LTC2378-20 pin FuncTions CHAIN (Pin 1): Chain Mode Selector Pin. When low, the BUSY (Pin 11): BUSY Indicator. Goes high at the start of LTC2378-20 operates in normal mode and the RDL/SDI a new conversion and returns low when the conversion input pin functions to enable or disable SDO. When high, has finished. Logic levels are determined by OVDD. the LTC2378-20 operates in chain mode and the RDL/SDI RDL/SDI (Pin 12): When CHAIN is low, the part is in Nor- pin functions as SDI, the daisy-chain serial data input. mal Mode and the pin is treated as a bus enabling input. Logic levels are determined by OVDD. When CHAIN is high, the part is in chain mode and the VDD (Pin 2): 2.5V Power Supply. The range of VDD is pin is treated as a serial data input pin where data from 2.375V to 2.625V. Bypass VDD to GND with a 10µF ceramic another ADC in the daisy chain is input. Logic levels are capacitor. determined by OVDD. GND (Pins 3, 6, 10 and 16): Ground. SCK (Pin 13): Serial Data Clock Input. When SDO is enabled, IN+, IN– (Pins 4, 5): Positive and Negative Differential the conversion result or daisy-chain data from another Analog Inputs. ADC is shifted out on the rising edges of this clock MSB first. Logic levels are determined by OVDD. REF (Pin 7): Reference Input. The range of REF is 2.5V to 5.1V. This pin is referred to the GND pin and should be SDO (Pin 14): Serial Data Output. The conversion result or decoupled closely to the pin with a 47µF ceramic capacitor daisy-chain data is output on this pin on each rising edge (X7R, 1210 size, 10V rating). of SCK MSB first. The output data is in 2’s complement format. Logic levels are determined by OVDD. REF/DGC (Pin 8): When tied to REF, digital gain compres- sion is disabled and the LTC2378-20 defines full-scale ac- OVDD (Pin 15): I/O Interface Digital Power. The range of cording to the ±V OVDD is 1.71V to 5.25V. This supply is nominally set to REF analog input range. When tied to GND, digital gain compression is enabled and the LTC2378-20 the same supply as the host interface (1.8V, 2.5V, 3.3V, defines full-scale with inputs that swing between 10% and or 5V). Bypass OVDD to GND with a 0.1µF capacitor. 90% of the ±VREF analog input range. GND (Exposed Pad Pin 17 – DFN Package Only): Ground. CNV (Pin 9): Convert Input. A rising edge on this input Exposed pad must be soldered directly to the ground plane. powers up the part and initiates a new conversion. Logic levels are determined by OVDD. FuncTional block DiagraM VDD = 2.5V REF = 5V OVDD = 1.8V to 5V CHAIN IN+ + SDO SPI RDL/SDI 20-BIT SAMPLING ADC PORT SCK IN– – CNV BUSY CONTROL LOGIC REF/DGC GND 237820 BD01 237820fb 8 For more information www.linear.com/LTC2378-20 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Converter Characteristics Dynamic Accuracy Reference Input Digital Inputs and Digital Outputs Power Requirements ADC Timing Characteristics Typical Performance Characteristics Pin Functions Functional Block Diagram Timing Diagram Applications Information Board Layout Package Description Revision History Typical Application Related Parts