Power distribution test plan

Owned by Josh Rong
Last updated: Aug 22, 2020
3 min read

Purpose and Aim

Since the power distribution and selection are two separate boards now, Power distribution includes the load switch to control and monitor each output, therefore the power distribution test mainly tests for the following component function:

  • Load switch enabling

  • Load switch current sensing

  • Load switch current output

  • I/O expander pin out

Load Switch

There are three types of load switch on the power selection board, they are all have current sensing function but with different maximum current loading and number of output channels.

Load Switch

Suggested Max Current

Number of Channel

Load Switch

Suggested Max Current

Number of Channel

BTS7200-2EPA

1.2

2

BTS7008-1EPP

11

1

BTS7040-1EPA

4.5

1

To enable the current sensing function the diagnose pin must be set to high, which is taken care of in hardware by connecting the pin to a 3v3 train.

Load Switch Enabling

During normal operation the load switch is enabled by the I/O expander through I2C, but assume if there is no firmware or exists a hardware issue that cause the I/O expander to not work as intended it is also possible to enable it via soldering. To pull the enable pin high you can bridge enable pin with the diagnose pin which is connected to a 3v3 bridge.

The left picture shows the BTS7040-1EPA and BTS7008-1EPP, the right shows the BTS7200-2EPA. The red circle shows where you need to bridge with solder.

After powering the board, look for the LED around the load switch to see if it is enabled. The LED is highlighted in purple.

Load Switch Current Sensing

The load switch current sense is a analog output from IS pin. When the board is powered and hooked up to a e-load, you can prob the resistor highlighted by the red marker with respect to ground. Record the current sense output value with the e load current draw and load switch name in a table.

Load Switch name

Load Switch name

Current Sense Output (V)

E-Load Current draw (A)

 

 

 

 

 

 

Load Switch Current Output

Each load switch has its own maximum current output suggested in the datasheet, but from previous experiments it is found that the load switch can indeed maintain function at a higher current before shutting down. Find out what is the actual max current each type of load switch by slowly increasing the e load value until the load switch is no longer enabled, indicated by the LED.

I/O Expander Pin Out

Ignore this test for now the, because in the I/O expander footprint, the I2C SDA and CLK pin are flipped therefore making it not work.