Hello all,
we have trouble with a design that should measure currents. A current sense amplifier LMP8640MKE-H drives the Input of an adc ADS8344NB via a RC lowpass filter of 100R/4.7nF. The amplifiers Output is about 120mV idle (no current through the shunt). If current flows through the shunt, the LMPs Output goes up, again with an Offset of 200mV. The LMP8640 alone behaves as expected, producing an analog output proportional to the current through the shunt. Hence we assume, that the amplifiers buffer is not able to drive capacitive loads. However, the datasheet states, it is capable to do so. We tried the setup without RC filter, LMP driving directly the Input of the ADS8344. However, then the ADCs input drops during sampling, giving worse results. So we assume the ADC requires some capacitance on its Input to buffer the voltage during sampling.
How much capacitance is the LMP8640 capable to drive? How much minimum capacitance does the ADS8344 require on its analog Input? Is there a application note or a General recommendation of low pass filters suitable for These devices?
Thanks in advance
Lothar