DC344 LTC2420 Demonstration Board Quick Start Guide Simple, Small, Accurate This demonstration board features the LTC2420, a 20-bit high-performance analog-to-digital converter (ADC). The LTC2420 combines exemplary DC accuracy (INL 4PPM, RMS noise 1.2PPM) with an easy- to-use SO8 package. Operating from a single 2.7 to 5.5v supply, the LTC2420 draws less than 250uA. Using an internal oscillator requiring no external components, the LTC2420 rejects line frequency noise (50Hz or 60 Hz +/-2%) at least 120dB. The LTC2420 also offers a Fast Mode. Output rates up to 100sps are possible with 16-bit noise and 12-bits total unadjusted error. The combination of a standard serial interface (SPI, Microwire compatible) and flexible analog input and reference ranges make this part simple to use. The input reference voltage range is 0v to Vcc, while the analog input range can go below ground and above Vref by 12.5%*Vref within the range of to -0.3V to Vcc+0.3V. User transparent zero and fullscale calibration result in offset errors below 2PPM and temperature drifts below 0.04PPM/degree C. Single conversion settling time results in latency-free results enabling multiplexed applications. The demo board allows the user to quickly confirm the accuracy of the LTC2420 while demonstrating its ease-of-use. The board connects directly to the serial port of any IBM compatible PC. The demonstration board derives its power from the computers serial port. The LT1460, used as a precision 5V regulator, drives the reference input to the LTC2420. The reference input to the converter is tied to Vcc, resulting in a -0.3 to +5.3 input range. The combination of the LTC1460 and two bypass capacitors are the only components required by the LTC2420. This manual shows how to use the LTC2420 demonstration board. Included are timing diagrams, schematics, and suggested experiments that allow the user to confirm the accuracy of the LTC2420. KEY FEATURES *Fast Mode enables switching between 7.5 readings per second and 100 readings per sec- ond. The demonstration board contains an oscillator tuned to 2.048MHz which may drive the F0 pin of the LTC2420 under software control. *Noise histogram and RMS noise calculations updated real time. *Single-shot output graph shows non-averaged output for determining peak-to-peak noise. *On-board LTC1460 reference can be replaced by an external reference *The reference is output is available for ratiometric measurements. *Power derived from computer serial port. *Scalable output for ratio-metric or absolute measurements. OPERATION The demonstration board and software were designed to allow the user quick and easy evaluation of the LTC2420. The operation is described in five sections: I hardware setup, II software setup, III acquiring data, IV Fast Mode, and V suggested experiments. I. HARDWARE SETUP STEP 1:Serial port connection Connect the demonstration board DB9 socket J5 to the serial port (COM1 or COM2) directly or through a male-to-female 9-pin extender cable (not provided). STEP 2:Rejection Frequency The internal oscillator on the LTC2420 can be configured to reject line frequencies of 50Hz or 60Hz by tying pin 8 (F0) to Vcc or Ground, respectively. This is achieved through jumper JP1 (defaulted for 60Hz rejection). While in the fast mode (to be described later) the LTC2420 outputs data at 100Hz with a corresponding 800Hz rejection. STEP 3: Select Reference The demonstration board contains an LTC1460 (5v) voltage reference. Jumper JP1 selects the LTC1460 as the reference for the LTC2420, or allows the user to apply an external reference (0.1v to 5V) through connector J1. Vcc remains 5V for the LTC2420 regardless of which reference voltage is selected. Additionally, the reference is output to connector J2 for ratiometric measurements.