MCP1416 Mosfet Driver randomly switching - Page 1
Forum section: electronics / beginners

author: DerGenaue
author_rank: Newbie
timestamp: January 28, 2023, 09:17:27 pm
content: Hi everybody,A friend and I are trying to build a 12V LED PWM driver, but the mosfet driver switches on erratically even though it should be off.Video here since the gif somehow is broken:In principle, the setup is really simple:ESP32 pin - Pulldown - series R - MCP1416T-E/OT Mosfet Driver - R - Mosfet - LEDsThe test PCB with only the necessary components and the "Direct Drive" trace cut:For some reason, after some time our channels start to behave very erratically:The light starts to flicker and turn on even though the signal pin is pulled low through 10kOhm.Measuring the "input" signal with a multimeter it feels like completely random noise:Some days, the signal line stays completely flat at 0V exactly like you would expect it to,then it fluctuates randomly around 1V for hours, triggering the driver and turning the LEDs on and off,and then it rises even higher to 8 or even 10V on the input(!) line which made us fear that the ESP could get damaged.If you measure the current that flows to ground, you get .6 or even up to 5 mA. depending on the voltage it currently is at.For random wireless interference that would be waaay to much in my opinion, and also way to stable.Our setup has one unusual characteristic that I can think of: the output and the input pin of the driver can be connected using a solder bridge.This bridge allows to use the same circuit board in a direct drive mode (without a mosfet driver) using a logic level mosfet.That setup works perfectly fine, but doesn't achieve some of the specs we aimed for.In a test board, I cut the trace for the bridge, but the issue still appears (see images).Probing the signals with an oscilloscope, I could not see any weird behaviour of the driver:The output was perfectly flat at 0 or high at 12V, seemingly no oscillation and when the light flickered, then it happened at a slow speed(200ms on, 100ms off, ...), not anywhere close to the speeds we do PWM at.The input pin fluctuates at the speed you can follow on the multimeter (see above) and there were no weird, high-frequency oscillations visible.This means that, to my eye, the driver was behaving exactly like one would expect if some little gremlin just injected the fluctuating voltage on the input pin.We had this happen on a couple of channels, one of the drivers I pulled off and put on the separate test board to isolate it, where I could reproduce the issue (images above).Do you have any idea where this could come from?Is there something wrong with our PCB setup or is the driver broken?If so: can you think of any obvious reason why this one and multiple others have been damaged?Since we don't intend to light a disco with it, this whole problem unfortunately is a big roadblock,so we'd be really glad if some of you had an idea what the source of the problem might be.Thanks for your help.

author: DerGenaue
author_rank: Newbie
timestamp: February 02, 2023, 12:35:34 am
content: Does anyone have an idea?Or maybe a hint on where else I could find people to help with this problem?(Btw: why do the embedded attachments in the original post not work?)

author: ledtester
author_rank: Super Contributor
timestamp: February 02, 2023, 01:43:38 am
content: Sorry, no answers -- just some questions...1. Do you have genuine chips? I ask because I noticed you can get the MCP1416 through ebay and aliexpress.2. Are you following the guidance in section 4.5 of the datasheet (PCB Layout Considerations). There it states:Quote3. What power supplies are involved?QuoteIt's a long-standing problem with the site and from what I understand it has to do with the way multiple servers are handling the site's traffic.

author: DerGenaue
author_rank: Newbie
timestamp: February 03, 2023, 10:07:20 pm
content: Thanks for the response,1. Sourced from Mouser, so I hope they're genuine 😅2. We tried to follow those guidelines as closely as possible, but had to do some compromises to achieve our design goals.I still think that our design (see the PCB Layout) matches the guidelines.Do you think this might cause these problems?If so, what would we need to change?3. An old PC power supply for testing (a bit unstable 12V) and a Chinese wall wart that came with the LED strip (nice, stable 12V)