Re: What's the hi-side current sense chip du jour?

On Sat, 30 May 2009 15:22:33 -0700, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

John Larkin wrote:
On Sat, 30 May 2009 13:46:46 -0700 (PDT), "miso@xxxxxxxxx"
<miso@xxxxxxxxx> wrote:

On May 29, 8:30 pm, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

[...]

They discontinued the part without warning, in fact when shipments
were long overdue. They then announced their "drop-in replacement"
- the MAX9691 - which is the only comparator I've ever heard of that
has BACK-TO-BACK DIODES BETWEEN ITS INPUTS. Imagine what that did to a
capacitor-linear-ramp/dac time delay trimmer circuit.

grrrrrr.

John
I can see this happening. My original comment was about parts being
non-functional right out the chute.

But the 9690 was a bipolar part. Hard to believe oxide has that
effect.

I don't know the physics. The behavior was as stated. Whatever went
wrong, it could be annealed out.


I've only used bipolar inputs in bicmos for ASICs. The clamping under
those conditional is not that unusual, then again, I'm setting up the
operating conditions. If you yank a differential pair far apart, two
ugly things can happen. One could be a polarity reversal in the
comparator, which depends on a lot of things. The other more sneaky
problem is the offset of the differential pair shifts. The whole
reason you went through the pain of using bipolar inputs (speaking
from a BICMOS point of view) is the low untrimmed offset off the
differential pair.

Clamps are fine for opamps; not for comparators. Don't be shocked, but
comparator + and - inputs are sometimes driven to *quite different
voltages*! On purpose!


Especially since they obviously wrote or said "drop-in replacement". The
engineer who ECO'd that statement should have his head examined.


That was a Gain Technology design. Those guys spent way too much time
in the Arizona sun and fried their brains. While you end users may
think you are the judge of component quality...

Yeah, what the hell do we know? When a comparator output is entirely
wrong, I should ask a process engineer if that's OK.


Old American business rule #2: A product is only as good as the customer
says it is.

I've found a number of horrible bugs in chips, some of which the chip
designers were unaware, some of which they knew about and did their
best to keep a secret.

John

.

Relevant Pages

  • Re: Whats the hi-side current sense chip du jour?
    ... comparator, which depends on a lot of things. ... problem is the offset of the differential pair shifts. ... Especially since they obviously wrote or said "drop-in replacement". ... I should ask a process engineer if that's OK. ...
    (sci.electronics.design)
  • Re: Whats the hi-side current sense chip du jour?
    ... comparator, which depends on a lot of things. ... problem is the offset of the differential pair shifts. ... I've found a number of horrible bugs in chips, ... Early LT1028 datasheets cut off the noise graph before the ugly ...
    (sci.electronics.design)
  • Re: Whats the hi-side current sense chip du jour?
    ... comparator, which depends on a lot of things. ... problem is the offset of the differential pair shifts. ... I've found a number of horrible bugs in chips, ... One Hittite switch data sheet states boldly that it works from DC to 4 ...
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  • Re: Whats the hi-side current sense chip du jour?
    ... comparator, which depends on a lot of things. ... problem is the offset of the differential pair shifts. ... from a BICMOS point of view) is the low untrimmed offset off the ... I should ask a process engineer if that's OK. ...
    (sci.electronics.design)
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