NMEA2000 CAN Interface¶

Circuit Overview¶

This circuit provides a galvanically isolated NMEA2000 CAN interface for an ESP32-S3 microcontroller. The design converts 12V boat power to isolated 5V, then uses an isolated CAN transceiver to communicate with the NMEA2000 network while protecting the microcontroller from electrical noise and ground potential differences common in marine environments.

Power Supply Section¶

Input Protection¶

BOAT_12V Input: Raw 12V from vessel electrical system
D16 (1N5819WS): Schottky diode for reverse polarity protection
D17 (SMBJ16CA): Bidirectional TVS diode for transient/surge protection
C7 (10µF): Input filter capacitor

Isolated DC-DC Converter (U11 - MCP3610AGQV-P)¶

Function: Isolated buck converter generating 5V_ISOLATED from protected 12V input
Isolation: Galvanic isolation between input (boat 12V system) and output (vessel CAN ground)
Switching Elements: Internal power MOSFETs on pins 6, 5, 4, 19 (SW nodes)
Bootstrap: Pin 11 (BST) provides gate drive for high-side MOSFET
Power Good: Pin 10 (PG) indicates output regulation status

Voltage Control Circuit¶

FB_MPM: Feedback voltage divider output that sets the target voltage for U11 buck converter
R40 (100k, 1%): Upper feedback resistor
R17 (19.1k, 1%): Lower feedback resistor to ISOLGND_CAN
Target Voltage: Vout = Vref × (1 + R40/R17) where Vref is internal reference of MCP3610AGQV

Output Stage¶

5V_ISOLATED: Regulated isolated 5V output
C36 (22µF, 16V): Primary output filter capacitor
C35 (1µF): Secondary filter capacitor
ISOLGND_CAN: Isolated ground referenced to vessel CAN ground

CAN Transceiver Section¶

Isolated CAN Transceiver (U7 - ISO1050DUB)¶

Function: Provides 2.5kV galvanic isolation between ESP32-S3 and CAN bus
Package: 8-pin SOIC with isolation barrier between pins 1-4 and 5-8

Power Connections¶

Pin 1 (VCC1): 3V3 supply from ESP32-S3 side (non-isolated)
Pin 4 (GND1): Connected to system ground (GND)
Pin 8 (VCC2): Connected to 5V_ISOLATED
Pin 5 (GND2): Connected to ISOLGND_CAN (vessel ground)

Signal Connections¶

Pin 2 (RXD): CAN receive data output to ESP32-S3 (RXDCAN signal)
Pin 3 (TXD): CAN transmit data input from ESP32-S3 (TXDCAN signal)
Pin 7 (CANH): CAN High differential signal
Pin 6 (CANL): CAN Low differential signal

CAN Bus Physical Interface¶

Standard CAN Connector (U18)¶

Function: Standard NMEA2000 CAN cable connector
CANP: CAN Positive signal
CANN: CAN Negative signal
Connection: Differential 120Ω impedance CAN bus

Bus Termination¶

R37 (120Ω): CAN bus termination resistor
J15: Jumper connection (2.54-1*2P)
Pin 1: Connected to CANP
Pin 2: Connected to CANN (through 120Ω termination)
Usage: Short J15 if this device is the last node on the CAN bus

ESP32-S3 Interface¶

Digital Signals¶

TXDCAN: CAN transmit data output from ESP32-S3 to U7 pin 3
RXDCAN: CAN receive data input to ESP32-S3 from U7 pin 2
3V3: Power supply for MCU side of ISO1050DUB (from ESP32-S3 board)

Power Consumption Analysis¶

Standby Conditions (CAN bus idle, no traffic)¶

MCP3610AGQV (U11): ~2-5mA quiescent current
ISO1050DUB (U7): ~15-20mA total (both sides)
Total Standby: ~20-25mA from 12V input

Active Conditions (Normal CAN traffic)¶

MCP3610AGQV (U11): ~2-5mA + load current
ISO1050DUB (U7): ~20-25mA during transmission
Load Current: Depends on 5V_ISOLATED rail loading
Total Active: ~25-30mA from 12V input

Sleep Mode (NOT SUPPORTED)¶

MCP3610AGQV (U11): Can be shut down via enable control
ISO1050DUB (U7): Has standby mode capability
Potential Sleep Current: <1mA if properly controlled

Circuit Operation¶

Power Conversion Flow¶

BOAT_12V → D16 (reverse protection) → D17 (surge protection) → U11 input
U11 buck converter creates 5V_ISOLATED referenced to vessel CAN ground
FB_MPM voltage divider sets target output voltage for regulation loop
5V_ISOLATED powers vessel-side of U7 transceiver
3V3 from ESP32-S3 board powers MCU-side of U7 transceiver

CAN Communication Flow¶

Transmit: ESP32-S3 → TXDCAN → U7 isolation → CANH/CANL → U18 connector
Receive: U18 connector → CANH/CANL → U7 isolation → RXDCAN → ESP32-S3

Ground Isolation¶

ESP32-S3 Ground: Referenced to microcontroller board ground
ISOLGND_CAN: Referenced to vessel CAN network ground
Isolation: Complete galvanic isolation prevents ground loops

Key Specifications¶

Input Voltage: 12V nominal (9-16V operating range typical)
Isolation Voltage: 2.5kV (ISO1050DUB specification)
CAN Standard: NMEA2000 compliant differential signaling
Connector: Standard NMEA2000 CAN connector (U18)
Termination: Selectable 120Ω via J15 jumper
Power Efficiency: >80% typical for MCP3610AGQV buck converter

Component Summary¶

U11 (MCP3610AGQV-P): Isolated buck converter (12V → 5V)
U7 (ISO1050DUB): Isolated CAN transceiver
U18: Standard NMEA2000 CAN connector
D16: Reverse polarity protection diode
D17: Surge protection TVS diode
R37: 120Ω CAN termination resistor
J15: Termination enable jumper