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INA195: Vsens < 20mv

Part Number: INA195
Other Parts Discussed in Thread: INA293

I have a design that has been in production for 1.5 years. Now suddenly seeing high failures.

Looks like I overlooked a critical detail in the INA195 specks regarding Vsens < 20mv.

The circuit controls a hydraulic proportional valve. This controls the speed of the equipment with a 70Hz PWM signal to regulate the valve current. Max speed is calibrated in the field, but is typically 700ma.

I selected my sense resistor of 50mOhm, thinking this would provide a nice dynamic range on a 5V ADC (.05 ohm X 1 Amp X 100 Gain = 5V)

However, it appears that some parts can output as much as 2V with zero current. This causes a problem where the firmware reads this 2V and thinks the speed is to high and shuts it down (closed loop current controlled)

I initially thought I could fix this issue in firmware, but looks like that would require running in open loop for the lower half of the speed (current) range.

Is this issue because the chip can handle bidirectional currents? If so, is there a unidirectional part that would work better at <20mV? Hoping to find a minimally invasive solution … not re-spin the entire board.

John