AD7457: Discontinuous clock

Question We need to connect the AD7457 to the SPI bus of the MPC8347E. The idea was to use a general purpose IO to control the CS\ of the AD7457, then read out the result of the conversion. We have 2 questions about this. 1: can the AD7457 work with a gapped clock? We would start the conversion by triggering the CS\ pin. At that moment there would be no SCLK. The SCLK would only become active during readout. The SPI SCLK clock of the MPC8274E is only active during transactions on the SPI bus. 2: can we connect two AD7457 to the same SPI bus, with separate CS\? In this case, they would sometimes see SCLK activity when the other AD7457 on the bus is accessed. Answer 1) The AD7457 will work fine with a discontinuous clock. 2) There should be no implications on the deselected device due to clock activity since the deselected device won't be converting at the time. The SDATA output of the deselected device will always be tri-stated.

AD7457: Filter requirements

Question 1) Is it necessary to use some antialiasing filter in the input of ADc for DC measuring only? (12bit, about 10 ksps, only DC signal) 2) Is it suitable to use 0.1uF ceramic capacitor in parallel with 10uF CERAMIC capacitor (both SMD, 0805 size) for decoupling ADi parts such as Operational Amplifiers, Voltage References, ADc,...(16 bit and 12 bit applications)? There is smaller, low-priced version of recommended 10uF tantalum in parallel with 0.1uF ceramic (various ADi datasheets). Answer 1)Without an antialiasing filter any noise picked up by the i/p pin can be aliased back to the passband of the ADC. So yes, an antialiasing filter is required even for DC i/p signals. 2)A ceramic 10uF capacitor should give no problems.

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