My Advanced Realistic Humanoid Robots Project

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• artbyrobot Posts: 83

  2026-01-17 05:20

  I was randomly talking to chatgpt about how I have been feeling burdened by having to make my own BLDC motor controllers for my robot lately and it randomly mentioned integrated half-bridge power modules as something I could use to cut down on my labor load in making these motor controllers. This immediately stood out to me as something I'd never heard of and something intriguing. I have so far been working on my lowside switch and highside switch which together form a half bridge. Many solder connections have been involved and alot of discrete components are involved. The concept of an integrated half bridge on a single chip - meaning two big power mosfets and all the drive circuitry for those power mosfets all condensed into a single chip would be a huge reduction in size and component count as well. So I researched if any are able to do 8v 30a for my 2430 BLDC motor's needs. Turns out there are some out there. At first I was looking at Texas Instruments CSD95377Q4M Half‑Bridge Driver (30 A) which can do 30a continuous so perfect for me. However, I didn't want to lock myself into a single vendor chip that may one day be discontinued. I prefer something ubiquitous with many competitors making it that can be purchased from aliexpress. Something commodity level. This way I future proof it and don't have to worry about any one manufacturer discontinuing parts I'm using and prices soaring because of that or simply the part becoming unavailable. So after a bit further digging I found CSD95481RWJ QFN chipset on aliexpress sold by several vendors and one was under $1 each. So it is equivalent to two power mosfets plus all drive circuitry for each power mosfet all for under $1. This one also has 60a continuous rating. It is only 5mm x 6mm in size which to me is insane. This is so much smaller than the setup I've been working on yet just as powerful. They are usually used for tiny buck converters and used directly on videocard PCBs and in servers and in automotive PCBs and much more. In any case, using 3 of these half bridge chips you can drive a BLDC motor. The consolidation of so many parts into such a tiny package is truly blowing my mind. So I ordered 60 of these chips - enough to drive 20 BLDC motors. I am leaning toward using these for all my motor controllers if working with them is easier than working with discrete components like I have been. They are cheaper to work with I think - I'd have to run the numbers on that though. They even have built in temp sensing we can read in which is a bonus. Their built in current sensing will not work for BLDC motors so I'll still need my shunt resistor current sensing circuit setup external to it but that's ok. All in all these appear to be a game changer in terms of reducing part count so less potential points of failure and also reducing board footprint so miniaturizing my electronics even more which is very good for us. I'm still needing to work out now how I want to hook these up in terms of PCB making for it and any discrete external components needed to support it. It is also top cooled which is interesting. I'm envisioning using silicone thermal adhesive to glue on a copper pad that has my braided solder wick wires already soldered to it. These will carry the heat away to my water cooled pipe system.

  

  I'm kind of amazed that nobody really seems to use these for BLDC motor controllers. They seem perfect for it. Maybe I'll start a trend. Assuming I don't find out the hard way why they are never used for this application!

  note: the full product title: "(5pcs)100% original New CSD95481RWJ 95481RWJ CSD59950RWJ 59950RWJ QFN Chipset"

  note: for my previous BLDC motor controller design I was needing to use 6 digital IO pins to drive a single BLDC motor controller's 6 power mosfets by way of their control circuitry. But for a BLDC motor controller design using 3 CSD95481RWJ H-bridge chips, I will only need to use 3 digital IO pins on the microcontroller. These CSD95481RWJ H-bridge chips use a pwm pin that is a tri-state pin - you can have high, low, and floating as the signal you send to it from your microcontroller. Digital output high and low are the usual digital output modes but the floating mode you do in your code by configuring the pin to be a digital input pin which makes it a floating pin. These 3 states fed into the chip makes it either give you V+ as its output or V- as its output or just off/floating as its output. This corresponds perfectly to the normal h-bridge 3 states we'd be using with our discrete components previous microcontroller design. So this savings in total digital I/O pin usage on the microcontroller means you can drive more motors per microcontroller in theory which is pretty cool.
• artbyrobot Posts: 83

  2026-01-18 08:30

  Well I deep dove into the CSD95481RWJ IC route. I estimate it will cut the work in half roughly for every motor controller made and cut the size taken up by about 60% compared to my previous discrete components approach.

  Now I will note that I did come across the BTN8982TA which is rated to 40v and can handle 30a continuous 50a peak short burst. But it's TO-263 form factor so about 4 times as big as the CSD95481RWJ. It also costs about $2 each so double the price. It's not a bad option though all things considered but just not quite as good as the CSD95481RWJ for the reasons mentioned. I note it here so I don't forget about it. It can be a great option if the CSD95481RWJ doesn't work out in the end or something.

  Anyways, for the thermal concern - which is my biggest concern, I plan to top cool the CSD95481RWJ using a .2mm plate thermal siliconed into place on top of the CSD95481RWJ and then solder a bundle of 4 braided solder wick wires to that and run that off to the water cooled copper pipe about 4" away. The top cooling only handles about 30% of the cooling according to chatgpt. The most important 70% is from the bottom cooling through its pads on its bottom. For this I plan to use double stacked .2mm thick copper plate soldered to its IC pads. So that's .4mm thick. Also it will be around 2mm wide where it attaches to the pads. It will then route out from under the chip and swing upward into free space and head over to the 8v+ and 8v- buses coming from the 8v motor battery banks in the robot's lower torso. These thick copper traces I will fork off of with braided solder wick wire right near the CSD95481RWJ IC chip for thermal conductivity reasons. This braided solder wick wire will be live so I will wrap it in fiberglass window screen so nothing can touch it - preventing short circuits. It will then be electrically isolated from where it connects to the water cooled copper pipe with thermal conductive tape. The braided solder wick wire attaching to these thick copper traces will be a bundle of 4 per trace. The various decoupling capacitors this chip calls for I will connect to its output pins using flat flex PCB DIY hand made. I'll be attaching this PCB first and attaching the thick copper traces to the underside pads second as a separate layer that goes underneath the flat flex PCB layer. The flat flex PCB layer will mostly stay around the outsides of the chip and have its center cut out and removed - the part of it that would get in the way of the underside main pads under the chip. So the flat flex PCB will just hug the outsides of the IC mainly in a U shape around the chip leaving the center of the bottom of the chip free to solder to with my thick copper traces.

  Note: the thick copper traces will be cut out with scissors from a roll of .2mm copper sheeting I bought on amazon which I mentioned a few posts back. Double stacking it wil double its thickness and increase its conductivity both electrically and thermally.

  Note: in a usual setup with this CSD95481RWJ IC, a multilayer board with a array of vias is used to bring the heat downward off the chip and into another lower layer within the multilayer board where it can then radiate on said layer outward in every direction. In my approach, I use thicker traces than the layers of a multilayer PCB has so I have alot more local copper in play. Then instead of the heat transferring down and then outward in all directions on very thin copper, mine travels down then in a single direction outward away from the IC on that trace. The trace will need to be as wide as possible as soon as possible. I expect to get it from 2mm width - the width of the pad - to 5mm width within a few mm. This rapid transition to a wider width combined with the use of much thicker copper compared to a multilayer PCB's copper thickness of its layers means I should be able to exceed the thermal performance of a multilayer board using my approach. Especially since I also plan to quickly fork off the main traces with bundles of 4 solder wick wire braids that will carry the heat off to a water cooled pipe 4" away.

  Note: in my attached schematic I only show a single CSD95481RWJ IC because they are all wired up the exact same way. It's just doing it 3 times for each of the 3 phase wires of the BLDC motor.

  Note: I will use a single electrolytic capacitor per motor controller also not pictured in the schematic.