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ADS1602IPFBT Datenblatt(PDF) 16 Page - Texas Instruments |
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ADS1602IPFBT Datenblatt(HTML) 16 Page - Texas Instruments |
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16 / 30 page ![]() S 1 S 2 10pF AINP ADS1602 8pF VMID S 1 S 2 10pF AINN 8pF VMID AGND 392W OPA2822 ADS1602 AGND OPA2822 40pF V (1) CM V (1) CM V (1) CM 100pF AINP AINN 100pF (3) 392W 40pF 100pF (2) (2) (2) (2) - V IN 2 V IN 2 392W 392W 392W 0.01 F m 0.01 F m 392W 1 F m 392W 1kW 1kW 1 F m 392W 49.9W 49.9W On S 1 S 2 Off On Off t = f SAMPLE CLK 1/ ADS1602 THS4503 22pF -VIN +V IN 100pF 100pF AINP AINN 100pF 24.9W 392W 392W 24.9W 392W 392W 22pF V CM ADS1602 SBAS341E – DECEMBER 2004 – REVISED OCTOBER 2011 www.ti.com INPUT CIRCUITRY drivers close to the inputs and use good capacitor bypass techniques on the supplies, such as a smaller The ADS1602 uses switched-capacitor circuitry to high-quality ceramic capacitor in parallel with a larger measure the input voltage. Internal capacitors are capacitor. Keep the resistances used in the driver charged by the inputs and then discharged internally circuits low —thermal noise in the driver circuits with this cycle repeating at the frequency of CLK. degrades the overall noise performance. When the Figure 39 shows a conceptual diagram of these signal can be ac-coupled to the ADS1602 inputs, a circuits. Switches S2 represent the net effect of the simple RC filter can set the input common-mode modulator circuitry in discharging the sampling voltage. The ADS1602 is a high-speed, capacitors; the actual implementation is different. The high-performance ADC. Special care must be taken timing for switches S1 and S2 is shown in Figure 40. when selecting the test equipment and setup used with this device. Pay particular attention to the signal sources to ensure they do not limit performance when measuring the ADS1602. Figure 39. Conceptual Diagram of Internal Circuitry Connected to the Analog Inputs (1) Recommended VCM = 1.5V. (2) Optional ac-coupling circuit provides common-mode input voltage. (3) Increase to 390pF when fIN ≤ 100kHz for improved SNR and THD. Figure 41. Recommended Driver Circuit Using the OPA2822 Figure 40. Timing for the Switches in Figure 39 DRIVING THE INPUTS The external circuits driving the ADS1602 inputs must be able to handle the load presented by the switching capacitors within the ADS1602. The input switches S1 in Figure 39 are closed for approximately one-half of the sampling period, tSAMPLE, allowing only ≉ 11ns for the internal capacitors to be charged by the inputs when fCLK = 40MHz. Figure 41 and Figure 42 show the recommended circuits when using single-ended or differential op amps, respectively. The analog inputs must be driven differentially to achieve optimum performance. The Figure 42. Recommended Driver Circuit Using external capacitors, between the inputs and from the THS4503 Differential Amplifier each input to AGND, improve linearity and should be placed as close to the pins as possible. Place the 16 Copyright © 2004–2011, Texas Instruments Incorporated |
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