Skip to main content
Topic: DSO ADG5436 replacement (Read 232 times) previous topic - next topic

DSO ADG5436 replacement

I already have the ADS831's and OPA2691's.  When I get the ADG5436's I will proto the circuit and test it with the OLS.
"Too many projects, so little time"

Re: DSO op-amp replacement? OPA2681 -> OPA2691?

Reply #1
I am still waiting on the Analog switches. 
"Too many projects, so little time"

Re: DSO op-amp replacement? OPA2681 -> OPA2691?

Reply #2
I will call Analog Devices in the morning to find out where the samples are.

McZ
"Too many projects, so little time"

Re: DSO op-amp replacement? OPA2681 -> OPA2691?

Reply #3
I can't seem to find the ADG5436. Are the key ADG5436 properties the on voltage (3.3volt compatible) and max voltage (>+/-15)?
Got a question? Please ask in the forum for the fastest answers.

Re: DSO op-amp replacement? OPA2681 -> OPA2691?

Reply #4
Not sure what you mean by "can't find the ADG5436" - you can't find a source to buy them from?

Here is the link to the ADG5436 on the Analog Devices site.

Re: DSO op-amp replacement? OPA2681 -> OPA2691?

Reply #5
Yup, I can't find them anywhere in quantity.

I've worked with SS relays before, but I've never used them in production so I don;t know what the 'go to' parts are for availability. I was just checking availability because I'm putting together a part order on monday and thought I'd order some. There's none at Digikey or Mouser, and I asked (but have not heard) about availability for Seeed.

Just checking parts, I found this that looks kind of similar but only one chan (though only 1.71 in singles, but only 0.63 by the reel). I'll do some more significant research as soon as I have time, might be tuesday though.
http://search.digikey.com/scripts/DkSea ... T1-E3CT-ND

Also at mouser. Lists the switch current at 30ma, I assume this is passing, and not the required on-current:
http://www.mouser.com/ProductDetail/Vis ... AYLQ%3d%3d
Got a question? Please ask in the forum for the fastest answers.

Re: DSO op-amp replacement? OPA2681 -> OPA2691?

Reply #6
[quote author="IPenguin"]
I looked for ADG5436s before, couldn't find them either at the usual suspects (common distributors) and talked about the sourcing
with Michael (via email I think). They are recently released parts. AD shows them as in production and available and Michael was
going to contact AD about samples and how to get them in quantities ...

ADG5436 - two independently selectable dual supply single-pole/single-throw (SPDT) switches - 9 V to 40 V single supply operation - ±9 V to ±22 V dual supply operation

DG449 - single dual supply single-pole/double-throw (SPDT) switch - 7 V to 36 V single supply operation - ± 4.5 V to ± 20 V dual supply operation

So yes, their specs look very similar - it should be possible to replace the ADG5436s with two DG449s in Michaels design. Maybe it will require some resistor values to be adjusted slightly.

[/quote]

I looked at the DG449 and the specs are similar.  In fact other than the single vs dual the DG449 maybe a better part at 100 Mhz.  I am using 100 Mhz as a reference.  The 30 mA is the clamping diode current limit.  If you do not exceed 30 mA the clamping diodes will protect the switch from overvoltage.

I have attached the pertinent graphs and chart of the important parameters. 

I think we should go with the DG449 if not other reason than cost and availability.

McZ
"Too many projects, so little time"

Re: DSO op-amp replacement? OPA2681 -> OPA2691?

Reply #7
They looked good to me too. I put in a mouser order and got some of these and a few others.

I will update the schematic and PCB too.
Got a question? Please ask in the forum for the fastest answers.

Re: DSO ADG5436 replacement

Reply #8
I have been thinking about the +- 15 v supply for the analog switches.  There are three ranges, 100:1,10:1 and 1:1.  Meaning that at the input to the ADC we have +- 1v which on the 100:1 range would be  +-100 v at the BNC.  But at the input to the analog switch we cannot have more than +-15v.   The clamping diodes (internal and discrete) will restrict the voltage to the +- 15 v which protects the switch.   

What am I forgetting here?
"Too many projects, so little time"

Re: DSO ADG5436 replacement

Reply #9
+/-15v on the first version is fine with me, and I thought that was the intended limit. Now that I look at the R values it's clear...

Maybe we should mod it for 1:1, 6:1 (3.3volt range), and 12:1 (5volt range)... Or some other reasonable range that gives decent resolution on the common values that are in play?
Got a question? Please ask in the forum for the fastest answers.

Re: DSO ADG5436 replacement

Reply #10
I spent some time going over the numbers for the design tonight, hoping to contribute to an intelligent conversation about the range divider.

A simplified diagram is attached.

Could the NO input of U1 be used for an additional division level or input type? It currently goes to ground, and if U5 is NO then it does nothing?
Got a question? Please ask in the forum for the fastest answers.

Re: DSO ADG5436 replacement

Reply #11
here's the png from dia

Re: DSO ADG5436 replacement

Reply #12
The reason for NO input on U1 is to gnd the input for zeroing the offset of the trace.  NC on U1 is the AC coupling. 
"Too many projects, so little time"

Re: DSO ADG5436 replacement

Reply #13
Hmmm, with max +/-15V AC/DC input for the DG449 and a 1:10 probe you get an effective input range of +/-150V max in theory ...

1:1 probe for 1:1, 1:0.1 and 1:0.01 --> +/-15V, +/-1.5V and +/- 0.15V
1:10 probe for 1:1, 1:0.1 and 1:0.01 --> +/-150V, +/-15V and +/-1.5V

So I wouldn't run the switches at their max rating of +/-15V but rather a bit more conservatively at +/-12V .. +/-13.5V, +/-15V will be ok.

[s:]There is a way to implement one more range divider with 4 switches but, like Michael said, it will not allow for auto-zeroing without extra circuitry ...[/s:]

/EDIT/Just saw it doesn't give us more ranges than the original design ... actually it's worse since it takes auto-zeroing away. /ENDEDIT/

I can easily adapt the drawing to whatever switch configuration we will use in the final design ... for our documentation.

Re: DSO ADG5436 replacement

Reply #14
Of course, it needs the ground to be zeroed. Thanks guys.

If we set a max 12volt input, then 12:1 gives full range at 12volts, 6:1 at 6volts and 1:1 at 1volt.
Got a question? Please ask in the forum for the fastest answers.