Is there a cheaper TLV431/LMV431?

Joerg wrote: ...

You might try adapting the following, eg substitute 22K in place of R2=30K. Note, MMBD7000 is a dual Schottky diode a lot like the BAV99. U2b doesn't do anything - it was merely simpler to breadboard as shown.

Vx U1a U1b Vi------R2-----+----->|--->|-------+ | | R1=10K | | R2=30K R1 | | U2a | Vo----+---------->|-------+---Vg +----------|

Are you saying the 'standard' 431 is on the way out ? Given the number used in supplies that seems astonishing.

Graham

How much do you pay for resistors ?

Graham

Pooh Bear wrote in news: snipped-for-privacy@hotmail.com:

I imagine that when the budget has tolerances like those, even their mounting pad or hole costs are considered...

Arrrrrrrrrrrrrr, like wot someone else almost said..... Go ratiometric.

Arrrrrrrrrr. Measure the answer measure the answer, do the sum do the sum.

Arrrrrr

DNA

They discontinued the CA3046 last year. As far as I'm concerned, now ANYTHING is possible.

(Actually National sitll makes their variant in surface mount, but all the major catalog suppliers had their shelf stock dry up within days of the CA3046 part being discontinued).

Tim.

Hello Graham,

No. Only some versions are obsolete. The 431 is here to stay. I'll probably be in a nursing home before that one retires.

Hello Graham,

Usually around 0.8c, fully burdened.

Hello James,

Pretty cool solution! A diode pre-regulator. The MMBD7000 can be had for around 2c a pop in qties (for a dual pack).

In this case it wouldn't work for me though since I have to clamp a uC port. This in order to provide a rather precise high level for a PWM. Besides tempco there is the job of muffling Vbat drift. Especially with alkalines this voltage can range from 2.5V to 3.2V.

Hello Fritz,

One application is a poor man's sigma-delta converter (SD). There you'd have to compare an input signal to a feedback signal and the only way to generate that on a cheap uC is PWM. You regulate that PWM signal to become equal to the input signal. Then you count how many high pulses you've got in a given window, say 1024 for a 10-bit conversion. This tells you the magnitude of the input signal. But it only works if you can be sure about the amplitude of those pulses and that's where the TLV431 comes in as a clamp.

In many cases I'd need the math horsepower of the 16-bit MSP430.

Hello Genome,

Huh? You still need a reference somewhere in the game. Else the system cannot know whether something is 1.24V or not.

You've got pretty good eyes if you can read to within 12.4mV on that graph- and that's just 1%.

You will? That's where it turns in its best performance. The 1mA pulsed waveform is visibly worse- plan on 10's microseconds for 1/2LSB error at any reasonable resolution.

Hi Joerg,

Genome may have a point. Is there a reason you need the absolute value of the voltage? Or is there a way to convert it to a ratio of something else?

Say you have a voltage divider. You can generate a PWM voltage and compare it to the output of the divider. When they are equal, the duty cycle of the PWM generator is equal to the resistor ratio. You know the value of one resistor, so a simple calc gives the other. It seems almost anything else can be done in a similar fashion.

For example, I have several inexpensive digital thermometers that run off a single watch battery of ~1.5V. Somehow they give accurate readings, and I'm pretty sure they don't have any voltage references buried inside:)

Regards,

Mike Monett

Mike Monett wrote in news:Xns97D516434AB5CNoemailadr@208.49.80.251:

Interesting. It reminded me af a zener problem I had, using two, and trying to get accurate relations between them. I solved my problem with one, and it;s wasn't a reference, merely a means to get some approximate constant, and I used a divider across it to get my other value, which remained locked to the zener voltage by proportion, solving all my problems at once.

The point being that any datum will do, so long as you choose it well, and use it as your sole reference. It certainly works for navigation on tides, and those are both complex, and with high risk stakes.

Hello Fred,

That's not how it works in a PWM application. On a micro the typical pulse widths are several ten usec. The TLV is pretty much hooked up like in the schematics next to figs 15 and 16, sans 50ohm of course. The absolute value doesn't have to be within a percent but it needs to get there really fast, and it needs to be remain the same.

What I was saying here is that the TLV431 ramps surprisingly fast for such a jelly-bean part.

You just need to push it up the ramp and then ease back.

Hello Mike,

Mostly I need the PWM circuit to provide a current or voltage of known magnitude, or measure it. The resistor ratio won't tell me that.

The ones with a diode as a sensor need some kind of reference and the versions I had seen actually had one. Thermometers with a temp-variable resistor don't, those can compare with a known resistor in the usual dual-slope arrangement. In the same way that an ohmmeter does not necessarily need a reference whereas a voltmeter does.