[sdiy] DG408 issues

Tim Ressel timr at circuitabbey.com
Fri Aug 11 17:27:25 CEST 2017


I have been bit by this so many times.  For example: AD633, different 
pinouts for dip and soic packages. Glad I could help. Makes me feel like 
I'm paying back for all the times this list helped me!

--tim


On 8/10/2017 9:13 PM, David Moylan wrote:
> 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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>>> Synth-diy at synth-diy.org
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>>>
>>
>
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com



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