SBAS655F September   2014  – January 2020

PRODUCTION DATA.

1. Features
2. Applications
3. Description
1.     Device Images
4. Revision History
5. Device Comparison Table
6. Pin Configuration and Functions
7. Specifications
8. Detailed Description
1. 8.1 Overview
2. 8.2 Functional Block Diagram
3. 8.3 Feature Description
4. 8.4 Device Functional Modes
9. Application and Implementation
1. 9.1 Application Information
2. 9.2 Typical Applications
1. 9.2.1 Frequency Inverter Application
2. 9.2.2 Isolated Voltage Sensing
3. 9.2.3 What To Do and What Not To Do
10. 10Power Supply Recommendations
11. 11Layout
12. 12Device and Documentation Support
13. 13Mechanical, Packaging, and Orderable Information

• DW|16
• DW|16

#### 9.2.2.2 Detailed Design Procedure

As indicated in Figure 56, the output of the integrated differential amplifier is internally biased to a common-mode voltage of 2 V. This voltage results in a bias current IIB through the resistive network R4 and R5 (or R4' and R5') used for setting the gain of the amplifier. The value range of this current is specified in the Electrical Characteristics table. This bias current generates additional offset error that depends on the value of the resistor R3. Because the value of this bias current depends on the actual common-mode amplitude of the input signal (as illustrated in Figure 57), the initial system offset calibration does not minimize its effect. Therefore, in systems with high accuracy requirements, TI recommends using a series resistor at the negative input (AINN) of the AMC1304 with a value equal to the shunt resistor R3 (that is, R3' = R3 in Figure 56) to eliminate the affect of the bias current.

This additional series resistor (R3') influences the gain error of the circuit. The effect can be calculated using Equation 5 with R5 = R5' = 50 kΩ and R4 = R4' = 2.5 kΩ (for the AMC1304x05) or 12.5 kΩ (for the AMC1304x25).

Equation 5.