Electronics > Beginners
MCP4812 10-bit DAC melting breadboard
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justinm:
Hoping for suggestions on what to try next:

I replaced a working MCP4725 I2C DAC with an SPI-driven MCP4812 (I wanted two channels from one component). 5V VSS was connected from the output of an Arduino Nano board.

I was able to confirm all the SPI signals were correct with the scope, but then before I could even get the multimeter on VOUTA or VOUTB (both floating, not pulled down) of the DAC I started to smell -- not the magic smoke -- but some melty breadboard.

I then disconnected all the SPI signals, connected Vss and Vdd -- still got warm.

I then swapped in a fresh chip and fresh breadboard -- same result.

Is it possible that the absence of a decoupling cap, or the floating output pins, could explain the heat? Stumped and afraid of wrecking more chips in my quest to build the simplest possible MCP4812 circuit.

Thanks for any debugging suggestions!
tsman:

--- Quote from: justinm on January 04, 2019, 06:12:53 pm ---I replaced a working MCP4725 I2C DAC with an SPI-driven MCP4812 (I wanted two channels from one component). 5V VSS was connected from the output of an Arduino Nano board.

--- End quote ---
Uhh. You didn't wire up 5V to Vss did you?
justinm:
 :-DD

Yes! Okay. I read and re-read the datasheet, but my eyes transposed those pins every time. That'll do it! Will report back after putting 5V on the correct pin tonight :)
justinm:
MCP4812: sturdy chip! Turns out it can get nice and hot and still come right back to life. Beautiful lines on the scope now. Thanks @tsman!
Buriedcode:
Current limiting in linear regulators and the fuses on USB power have saved a couple of micro's I've mis-connected.  USB isn't a bad way to power up stuff for the first time - as long as it's 2.0, limited to 500mA, and adheres to the standard.
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