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DescriptionRear Power Distribution
Target releaseMSXIV
Epic
Document owner


Project leadsArshan Khanifar
Team members

Arshan Khanifar Rohan Gupta

Goals

  • Supply power to other components depending on the car's power states

Background and strategic fit

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CAN Communication

Different scenarios:

  1. Centre Console sends a message to turn on BMS Carrier
  2. Centre Console sends a message to turn on Motor Controller Interface/Pre-Charge

    1. Centre Console sends a message asking if DC-DC has connected
    2. Rear Power Distribution responds with a boolean

    1. Centre Console sends a message asking to close all switches
    2. Rear Power Distribution responds a boolean (represents whether there is a fault or not)

Requirements

  • Turn on BMS Carrier
  • Turn on Motor Controller Interface/Pre-Charge
  • Determine if DC-DC has connected (means power is being retrieved from Main Battery)
  • Close all switches connected to board
  • Determine if there are any faults with any of requirements above

Questions

QuestionAnswer
How do you control the rear lights?

The lights are controlled by the GPIO pins of the MCP23008 I/O expanders. These I/O expanders are accessible over the I2C bus. The two which control the rear lights are address 0x20 and 0x22.

The expander at 0x20 is used to set the diagnostic selection pins for the strobe light (GP1), rear brake lights (GP2), and rear turning lights (GP3)  - active high. 

The expander at 0x22 is used to enable each of the rear lights (GP2-7) - active high.

I/O Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/MCP23008-MCP23S08-Data-Sheet-20001919F.pdf

Power Switch Datasheet: https://www.infineon.com/dgdl/Infineon-BTS7200-2EPA-DS-v01_00-EN.pdf?fileId=5546d462636cc8fb016421e548a61215

How to control the power of each board?

We can't control how much current each board draw, that is determined by the board's current action but we can turn the power going to the boards on and off, this is done by using the load switches. To turn on the load switch, an enable signal (high) need to be send to the load switch enable pin this allows the boards to get power. The controller board controls the load switch through I/O expanders explained on previous question.


2ch load switch: https://www.infineon.com/dgdl/Infineon-BTS7200-2EPA-DS-v01_00-EN.pdf?fileId=5546d462636cc8fb016421e548a61215

What are the incoming CAN messages?
What are the outgoing CAN messages?
How do you manage power when the car turns on?
How do you manage power when the car turns off? 
What is still powered when there's been a BMS fault?
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