DRV421_16 Datasheet, PDF (32/44 Pages) Texas Instruments – Integrated Magnetic Fluxgate Sensor for Closed-Loop Current Sensing

DRV421
SBOS704B – MAY 2015 – REVISED MARCH 2016
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Typical Application (continued)
8.2.2.1 Design Requirements
As with the previous application, the compensation current creates a voltage drop across the shunt resistor. The
maximum shunt resistor value is limited by supply voltage V_DD, the compensation current range, and the
resistance of the compensation coil; see Equation 7.
However, in applications that sense leakage or residual currents, the difference between the primary currents is
zero in normal operation. In fault condition only, there is a small difference current that is sensed in order to shut
down the system to prevent damage to the device or the user. In this case, the compensation current is also very
low, usually only in the range of few mA. Therefore, use a higher shunt resistor value in this case to support high
sensitivity on system level. Consider the impact of shunt resistor value on gain and gain flatness as decribed in
application report SLOA223, Designing with the DRV421: Closed Loop Current Sensor Specifications.
8.2.2.2 Detailed Design Procedure
For differential current sensing modules with a large shunt resistor and medium compensation coil inductance,
use the gain setting that features the higher cross-over frequency of 3.8 kHz: GSEL[1:0] = 01.
8.2.2.3 Application Curve
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
0.0001
0.001
0.01
0.1
1
Primary Current (A)
D055
Figure 69. Current Error of a DRV421-Based
Differential Closed-Loop Current Sensing Module
32
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