A tree can be long, tall with vibrant green leaves and mandarins because it has strong roots and a system that can deliver its nutrients effectively without overloading or bottlenecks.
The simple structure is that a stronger entity supports a smaller one and then repeats itself. The energy to make a leaf grow will be less than the one used for growing a branch (or so I think so as I am not a biologist). And as we can assume, a branch is capable of supporting a certain amount of leaves and fruits and of delivering the nutrients and water from the roots. I think I have never seen a healthy tree with a branch with too many leaves and fruits to the point of damaging the rest of the tree because of overweight or the energy demand of the leaves and fruits is too much.
From this quick analysis we can take that a properly designed system (such as a tree that has millions of years of evolution) has the following characteristics:
- The sum of all entities branching out from a point will never demand more than what the previous entity from that same point can deliver.
- There is a finite amount of entities that can branch out from another entity
OK so enough of me pretending to know about trees and let’s get into electronics 🙂
The purpose of the previous analysis and bullet points was to introduce you to one of the most important parts of your design: your powertree or more formally known as power planning.
What is a powertree?
A power planning analysis is both a diagram of the power nets and components and calculations of the current consumed by each device in an electronic circuit.
With the diagram, you can easily visualize how the different elements are distributed and from what supply are they hanging from.
With the calculations, you can determine how much current goes through each branch so you can design your voltage regulators, fuses, switches, PCB tracks and heat dissipation accordingly.
Why is this work product essential?
You need to design the roots of your tree strongly! if you don’t look properly into the power consumption of each component and how much they sum up, you might end up with a voltage regulator that cannot supply the required current. Resulting in a circuit that does not work properly and overheats.
Also, in most electronic products, you will have a requirement of maximum power consumption. With the data from the power planning analysis, you can easily calculate this number and apply power budgeting if required.
And finally, it is a clever way to visualize how your power nets and supplies are all interconnected, allowing you to implement changes easier.
Example of powertree diagram and analysis
The following is an example of a powertree diagram of the Mini Electronic Congas:
For this product, it is quite straightforward. There is only one power regulator and everything hangs from it. But if your design has a couple of regulators and power is drawn from different power lines in different locations this diagram could really help you to visualize this intricate and complex structure so it can be analysed properly.
For the analysis, because there are some calculations involved, it is recommended to use a spreadsheet software such as Microsoft Excel or Google Sheets.
Using your diagram, create tables with the following parameters:
Table1 [Name of the power regulator]
Function type: name of diagram block, ex. DAC
Part: component part number, ex. WM8727
Quantity: number of these blocks present in the circuit
Current used by the device extracted from the datasheet or calculated
Total current consumption of regulator: the sum of all currents from components
Table2 [Total power consumption]
Sum of all power regulators current consumption
Currents from any device connected directly to the main power source
Power consumption calculation: power source voltage*total current consumption
Normally, I like to have 3 different tabs:
- Nominal consumption: in here you will use the values found in component’s datasheets for typical current consumption. This will serve to know the average expected consumption of your device.
- Worst case consumption: in here you will use the values found in component’s datasheets for maximum current consumption. This will serve to know the maximum consumption of your device and should be a starting point to select the maximum current of the voltage regulator used and thermal stress analysis.
- Sleep: some devices that require to always be on will have a low power mode or sleep state. In this state, most of the components are turned off so the consumption drops dramatically. You can calculate the device’s total power consumption using the powertree analysis.
If you would like to see an example and have a template of a powertree analysis there is a spreadsheet available in the Resources section to download.
In this article, we have seen that a powertree diagram and analysis is both a graphical representation and a calculation of our power nets and regulators to determine its power consumption in order to make sure we have not overloaded any component and that we have a sensible power consumption.
Do you know of any other method to analyse the power consumption of a device? Have you use it in a very complex system and found weakness in it? please share your thoughts below!
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