DEMO MANUAL DC1925A LTC2378-20/LTC2377-20/LTC2376-20 20-Bit,1Msps/500ksps/250ksps, Low Power, SAR ADCs with 104dB SNR DESCRIPTION peak-to-peak noise and DC linearity. Use the DC890 if The LTC 2378-20, LTC2377-20 and LTC2376-20 are 20-bit, precise sampling rates are required or to demonstrate AC low power, low noise SAR ADCs with serial outputs that performance such as SNR, THD, SINAD and SFDR. The operate from a single 2.5V supply. The following text demonstration circuit 1925A is intended to show recom- refers to the LTC2378-20 but applies to all parts in the mended grounding, component placement and selection, family, the only difference being the maximum sample routing and bypassing for this ADC. rate. The LTC2378-20 supports a 5V fully differential input range with a 104dB SNR, consumes only 21mW Design files for this circuit board are available at and achieves 2ppm INL max with no missing codes at 20 DEMO MANUAL DC1925A ASSEMBLY OPTIONS Table 1. DC1925A Assembly Options ASSEMBLY VERSION U1 PART NUMBER MAX CONVERSION RATE NUMBER OF BITS MAX CLK IN FREQUENCY DC1925A-A LTC2378CMS-20 1Msps 20 80MHz DC1925A-B LTC2377CMS-20 500ksps 20 40MHz DC1925A-C LTC2376CMS-20 250ksps 20 20MHz DCDC890890 QUICKQUICK STARTSTART PROCEDUREPROCEDURE Check to make sure that all switches and jumpers are Run the PScope software (PScope.exe version K73 or set as shown in the connection diagram of Figure 1. later) supplied with the DC890 or download it from www. In particular make sure that VCCIO (JP3) is set to the linear.com/software. 2.5V position. Operating the DC1925A with the DC890 Complete software documentation is available from the while JP3 is in the 3.3V position will cause noticeable Help menu. Updates can be downloaded from the Tools performance degradation in SNR and THD. The default menu. Check for updates periodically as new features connections configure the ADC to use the onboard refer- may be added. ence and regulators to generate the required common The PScope software should recognize the DC1925A and mode voltages. The analog input is DC coupled. Connect configure itself automatically. the DC1925A to a DC890 USB high speed data collection board using connector P1. Then, connect the DC890 to a Click the Collect button (See Figure 5) to begin acquiring host PC with a standard USB A/B cable. Apply 9V to the data. The Collect button then changes to Pause, which indicated terminals. Then apply a low jitter differential sine can be clicked to stop data acquisition. source to J2 and J4. Connect a low jitter 80MHz 2.5V P-P sine wave or square wave to connector J1. Note that J1 has a 50 termination resistor to ground. DC590 SETUP IMPORTANT To avoid damage to the DC1925A, make Run the QuikEval software (version K92-01 or later) sup- sure that VCCIO (JP6) of the DC590 is set to 3.3V before plied with the DC590 or download it from www.linear. connecting the DC590 to the DC1925A. com/software. The correct control panel will be loaded automatically. Click the Collect button (See Figure 6) to VCCIO (JP3) of the DC1925A should be in the 3.3V position begin reading the ADC. for DC590 operation. To use the DC590 with the DC1925A, it is necessary to apply 9V and ground to the 9V and GND terminals. Connect the DC590 to a host PC with a standard USB A/B cable. Connect the DC1925A to a DC590 USB serial controller using the supplied 14-conductor ribbon cable. Apply a signal source to J4 and J2 or J4 depending on how the DC1925A is configured. dc1925af 2