[sdiy] DG408 issues

[Tom Bugs]

Where is this max +5V reading coming from for the Dig line?

Both Intersil & Maxim datasheets say "(V-) - 2 to (V+) + 2,or 20 mA, 
whichever occurs first"

Only a quick reading by me at the moment, but I couldn't see anything 
else obvious that suggested otherwise.
As long as the digital control goes over 2.4V it registers HI.

I think the original issue is the Low Voltage chip variant - I had that 
issue once DG4xxLDY rather than DG4xxDY

Tom


On 11/08/2017 05:14, Ben Bradley wrote:
> "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."
>
> The way I read the data sheet(s) for this DG series, there's a +V
> input (+15v), -V (-15V) and GND, and these are for the analog switch
> section. All digital inputs should be at least at GND pin and at most
> +5V above GND pin. There's internal level translation for the
> switches. 8V sounds way too high for a digital input, even if it's got
> little current going into it through a high value resistor. I think
> it's turning on something that shouldn't be turning on, and pulling
> lots of current through the +15V and/or -15V power inputs, and that's
> what's causing heating.
>
> Make the resistive dividers so the digital inputs are at most +5V, and
> at lowest, the potential of the DG's GND pin. Both Vishay and Intersil
> say a digital input over 2.4V is a Logic 1, and below 0.8V is a logic
> 0. I might make the 1 voltage 3.3V
>
> On Thu, Aug 10, 2017 at 11:55 PM, Tim Ressel <timr at circuitabbey.com> 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
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at synth-diy.org
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>>>
>> --
>> --Tim Ressel
>> Circuit Abbey
>> timr at circuitabbey.com
>>
>>
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