data/text/DLP4/900293

INA233 input filter

Hello, I'm planning to use INA233AIDGST in my application. According to Figure 1: Frequency response (attached below) from datasheet of INA233, we can see that bandwith of diff. amp. is around 300 Hz. I try to calculate input filter (suggested on page 15, figure 25) consist of two 10R resistor and 100n capacitors. It must be around 160 kHz. (fc=1/(2*pi*R*C)). With INA233 I would like to measure current and voltage at switcher regulator input and output with switching frequency 120k or 215kHz (I will decide later). I think that it is better to use filter capacitor with higher value. 470n will bring cut off frequency of around 39 kHz which sounds better (120k of switcher is 3 times higher). What do you think? You reccomend to use filter resistor no large than 10R - is this value connected to current flowing in to IN+/IN- input of INA? How is the frequency bandwith of INA233 (which is around 300 Hz) connected to cut off frequency of external filter? I can not imagine how much the filter with much higher cut off frequency helps here? Doest the INA260 consist of INA233 with 2mR resistor integrated in reality? Many thanks!

Hey Dejan, We recommend the input resistors to be less or equal than 10-Ohm because of an imbalance in IB+ and IB- due to input differential impedance of around 10 kOhm. As described in section 7.4.4, the input filter/resistors are only really needed if there are load current transients that occurs at the device’s sampling frequency (500kHz +/-10%) or if there are fast common-mode voltage transients at the input pins. In the latter scenario, the input resistors help limit any input ESD conduction current. Yes, the INA260 is essentially an INA223, but with an integrated 2mOhm shunt resistor. Sincerely, Peter