Wiki Index / Hardware Interfaces / Rivian BVT Passive Board: BMS Interface

Rivian BVT Passive Board: BMS Interface_

Last updated by i5ys0p on October 18, 2026

History

Parsing content...

**Status:** Reverse-Engineering in Progress
**Applies To:** Rivian R1T / R1S Battery Modules

### Overview
The Battery Voltage and Temperature (BVT) passive board is the integrated monitoring circuit mounted directly to the Rivian battery modules. Instead of routing dozens of fragile analog voltage tap wires back to a central BMS, Rivian uses these passive boards to measure cell voltages and temperatures locally, digitize the data, and send it over a robust serial daisy-chain.

### Core IC: Analog Devices LTC6810-1
Based on visual IC identification, the Rivian BVT board utilizes two **Linear Technology / Analog Devices LTC6810-1** multicell battery stack monitors.

**Chip Specifications:**
*   **Cell Capacity:** 6 series-connected cells per chip (12 series cells monitored per BVT board).
*   **Accuracy:** < 1.8mV total measurement error (Automotive AEC-Q100 qualified).
*   **Balancing:** Internal passive cell balancing with programmable PWM.
*   **Auxiliary I/O:** 4 General Purpose I/O lines per chip (typically used by Rivian to read the module's thermal cooling plate thermistors).

### Communication Protocol: isoSPI
The presence of the 4-pin Molex connector and the `-1` variant of the LTC6810 confirms the communication protocol: **isoSPI** (Isolated Serial Peripheral Interface).

Standard SPI requires 4 wires (MOSI, MISO, SCK, CS) and is highly susceptible to electromagnetic interference (EMI) from inverter switching noise. Analog Devices' isoSPI translates those 4 wires into a 1Mb, 2-wire differential signal that can run over twisted pairs for up to 100 meters.

**The 4-Pin Molex Pinout (Theoretical):**
Because the LTC6810-1 is designed for a stackable daisy-chain architecture, a 4-pin connector on the board almost certainly handles the incoming and outgoing differential pairs linking the modules together.
*   `Pin 1:` isoSPI IN (+)  *(from Master BMS or previous module)*
*   `Pin 2:` isoSPI IN (-)
*   `Pin 3:` isoSPI OUT (+) *(to next module in the stack)*
*   `Pin 4:` isoSPI OUT (-)

*(Note: Exact pin mapping on the Molex connector requires continuity testing to the `IPA/IMA` and `IPB/IMB` pins on the LTC6810-1).*

### Interfacing with an Aftermarket VCU
To read this board directly using an aftermarket VCU:

**Hardware Required:**
You will need an **isoSPI Transceiver IC (like the LTC6820)**. 
1. The Teensy 4.1 sends standard SPI to the LTC6820 chip.
2. The LTC6820 translates the SPI into the 2-wire differential isoSPI signal.
3. The isoSPI signal connects to the `isoSPI IN` pins on the Rivian 4-pin Molex.
4. The Teensy can then request cell voltages and command passive balancing directly to the original Rivian BVT boards using standard Analog Devices C++ libraries.

▲ 0 Upvotes