience with UL/IEC 62368-1, IEC 61000 series, or similar consumer safety and EMC standards, where the charger must operate safely in a household environment with untrained users
Power factor correction firmware — implementation of active PFC control loops (boost, bridgeless, totem-pole) in firmware, including transient response tuning and THD optimization
Digital power control — experience implementing compensator algorithms (PID, type-II/III) in firmware for voltage and current mode control of switched-mode converters, including discrete-time loop design and stability analysis
Thermal management firmware — experience with firmware-controlled thermal derating, fan speed management, or power limiting based on real-time temperature monitoring of power stage components
Experience contributing to hardware architecture or system-level design decisions
Familiarity with real-time operating systems (FreeRTOS, SafeRTOS, or similar)
Experience supporting hardware through prototype and production phases

Responsibilities

Develop and maintain charger firmware controlling AC-DC power conversion stages, including power factor correction and isolated DC-DC conversion topologies
Implement charge profile management for multi-series lithium-ion packs: constant- current, constant-voltage, and taper phases with cell-chemistry-appropriate voltage and current limits
Architect the charger-to-BMS communication interface over CAN or similar embedded bus, coordinating charge current requests, pack voltage feedback, temperature limits, and fault signaling between the two subsystems
Responsible for the testing, validation, and verification of initial firmware releases to ensure functionality, reliability, and performance requirements are met
Implement power converter control loops in firmware: voltage regulation, current regulation, and soft-start sequencing with stability under varying line and load conditions
Develop fault detection and protection firmware: input overvoltage/undervoltage, output overcurrent, overtemperature, ground fault, and loss-of-communication with the BMS, each with defined safe-state transitions
Support EMC compliance by understanding how firmware-controlled switching frequencies, gate drive timing, and measurement sampling interact with conducted and radiated emissions performance
Collaborate with hardware architects to define charger hardware requirements, converter topology trade-offs, and the boundary between hardware protection and firmware protection
Implement production test modes and end-of-line validation routines for charger acceptance, including efficiency measurement, regulation accuracy, and protection trip- point verification
Develop diagnostic logging and telemetry for charge cycle data, fault history, and component health trending
Document firmware architecture, interfaces, and assumptions; improve code structure, readability, and maintainability