Testing bus transceivers

Guy Sotomayor ggs at shiresoft.com
Mon Nov 16 10:27:36 CST 2015

On 11/16/15 8:21 AM, Noel Chiappa wrote:
> So, I have bought a number of DS8641 bus transceivers from a source in China,
> and cognizant of the claims that there are a lot of counterfeits coming from
> China, how can I test them to make sure the meet specs?
> I have a QBUS test board which I have constructed (it's basically just a
> single read/write register), so I can verify their _basic_ functionality; but
> the UNIBUS/QBUS specs give a number of analog qualifications, and it's those
> I'd like to check.
> Some of them I can figure out how to test, although a couple of them would
> seem to need special test rigs, e.g. input high threshold of 2.5V and low
> threshold of 1.4V, but I _think_ I can work out how to test those - a board
> with a pot on it, so I can vary the input voltage, and see where the output
> switches. (I'm not necessarily going to test every last chip, but I'd like to
> do random samples.)
> However, there are others of which I'm not at all clear how to test, e.g.
> output high leakage current of 25 uA. How would I test that? (And replies of
> the form 'use such and such an approach' probably aren't detailed enough for
> me - my analog-fu is pretty weak - so details would be most greatly
> appreciated! ;-)
A number of data books have circuits that were used to measure the 
parameters (including
rise/fall times) so you might want to look at some of them (substituting 
values for the 8641
vs the part in the data book).  They all look to be about the same as 
far as testing goes
(except for parameters obviously).  Just look for parts that are as 
similar as possible in terms
of input/output configurations (ie don't use a test configuration that 
was spec'd for totem
poll outputs vs open collector, etc).

TTFN - Guy

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