SBAS897C March 2018 – June 2022 AMC1311-Q1
PRODUCTION DATA
The 100-μA, cross-current requirement at the maximum DC bus voltage (600 V) determines that the total impedance of the resistive divider is 6 MΩ. The impedance of the resistive divider is dominated by the top portion (shown exemplary as RX1 and RX2 in Figure 8-1) and the voltage drop across RSNS can be neglected for a moment. The maximum allowed voltage drop per unit resistor is specified as 100 V; therefore, the minimum number of unit resistors in the top portion of the resistive divider is 600 V / 100 V = 6. The calculated unit value is 6 MΩ / 6 = 1 MΩ and matches a value from the E96 series.
RSNS is sized such that the voltage drop across the resistor at the maximum DC-bus voltage (600 V) equals the linear full-scale range input voltage (VFSR) of the AMC1311-Q1, which is 2 V. The value of RSNS is calculated as RSNS = VFSR / (VDC-Bus, max – VFSR) × RTOP, where RTOP is the total value of the top resistor string (6 × 1 MΩ = 6 MΩ). RSNS is calculated as 20.07 kΩ. The next closest, lower value from the E96 series is 20 kΩ.
Table 8-2 summarizes the design of the resistive divider.
| PARAMETER | VALUE | |
|---|---|---|
| Unit resistor value, RX | 1 MΩ | |
| Number of unit resistors | 6 | |
| Sense resistor value, RSNS | 20 kΩ | |
| Total resistance value | 6.02 MΩ | |
| Resulting current through resistive divider, ICROSS | 99.7 μA | |
| Resulting full-scale voltage drop across sense resistor RSNS | 1.993 V | |
| Power dissipated in unit resistor RX | 9.9 mW | |
| Total power dissipated in resistive divider | 59.8 mW | |