Other Parts Discussed in Thread: INA351, INA181, , INA281, INA213, INA191, INA190
Dear Community,
We're working on 2 highly cost-sensitive application use cases where we have to measure the voltage drop across a Resistor connected in series to the analog signaling circuit. Both Signaling circuit & the measuring circuits have separate grounds & potential voltages.
Accordingly, based on our initial research so far, we are exploring the TI-suggested Current Sense Amplifier (CSA - INA181, INA185, INA213-C) and Instrumentation Amplifier (IA - INA351) for their cost-optimized, higher accuracy with reduced footprint & overall solution size. We have queries regarding the interpretation of datasheets and suitable selection.
Our Queries:
Datasheet Specifications Interpretation - Typical or Maximum?
In INA181's datasheet, should we consider Typical or Maximum values for cost-optimized designs?
The low-probability extremes of OpAmp Input Offset Voltage are -280µV to 240µV in the graph published in the datasheet & do not match the stated ±500µV maximum offset limit. Similar is the case with Gain Error values. Are we missing something in our interpretation here?
What to refer to for our use case where cost-optimized selection is the key?
Potential elimination of Offset Voltage Error with Zero Reference Calibration:
Can implementing single Zero Reference Calibration across the AFE signal chain minimize offset voltage errors device-to-device? How much error reduction can be expected in practical circuits where the ADC input is a Unipolar positive range of 0-3.3V?
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Now kindly consider the following use cases:
4-20mA Receiver Circuit:
System specifications:
- Current: 4-20mA (Unipolar DC waveform)
- Voltage:
- Current Loop: 0-36V (0-24V acceptable)
- Measuring circuit: 0-3.3V
- BW: 1kHz maximum
- Shunt resistor: between 0.5mΩ to 160Ω
- Error budget: 0.2-0.4%
If opting for INA213-C (improved Offset & Gain errors wrt to INA181), are these error calculations correct?
Key Error budgeting:
- Gain Error:
- 0.02% (Typical),
- 0.5% (Maximum)
- Offset Voltage:
- ±5µV (Typical),
- ±100µV (Maximum)
- Post Zero reference calibration:
- Total Error: ~0.1% to 0.75% (mostly dominated by Gain Error)
Selection of Devices - INA213-C vs INA185:
Are INA213-C and INA185 suitable choices considering they're budget-friendly with better performance (of Voffset & Gain Error) compared to INA181?
Current Transformer Design:
System Specifications:
- BW: 1kHz,
- CMV: <5.5V,
- Current: 0-30mA (Bipolar AC waveform),
- Burden Resistor: 0.5mΩ to 50Ω
- Error budget: 0.2-0.4%
Considering INA181, INA185 & INA213-C. Is INA351 suitable for measuring CT's Burden Resistor Voltage drop, assuming Voffset is minimized by Zero Reference Calibration? Is there a parameter overlooked while evaluating INA351?
Additionally, can INA181 handle a secondary side AC voltage signal swing of +/-160mV given its CMV of -0.2V to 26V and input Voltage of 2.7 to 5.5V (positive)?
Vsense circuit when measured across terminals of Shunt resistor:
This design however seems too simplistic for robust industrial use cases.
We would like your insights & support for the impact of ESD TVS diodes as well as RC-LPF on the input side of this circuit on the stability of the overall Amplifier circuit.
We look forward to your advice and guidance.
Regards