Datasheet-a-Day W29 2020

19 Jul 2020electronicsreading

More datasheets!

INA199 26-V, Bidirectional, Zero-Drift, Low- or High-Side, Voltage-Output, Current-Shunt Monitor

This is basically a current sense amplifier.

They make a thing of being able to deal with drops across the shunt as low as 10mV full-scale. Which makes me think that’s quite a difficult thing to do, and my Teensy Load design might have some trouble with what I’m trying to do there.

These are fixed gain devices (50, 100 or 200) that run off a single supply (2.7 - 26V). They’re designed specifically for high-side sensing, and can amplify differential signals with common mode voltages much higher than supply voltage (e.g. small signals imposed on 26V common mode running from 2.7V supply).

Even here, for sensing close to zero current (i.e. sense voltage close to ground), they suggest biasing the amplifier into its linear region away from ground.

IPC-SM-782A Surface Mount Design and Land Pattern Standard

I’m not sure whether this is an official source for this, but I got it from here.

This seems like it should be dry and boring (it’s an international standard about SMD footprints!), but it actually has some quite interesting stuff in it about PCB assembly.

One thing is about test points: the recommendation in the standard is to bring out a test point for every node in your circuit, all on a fixed grid to make probing easier. (I’ve never seen this, but it is apparently something people do for high-volume/cost designs.)

This thing is quite dull, but worth seeing! It’s also quite long, which is why there are only four entries this week, instead of five. It took two goes to get all the way through this...

I2C-Programmable Any-Frequency CMOS Clock Generator + VCXO (Si5351A/B/C-B)

All the clock generator you might ever need?

Produces multiple clock outputs at any frequency (2.5 kHz - 200 MHz), all driven from a single crystal (or an internal reference oscillator). There are variants with external clock inputs, different numbers of clock outputs, internal oscillator, etc.

One quite neat thing is that you can run the different clock outputs at different voltages, by providing a supply voltage to go with each output.

There is also support for differential clocks. This is for PCI, I think, but I don’t know anything about it.

These are interesting parts!

Application Design Guidelines for LM339, LM393, TL331 Family Comparators Including the New B-versions (TI SNOAA35A)

These parts are often thought of as jellybean comparators, I think. There are lots of parts, lots of numbers, lots of grades.

The basic circuit for these things is pretty simple: 12 transistors, 4 diodes, plus a few others not shown. (Simple is a relative term. I still don’t understand it yet!)

Most of this app note reads as a caution about using these parts. They are quite old-fashioned components, with lots of rules about how to use them. There are better comparators available now, so the main lesson seems to be: don’t use these!

A couple of those rules/constraints: