DRV411_15 Datasheet, PDF (14/34 Pages) Texas Instruments – Sensor Signal Conditioning IC for Closed-Loop Magnetic Current Sensors

DRV411
SBOS693B – AUGUST 2013 – REVISED DECEMBER 2013
FUNCTIONAL DESCRIPTION
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OVERVIEW
The DRV411 is a complete sensor signal conditioning circuit that directly connects to the current sensor,
providing all necessary functions for the sensor operation. The DRV411 operates from a single +2.7-V to +5.5-V
supply, and provides magnetic field probe (Hall sensor) excitation, signal conditioning, and compensation-coil
driver amplification. In addition, this device detects error conditions and handles overload situations. A precise
differential amplifier allows translation of the compensation current into an output voltage using a small shunt
resistor. A buffered voltage reference can be used for comparator, analog-to-digital converter (ADC), or bipolar
zero reference voltages. Dynamic error correction ensures high dc precision over temperature and long-term
accuracy.
The DRV411 uses analog signal conditioning circuitry; the internal loop filter and integrator are switched
capacitor-based circuits. The DRV411 can be combined with high-precision sensors for exceptional accuracy and
resolution. An internal clock and counter logic control power-up, overload detection and recovery, error, and time-
out conditions. The DRV411 is built using a highly reliable CMOS process. Unique protection cells at critical
connections enable the design to handle inductive energy.
HALL SENSOR INTERFACE
The DRV411 works best with symmetrical InSb Hall elements, such as the HW322 and HW302 from AKM or
other vendors. Symmetrical Hall elements are Hall elements where input impedance and output impedance are
closely matched. However, hall elements suffer from offset and offset drift across temperature that affects the
accuracy and linearity of the current sensor. The DRV411 contains patented excitation and conditioning circuitry
that significantly reduces offset and offset drift. The excitation circuit regulates the voltage across the hall
element to a maximum voltage of 0.95 V. This voltage is very stable across the full temperature range. The
excitation current varies with temperature in order to keep the hall sensitivity constant. A special current limiting
circuit limits the current delivered to the hall element to a maximum current of 10 mA regardless of the
temperature or the impedance of the hall element.
DYNAMIC OFFSET AND NOISE CANCELLATION USING SPINNING CURRENT METHOD
The DRV411 incorporates dynamic offset cancellation circuitry that helps eliminate offset drift and 1/f noise of the
hall sensor. The excitation current is spun through the hall sensor in orthogonal directions at a fixed clock
frequency using rotation multiplexer switches, as shown in Figure 47 (a) to (d). The excitation source ensures a
constant current during each spin cycle but keeps the sensitivity of the hall sensor independent by varying the
current across temperature for impedance variations from 100 Ω to 2 kΩ. The corresponding Hall output is
averaged across the four orthogonal directions to effectively cancel the Hall offset and the 1/f noise. The DRV411
continuously monitors the offset of the Hall element and triggers an error flag if the offset remains > 50 mV as a
result of any damage to the Hall sensor. Refer to the Error Conditions section for more details.
IEXCIT
VHALL ¤
VHALL +
R1
R2
R1
R2
VHALL +
VHALL ¤
IEXCIT
B
R3
R4
Hall Sensor
B
R3
R4
Hall Sensor
VHALL +
R1
VHALL ¤
B
R3
Hall Sensor
IEXCIT
R2
VHALL +
R4
R1
B
R3
Hall Sensor
VHALL ¤
R2
IEXCIT
R4
(a)
(b)
(c)
(d)
Figure 47. Hall Sensor Current Spinning Method
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