[sdiy] DG408 issues

David Moylan dave at westphila.net
Fri Aug 11 06:13:20 CEST 2017


This is why I love Synth-DIY!  Feeling a little foolish, but yeah, I 
managed to order DG408LE which are only spec'd for +-8 Volts.  I've got 
+-15 across it.  Surprised it's held out this long.

Thanks, Tim!

Dave

On 08/10/2017 08:55 PM, Tim Ressel wrote:
> Check the datasheet for the exact DG408 you have. Some have narrower 
> voltage maximums.
> 
> --timbo
> 
> 
> On 8/10/2017 8:47 PM, David Moylan wrote:
>> As mentioned in my other thread I'm using a DG408 to switch modes on a 
>> Roland IR3109 filter.  Can't quite figure out why the DG408 is so hot. 
>> The digital inputs are rather large as they're coming from the outputs 
>> of 3 opamps set up as a 3-bit ADC.  However, I'm sending them through 
>> large resistors (220k) and they don't appear to be drawing much 
>> current, approximately .13 mA.
>>
>> Datasheet suggests that anything within the supply range is ok. 
>> However, I'm not sure if the negative supply should be considered 
>> ground for the digital inputs.  Even so, if I set the ADC to all 
>> positive outputs so there's no negative voltage on the digital pins 
>> the chip is still just as hot.
>>
>> I had tied the enable pin directly to the +15 supply, but hacked in a 
>> resistor to tie it to a divider that was already in use, after seeing 
>> a comment online that the chip doesn't like large voltages on the 
>> digital pins.  There's about 8V on the pin with 120k to +15.
>>
>> Voltages at all pins appear normal, but the chip is very hot. Can't 
>> keep my finger on it for more than a few seconds.  Other than that 
>> symptom everything works correctly.
>>
>> Anyone experienced problems with this chip?
>>
>> Thanks.
>>
>> Dave
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> 




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