INA240-Q1: INA240A2 - R_Sense calculation

Hi,

If the ADC internal reference is availabe, of course you can take advantage of it. But the ref voltages of INA240 and the ADC can be decoupled from each other.

For load current of ±1A, it is customary to configure INA240 in bidirectional mode, with ref voltage equal to somewhere around half supply, or 2.5V here. The output would then be able to swing toward supply rail when load current is positive, and ground when load current is negative. 1A is treated as max. As an example, suppose you chose Rshunt=100mOhm, and INA240A1 Gain=20, then the max Vout (relative to ground) is 2.5V+20*1A*100mOhm=4.5V; the min is 2.5V-20*1A*100mOhm=0.5V. The corresponding differential input seen by ADC is 2V and -2V respectively with the ADC you chose.

As far as setting the ref voltage, using a resistor divider is the simplest, but the price to pay is considerable current draw. It also introduces a small error even with the configuration you chose, although the error is much smaller than single-ended configuration.

From performance perspective, an improvement would be to pair a buffer with a larger divider, as shown here:

Regards, Guang