Alot of questions, I'll try to answer all of them!
DonaldBecker wrote: ↑Mon Oct 07, 2019 5:50 pm
What injector drivers are you planning on using?
Why do you have freewheeling diodes?
Seems as I forgot to update the nmos specs to the drivers that I was thinking of using
The freewheeling diodes are just if you're using something that needs them.
DonaldBecker wrote: ↑Mon Oct 07, 2019 5:50 pm
Generally you don't want freewheeling diodes or snubbing circuits. They delay the injector closing by allowing the current to decay, and that delay introduces fueling inconsistency. Instead you want specialized drivers that have clamps -- they allow the low side voltage to spike to +40V-70V, then turns on the transistor just slightly to hold it there until the energy dissipates. That snaps the injector shut cleanly.
Plus drivers with clamping circuits also usually include other protection e.g. over-current and thermal. These often signal the fault by pulling the gate input low, so you need a larger gate resistor. But in exchange you generally don't need a pull-down resistor, as the gate doesn't "float" half-open.
Hmm, did not know. Thanks for mentioning!
DonaldBecker wrote: ↑Mon Oct 07, 2019 5:50 pm
Your "launch switch" input should have a high value resistor in series, and probably a diode in series. Imagine what will happen when 12V is applied. The diode clamp will vanish in milliseconds.
The launch switch is meant to pull down 5v via a high value resistor to gnd or supply 5v from sensor supply. Might be a dumb solution.
DonaldBecker wrote: ↑Mon Oct 07, 2019 5:50 pm
26pf seems a little high for the 8MHz crystal. Generally 12-20pf is appropriate for a regular crystal on a 2 layer board.
I followed ST's technical document on crystal design for the STM32 and this is the result I got.
DonaldBecker wrote: ↑Mon Oct 07, 2019 5:50 pm
Why did you select those specific gate drivers for the ignition? Local availability?
They already have pull-downs, and the series resistors are pointless.
Increase the physical size of the output resistors. Calculate their power burn when shorted to ground or +14V. If you know the coils you will be using, you are better off using a specific circuit (e.g. a PNP+diode) rather than gate drivers.
I chose the NCP81071B due to availability but thanks for mentioning the internal pull down, must have skipped that part.
I'm using the ESR03EZPJ101 (Digi: RHM100DCT-ND) which have a 1/4W power rating there, I've not updated the schematic in the first post yet.
DonaldBecker wrote: ↑Mon Oct 07, 2019 5:50 pm
Do you mean to specify a MAX9924 rather than the MAX9925? The '25 doesn't have the gain resistors on the opamp, expecting them to be provided externally.
You might consider switching to the lower cost dual-channel 9926, and configure the second channel with a different input structure. It's easier to change the config to use the second channel than change SMD resistors on the road.
You can omit the 10K pull-up on the output if you configure the input pin with internal pull-up.
Yeah it's a MAX9924 that's supposed to be used and this ecu won't be road driven so changing config isn't something to worry about. Totally forgot about internal pull-up of the STM32.
Thanks for correcting me, I really appreciate the help!