CDP68HC68A2

® Data Sheet CDP68HC68A2 April 2002 FN1963.4 CMOS Serial 10-Bit A/D Converter The CDP68HC68A2 is a CMOS 8-bit or 10-bit successive approximation analog to digital converter (A/D) with a standard Serial Peripheral Interface (SPI) bus and eight multiplexed analog inputs. Voltage referencing is user selectable to be relative to either VDD or analog channel 0 (AI0). The analog inputs can range between VSS and VDD. The CDP68HC68A2 employs a switched capacitor, successive approximation A/D conversion technique which provides an inherent sample-and-hold function. An onchip Schmitt oscillator provides the internal timing for the A/D converter. The Schmitt input can be externally clocked or connected to a single, external capacitor to form an RC oscillator with a period of approximately 10-30ns per picofarad. Conversion times are proportional to the oscillator period. At the maximum specified frequency of 1MHz, 10-bit conversions take 14μs per channel. At the same frequency, 8-bit conversions consume 12μs per channel. The versatile modes of the CDP68HC68A2 allow any combination of the eight input channels to be enabled and any one of the selected channels to be specified as the “starting” channel. Conversions proceed sequentially beginning with the starting channel. Nonselected channels are skipped. Modes can be selected to: sequence from channel to channel on command; sequence through channels automatically, converting each channel one time; or sequence repeatedly through all cha...