SPRADA5 April   2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Supplementary Information
    2. 1.2 Features
    3. 1.3 Block Diagram
    4. 1.4 Operation Modes
  5. 2Use Cases
    1. 2.1 Buffer Mode for High-Impedance Source
    2. 2.2 Battery Voltage and Current Monitoring
    3. 2.3 Low-Side Shunt Current Monitoring
    4. 2.4 Three-Phase Low-Side Current Sensing
    5. 2.5 Bidirectional Current Sensing
    6. 2.6 Non-Inverting Amplifier for Low-Voltage Sensors
    7. 2.7 Non-Inverting Amplifier for Bipolar Signals
    8. 2.8 Standalone Mode for Various Applications
  6. 3Summary
  7. 4References

2.6 Non-Inverting Amplifier for Low-Voltage Sensors

Given a small positive signal, the PGA can amplify the signal to increase the dynamic range of ADC sampling and comparator trip monitoring. For example, as shown in Figure 2-9, the PGA module configured in 4x mode amplifies an input signal with a valid range between 0.25V and 0.75V to produce an output signal between 1V and 3V. Please note that no PGA_INM pin connection is needed in this application while using the internal connection to VSSA. Even though the non-inverting mode is supported in Type-1 PGA, using Type-2 PGA helps save a pin to use for other functionalities, such as ADC pin and digital inputs and outputs (AGPIO).

GUID-20230227-SS0I-XGMV-MHG4-ZL02D4XDXMTZ-low.svg Figure 2-9 Non-Inverting Amplifier Implementation Using a PGA Module

The amplified output voltage is calculated as follows.

Equation 6. V P G A _ O U T = ( 1 + R i b R i b ) V S i g n a l

The following code snippet shows where to add custom code to adjust the gain value using the internal gain resistors Ria and Rib, as well as selecting the appropriate filter resistor RFILT connected internally to the output of the PGA module.

//
// Gain
//
#define PGA_GAINVALUE PGA_GAIN_4

//
// Filter Resistor
//
#define PGA_FILTERVALUE PGA_LOW_PASS_FILTER_RESISTOR_50_OHM

//
// P-MUX selection
//
#define PGA_PMUXINPUT PGA_PMUX_POS 

//
// N-MUX selection
//
#define PGA_NMUXINPUT PGA_NMUX_RTAP

//
// M-MUX selection
//
#define PGA_MMUXINPUT PGA_MMUX_NON_INVERTING_GAIN_VSSA

In the code snippet, PGA_GAINVALUE represents the desired gain value for the PGA module, and PGA_FILTERVALUE represents the desired value for the filter resistor RFILT. Please make sure to consult the documentation or reference manual for your specific device to find the available RFILT and gain values, and then replace PGA_GAINVALUE and PGA_FILTERVALUE with the actual values you want to use in your circuit.