SBASAA7A May   2021  – September 2021

PRODUCTION DATA

1. Features
2. Applications
3. Description
4. Revision History
5. Pin Configuration and Functions
6. Specifications
7. Detailed Description
1. 7.1 Overview
2. 7.2 Functional Block Diagram
3. 7.3 Feature Description
4. 7.4 Device Functional Modes
8. Application and Implementation
1. 8.1 Application Information
2. 8.2 Typical Application
3. 8.3 What To Do and What Not To Do
9. Power Supply Recommendations
10. 10Layout
11. 11Device and Documentation Support
12. 12Mechanical, Packaging, and Orderable Information

• DWL|8

### 8.2.2 Detailed Design Procedure

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 (VFSR) of the AMC1411 that is 2 V. This voltage is calculated as RSNS = VFSR / (VDC-link, max – VFSR) x RTOP, where RTOP 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.

Table 8-2 Resistor Value Example
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, ICROSS 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