Current sense amplifiers (also called current shunt amplifiers) are special purpose operational amplifiers (op amps) that output a voltage proportional to the current flowing in a power rail. They utilize a "sense resistor" to convert the load current in the power rail to a small voltage, which is then amplified by the current sense amplifier. Renesas offers unidirectional high-side and low-side current sense amplifiers.
What are Current Sense Amplifiers
Current sense amplifiers simplify the design of complex current monitoring circuits. The addition of a ground-sensing measurement capability enables a new level of fault detection that are useful in a wide range of power applications. Their unique features and wide range of gain and accuracy choices make them suitable for use in compact enclosures where high accuracy and low power dissipation are important.
The ISL28005 and ISL28006 are ground-sensing current sense amplifiers that amplify milli-volt current signals developed across sub-1Ω sense resistors. The simplest type of current sense amplifiers use single stage op amp circuits that take their power from the same voltage source that generates the current to be measured. These are realized using an op amp and a handful of external components to condition the amplifier to requirements of the application. As long as the measured current signal remains within the common mode voltage range of the op amp, these circuits are simple.
Current Sense Amplifier Applications
Applications where the amplifier operates from a different power source than the load adds complexity, particularly when the measured current is at voltage levels much higher than the op amp supply voltage. In many cases an additional amplifier circuit is needed to perform the voltage translation to step-down the current sense signal to match the common mode input range of the current sense amplifier.
Current sensing in multi-output power supply systems is one application where one or more power supply output voltages must be measured using current sense amplifiers powered from a much lower supply voltage. The ISL2800x family of current sense amplifiers are ideal for these applications because they perform precise current sensing operating from supply voltages as low as 3.3V, while sensing from supply voltages as high as 28V. These current sense amplifiers are very simple, self-contained solutions requiring only an external current sense resistor. The space-saving SOT-23 package and low component count results in very small footprint.
For more design information, see AN1567: Unidirectional Current Sense Amplifiers.
Renesas provides a complete portfolio for power monitor and current sensing solutions: