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Low Side Current Sensing

How It Works

Low side current sensing techniques connect the current sensor element between the load and ground. Current is measured by looking at the voltage drop across a resistor placed between the load and ground (see figure 2)

Figure 2: Sense resistor between load and ground

Advantages

  • Straightforward, easy, and rarely requires more than an op-amp to implement
  • Inexpensive and precise

Increasing demands for precision are driving the interest in using high precision devices such as the OPA335 in low side current sensing applications (see figure 3)

Low side current sensing using the TI OPA335

Figure 3: Low side current sensing using the TI OPA335

Disadvantages

  • Adds undesirable resistance in the ground path
  • May require an additional wire to the load that could otherwise be omitted

When to Choose Low Side Current Sensing

  • When you can!
  • Choosing low side current sensing is almost always the best option if your application can tolerate the extra disturbance in the ground path.