AD1256

Application information

General advice

  AD1256 It has very high resolution A/D converter . In order to give full play to its best performance, we need to pay special attention to its Power supply circuit and PCB The design of the . chart 25 Provides AD1256 Basic connection . It is especially recommended that both analog and digital power supplies use a ground . This ground should be shared with bypass capacitors and analog conditioning circuits . But avoid using the ground plane with interference such as single chip microcomputer . If ADS1255/6 Adopt separate ground plane , We need to ensure that the analog and digital planes are connected . Make sure ADS1255/6 Simulate AGND And digital DGND There is no voltage difference between .
   Like any precision circuit , All need to use good power bypass technology . It is better to use small ceramic capacitors in parallel with large capacity tantalum capacitors or large capacity low-voltage ceramic capacitors . The capacitor needs to be placed close to the power pin , Especially ceramic capacitor . Secondly, use digital logic circuits with the lowest voltage . This will help reduce coupling feedback to analog inputs .Avoid ringing on the digital inputs. Connect a small resistor in series on the digital pin (≈100Ω) It helps to control the channel impedance . If not used $\overline{RESET}$ perhaps $\overline{SYNC}/\overline{PDWN}$ Input , Then you can connect the topic directly to ADS1255/6 Of DVDD Pin .
  ** Special attention should be paid to the reference source and analog input . This is the most important circuit .** At the input of the voltage reference , Use low equivalent series resistance (ESR) Capacitor bypass . Make sure these capacitors are as large as possible , To maximize the filtering ability on the reference output .ADS1255/6 It has very excellent performance , If you don't choose a good voltage reference carefully , Then it is easy to limit the overall performance . When using an independent voltage reference , Make sure it has very low noise , Very low drift , And can drive ADS1255/6 Reference input . For not suitable for direct drive ADS1255/6 Voltage reference ( for example , High output impedance reference or resistance voltage divider ), You can use as shown in the figure 26 The recommended buffer circuit shown .Ratiometric measurements,where the input signal and reference track each other, are somewhat less sensitive, but verify the reference signal is clean.

   Usually , Input only needs a simple RC filter ( Pictured 25 Shown ). This circuit limits the high-frequency noise near the modulator frequency ; See the frequency response section . Avoid using low-grade capacitor dielectric , To reduce temperature changes and leakage . Keep the input track as short as possible , And place the component close to the input pin . When using ADS1256 when , Please make sure to filter all input channels in use .