Part Number: INA240
Good day,
According to datasheet, maximum capacitive load for INA240 is1 nF. Customer wants yo use low pass RC - filter, 27 Ohm/0,1µF after INA240 before ADC as recommended. Will INA240 be stable in this case, what is the maximum capacitive load for 27 Ohm resistance?
Thank you,
Daria
Hi Daria,
while the small signal transient response looks promising:
the large signal transient response demonstrates that the output stage of INA240 cannot adequately charge the capacitive load:
Here with zoom:
Kai
Daria,
I recreated Kai's model and am in agreeance with his findings. I've run the same simulation, and received the same result. As requested I've attached a copy at the bottom. The issue here is not actually with the capacitive load, but with the parts output stage and its ability to provide current. Here is a series of curves of the part driving capacitance up to around 60uF through your 27Ω resistor:
As you can see, as you would expect, the RC response of the filter becomes flatter as capacitance grows, until you no longer reach a correct "final" value somewhere at a value between 50uF and 60uF. However, at 50nF, we would expect a 98% settling time to be 4 time constants, or 4*27*50nF = 5.4us. What the simulation shows is that it actually takes nearly 76us to reach a settled value, and this is due to the limitation of current from the output stage. The INA240 is mainly a signal chain device, and is not meant to drive large amounts of current through it, and therefore cannot handle a load of 27Ω:
Can I ask, why is the customer adamant on a 27 ohm resistance? Can this not be increased to help alleviate current constraints here? This would also take the burden off of the capacitance.
