Design Description

Current shunt monitors are amplifiers that are optimized to read small shunt voltages over very wide common mode ranges. This example application uses the INA190A4 to translate a ±6-A current into a 0-V to 3-V range for the ADC. Note that this is a high sided current measurement with a 40V common mode range. Detailed theory on current sensing is covered in Using current sense amplifiers to solve today’s current sensing design challenges. Compared to other current shunt devices the INA190 has very low offset voltage, bias current, and drift. This excellent DC performance allows smaller for smaller input voltage ranges without compromising accuracy as the offset is small compared to the input signal. The use of small shunt resistors is an advantage as the power dissipated in the shunt is smaller for smaller resistors for a given current level. The ADS7042 is a 12-bit 1MSPS SAR ADC with a 3V analog input range. The design shown in this document can be modified for other data converters and input ranges. This design can be used a wide range of applications where current needs to be monitored such as notebook computers, cell phones, and battery management.

Design Notes

1. The tolerance in the shunt resistor, R_SENSE, will translate into a gain error. Choose the tolerance according to your error budget. Note that the maximum specified gain error for the INA190A4 is 0.3% and a common tolerance 1-m resistor is 0.5% to 1.0%.
2. Selection of the shunt resistor is covered in the component selection section. The objective is to minimize power dissipation while maintaining good accuracy.
3. Use a C0G capacitor for C_FILT to minimize distortion.
4. The example design is for a bidirectional current source (for example, ±6A). A similar approach can be followed for an unidirectional current source (for example, 0A to 12A). The main difference is that the reference input pin would connect to ground as opposed to 1/2 V_REF.

Component Selection

AC Transfer Characteristics

The data sheet specified bandwidth of 33kHz for the INA190A4 closely matches the simulated 35kHz bandwidth. The input ADC filter is designed to minimize charge kickback and does not limit the bandwidth ( f_{c(ADC filter)} = 312kHz ). See TI Precision Labs - Op Amps: Bandwidth 1 for more details on this subject.

Noise Simulation

The noise hand calculation follows. This calculation assumes that the filter is a first order but inspection of the bandwidth simulation shows a more complex response.

Note that the calculated and simulated match well. Refer to TI Precision Labs - Op Amps: Noise 4 for detailed theory on amplifier noise calculations, and Calculating the Total Noise for ADC Systems for data converter noise.

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Link to Key Files

Texas Instruments, TINA source files, software support