[sdiy] DG408 issues

Tim Ressel timr at circuitabbey.com
Fri Aug 11 05:55:10 CEST 2017

Check the datasheet for the exact DG408 you have. Some have narrower 
voltage maximums.


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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--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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