Burning ADC....help plz..!!!

[amandeep_pec]

Hi,

I am trying to build a small circuit using Analog Devices AD9240 Analog to Digital Convertor. I am giving supply voltages of (+5=AVdd) to the ADC. However, as soon as I connect the supply to the ADC a smoke starts to come from AVDD pin, and on testing it using a multimeter it starts showing a resistance of 1-2ohms between AVDD and ground. I have tried to test the same on around 7-8 ADCs bt am facing the same problem each and every time. I also tried to just connect the ADC and not interface it with ny of the components in the system, but I face the same problem.

Any help would be appreciated

Thanks a lot,

Regards,

 

[yego]

Your problem may be caused by several factors:
1) Your supply is not 5V,
2) Your supply is incorrectly connected to the IC,
3) Your ICs are DOA,
4) Your PCB has routing problems.

Check all, assume nothing.

 

[wp100]

Hi,

Sounds like you have a dead short on the pcb or between the pins of what I assume can only be a smd device.

You need a powerful magnifier to see some of those solder whiskers that can short out things.

The other things I would check, does the chip measure a short before you solder it ?

Also what pins are you actually connecting +5v and 0v to, there is a total of 6 pins for supply to D and A.

Its also very easy to both mount your smd part the wrong way and also get your pcb image wrong /inverted.

Perhaps you could post your schematic.

 

[amandeep_pec]

Hi all,

Thanks for your comments.

I have checked all the connections and voltages etc and they are good.

@Yego : What do you mean by DOA ? All other connections look good.

@wp100 : I am a bit confused about your comments on the supply connections. The ADC I am using has in total 8 ground and supply pins, namely : DVDD-DVSS (Digital supply pair ), DRVDD-DRVSS(Driving Supply Voltage), and 2 pairs of AVDD-AVSS(Analog supply). I am connecting +5, 0V tp DVDD-DVSS pair / +5-0V to DRVDD-DRVSS pair and +5/0 to both the analog supply pins..i.e. 2 AVDD @ 5V and 2 AVSS @0V. Do i need to connect only one AVDD-AVSS pair ???

Also, although I am using a smd device...i could nt find any dead shorts on the PCB or the Chip. The ADC also burns when running it on a breadboard. I burnt 3 ADCs before finally one worked on the breadboard and now when I am soldering it to the final PCB I have already burnt 7 ADCs..!!!

 

[wp100]

Hi,

Sounds like you have got real probelms !

DOA means that the chips are faulty when you bought them - Dead On Arrival

Sorry about missing two off the supply connections, my point was that there are so many supply voltage connections to make that there is a greater chance of making a mistake - similarly getting the chip positioned correctly and even getting the smd pcb done correclty can be a real problem.

If you cannnot measure a short between any of the pairs of supply pins Before you connect anything up, then I would suggest you just connect only the Digital power and see what happens so you can isolate where the short is occuring.

Having soldered a few smd I do wonder how you have connected a smd chip to a breadboard , there is little space for soldering wires to the pins.

If possible, some photos of your boards might help us understand what you are doing.