Author Topic: The many faces of the XX431 precision shunt regulator  (Read 714 times)

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Offline JohnnyBergTopic starter

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The many faces of the XX431 precision shunt regulator
« on: November 05, 2019, 08:30:57 am »
I am building a precision voltage to current converter, that shifts the voltage level of a Li-ion battery pack to a level that a micro-controller can read. Furthermore, I am not interested in the first 2,5V, the cell is just dead under that level.
I have a 12 bit ADC and want to use those 12 bits in the range 2.5 to 4.4V, giving me a base resolution of approx. 0,5 mV.

In my design I use a XX431, and that is where its gets messy. For me, 2 factors are of importance: the current needed for regulation Ika (its is a battery operated thing, smaller is better) and the current into the reference pin, witch gives an error in the conversion.

Voltage  reference have a grade, the xx431 is no exception: the A grade gives 1% accuracy, the B grade 0.5%. There are also C types, they are 2% (I fail to see the logic). Accuracy is not important, as each cell measurement is calibrated.

But here is where the shit hits the fan: a XX431 from supplier Y is not the same as the one from supplier Z.

Examples (all max values, price per 10):
Classic TL431 from TI: Ika = 1mA, Ivref=4 uA $0.20
Changjiang Electronics CJ431: Ika = 1mA, Ivref=4 uA $0.03
Seaward Elec SD431: Ika = 300uA, Ivref $ 4uA $0.04

In my quest for the best I found this one:
ATL431 from TI: Ika = 35uA, Ivref=150nA $0.40

Is this the one?

edit: found the AS431 from Diodes Inc.: Ika 50uA, Ivref=500nA $0.05 .. not as good as the ATL431 but much better price level. Designing  is like marriage .. you have to compromise ..
« Last Edit: November 05, 2019, 08:48:46 am by JohnnyBerg »

Offline AE7OO

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Re: The many faces of the XX431 precision shunt regulator
« Reply #1 on: March 11, 2020, 05:24:24 am »
I know it's old...

I think I've got your system figured out.

You might want to take a look at the OnSemi NCP431/NCP432 in the future.

Iref 190nA
Ika  60uA

These stats are the same for all of the various grades, from AC to BV.
$00.30 qty 10
Not super cheap, but not bad either.

As of 10MAR20, for whatever reason, Mouser has the 432BV's for $00.26, which has the greatest temp range -40 to 125 and 0.5% initial.

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