DEMO MANUAL DC571A LTC2418 8-/16-Channel Differential 24-Bit ADC DESCRIPTION The LTC 2418 is a high resolution, 24-bit ADC with signals while using the DC590 USB serial controller board 5ppm INL and 5V offset. Channel selection is programmed and supplied software to measure performance. through a simple serial interface. Since there is no latency, After evaluating with LTCs software, the digital signals can each conversion is valid, even after a change in input be connected to the applications processor/controller for channel. development of the serial interface. DC571A is a member of Linear Technologys QuikEval Design files for this circuit board are available at family of demonstration boards. DEMO MANUAL DC571A HARDWARE SETUP JUMPERS CONNECTION TO DC590 SERIAL CONTROLLER JP1: Select the connection for the common pin, either J1 is the power and digital interface connector. Connect ground or external connection. Single-ended measure- to DC590 serial controller with supplied 14-conductor ments are taken with respect to this pin. ribbon cable. JP2 and JP3: Select the source for differential reference. ANALOG CONNECTIONS Selecting 5V and GND will use the onboard 5V reference. Select EXT to use an external reference. Analog signal connections are made via the turret posts along the edge of the board (CH0 to CH15.) Also, if you are JP5: Select notch frequency, 60Hz or 50Hz. Alternatively, connecting the board to an existing circuit, make full use this jumper may be removed and an external conversion of the four ground connections at the corners of the board. clock applied to the center pin of JP5. EXPERIMENTS Figure 2 shows a number of applications for the LTC2418. CH7 Channel 7 measures the output of a resistive attenuator. CH0, CH1, CH2 Channels 0 and 1 measure the differential output of an CH8, CH9 Intersema MS5401 absolute pressure sensor. The 6.8k Channels 8 and 9 measure the drop across a Deltec SWE- resistor performs a first order temperature compensation 3000-50 current shunt. Up to 3000A can be measured, of the bridge output. CH2 measures the bridge voltage, with a resolution of 60mA. With careful grounding, both which provides a convenient temperature measurement. positive and negative currents can be measured. Care This can also be used to perform further temperature must be taken to ensure that both inputs stay more posi- compensation in software. tive than GND0.3V. CH3 CH10 Channel 3 measures the output of a thermistor in a half Channel 10 is buffered with an LT1793 FET input amplifier bridge circuit. Many thermistors will work, the constraints suitable for very high source impedance measurements. are that the bridge output must have an impedance of less than 20k and the voltage must not go above V /2. REF CH11 CH4 Channel 11 measures the output of a precision rectifier. Channel 4 measures the output of a type J thermocouple. CH12, CH13 The circuit shown for channel 3 can be used for cold junc- tion compensation. The cold junction sensor should be Channels 12 and 13 measure a 3-wire RTD. The differential close to the connections of the thermocouple to the board. voltage is the output, and CH12 single-ended reading is the ground lead compensation. CH5 CH14, CH15 Channel 5 measures the output of an Omega OS36-01 infrared thermocouple. This can be used for remote tem- Channels 14 and 15 measure the output of a 350 bridge. perature measurement. This is standard for a wide variety of sensors. Typically the full-scale output voltage is only 10mV. However, the CH6 LTC2418 still gives 13 effective bits of resolution with no Channel 6 measures the photocurrent of a Hamamatsu amplification. S1336-5BK photodiode. dc571af 2