SBASAA7A May 2021 – September 2021 AMC1411
PRODUCTION DATA
The 300-μA cross-current requirement at the maximum DC-link voltage (1200 V) determines that the total impedance of the resistive divider is 4 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 75 V; therefore, the minimum number of unit resistors in the top portion of the resistive divider is 1200 V / 75 V = 16. The calculated unit value is 4 MΩ / 16 = 250 kΩ and the next closest value from the E96 series is 249 kΩ.
RSNS is sized such that the voltage drop across the resistor at the maximum DC-link voltage (1200 V) equals the linear full-scale range input voltage (V_{FSR}) of the AMC1411 that is 2 V. This voltage is calculated as RSNS = V_{FSR} / (V_{DC-link, max} – V_{FSR}) x R_{TOP}, where R_{TOP} is the total value of the top resistor string (16 x 249 kΩ = 3984 kΩ). RSNS is calculated as 6.65 kΩ and matches a value from the E96 series.
Table 8-2 summarizes the design of the resistive divider.
PARAMETER | VALUE | |
---|---|---|
Unit resistor value, RX | 249 kΩ | |
Number of unit resistors | 16 | |
Sense resistor value, RSNS | 6.65 kΩ | |
Total resistance value | 3990.65 kΩ | |
Resulting current through resistive divider, I_{CROSS} | 300.7 µA | |
Resulting full-scale voltage drop across sense resistor RSNS | 2.000 V | |
Power dissipated in unit resistor RX | 22.5 mW | |
Total power dissipated in resistive divider | 361 mW |