Hi guys, I posted in the last thread my problem, concerning the measurement of uP current. Energy micro has an open source circuit which measures the current flowing through a sense resistor connected at the supply line of the uP. please forgive my limited analog design knowledge, and explain to me what are the two (green highlighted) circuit parts good for? I thought it is sufficient when the output of the sense amplifier goes directly to the ADC. Thx!
Please translate this: Ich kann nicht in englischer Sprache schreiben, bitte übersetze das mit einem Translator-Programm: Auf der linken Seite sitzt ein LC-Filter, um die Betriebsspannung für den Shunt-Schaltkreis zu "reinigen" Auf der rechten Seite ist ein Tiefpass-Filter 2.Ordnung zu sehen, um Störsignale mit hoher Frequenz auszublenden. Greetings Paul
left hand side: 2nd order passive LC low pass filter for filtering pesky noise on the supply lanes. to place close to the diff-amp. right hand side: also 2nd order but active low pass filter (with optional gain via R376) for cutting off high-frequency noise gathered anywhere in the measurment path. cutoff-frequency 100kHz.
in case you want more description on the active low pass filter it's called sallen key and may also be configured to pass high frequency components of the signal http://en.wikipedia.org/wiki/Sallen%E2%80%93Key_topology you could also use LTspice to analyse the green circuits in the frequency domain
Hi guys, Thank you very much for your detailed answers! When I was looking at the circuit I was not even able to imagine what each element is responsible for... But now I think I can understand the things better! Appreciate it.
Please guys I have one more question: for the lower current range, a SMALL SIGNAL SCHOTTKY DIODE was connected in front of the amplifier. I think it is used to limit the output voltage of the amplifier to the reference voltage of the ADC, where the latter signal goes to. So now how can I figure out, to which value was the voltage limited to? which parameter is that of the diode? I attached the data sheet for you review. Thanks
In the datasheet you will find the formula for the output current of LTC6102. Calculate the maximum current and imagine that this current is flowing only through D10. Now have a look into datashett of D10 and find out what voltage drop corresponds to this current. By this you get the maximum voltage that is clamped by D10. In reality only a fraction of this current is actually flowing through D10, because some current needs to flow through R127 also. So, the maximum clamped voltage will be slightly lower.