tps65070 capacitance on touch lines

I am not able to provide an exact answer because it is a function of how you use your system and your requirements. A larger capacitance creates a longer time constant which reduces the number of measurements you can make per second.  Texas Instruments has many application notes on touch screen controllers that will be useful in helping you to understand their functionality and limitations.  One application note recommends that you wait nine timeconstants before making a measurement.  This allows the voltage to stabilize and povide an accurate reading.

http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=636&uiTemplateId=NODE_STRY_PGE_T

http://focus.ti.com/lit/an/sbaa036/sbaa036.pdf