quick start guide for demonstration circuit 586 20-bit differential input delta sigma adc 1 ltc2431 description demonstration circuit 586 features the ltc2431, a 20-bit high performance ? analog-to-digital con- verter (adc). the ltc2431 features 3ppm linearity, 10ppm full-scale accuracy, 1ppm offset, and 0.56ppm noise. the inputs and reference are fully differential, with input common mode rejection of 110 db. the ltc2431 is available in a 10 pin ms package and has an easy to use spi interface. dc586 is a member of linear technology?s quickeval? family of demonstration boards. it is de- signed to allow easy evaluation of the ltc2431 and 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. the exposed ground planes allow proper grounding to prototype circuitry. after evaluat- ing with linear technology?s software, the digital sig- nals can be connected to the end application?s proc- essor / controller for development of the serial inter- face. design files for this circuit board are available. call the ltc factory.
quick start guide for demonstration circuit 586 20-bit differential input delta sigma adc 2 quick start procedure connect dc586 to a dc590 usb serial controller us- ing 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 pro- gram will be loaded automatically. click the collect button to start reading the input voltage. details on software features are documented in the control panel?s help menu. tools are available for logging data, changing refer- ence voltage, changing the number of points in the strip chart and histogram, and changing the number of points averaged for the dvm display.
quick start guide for demonstration circuit 586 20-bit differential input delta sigma adc 3 hardware set-up jumpers jp1 ? select the source for ref+, either external or 5.00 volts from the onboard lt1236 reference (de- fault.) jp2 ? select the source for ref-, either external or ground (0 volts, default.) jp3 ? trigger mode, either normal (default) or ex- ternally triggered. jp4 ? notch frequency. thi s selects either 50hz or 60hz rejection mode. remove this jumper when supplying an external clock to the fo turret. jp5 ? trigger input signal. pin 1 is a 5 volt logic signal, pin 2 is ground. when triggered mode is selected on jp3, a rising edge starts a new conver- sion. connection to dc590 serial controller j1 is the power and digital interface connector. connect to dc590 serial controller with supplied 14 conductor ribbon cable. an external conversion clock may be applied to the fo turret to modify the frequency rejection charac- teristics or data output rate of the ltc2431. be sure to remove jp4 before applying an external fo clock! this should be a square w ave with a low level equal to ground and a high level equal to vcc. while up to a 2mhz clock can be used, performance may be compromised. refer to the ltc2431 data sheet. analog connections analog signal connections ar e made via the row of turret posts along the edge of the board. also, when connecting the board to an existing circuit, the ex- posed ground planes along the edges of the board may be used to form a solid connection between grounds. gnd ? ground turrets are connected directly to the internal ground planes. vcc ? this is the supply for the adc. do not draw any power from this point. ref+, ref- ? these are connected to the ltc2431 ref+ and ref- pins. if the onboard reference is be- ing used, the reference voltage may be monitored from this point. an external reference may be con- nected to these terminals if jp1 and jp2 are con- figured for external reference. in+, in- ? these are the differential inputs to the ltc2431.
quick start guide for demonstration circuit 586 20-bit differential input delta sigma adc 4 experiments input noise solder a short wire from th e in- turret post to the in+ turret post. noise should be approximately 0.56ppm (2.8 v.) common mode rejection tie the two inputs (still connected together) to ground through a short wire and note the indicated voltage. tie the inputs to ref+; the difference should be less than 16uv due to the 110 db cmrr of the ltc2431. resolving milliamps with milliohm shunts one application that can benefit greatly from the ltc2431?s input resolution is current measurement. it is advantageous to use a very low resistance shunt to minimize the voltage drop. to demonstrate this, make a simple current shunt by soldering a 1 inch length of 24 gauge copper wire from the in+ turret to the in- turret. thi s is a resistance of ap- proximately 2.4 milliohms. connect the in- turret to the gnd turret through a short wire. start the dem- onstration software and note the initial voltage, which should be close to zero. next, connect in+ to ref+ through a 1k resist or, which will allow ap- proximately 5ma to flow through the shunt. the indicated voltage should increase by approximately 12uv (the actual increase will depend on the toler- ance of the wire material, diameter, and length.) since the common mode range of the inputs ex- tends from ground to vcc, the current shunt can also be used at the ?high side.? to do this, tie the in+ turret to vcc and connect the resistor from in- to ground. thus the current of a circuit can be monitored with minimal impact on supply voltage and without breaking any ground connections. bipolar symmetry to demonstrate the symmetry of the adcs transfer function, connect a stable, low noise, floating volt- age source (with a voltage less than vref/2) from in+ to in- and note the i ndicated voltage. reverse the polarity; the indicated voltage will typically be within 15uv of the first reading multiplied by ?1. one convenient voltage source for this experiment is a single alkaline battery. while a battery has fairly low noise, it is sensitive to temperature drift. it is best to use a large (d-size) battery that is insulated from air currents. a better source is a battery pow- ered series reference such as the lt1790. this part is available with output voltages of 1.25v, 2.048v, 2.5v, 3v, 3.3v, 4.096v and 5v. input normal mode rejection the ltc2431?s sinc4 digital filter is trimmed to strongly reject 50 or 60hz line noise when operated with the internal conversion clock. to measure in- put normal mode rejection, connect in- to a 2.5 volt source such as an lt1790-2.5 reference or a power supply. apply a 10hz, 2v peak-to-peak sine wave to in+ through a 1uf capacitor. 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 60hz. the noise should be almost undetectable in the graph. note that the indicated noise in ppm may still be above that of the datasheet specification because the inputs are not connected to a dc source.
quick start guide for demonstration circuit 586 20-bit differential input delta sigma adc 5
linear technology corporation ltc3407ems parts list dc568a rev 3 7/9/2003 item qty re f des c part number 1 3 cout1,cout2,cin cap, x5r 10uf 6.3v 20% 0805 taiyo yuden jmk212bj106mg 2 2 c2,c1 cap, npo 10pf 50v 10% 0402 avx 04025a100kat 3 0 c3,c4 cap, 0805 tbd 4 1 c5 cap, tant 47uf 10v 20% 6032 avx tajw476m010r 5 7 e1,e2,e3,e4,e5,e6,e7 turrets mill-max 2501-2 6 3 jp1,jp2,jp4 header, 3p 2mm comm con 2802s-03-g1 7 1 jp3 header, 3x2 2mm comm con 2202s-06g1 8 2 l1,l2 ind, 2.2uh taiyo yuden lqlbc25182r2m 10 3 r1,r3,r10 res, 4.7m ohms 5% 1/16w 0402 aac cr05-475jm 11 1 r2 res, 100k ohms 1% 1/16w 0402 aac cr05-1003fm 12 2 r4,r5 res, 604k ohms 1% 1/16w 0402 aac cr05-6043fm 13 1 r6 res, 887k ohms 1% 1/16w 0402 aac cr05-8873fm 14 1 r7 res, 280k ohms 1% 1/16w 0402 aac cr05-2803fm 15 1 r8 res, 402k ohms 1% 1/16w 0402 aac cr05-4023fm 16 1 r9 res, 301k ohms 1% 1/16w 0402 aac cr05-3013fm 17 1 u1 ic, ltc3407ems linear tech. ltc3407ems 1 of 1
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