Hello Denny,

I didn't mention it but actually the effective operating temperature is
"around ~110C" I am actually more concerned with the -55C operating
specification. If what you say is true then the slew rate would slow at low
temperatures.

I suppose I will have to reduce the peak-to-peak voltage of my 25kHz
triangle wave to 1V to lower the slew rate requirement to ~1/10th the rated
slew rate.

I like the specifications on the OPA211 but I suspect price ($77 per chip
vs $0.28/chip) may a limiting factor here.

-Jason White

On Tue, Jul 10, 2018 at 12:24 PM, Denny Esterline <desterline@gmail.com>
wrote:

> Interesting question. Unfortunately all I have is wild speculation.
> A brief glance at the datasheet shows a bipolar output stage.
> In general, bipolar passes more current and has higher leakage at
> elevated temperatures. Into a fixed load, I would expect that to
> increase slew rate.
> Part of the problem is that the load and all the other parameters
> have temperature dependencies as well. The combined effect is
> very unpredictable. Be fun to build a test fixture and measure
> it though.....
>
> The other thing I noticed in the datasheet is that the part is spec'd
> to an absolute maximum junction temperature of 125 C.  Effectively
> that means you cannot use it at an ambient temperature of 125 C
> as it wouldn't be able to dissipate any heat. That may or may not be
> a problem for you, depending on whether the 125C is a real spec
> or a "marketing spec".
>
> I don't really know your application and design constraints, but a bit of
> research found this one:
> http://www.ti.com/product/OPA211-HT
> Which has a slew rate of 27V / uS and is specified to a high temp of
> 210 C !!! (holy s*!t)
>
>
>
>
> On Tue, Jul 10, 2018 at 7:29 AM, Jason White <
> whitewaterssoftwareinfo@gmail.com> wrote:
>
> > In my current design the operating temperature range is rather large:
> -55C
> > to 125C.
> >
> > I am planning on using the LM124DT from ST in an analog PWM circuit. My
> > design uses a 0.5 to 4.5v triangle wave at 25kHz (required slew rate
> > 0.2V/us).
> >
> > The LM124DT has a "typical" slew rate of 0.4V/us at 25C. A minimum slew
> > rate is not specified and slew is not specified at other temperatures.
> > Other manufacturers such as TI don't seem to specify this either.
> >
> > I would like to get an intuitive sense of how (or if) slew rate might
> > change over temperature. Additionally I'd like to get some opinions as =
to
> > whether 0.2V/us could be too fast for the LM124.
> >
> > Thanks,
> > Jason White
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