DRV411_15 Datasheet, PDF (15/34 Pages) Texas Instruments – Sensor Signal Conditioning IC for Closed-Loop Magnetic Current Sensors

DRV411
www.ti.com
SBOS693B – AUGUST 2013 – REVISED DECEMBER 2013
Low-frequency noise can be a concern for Hall sensors with constant voltage and current excitation. The
dynamic offset cancellation technique eliminates 1/f noise from the Hall sensor. Figure 48 shows the effect of
current spinning on the Hall sensor, referred to primary current noise.
100^-2
Hall Sensor only
100^-3
100^-4
100^-5
100^-6
DRV411 + Hall Sensor
100^-7
0.1
1
10
100
1k
Frequency (Hz)
10k
100k
C04
Figure 48. Effect of Noise Cancellation with Current Spinning
COMPENSATION COIL DRIVER
The compensation coil driver provides the driving current for the compensation coil. A fully differential driver
stage offers the high-signal voltage to overcome the wire resistance of the coil with only a 5-V supply. The
compensation coil is connected between ICOMP1 and ICOMP2, both generating an analog voltage across the
coil (see Figure 51) that turns into current from the wire resistance (and eventually from the inductance). The
compensation current represents the primary current transformed by the turns ratio. A shunt resistor is connected
in this loop and the high precision differential amplifier translates the voltage from this shunt to an output voltage
(see the Functional Principle of Closed-Loop Current Sensors with a Hall Sensor section).
Both compensation driver outputs provide low impedance over a wide frequency range that insures smooth
transition between the closed-loop compensation frequency range and the high-frequency range, where the
primary winding directly couples the primary current into the compensation coil according to the winding ratio
(transformer effect).
The two compensation driver outputs are specially protected to handle inductive energy. However, it might be
necessary to use high-current sensors to add external protection diodes (see the Protection Recommendations
section).
GAIN SELECTION AND COMPENSATION FREQUENCY
Proper selection of the GSEL mode enables the sensor designer to create a sensor with stable gain over a wide
frequency range and excellent loop stability. Modes Gain_1 to Gain_3 allow for different fixed gain and zero-
frequency options to be selected according to the requirements of the individual sensor. See Table 1 for more
information. Evaluate Gain_3 mode (GSEL [1,0]) first because it works with most common sensors.
Mode Selection
Gain_1 Mode For use with sensors with compensation coil inductance < 50 mH.
Gain_2 Mode For use with sensors with very small form factor (small core diameter), where the transformer
effect starts to dominate the transfer function at frequencies significantly above 3.8 kHz. Typically the
inductance of the compensation coil would be very small.
Gain_3 Mode Works well with a wide selection of sensors with compensation coil inductance typically ≥ 50 mH.
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