Most analog chips (comparators, op amps, instrumentation amplifiers, reference sources, filters, etc.) are used to process voltage signals. When used to process current signals, designers have fewer choices and more headaches. This is unfortunate because direct monitoring and measuring current has great advantages. For motor torque, solenoid force, LED brightness, solar cell illumination, and battery energy, the best way to monitor current is by observing the current. Therefore, there is a need for a circuit capable of accurately detecting a current and converting the current into a voltage that is easy to amplify, adjust, and measure in a common voltage type device (amplifier, comparator, ADC, etc.).
Although a resistor can convert current into voltage, the resistor itself does not provide a complete solution. The most common solution is to use a sense resistor that is placed in series directly in the current path, and an amplifier is used to isolate and regulate the voltage across the resistor (VSENSE).
Figure 1: Principle of the current detection circuit.
Figure 2: Actual current detection circuit.
Combine amplifiers and sense resistors
At first glance, connecting a resistor to ground in series seems to be very similar to the most straightforward current sensing scheme. This technique is known as low-side current sensing (Figure 3A), which requires no ground path to exist because the ground path shunts the current around the sense resistor or causes adjacent circuits to contribute current. Especially when the mechanical housing is system ground, it is not practical to connect a sense resistor in series. Similarly, because the ground is not a good conductor, the ground voltages at different points in the system will be inconsistent, requiring a differential amplifier for precision measurements (Figure 3B).
Figure 3A: Low-side current sensing topology.
Figure 3B: Low-end current detection circuit implementation
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- Ultrafast respond time and high efficiency.
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- Full protection: OVP/OCP/OPP/OTP/SCP
- Voltage drop compensation by remote sense line.
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