Current sense amplifiers
ST's current sense amplifier IC portfolio offers a large variety of high-performance devices.
The main features of ST's portfolio of current sensing ICs ensure robustness and application safety:
Tolerance to high voltage ranges and protection mechanisms to handle negative voltage are essential in high-power systems such as batteries in electric vehicles. Our current sense amplifiers can work in high voltage applications avoiding additional external protections components and simplifying the final schematic.
Precision / high-accuracy
Using a precision current sense amplifier allows designers to measure small voltage drops across shunt resistors with minimal error. Small shunt resistors values are necessary to minimize the power dissipation. Thanks to highly accurate current measurements, precision current sense amplifiers offer a better efficiency and thermal performance.
What is a current sense amplifier?
A current sense amplifier is a differential amplifier providing an analog output voltage proportional to the current flowing into a load connected on its input. This device provides several benefits for designers, including the possibility to:
- measure current ranging from a few milli amperes to several hundreds
- perform real-time current measurement in several topologies
- precisely measure current, thanks to an integrated matched resistive gain network
- reduce PCB size thanks to integrated gain resistance
- sustain extended input common mode voltage, far beyond the power supply rail
How does a current sense amplifier work?
The working principle of a current sensing amplifier is based on Ohm's law. When load current flows through a shunt resistor (Rshunt) present on inputs, it generates a voltage drop called VSENSE. This voltage is generally small to limit power dissipation losses.
VSENSE is then amplified with an internal instrumentation amplifier. The resulting output voltage (VOUT) is a voltage which is proportional to the Ioad current. It can then be processed with an ADC (analog-to-digital converter).
What are the main types of current sense amplifiers?
The current is measured between the supply rail and the load. The DC voltage applied on the input pins can be much higher than the power supply.
- Short-to-ground fault detection
- High immunity against ground disturbance
- Current monitored directly from the source
- High-input common-mode voltages
- Support fast variation of input common mode voltage
The current is measured between the load and the ground. The voltage applied on the input pins is close to the ground.
- Simple implementation
- Cost-effective solution
- VICM (input common-mode voltage) close to GND (zero-voltage point)
- Difficult to detect short-cut to ground
- Multiple output power supply (all current are combined in GND line)
- May disturb the ground voltage seen by the load
Bi-directional VS unidirectional
In some applications, the current can flow into the load in both directions. This is the case for motor control applications used in H-Bridge topologies. In this case, the current sense amplifier must have one additional pin, called VREF. The VREF pin allows designers to set the output reference anywhere within the power supply range. A bidirectional amplifiers can be used as a unidirectional current sense amplifier, setting the reference to one voltage rail.
How to choose the right current sense amplifier for your design?
Define the configuration required for your device
High-side configuration: Select the current sense amplifier depending of the max common mode voltage (VICM) required by the application and its power supply (VCC).
Low-side configuration: Select a current sense amplifier that can work with a common mode voltage close to 0 volts.
Operational amplifiers can be also used, adding 4 external resistors to set the gain. However, the size of the PCB will be larger and accuracy can be lower.
Look into the direction of current flows
After defining the configuration required, ask yourself if the current in your application needs to flow in both directions, in order to choose a bidirectional or unidirectional current sensing.
If accurate measurements are needed
Several parameters related to the application must be taken into account. Depending on the current range to be measured and the shunt resistor used, the voltage drop into the shunt resistor can be very small (hundreds of µV). For better accuracy, it is important to consider the error related to offset and accuracy gain.