This high-speed, low-side over-current detection solution is implemented with a single zero-drift fast-settling amplifier (OPA388) and one high-speed comparator (TLV3201). This circuit is designed for applications that monitor fast current signals and over-current events, such as current detection in motors and power supply units.
The OPA388 is selected for its widest bandwidth with ultra-low offset and fast slew rate. These parameters allow the circuit to be a well-balanced, high-speed solution in order to accurately detect high frequency current components. In applications that only require average current detection, devices with less bandwidth can be used like the LPV821. In applications that require faster response time, devices with larger bandwidth can be used like the THS4521.
The TLV3201 is selected for its fast response due to its small propagation delay of 40 ns and rise time of 4.8 ns. This allows the comparator to quickly respond and alert the system of an over-current event all within the transient response time requirement. The push-pull output stage also allows the comparator to directly interface with the logic levels of the micro-controller. The TLV3201 also has low power consumption with a quiescent current of 40 µA.
Typically for low-side current detection, the amplifier across the sense resistor can be used in a non-inverting configuration. The application circuit shown, however, uses the OPA388 as a differential amplifier across the sense resistor. This provides a true differential measurement across the shunt resistor and can be beneficial in cases where the supply ground and load ground are not necessarily the same.
Dedicated current sense amplifiers can also be an option for high-speed current detection. The trade-offs for each option should be taken into account when deciding on a current sense solution. Integrated solutions can provide larger bandwidth and savings on board space, but can be more costly and offer limited customization. Discrete solutions can be lower cost and easily customizable, but could require precision resistors to increase measurement precision.
Download PDF: High-Speed-Overcurrent-Detection
Source: Texas Instrument