Forum Post: RE: ADS1256 strange problems

dear 

i am glad that i got very good response from TI and their application engineer and i will be very thankful for you about further help regarding to my application  i will request that redirect some one from power and dac relating application engineer who will give me better way about components choice and their  application either here on community or on my email address 

                 at this point  lets start the designing process my maximum voltage reading will be 100.0000 volt dc and 10.00000 amperes dc i mentioned digits to show the scale factor where two channel will shows 100.0000 volts dc range (one for positive and one for negative volts with 100u volt precision)and one will shows 10.000000 positive dc volt (10u volt precision) three channel will shows 10.00000  ampere dc  (two positive dc amperes and one negative dc amperes @ 10u ampere precision) range while per channel sample rate should be minimum 2sample/sec so total 12 samples/sec and preferred is 4 (samples/sec)/channel and total gross 24 samples/sec

where channel means volt or ampere reading input 

                     we have our own pcb manufacturing   but only for single and double layer pcb's mostly time we prefer single layer pcb for quick production and cost reduction purpose while double sided pcb consume more time and cost is high so my prefer target is 1)single sided pcb or 2)single side routing with other side  layer of ground plane and at last is 3) full double sided pcb  so  guide me as per described basis that what is best pcb layout to get target performance

          currently i have these components available in my inventory list and i will be glad if you help me out to find better and economical components relating to my application if email support is faster then plz proceed via email so this is my inventory list

now you can see the manufacturing cost is the major issue 

ads8517 /ads8515 built in ref and ref driver circuitry easy input drive can be used with analog multiplexer and over sampling with dither method will give high resolution even with high sample rate then delta sigma adc i also posted about this thing in this link but did not get any attention from any one 

http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/310318.aspx

ads8555 built in ref and 6 sar adc in a single package but requires input driver for each adc channel same thing oversampling for high resolution and nearest driver for input is ne5532 with compare to opa211 / opa2211 and very price competitive little loss of performance can be gained from oversampling if using ne5532 for driver stage 

ads1282 very costly but have good specifications 

 ads1248 every thing is best

Low-Noise PGA: 48nV at PGA = 128 4

Differential/7 Single-Ended Inputs 

Very Low Drift Internal Voltage Reference 

Analog Supply Unipolar (+2.7V to+5.25V)/Bipolar (±2.5V) Operation

Internal Temperature Sensor which is usable to determine voltage ref temp drift error for compensation 

Self and System Calibration

Single-Cycle Settling for All Data Rates

Simultaneous 50/60Hz Rejection at 20SPS

and price is also very economical but ohhh noooo input impedance that's very wrong 400 ohm only what to do about that input impedance

ads1259 have good specifications but single channel and requires input driver and multiplexer for reading six channels which increase cost and complexity but if economical driver stage and multiplexer option is available then its far best due to its data sheet specifications

ads131e08/06 for eight /six channel Analog Front-End but did not got chance to test the performance and price is also very good can you plz give me review about this part that what maximum output performance can be achieved using this ic by extra oversampling like using 1k sample/sec and further oversampling down to 4 or 2 sample/sec in external micro-controller

ads1252 very difficult to interface no voltage reference and no input stage driver poor performance high cost

ads1271 high sample rate but i have seen 17 bit performance with normal buffer opamp driver on bread board and i belive that oversampling will give the required performance but again cost is issue

ads1256 this is good ic but tough to drive in my past experience single channel 20-bit result on prototyping with application circuit described for voltage ref in datasheet and input shorted settling time is another issue voltage reference and buffer itself is very costly causes to increase the manufacturing cost

now this is my servey about TI adc ic's price feature performance description and distributor price may be i left some things far more better and economical components from TI that's why i am here to get help from application specialist hoping for better guide from TI application engineer

regards

Shams Iqbal