8.3.1 Analog Input

The input stage of the ISO224 feeds a switched capacitor, feed-forward ΔΣ modulator. The modulator converts the analog signal into a bitstream that is transferred over the isolation barrier, as described in the Isolation Channel Signal Transmission section. The high-impedance and low bias-current input of the ISO224 makes the device suitable for isolated voltage sensing applications.

Figure 41 visualizes the difference in the transfer function of the ISO224 depending on the input signal V_IN, as specified in the Recommended Operating Conditions table. With the input voltage within the specified full-scale range V_FSR, the output of the device changes in a linear way with small error as specified by the nonlinearity parameter in the Electrical Characteristics table. If the input signal exceeds the V_FSR range, the nonlinearity of the output signals increases and the amplitude clips at V_IN = V_CLIPPING.

Figure 41. Transfer Function of the ISO224

There are two restrictions on the analog input signal at the IN pin. First, if the input voltage V_IN exceeds the range of –15 V to 15 V, the current must be limited to 10 mA to prevent damage to the input clamp, see the Input Clamp Protection Circuit section for further information. In addition, the linearity and noise performance of the ISO224 are ensured only when the analog input voltage remains within the specified linear full-scale range (V_FSR).