| Electronics > Projects, Designs, and Technical Stuff |
| The many faces of the XX431 precision shunt regulator |
| (1/1) |
| JohnnyBerg:
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 .. |
| AE7OO:
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. |
| Navigation |
| Message Index |