LTC1279 UUUPI FU CTIO SAIN (Pin 1): Analog Input. 0V to 5V (Unipolar), ±2.5V conversion. The LTC1279 responds to CONVST signal (Bipolar). only if the signal applied to CS is a logic low. VREF (Pin 2): 2.42V Reference Output. Bypass to AGND RD (Pin 20): READ Input. A logic low signal applied to (10µF tantalum in parallel with 0.1µF ceramic). this pin enables the output data drivers when the signal applied to the CS pin is a logic low. AGND (Pin 3): Analog Ground. CS (Pin 21): The CHIP SELECT input must be a logic low D11 to D4 (Pins 11 to 4): Three-State Data Outputs. for the ADC to recognize the signals applied to the D11 is the Most Significant Bit. CONVST and RD inputs. DGND (Pin 12): Digital Ground. BUSY (Pin 22): The BUSY output shows the converter D3 to D0 (Pins 13 to 16): Three-State Data Outputs. status. It is a logic low during a conversion. DVDD (Pin 17 ): Digital Power Supply, 5V. Tie to AVDD pin. VSS (Pin 23): Negative Supply. – 5V will select bipolar SHDN (Pin 18): Power Shutdown. The LTC1279 pow- operation. Bypass to AGND with 0.1µF ceramic. Tie to ers down when SHDN is low. analog ground to select unipolar operation. CONVST (Pin 19): Conversion Start Input. It is active AVDD (Pin 24): Positive Supply, 5V. Bypass to AGND low. The falling edge of the CONVST signal initiates a (10µF tantalum in parallel with 0.1µF ceramic). UUWFU CTIO AL BLOCK DIAGRA CSAMPLE A AV IN DD ZEROING SWITCH DVDD 2.42V REF VSS (0V FOR UNIPOLAR MODE V OR –5V FOR BIPOLAR MODE) REF COMPAR- 12-BIT CAPACITIVE DAC ATOR 12 AGND 12 D11 SUCCESSIVE APPROXIMATION • OUTPUT LATCHES • REGISTER • DGND D0 1279 BD INTERNAL CONTROL LOGIC CLOCK SHDN CONVST RD CS BUSY 7