80A H-Bridge  - Page 1
Forum section: electronics / projects

author: Nico1320
author_rank: Newbie
timestamp: May 17, 2025, 05:45:28 pm
content: Hi everyone,I'm currently building an H-bridge for a university project and planning to order the components soon. Before I move forward, I’d like to make sure I’m not overlooking anything that could cause issues, especially since this is my first time designing a high-power PCB.Here’s a quick overview of the main components I’m using:Gate driver: TI DRV8703MOSFETs: 16x Onesmi NVMJST3D3N04CSnubber network: 22nF + 4.7kΩ RCGate resistors: 4.7ΩBulk caps: 6x 470µF electrolytic and 22x 22µF X7R MLCC, 50VThe system is powered with 12/24V lead-acid / AGM. The power board is 6-layers, with the 2 ground planes on the inner layers. The driver board will likely use 2-layers.What’s currently concerning me is potential EMI coupling from the power board to the driver board, and inrush current due to the large total capacitance. I’d really appreciate any tips or suggestions!

author: johansen
author_rank: Super Contributor
timestamp: May 17, 2025, 06:11:38 pm
content: Where people usually go wrong is they don't understand that energy stored in the inductance follows the square of the current.I think that your capacitors are adequate to handle the ripple current, depending on the inductance of the battery, and although it would be difficult, you could get by with a 2 layer board for this circuit. 4 layers makes it easy, i don't see a need to do 6 layers. basically, switching 80 amps isn't a problem. take a look at some 1500 watt ebike controllers for inspiration lol. when you get into the 800 amp range, then removing the last 10 nanohenries with a 6 layer board becomes useful.your electrolytic caps will get warm before they explode, but even if they do, you probably have adequate ceramic caps to prevent over voltage spikes from destroying the driver, which again depends on the inductance of the battery.as for the emi getting to your driver board, emi probably won't be the problem here, if the switching speeds are slow enough to prevent high frequency emissions.however, what I can imagine going wrong: if you connect your driver board to the battery negative terminal, but you have several feet of wire from the battery negative lead to the H bridge, then what happens is you get a bad connection, the H bridge turns on and now its at +24 or +12 relative to the driver board. if the driver is grounded to both, then its going to be somewhere in the middle.so you need to make the driver board be the slave to the voltage at the H bridge, not the other way around, unless you use an isolated circuit that can handle the battery voltage plus the extra voltage from the load dump when the h bridge turned off because the driver board faulted.as i understand the datasheet, the voltage at SH1 and SH2, cannot go below ground more than -.3 volts. (in reality it will probably survive more than that)if that's a problem for your circuit, which i don't think it will be, you can add an extra schottky diode at the driver chip, and put like a 1 ohm resistor in the trace that connects the driver to the middle node of the switched H bridge. this resistor however will be added to the h bridge gate resistor, and it will also reduce the current flowing through the boot strap diode to charge up the driver. again, won't be a problem.basically if your shunt resistor is a big inductor, you'll have this problem.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 18, 2025, 06:27:22 am
content: H-bridgefor what? What are you actually doing?

author: Psi
author_rank: Super Contributor
timestamp: May 18, 2025, 07:04:19 am
content: Maybe consider moving the power and ground terminals to the middle so they are equally close to each fet bank, and splitting the caps between the left and right ends of the PCB.Just a thought. I'll let others confirm if its a good idea but afaik is always better to keep things symmetrical so the inductances are the same. Or as close as practical.