QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1010 2/4 CHANNEL 24,16,16/PGA-BIT ADC WITH I2C LTC2493, LTC2489, LTC2487 DESCRIPTION Demonstration circuit 1010A-A features the LTC2493 2/4 Channel, 24-Bit ADC with I2C. Key DC specifications include 2ppm INL, 1ppm offset, 25ppm fullscale error and 10nV/C offset drift. In the 6.8Hz/600nVRMS mode, input normal mode rejection of 50Hz and 60Hz noise is better than 87dB. The LTC2493 also includes an internal temperature sensor that is accurate to 2 degrees C over the operating temperature range. 256 and the same temperature sensor as the LTC2493. The DC1010A-B features the LTC2489 16-Bit ADC that is pin out and software compatible with the LTC2493. The DC1010 is a member of Linear Technology`s QuickEvalTM family of Demonstration Boards. It is designed to allow easy evaluation of the LTC2493, LTC2489 or LTC2487. DC1010 may be connected directly to the target application's analog signals while using the DC590 USB Serial Controller board and supplied software to measure performance. After evaluating with LTC's software, the digital signals can be connected to the application's processor / controller for development of the serial interface. The DC1010A-C features the LTC2487 16-Bit ADC that also includes a PGA with a gain range from 1 to Design files for this circuit board are available. Call the LTC factory. LTC is a trademark of Linear Technology Corporation Figure 1. Proper Measurement Equipment Setup 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1010 2/4 CHANNEL 24,16,16/PGA-BIT ADC WITH I2C QUICK START PROCEDURE Connect the DC1010 to a DC590 USB Serial Controller using the supplied 14 conductor ribbon cable. Connect DC590 to the host PC with a standard USB A/B cable. Run the evaluation software supplied with DC590 or downloaded from www.linear.com. The correct program will be loaded automatically. Click the COLLECT button to start reading the input voltage. The software allows for selecting the input channel, single ended or dif- ferential mode and 50/60 Hz rejection settings. Selecting 2x Speed located at the bottom of the stripchart display will double the data output rate at the expense of offset accuracy (LTC2493 and LTC2487 only). Tools are available for logging data, changing reference voltage, changing the number of points in the strip chart and histogram, and changing the number of points averaged for the DVM display. 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1010 2/4 CHANNEL 24,16,16/PGA-BIT ADC WITH I2C HARDWARE SET-UP JUMPERS ANALOG CONNECTIONS JP1, JP2 - Select the source for REF+ and REF-, respectively. REF+ can be 5.00 volts from the onboard LT1236 reference (default) or supplied externally. REF- can be Ground (0 volts, default) or supplied externally. Analog signal connections are made via the row of turret posts along the edge of the board. JP3, JP4 - Control for I2C address lines A0 and A1 respectively. These lines can be floated by removing the jumpers, grounded (Low) or tied to Vcc (High). The default mode is JP3, JP4 tied to Vcc. This is required for use with Quick Eval software. The addresses generated are shown below. CA1 LOW LOW LOW HIGH HIGH HIGH FLOAT FLOAT FLOAT CA0 LOW HIGH FLOAT LOW HIGH FLOAT LOW HIGH FLOAT ADDRESS 0010100 0010110 0010101 0100110 0110100 (Default) 0100111 0010111 0100101 0100100 GND - Ground turrets are connected directly to the internal analog ground plane. VCC - This is the supply for the ADC. Do not draw any power from this point. External power may be applied to this point after disabling the Vcc supply on DC590. See the DC590 quick start guide for details. REF+, REF- - These turrets are connected to the LTC2487/2489/2493 REF+ and REF- pins. If the onboard reference is being used, the reference voltage may be monitored from this point. An external reference may be connected to these terminals if JP1 and JP2 are configured for external reference. CH0 - CH3 - These are the differential inputs to the LTC2493/2489/2487. They may be configured as single-ended inputs with respect to the COM pin, or as differential inputs (CH0-CH1, CH2-CH3) with the polarity software selected. DIGITAL CONNECTION CONNECTION TO DC590 SERIAL CONTROLLER J2 is the power and digital interface connector. Connect to a DC590 serial controller with the supplied 14-conductor ribbon cable. Digital signals are also connected to through-hole test points on the circuit board. FO - Connects to the Frequency Control Pin. When FO is connected to GND (Default connection), the converter uses its internal oscillator running at 307.2 kHz. The conversion clock may also be overridden by driving the FO pin with an external clock in order to change the output rate and the digital filter rejection null. 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1010 2/4 CHANNEL 24,16,16/PGA-BIT ADC WITH I2C EXPERIMENTS INPUT NOISE Solder a short wire between the CH0 and CH1 turrets. Connect the inputs to ground through a short wire and start taking data. LTC2493 Noise should be approximately 0.12ppm of 5V (600nV RMS.) The electrical noise of the LTC2489 is also 600nV RMS, however this is masked by the 76.3V quantization level. If the input is well between code transitions, the noise level will read zero. If the input is exactly between two codes such that the two adjacent output codes have equal probability, the noise level will be approximately 7.9ppm. The input noise of the LTC2487 is apparent at very high gain settings (128 or 256.) Note that with a 5V reference and gain set to 256, 1LSB is equal to 298nV - which is lower than the 600nVRMS electrical noise of the input stage. COMMON MODE REJECTION Tie the two inputs (still connected together from previous experiment) to ground through a short wire and note the indicated voltage. Tie the inputs to REF+; the difference should be less than 0.5 V due to the 140 dB+ CMRR of the LTC2493. The LTC2489 will produce less than 1LSB difference. INPUT NORMAL MODE REJECTION The LTC2493 and LTC2487 SINC4 digital filter can be software selected to reject 50Hz, 60Hz by 110dB, or both 50 and 60Hz by 87dB. The LTC2489's SINC4 filter is fixed at 50/60Hz. To measure input normal mode rejection, connect COM to a 2.5 volt source such as an LT1790-2.5 reference or a power supply. Connect any other input (CH0 - CH3) to the same supply through a 10k resistor. Apply a 10 Hz, 2V peak-to-peak sine wave to the input through a 1uF capacitor. Set the rejection frequency to 55Hz (LTC2493 only) and start taking data. The input noise will be quite large, and the graph of output vs. time should show large variations. Next, slowly increase the frequency to 55 Hz. The noise should be almost undetectable in the graph. 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1010 2/4 CHANNEL 24,16,16/PGA-BIT ADC WITH I2C 5