1. OPA340 driving ADS7816 - 12bit ADC
Errol Leon, Analog Applications
Precision Linear Analog Applications
October 5, 2016

2. Summary Assumptions of ADC 5V supply same as Vref Fclk runs at 3.2MHz
Model is ½ LSB accurate
Model and simulate 12 bit ADC from ADS7816 datasheet
Model and simulate OPA340 directly driving 12 bit ADC ADS7816
Model and simulate OPA340 directly driving 12 bit ADC ADS7816 with Rflt and Cflt
Summary and recommended circuit

3. Modeling ADS bit ADC

4. ADS7816 - ADC Modeling - Calculations

5. ADS7816 - ADC Modeling - Calculations

6. ADS7816- ADC Modeling- Schematic
Equivalent circuit of ADC
CSH - sample capacitor 25pF
RSW – switch resistance 187Ω
R1 – voltage source interface resistance 100Ω

7. ADS7816- ADC Modeling- Simulation

8. Modeling OPA340 directly driving ADS7816

9. OPA340 directly driving ADS7816- ADC Modeling- Schematic
R2, R3, and R4 are used only for simulation convergence.

10. Transient Analysis of OPA340 directly driving ADS7816 circuit Settling Time
Settling time within a ½ LSB of Verror at 11.61uV

11. Modeling OPA340 with RC Filter ADS7816

12. OPA340 with RC Filter to ADS7816- ADC Modeling- Schematic
R2, R3, and R4 are used only for simulation convergence.

13. Transient Analysis of OPA340 directly driving ADS7816 circuit Settling Time
Settling time within a ½ LSB of Verror at 438.1uV

14. Transient Analysis of DC Voltage Circuit Settling Time - Summary
Both circuits are within a 1/2 LSB setting time.
Recommended to use RC filter to mitigate 2nd and 3rd order effects based off of parasitic switching capacitance from the ADC as well as filtering high frequency noise..

15. Op Amp Reference
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All Embedded Schematics in this presentation can be run in the Free TINA_TI SPICE simulator available at: