The INA250 current-sense amplifier can be configured to measure both unidirectional and bidirectional currents through the reference voltage level applied to the reference pin, REF. The reference voltage connected to REF sets the output level that corresponds with a zero input current condition.  For unidirectional operation, tie the REF pin to ground so that when the current increases, the output signal also increases upwards from this reference voltage (or ground in this case).  For bidirectional currents, an external voltage source can be used as the reference voltage connected to the REF pin to bias up the output.  Set the reference voltage to enable sufficient range above and below this level based on the expected current range to be measured. Positive currents result in an output signal that increases from the zero-current output level set by the reference voltage whereas negative currents result in an output signal that decreases.

For both unidirectional and bidirectional applications, the amplifier transfer function is shown in Equation 1:

where:

• I_LOAD is the current being measured passing through the internal shunt resistor,
• GAIN is the corresponding gain (mA/V) of the selected device, and
• V_REF is the voltage applied to the REF pin

As with any difference amplifier, the INA250 common-mode rejection ratio is affected by any impedance present at the REF input. This concern is not a problem when the REF pin is connected directly to a reference or power supply. When using resistive dividers from a power supply or a reference voltage, buffer the REF pin with an op amp.