OA1ZHA Datasheet, PDF (25/35 Pages) STMicroelectronics – Fitness and healthcare

OA1ZHA, OA2ZHA, OA4ZHA
Application information
Vout can be expressed as follows:
Equation 4
V_{ou t}
=
R_{shun t ×}
I
1
–
R_g
R_g2
2 ^{+ R}f2
1
+
R_f1
R_g1
+ I_p
R_{g2 ×} R_f2
R_g2 + R_f2
×
1
+
R_f1
R_g1
– l_n × R_f1 – V_io
1
+
R_f1
R_g1
Assuming that Rf2 = Rf1 = Rf and Rg2 = Rg1 = Rg, Equation 4 can be simplified as follows:
Equation 5
V_out
=
R_shunt
×
I
R_f
R_g
– V_io
1
+
R_f
R_g
+ R_f × I_io
The main advantage of using the chopper of the OA1ZHA, OA2ZHA and OA4ZHA, for a
low-side current sensing, is that the errors due to Vio and Iio are extremely low and may be
neglected.
Therefore, for the same accuracy, the shunt resistor can be chosen with a lower value,
resulting in lower power dissipation, lower drop in the ground path, and lower cost.
Particular attention must be paid on the matching and precision of Rg1, Rg2, Rf1, and Rf2, to
maximize the accuracy of the measurement.
DocID025994 Rev 2
25/35