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Mar 29, 2017, 07:46 PM
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# A simple 2 layer ESC and some rambings about a resistor.

This esc is an all nfet design similar to what you find in the blueseries escs or afro esc's or many others. How this design works is by using a simple charge pump arrangement to drive the gate of the upper nfet. Slow to turn on because the gate has to be turned on through a resistor that also limits the current while the gate is off. Fast to turn off.
Because the gate is in the off state more than on, current is flowing through that resistor most of the time and because of the thermal limits of the resistor.. This will be the limiting factor for this type of esc high side turn on time. Knowing this you can play around with the value depending on the voltage you intend to use. If you only need it to run on 2s then you can lower the value of this resistor and have a higher current to turn the gate on.
This goes for all ESC's using this type of nfet charge pump drive. R29 in this picture below.

The common value chosen is 2200Ohms by most manufacturers, this allows safe running at 16 volts. 16V / 2200 = 0.0072, i^2 * r = P = 0.11 Watts. This is even still slightly over the package 1/10 watt limit for 603 sized but under for 805 sized resistors. There is also a diode drop and the fact that its only conducting 2/3 of the time so its fine. If you only use it for 8 volts then you can lower the resistor. You cant just bypass the resistor out because then you would have a short from V to ground though the diode that charges the cap.

The low side switching time will be dependent on the mosfet choice and gate resistor. The Atmega has a current limit per pin of about 40ma as per datasheet so try and stay within that limit ( or close to).

To summarize the gates of this type of design have the following drive currents with and example of 2200Ohm resistor.
Upper Nfet On -- 0.0072 or 7.2 mA. Limited by the resistor 29
Upper Nfet Off--- limited only by transistor current limit.
Lower Nfet On/Off- 40 mA -- with 5v gate drive

Anyway, rambling too much.. this board has the same-pinout as the blueseries, all 805 bits, not for a quad ( its pretty huge). The schematic is really pretty basic but I never actually cleaned it up so i'll include the diptrace files again if someone wants to take a look. ( you can look online for examples of the nfet design too , they are all the same really) You can use the freeware version of diptrace to view/edit this. Its big but its two layer and an easy board to solder. I use it with simonk firmware with reverse enabled on my rc truck but will work with Blheli as well, treat like a blueseries 30A ESC. I have no idea how much current it can handle but the pours are pretty wide.

The mosfets I use are PSMN1R2-25YDL. Any of the power lfpak56 mosfets will work ( there's a lot to choose from). To keep a reasonable switching speed I aim for mosfets with a gate charge of less than 35nC at 4.5v.

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