SENSING TECHNIQUES: HIGH SIDE Vs LOW SIDE SENSING
There are two basic techniques for current sensing applications, viz., low side current sensing and high side current sensing, based upon the placement of sense resistor(between the supply and load or between load and ground).
· Low-Side Current Sensing
Low-side current sensing connects the sensing resistor between the load and ground. Normally, the sensed voltage signal (VSEN = ISEN × RSEN) is so small that it needs to be amplified by subsequent op amp circuits to get the measurable output voltage (VOUT).
¨ Low input Common mode voltage
¨ Ground referenced input and output
¨ Simplicity and low cost
¨ Ground path disturbance
¨ Load is lifted from system ground since RSEN adds undesirable resistance to the ground path.
¨ High load current caused by accidental short goes undetected
Low –side current sensing should be chosen when short circuit detection is not required and ground disturbances can be tolerated.
· High-Side Current Sensing
High-side current sensing connects the sensing resistor between the power supply and load. The sensed voltage signal is amplified by subsequent op amp circuits to get the measurable VOUT.
¨ Eliminates ground disturbance
¨ Load connects system ground directly
¨ Detects the high load current caused by accidental shorts
¨ Must be able to handle very high and dynamic Common mode input voltages
¨ Complexity and higher costs
High –side current sensing should be chosen when VCM range of the Difference amplifier is wide enough to withstand high Common mode input voltages