DC358A Quick Start Guide Description Simple, Small, Very accurate The LTC2411, a differential input No Latency 24-Bit ADC in MSOP is featured on the DC358A demonstration board. The LTC2411 features 2-ppm linearity, 4-ppm full-scale accuracy, 1-ppm offset accuracy, and 0.29-ppm RMS noise. The LTC2411 operates from 2.7 to 5.5V supplies, drawing less than 300 uA of current and 2uA sleep mode current. It provides normal mode line frequency rejection of 110 dB, and DC and line frequency common mode rejection of 140 dB. Single conversion settling time yields latency-free results, thus enables multiplexing , correlated double sampling and other interleaved sampling schemes. The LTC2411 performs auto-zero and calibration in every output result, which are transparent to the user. The device does not require initialization. The board includes a precision 2.5V band gap reference (LT1019-2.5), and a precision 5V buried zener reference (LT1236-5), as well as bypassing capacitors, and jumpers to select line frequency rejection and various on board /external references. The demonstration board is designed to interface to a personal computer, as well as give an example of good placement of bypass and partitioning of an analog and digital ground. The demo board allows the user to quickly evaluate the LTC2411 performance while demonstrating its ease of use. The board connects directly to the RS232C port of any IBM compatible PC. The demo board derives its power from the RS232 port. The on board LT1236 ordinarily powers the LTC2411, and may be used as a 5V reference. Alternatively, the 2.5V reference may be used as reference, and the 5V output from the LT1236 may be used as excitation for a bridge application, although, an external power supply is likely required in this case. The 2.5V output from the LT1261 can also be used as a bias source for sensing single ended bipolar signals that must be able to accommodate the full +/- 2.5V input range. If, for example, an instrumentation amplifier were to be used to drive the demo board, the reference terminal of the instrumentation amplifier can be connected to the 2.5V output. Alternatively a differential amplifier scheme can be biased such that its differential outputs are centered at 2.5V. The software included in this package presents a 7.5 digit display, as well as a histogram display, and calculated noise figure , all updated in real time. The demonstration program also provides averaging capability, zero and full scale cal functions, and raw data output to a file, for offline evaluation. The demo board has a group of banana jacks for 6 wire connections to a bridge or other source, as well as a group of turrets for connection to external power. See schematic. Operation Instructions for installation and operation of the demo program are included at the end of this document. Hardware set-up Step 1: Serial Port Connection Connect the demo board DB9 socket to the serial port of the computer (Com1-4). Port selection is done in the demo program. Step 2: Rejection frequency The internal oscillator can be configured to reject line frequencies of 50Hz or 60Hz by tying pin 14 to Vcc or ground. Jumper JP4 has a default setting of 60 Hz (pin 2-3) This pin (Fo) can also be driven by an external clock. Step 3: configure reference/power jumpers Jumper JP1 Connects excitation terminal (Vex (J4) banana jack) to Vcc (may be 5V from LT1236, or external), or 2.5V reference from LT1461. Jumper JP2 connects the output of the LT1236 precision 5V reference to the Vcc rail. You may elect to use an external Vcc supply, for example, for testing 2.7V, 3.3V or other supply sensitivity issues. If JP2 is installed, do not apply external power to Vcc (J3). Jumper JP3 allows selection of 2.5V or 5V reference. If Jumper JP2 is removed, REF+ (J6 banana jack) may be connected to an external force sense, or other external reference schemes for 6 wire ratiometric operation. REF+ must be within the range from Vrefmin above REF- to Vcc. Jumper JP5 is analogous to JP3, for the REF- terminal. If installed, it connects REF- to ground. If removed, REF- (J7 banana plug) may be connected to an external reference within the range 0V toVcc- Vrefmin. Step 4: Apply input signal(s) There are a number of valid configurations for the inputs of this device 1) Single ended 0-2.5V input Connect Vin-(J9) to ground (J10) REF- (J7) to ground (J10), or JP5 installed. (Experiment with this) External 0V-2.5V signal to VIN+ (J8) (using ground at J10) JP3 select 5V JP2 installed VEX(J4) & REF+(J6) and turrets not used 2) full bridge with 5V excitation Connect REF+ (J6) to bridge sense+ REF- (J7) to bridge sense- VIN+(J8) to bridge out + VIN- (J9) to bridge out - Bridge force- to Ground (J10) Bridge force+ to VEX (J4) JP3 & JP5 removed JP1 select Vcc JP2 installed External power (9V-12V)will be required at J1 for 350 ohm bridge. (for silicon strain gauge bridges with 5K+ impedance, external power may not be required, depending on the RS232 line driver on the computer. Laptops, and some newer computers may require external power in any case.) 3) Half bridge (RTD or strain) Connect REF+ (J6) to reference arm+ REF- (J7) to reference arm- VIN+(J8) to variable arm + VIN- (J9) to variable arm - Bridge force- to Ground (J10) Bridge force+ to VEX (J4) JP3 & JP5 removed JP1 select Vcc JP2 installed Reference arm may be on top, or bottom.