Q1.Our printed circuit board is a multi layer card . It has one layer of an
uninterrupted low impedance ground plane, so that the voltage difference
between different ground points are small. Would it be possible to connect the
analog ground and the digital ground to the same ground plane?
2.We found out that sclock and sdata lines have rise rime of more than 200
nanosecond. What is the reason for that? Is it aloud to use 1 K Ohm pull up
resistor in order to get shorter rise time for these signals?
A1. The analog and digital ground pins of the AD7872 should be connected to the
same ground plane. The problem exists when there is a lot of other noisy logic
on the board which is also connected to this same ground plane. Then, the well
known phenomena of ground bounce will increase the noise on the conversion
result. How serious this is depends on how noise the digital logic is.
2. SCLK and SDATA are open-drain outputs and require pull up resistors (2k for
SCLK, 4k7 for SDATA). This is noted in the pin function description.