Electronics > Projects, Designs, and Technical Stuff
Maxim ADC Heat Problem
racerxdl:
Hi all, I'm new at forum :D
I work with Eletronics a long time ago, and I have a website about experiments (EnergyLabs Brasil http://www.energylabs.com.br), and I am playing with samples of MAX1421 (40Msps 12BIT ADC from Maxim).
But I have a BIG problem. When I power it up after a few time, I got smoke from the ADC. But now from ADC itself, but smoke from between pins (All times that I saw, it was in the middle of a VDD and GND pin), and if I stay more time, it starts to blink like if there is burning.
First, I think of that I may shorted some pin or so, so I got a new board, new ADC from the sample package and soldered, measure ALL pins with multimeter in conduction mode to see if there was any short, after that measuring all pins to see if there was a low resistance between any pins (the datasheet says that from any input to GND the resistence is about 10k. All of it was correct. Checked with a Lens too, nothing wrong. After soldered all wires, I triple checked if there was some wiring mistake, and nothing found. So I decided to hook up on FPGA again (Xilinx Spartan 3A) and it was seens to be working (I actually dont know if it was working correct, because I didnt hook up any signal, so I was only picking up noise), but after some time, it stoped to get output and few secs later, smoke too.
Got angry with that, its free samples from Maxim but, I dont want to destroy it. But okay, got to search for problems. After that, I only hooked up the ADC to 3.3V Power Supply, and it got smoke, so I think that ADC is dead.
Asked my dad about it, see what he thinks about (he is eletronics technician too) and he said that might the wires got melt with the solder iron and nearly shorted the pins. Makes sense, so I got a new board, another ADC, soldered on the board and I make only the Power Supply connections, and this time, one wire far from the other (the max that I can do). Triple checked all things again, all correct. Got decoupling caps at the inputs as the ADC Datasheet says, and hooked up ONLY to the 3.3V Power supply. Started, and few secs later, smoke again, and light between VDD and GND Pins (random).
I really dont know what is happening, there is no short, no pins has resistance less than 10K, and the powersupply supplies 3.32V correct (also I used the same supply to a LCD Screen).
The funny thing is that, all the times I measured the current that ADC draws and all stays lower than 1mA. Only hooked at the FPGA with the clock singal (without it is the same, below 1mA) it draws near 20mA (on the datasheet this is lower than usual current, it makes sense, because I only clocking it at 16MHz not 40MHz).
I already sent a email for Maxim IC, but they didnt returned me. Someone knows what can be the problem? Here are few pics of the first board (I know, its crap, but the last one that I Didnt take pic its better, and I was carefull to not make any short or things like that):
The ADC has a PD input (Power Down, that makes the ADC got to shutdown mode). With that on 1 (shutdown state) the current is lesser than 500uA. With that in 0, the current is about 800uA to 1mA. (Of course, without the clock signal, only power supply. Also the PCB is correct, I have more 6 of them here, but only one ADC.
Thanks !
xygor:
Maybe foreign object debris on the board such as steel wool?
Psi:
--- Quote from: racerxdl on March 11, 2011, 11:49:15 pm ---The funny thing is that, all the times I measured the current that ADC draws and all stays lower than 1mA.
--- End quote ---
If you're only supplying 1mA at 3.3V then that isn't enough to make it smoke. There must be some other voltage coming into the circuit from somewhere else.
Here are a few things you could check..
-Check that there is no AC voltage ontop of the 3.3VDC
-Check that there is no voltages coming into your circuit from other areas. Maybe you have two GND connections at different voltages or something is floating.
-Check that any other IC's you have connected to the ADC are 3.3V i/o. If they're 5V i/o check they are current limited with a resistor before being connected to adc.
A few other general things to check.
-Check that the IC is soldered onto the PCB around the correct way, maybe vdd and gnd are not where they're supposed to be. The silkscreen pin numbering could be wrong. Or the IC footprint could have got set to 'mirror image' when the board was designed.
-Check you are using analog ground (AGND) and digital ground (DGND) correctly
-Check you have connected all AGND's pins together, its rare but some ICs requires you to do this yourself and don't connect them internally (ive not checked that ic)
-Check you have connected all DGND's pins together, its rare but some ICs requires you to do this yourself and don't connect them internally
-Some IC's require a clock frequency within a specific range and can burn out if there is no clock connected or the clock is oscillating too slowly.
-Check you dont have an adc output connected to VCC/GND.
Alex:
It sounds like the smoke is coming from the part itself. Smoke from inside an IC can be generated at low power levels and vent from the plastic package.
Check the wiring, pin functions and descriptions against your schematic.
Also check your voltage levels.
From Psi's post, the minimum clock frequency for this part is 100kHz.
racerxdl:
--- Quote ---If you're only supplying 1mA at 3.3V then that isn't enough to make it smoke. There must be some other voltage coming into the circuit from somewhere else.
--- End quote ---
Yes, that I was think about, but there is ONLY 3.3V going to the board. The supply doesnt make any other voltage.
--- Quote ----Check that the IC is soldered onto the PCB around the correct way, maybe vdd and gnd are not where they're supposed to be. The silkscreen pin numbering could be wrong. Or the IC footprint could have got set to 'mirror image' when the board was designed.
-Check that there is no AC voltage ontop of the 3.3VDC
-Check that there is no voltages coming into your circuit from other areas. Maybe you have two GND connections at different voltages or something is floating.
-Check you are using analog ground (AGND) and digital ground (DGND) correctly
-Check you have connected all AGND's pins together, you shouldn't rely on the IC to do this.
-Check you have connected all DGND's pins together, you shouldn't rely on the IC to do this.
--- End quote ---
The Board is a universal LQFP48 to PIN adapter from futurlec ( http://www.futurlec.com/SMD_Adapters.shtml ), its all correct, that is the first thing I done when the boards arrived.
The VDD and GND pins are both correct, and all connected to 3.3V Power Supply. Already tested all seeing datasheet specifications
And as I said, the power supply is a switch mode power supply with good decoupling caps and a LCD Screen was tested on it and its working fine without any issues.
--- Quote ----Check that any other IC's you have connected to the ADC are 3.3V i/o. If they're 5V i/o check they are current limited with a resistor before being connected to adc.
--- End quote ---
It cant be that, Xilinx Spartan 3A FPGA only works with 3.3V and less.
--- Quote ----Some IC's require a clock frequency within a specific range and can burn out if the clock pin is not oscillating or is oscillating too slow.
--- End quote ---
Isnt that, the ADC works from 1kHz clock to 40MHz clock, the datasheet says that even with less than 100kHz clock, it may only have output erros.
--- Quote ----Check you dont have an adc output connected to VCC/GND.
--- End quote ---
I triple checked, nothing is connected as not should be, I review three times, and it was three boards.
--- Quote ---Maybe foreign object debris on the board such as steel wool?
--- End quote ---
Checked about steel wool (I didnt used that, but who knows) and other things that can be on the board, and nothing found. The board is very clean.
Its REALLY strange thing. The only thing that can be, is that maxim datasheet is wrong. My part is MAX1421 ECM and I am using the datasheet from maxim website: http://datasheets.maxim-ic.com/en/ds/MAX1421.pdf. Also I checked the MAX1420 Evaluation Kit (1420, 1421 its pin to pin compatible): http://datasheets.maxim-ic.com/en/ds/MAX1420EVKIT.pdf and all seens wired like mine, so it should work.
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