DRV421_15 Datasheet, PDF (30/44 Pages) Texas Instruments – DRV421 Integrated Magnetic Fluxgate Sensor for Closed-Loop Current Sensing

DRV421
SBOS704A – MAY 2015 – REVISED JULY 2015
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Typical Application (continued)
8.2.1.1 Design Requirements
A closed-loop current sensing module contains the DRV421, the magnetic core with a compensation coil, and a
shunt resistor. To increase the robustness of the module to high primary current peaks, use additional protection
diodes. See application report SLOA223, Designing with the DRV421: Closed Loop Current Sensor
Specifications, for additional information on the magnetic core and compensation coil design. The DRV421
output voltage is calculated as described in Equation 6:
V_OUT
I_PRIM
u
§
¨
N_PRIM
© ^NWINDING
·
¸
¹
u
R_SHUNT
u
G
where:
• I_PRIM = primary current value
• N_PRIM = the number of windings of the primary current conductor
• N_WINDING = the number of windings of the compensation coil
• R_SHUNT = shunt resistor value
• G = shunt sense amplifier gain; default value is 4
(6)
8.2.1.2 Detailed Design Procedure
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, as
described in Equation 7:
R_SHUNT
 R_COIL
d
V_ICOMP(MIN)
I_ICOMP
(7)
The voltage drop across the shunt resistor is sensed by the DRV421 shunt sense amplifier with a gain of four.
For proper operation, keep the resulting output voltage at VOUT pin within the voltage output swing range
specified in the Electrical Characteristics.
8.2.1.3 Application Curves
1.06
1.04
1.02
1
0.98
0.96
0.94
1
10
100
1000
10000 100000
Frequency (Hz)
D053
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)
10
100
D054
Figure 66. Gain Flatness of a DRV421-Based Closed-Loop
Current Sensing Module
Figure 67. Current Error of a DRV421-Based Closed-Loop
Current Sensing Module
30
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