Electrical Design Requirements

Status: Reference Version: v.0.1.0 Last Updated: 2026-08-16

1. Component Rules (The "Museum-Grade" Standard)

• Dielectric: X7R for all ceramic capacitors (Strictly no Y5V or Z5U).
• Derating: 2.5x Voltage rating for all power capacitors (e.g., 50V caps on 15V rails).
• Tolerance: 1% precision resistors for eFuse ladders and INA219 current-sense shunts.
• Vias: Teardrops on all signal/power vias; 0.3mm drill standard; VIPPO (Via-In-Pad) for high-density CM5/eFuse pads to prevent solder wicking.

2. I2C Bus Address Table

I2C Address	Device	Module	Function
0x09	LTC3350	Power Module	Supercap charger / health monitor
0x0B	Smart Battery	Power Module	Smart battery / SMBus monitor
0x28	STUSB4500	Power Module	USB-C PD Controller
0x38	PCA9534A	Cypher-Input (all variants)	Single fixed address (U4); variant identified via BOARD_ROLE_ID[3:0], not I2C address; Space + Enter GPIO on the 64-Character variant only - see Cypher-Input/Design_Spec.md §3a
0x3F	PCA9534A	Power Module	PM-local GPIO expander (POE_STAT, SYS_FAULT, BATT_PRES_N, USB_STAT, SW1 RGB control)
0x40	INA219	Power Module	5V_MAIN current/power monitoring (10mΩ Kelvin-sense shunt R16)
0x20	MCP23017	Stator	ENC monitor expander (U6)
0x21	MCP23017	Stator	Virtual keypress / SOURCE_SEL / CPLD_RESET_N expander (U7)
0x22	MCP23017	Stator	CPLD configuration output expander (U8)
0x23	MCP23017	User Settings Module	Switch input expander (U1)
0x24	MCP23017	User Settings Module	Bank 1 LED controller (U2)
0x25	MCP23017	User Settings Module	Bank 2 LED controller (U3)
0x45	INA219	Stator	Rotor stack power telemetry (CSS2H-2512R-R010ELF 10mΩ shunt R1)

Note: This document captures global electrical design rules. Board-specific design rules are in each board's Design_Spec.md. Full design decision history: See design/Design_Log/index.md.