DEMO MANUAL DC2289A LTC2380-24/LTC2368-24: 24-Bit, 2Msps/1Msps, Low Power, SAR ADCs with Digital Filter DESCRIPTION The LTC 2380-24 and LTC2368-24 are low power, low performance such as peak-to-peak noise and DC linearity. noise, high speed, 24-bit SAR ADCs with an integrated Use the DC890 if precise sampling rates are required or to digital averaging filter that operates from a single 2.5V demonstrate AC performance such as SNR, THD, SINAD supply. The following text refers to the LTC2380-24 but and SFDR. The Demonstration Circuit2289A is intended applies to both parts. The LTC2380-24 has fully differential to show recommended grounding, component placement inputs and samples at 2Msps, while the LTC2368-24 has and selection, routing and bypassing for this ADC. pseudo-differential inputs and samples at 1Msps. The Design files for this circuit board including the LTC2380-24 has 117dB THD, consumes only 28mW and schematic, BOM and layout are available at achieves 3.5ppm INL max with no missing codes at 24 DEMO MANUAL DC2289A ASSEMBLY OPTIONS Table 1. DC2289A Assembly and Clock Options ASSEMBLY U1 PART MAX SAMPLE RATE NUMBER OF MAX CLKIN FREQUENCY VERSION NUMBER (Msps) BITS (MHz) MODE DIVIDER DC2289A-A LTC2380IMS-24 1.515 24 100 Normal 66 1.205 100 Normal/Verify 83 1.923 100 Distributed Read 52 DC2289A-B LTC2368IMS-24 0.909 24 60 Normal 66 0.746 62 Normal/Verify 83 1.0 52 Distributed Read 52 DC890 QUICK START PROCEDURE Check to make sure that all jumpers are set as described menu. Check for updates periodically as new features in the DC2289A Jumpers paragraph. In particular make may be added. sure that VCCIO (JP3) is set to the 2.5V position. Con- The PScope software should recognize the DC2289A and trolling the DC2289A with the DC890 while JP3 of the configure itself automatically. The default setup is for a DC2289A is in the 3.3V position will cause noticeable normal data capture with the number of averages set to performance degradation in SNR and THD. The default one. To change this, click on the Set Demo Bd Options jumper connections configure the ADC to use the onboard setting of the PScope Tool Bar as shown in Figure 2. The reference and regulators. The analog input is DC coupled Configuration Options box shown in Figure 3 allows the by default. Connect the DC2289A to a DC890 USB High number of averages and data capture mode to be selected. Speed Data Collection Board using connector P1. (Do Normal mode clocks out 24 bits of data. If Verify is selected not connect a PScope controller and QuikEval controller the number of bits clocked out is increased to 40 which at the same time.) Next, connect the DC890 to a host PC includes the number of samples taken for the current with a standard USB A/B cable. Apply 9V to the indicated output. Distributed Read allows a slow clock (one clock terminals. Next apply a low jitter differential sine source pulse per conversion) but requires the number of averages to J2 and J4. (The voltage applied at the inputs J2 and J4 to be at least 25. With Distributed Read selected, Verify should be out of phase and have a common mode voltage is not allowed. The number of averages can be set to an of V /2 100mV.) Connect a low jitter 2.5V sine wave REF P-P integer between 1 and 65535. Increasing N will improve the or square wave to connector J1, using Table 1 as a guide SNR. Theoretically, SNR will improve by 6dB if the number for the appropriate clock frequency. Note that J1 has a of averages is increased by a factor of four. In practice, 49.9 termination resistor to ground. reference noise will eventually limit the SNR improvement. Run the PScope software (PScope.exe version K80 or Increasing the REF bypass capacitor (C20) or using a lower later) supplied with the DC890 or download it from www. noise external reference will extend this limit. linear.com/software. Click the Collect button (see Figure 4) to begin acquiring Complete software documentation is available from the data. The Collect button then changes to Pause, which Help menu. Updates can be downloaded from the Tools can be clicked to stop data acquisition. Figure 2. PScope Toolbar dc2289afa 2