This discussion covers the 230-V_RMS example. The procedure for calculating the resistive divider for the 120-V_RMS use case is identical.

The 100-μA crosscurrent requirement at peak input voltage (360 V) determines that the total impedance of the resistive divider is 3.6 MΩ. The impedance of the resistive divider is dominated by the top and bottom resistors (shown exemplary as RL11 and RL12 in Figure 8-1) and the voltage drop across RL1SNS can be neglected for a moment. The maximum allowed voltage drop per unit resistor is specified as 75 V, therefore the total, minimum number of unit resistors in the top and bottom portion of the resistive divider is 360 V / 75 V = 5. The calculated unit value is 3.6 MΩ / 5 = 720 kΩ and the next closest value from the E96-series is 715 kΩ.

RL1SNS is sized such that the voltage drop across the resistor at maximum input voltage (360 V) equals the linear full-scale range input voltage (V_FSR) of the AMC3336-Q1 that is +1 V. This voltage is calculated as RL1SNS = V_FSR / (V_Peak – V_FSR) x (R_TOP + R_BOT), where (R_TOP + R_BOT) is the total value of the RL11 and RL12 resistor strings (5 x 715 kΩ = 3575 kΩ). RL1SNS is calculated as 9.96 kΩ and the next closest value from the E96-series is 10 kΩ.

Table 8-2 summarizes the design of the resistive divider.

The AMC3336-Q1 requires a single 3.3-V or 5-V supply on its low-side. The high-side supply is internally generated by an integrated DC/DC converter, as explained in the Section 7.3.5 section.