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X13 Distribution
| PCB Summary | |
|---|---|
| Vehicle | X13, ROV Triton |
| Contributors | Sam Kovnar |
| Predecessors | X12-Distribution |
| Success? | Yes |
Architecture Link
SID Link
REPO Link
The Distribution Board delivers input power to the Conversion Board, the Power Brick Boards, and the Backplane. It provides an ON/OFF signal to the power bricks once tether voltage reaches a certain level to turn them on. It uses an OR-ing MOSFET circuit to combine the voltages from the two bricks. It also has a reverse voltage protection circuit to prevent power issues with the tether.
It connects to the tether, Conversion Board, Power Brick Boards, and Backplane. It also has two connectors to power the ethernet switch, one which provides 48 volts and one which provides 5 volts.
48 volts are provided to each of the bricks via 2x5-pin SAMTEC connectors, one for positive and one for ground. 12 volts are provided from the bricks to the Distribution Board via 2x10-pin SAMTEC connectors, one for positive and one for ground. Each brick also connects to the Distribution Board via a 2x3 pin signal connector. These pins all have the same mated height of 25mm.
The Distribution Board connects to the Backplane via a 2x6 logic wire connector and an androgynous power connector.
The tether connects to distribution via a 1x6 connector.
What priorities did you have in your design? What design considerations did you have? What methodologies did you follow? (routing a differential pair, keeping something separate for isolation, etc)
Added current capacity, direct connection between Backplane and distribution. We also added a different OR-ing FET controller to combine the 12 volt supplies from the bricks and changed the threshold for the ON/OFF circuit to ensure that the bricks remained on at all times. The tether connector was changed, as was the connector to the ethernet switch.
Arrangement of the other boards affected both clearance constraints and connector positioning.
The reverse voltage protection circuit is modified from previous years to use an N-channel MOSFET instead of a P-channel MOSFET to have a lower voltage drop over it with the benefit of being cheaper and having the same part that can be used for or-ing.
The on/off controller circuits are taken directly from the LM5050-1 High-Side OR-ing FET Controller datasheet:
30 A of current at 48 V are received from the tether. Each brick board receives about half of the current (16 A) and sends 50 A at 12 V back to the Distribution Board. This current is then combined to send a maximum of 90 A at 12 V to the Backplane. Conversion sends and receives a much lower amount of current (about 1 A at 12 V, 3 A at 5 V, and 1 A at 3.3 V).
DATA, ALERT, CLK, ON/OFF, and C2 signals are sent and/or received between the brick boards and the Distribution Board. DATA, ALERT, CLK, and C2 are sent and/or received between the Distribution Board and the Backplane.
The LM5050-1 was used instead of the LM74610 due to functionality issues with the original component. The LM74610 is made to operate without and ground connector and gets power by turning the mosfet off for ~2% of the time and charging its capacitors with the forward voltage of the mosfet body diode. The LM5050 is better suited to our application as we use 12V and would like it on all the time as two must or at the same time.
Zener diodes were picked according to predicted voltage differences and accepted error margins.
Connectors were picked to match the amount of current flowing through them. Connectors are as follows:
INSERT TABLE
Why did you pick certain components for your board? (If you don't know the answer/were told, now is a great time to ask)
The clearance between the Conversion board and the Distribution Board required that certain tall components be moved farther to the left than would otherwise be necessary, namely the decoupling capacitor between +12 V and ground.
Because the goal of X13 was to increase the amount of current sent to the Backplane, other design features were compromised to maximize the amount of current flow, such as increasing the sizes of thermals.
Thermals were sometimes enlarged or omitted to maximize current transfer, which adversely affected ease of soldering. Small components connected to the large +48V and 48V_GND polygons were particularly difficult to solder.
The LEDs used to indicate ORing MOSFET activity malfunctioned and needed to be removed due to loading concerns.
There are 5 blocks of connectors used between the Power Brick Boards and the Distribution Board. This causes a significant amount of friction. As a result, a large amount of force is needed to separate the two, which can cause connectors to become bent.
There were minimal changes that had to be made due to mechanical concerns. Most integration difficulties were between the Distribution Board and other boards, due to the many different connections. Mounting holes were early additions in the design process and did not need to be moved.
The connectors between the Power Brick Boards and the Distribution Board are mated to ensure a 25mm space between the two boards.
A height significantly greater than 25mm would cause the Distribution Board to hit the subconn.
A height significantly less than 25 mm would cause the Backplane to be lower, resulting in the Electronic Speed Controllers hitting the Ethernet Switch.
The diodes and resistors used in the ON/OFF detection circuit were difficult to solder because they were connected directly to large traces which did not heat evenly. This caused the connections to be unstable and for the circuit not to function during initial tests.
The threshold voltage for the ON/OFF circuits was lowered during testing to ensure that fluctuations in the +48 V line would not cause the ON/OFF logic signal to transition during operation. During further pool tests, the lower voltage was still found to cause brown outs. So the on/off signal was shorted to ground and diodes were added to the schematic to latch the signal on once it turns on. A solder jumper was also added to easily short it to ground if needed. The rise time of the 48V rail was also measured and found to be faster than the minimum rise speed needed for good simultaneous turn on (see this picture and page 12 of the bricks datasheet). The bricks also start under no load and with sharing fets, so there's not a large concern of a super high load being placed onto one brick or damage.
- Merge the 5 connector blocks between the bricks and distribution into two 2x20 blocks
- Distance small parts (such as diodes) away from large polygons
Tether input 15 A * 3 pins = 45A which is well over the 30A needed. Distribution to bricks (can just link the bricks doc since the calculation is there) Samtec MPPT
- Distribution to backplane, see page 19
- Any fun side details
Search keywords.
The Distribution Board receives 48 V from the tether and sends it to the Power Brick Boards which provide a 12V supply to the Distribution Board. It sends this 12V supply to the Conversion Board which provides 5V and 3.3V supplies to the Distribution Board. The Distribution Board additionally provides 12V, 5V, and 3.3V supplies to the Backplane. Power supply or-ing is implemented on the Distribution board for the 12V supply from the bricks to achieve greater power output and redundancy.
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