SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
Low-side current sensing connects the sensing resistor between the load and ground. To not adversely affect current flow, the current resistors have a small value that produces a proportionally small voltage across them. The small voltage across the shunt resistor must usually be boosted from tens or hundreds of millivolts to tenths of a volt or volts for upstream conversion by an analog-to-digital converter (ADC). This task can be performed by PGA. Figure 18-17 shows the low-side current sensing using PGA.
In this circuit, the amplifier gain is set by the ratio of Rib divided by Ria. If the divider resisters R1=Rib and R2=Ria, then the amplified voltage can be calculated by:
If low-pass filtering is desired, an external capacitor in conjunction with internal filter resistors RFILT can be used. The filter cutoff frequency is estimated using: