Overvoltage limiter controller ( automotive / mega2560 ) - MAX6398 - Page 1
Forum section: electronics / beginners

author: misiek303
author_rank: Contributor
timestamp: May 14, 2023, 12:46:53 am
content: I am looking for a better way to regulate the 12V for my mega 2560 that will be used on the motorcycle. Currently, I have a buck converted but it takes a significant space and not sure if that is the best idea anyway.I found that for the automotive implementation, they use the MAX family overvoltage limiter controller. Today I am looking at the datasheet of MAX6398https://www.analog.com/media/en/technical-documentation/data-sheets/MAX6397-MAX6398.pdfhttps://www.analog.com/en/products/max6398.html#product-overviewI am not EE at all, and no idea how to design this circuit. Need some help choosing Mosfet, resistors and a cap.I need this circuit to handle 12-14V INPUT and OUTPUT anything between 7-12V ( its for mega2560 pro board )( 14V when the motorcycle is powered on, it generates a little more to charge the battery )Can you guys help me out with it ?

author: Nusa
author_rank: Super Contributor
timestamp: May 14, 2023, 02:09:14 am
content: That adds protection for your electronics. It doesn't eliminate the need to have a DC-DC converter for normal operation. Also, you should define what your power requirements are, not just the target voltages. If they are modest, you may simply need to look for a more space-efficient buck converter or voltage regulator.

author: Ian.M
author_rank: Super Contributor
timestamp: May 14, 2023, 02:21:08 am
content: Depending on where you connect the top end of the voltage sense potential divider resistors, a MAX6398 can operate in one of two modes, either switching off the external MOSFET on input overvoltage, or operate as a hysteric regulator, pulsing the gate drive to limit the output voltage by 'dithering' the MOSFET gate voltage in its linear region. Obviously, if a sustained supply is required, the first mode is unsuitable for reducing persistent overvoltage, and the second 'burns off' the excess voltage (times the load current) as heat in the MOSFET, just like a linear regulator, without the benefit of SOA protection that nearly all regulator ICs provide. For any load current over a few tens of mA, the size of MOSFET and heatsink required to limit the output voltage would most likely be significantly greater than an appropriately chosen switching buck regulator.Where a MAX6398 comes into its own is to protect a high current switching regulator in an automotive application against transient input over-voltage.To determine whether a MAX6398 could be of any benefit in your application, we'd need to know the maximum current the Arduino running your application could draw, and if you are going to have any other loads on the reduced voltage, overvoltage protected (Arduino) Vin.

author: misiek303
author_rank: Contributor
timestamp: May 14, 2023, 03:00:17 am
content: I wish I could give you the answers but I think I blindly trying to design something. But this is what I am working on..It is a Motorcycle Switch controller, it will control all lights, and signal start the bike. Similar to the ST-NET Switch Controller (https://nwtamerica.com/). I dream to make it my own because I am a software programmer and later on I will add on features. But for now just basic operations.I am making an expansion board for Mega2560 Pro. The mega will control 4x double ProFets for 8x 12V outputs. Yes, I know about the solenoid kickback and will also add the DIODE separately.This is the ProFet I selected:https://www.infineon.com/dgdl/Infineon-BTS7008-2EPA-DataSheet-v01_20-EN.pdf?fileId=5546d46258fc0bc101590212356876b1I attached:- mega 2650 pro that I am going to use- current ProFet Circuit- DC-DC buck converter ( you noticed it is adjustable because I have no idea how to calculate the output best 7V for VIN - I guess this also will allow me do some experiments )- current PCB designThe only thing is to find the best way to step down from 14V to 7V with overvoltage protection.Hope this help. I appreciate for you help

author: Ian.M
author_rank: Super Contributor
timestamp: May 14, 2023, 05:56:26 am
content: Your ProFet datasheet recommends the use of a 33V TVS diode across the 12V supply to protect it against high voltage transients. This will also protect whatever regulator you use to supply the Mega2560 Pro Arduino clone, as long as it has a high enough input voltage rating to withstand the max. clamping voltage of the chosen TVS diode. Although the Mega2560 Pro Arduino clone claims to have an output current of up to 800mA (for its 5V regulator - seehttps://joy-it.net/en/products/ARD_MEGA2560PRO), if you use a similar setup to the ST-NET Switch Controller, with the only non-logic loads on the Arduno 5V regulator being switches with integral LEDs driven by I/O pins, depending on the number of LEDs the Arduino could possibly draw under 100mA, and most probably under 200mA. 100mA with <10V input to output drop is low enough for a linear regulator to be viable*but 200mA is edging into the territory where a switching buck regulator will be beneficial to reduce dissipation.* unless you park a black bike in the summer sunshine in Death Valley!

author: misiek303
author_rank: Contributor
timestamp: May 14, 2023, 06:54:03 pm
content: Quote from: Ian.M on May 14, 2023, 05:56:26 amCorrect this is what I have DZ2 as a fly-back. The max 53.3V maybe not enough, I will find a better.Quote from: Ian.M on May 14, 2023, 05:56:26 amSo, Should I leave the buck-converted circuit as is or seek another solution? Again, I really look for a lower footprint than my buck converter. Have a look at the attached and how much space it takes.Let me ask a question a different way.a) Do I need a buck converter at all if I have a fly-buck to protect overvoltage andMaga2560 Prohas already 12V Regulator on board. ( Will it handle 14V? )b) How would YOU connectmega2560 proto the motorcycle/auto battery?

author: Nusa
author_rank: Super Contributor
timestamp: May 15, 2023, 07:04:30 am
content: Quote from: misiek303 on May 14, 2023, 06:54:03 pmA solid maybe. In the world of clones with identical names, we can't make any assumptions about which components your particular clone has installed. I'd look up the regulator on the board you have and read the datasheet to see what it can handle.

author: Ian.M
author_rank: Super Contributor
timestamp: May 15, 2023, 07:17:17 am
content: Also, look at the copper track and ground plane area near and directly connected to the onboard regulator, as even if its got a high enough voltage rating, its likely to be dissipation limited at high input voltages, and the Mega2560 Pro probably doesn't have as much copper area round the regulator as its datasheet recommends.Odds are, you can reduce the area required for the buck converter by choosing a different buck IC, with integrated switch and catch diode, operating at a higher frequency to minimise inductor and capacitors physical size. Also there is absolutely no need for a multi-turn preset. Use a pair of 1% fixed resistors to set the output voltage required.

author: max_torque
author_rank: Super Contributor
timestamp: May 15, 2023, 09:46:08 am
content: First step is to read up about "automotive load dump", when you've done that, you can estimate what actual voltages you might see on your system and for how longThen you need to decide if your system must remain operational across what voltage range (normally low voltage for cold cranking is issue here, because if your system is controlling the start then it needs to be running during the start.....)For a 5v micro, even at 8v or a bit less you can pretty much always have enough voltage headroom to get the 5v rail up and running, and of course, an AVR can run at less than 5v (with some max clock speed limitations) as well.Realistically, an automotive rated linear regulator, TVS diode, PTC fuse and possibly an additional series dropper R to take some of the thermal load off that reg is the solution i use for simple deviceseghttps://www.infineon.com/cms/en/product/power/linear-voltage-regulator/linear-voltage-regulators-for-automotive-applications/tle4266-2g/

author: Miha
author_rank: Contributor
timestamp: May 22, 2023, 05:43:09 am
content: Quote from: misiek303 on May 14, 2023, 03:00:17 amReview the guidelines for traces your DCDC again. PCB is not good.And, of course, when engine starts battery voltage drops much. Thus your MCU can restart to.Read carefully all recommendations in this topic.

author: misiek303
author_rank: Contributor
timestamp: May 22, 2023, 04:26:19 pm
content: Quote from: Miha on May 22, 2023, 05:43:09 amHi. Thanks. Any clues on what's no good?