DRV401_15 Datasheet, PDF (13/36 Pages) Texas Instruments – Sensor Signal Conditioning IC for Closed-Loop Magnetic Current Sensor

DRV401
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FUNCTIONAL DESCRIPTION
The DRV401 operates from a single +5V supply. It is a
complete sensor signal conditioning circuit that directly
connects to the current sensor, providing all necessary
functions for the sensor operation. The DRV401 provides
magnetic field probe excitation, signal conditioning, and
compensation coil driver amplification. In addition, it
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 DRV401 uses
analog signal conditioning; the internal loop filter and
integrator are switched capacitor-based circuits.
Therefore, the DRV401 allows combination with
high-precision sensors for exceptional accuracy and
resolution. The typical characteristic curve, DRV401 and
Sensor Linearity, shows an example of the linearity and
temperature stability achieved by the device.
A demagnetization cycle can be initiated on demand or on
power-up. This cycle reduces offset and restores high
performance after a strong overload condition. An internal
clock and counter logic generate the degauss function.
The same clock controls power-up, overload detection and
recovery, error, and time-out conditions.
The DRV401 is built on a highly reliable CMOS process.
Unique protection cells at critical connections enable the
design to handle inductive energy.
MAGNETIC PROBE (SENSOR) INTERFACE
The magnetic field probe consists of an inductor wound on
a soft magnetic core. The probe is connected between
pins IS1 and IS2 of the probe driver that applies
approximately +5V (the supply voltage) through resistors
across the probe coil (see Figure 2a).
SBVS070B − JUNE 2006 − REVISED MAY 2009
The probe core reaches saturation at a current of typically
28mA (see Figure 2a). The comparator is connected to
V_REF by approximately 0.5V. A current comparator detects
the saturation and inverts the excitation voltage polarity,
causing the probe circuit to oscillate in a frequency range
of 250kHz to 550kHz. The oscillating frequency is a
function of the magnetic properties of the probe core and
its coil.
The current rise rate is a function of the coil inductance:
dI = L × V × dT. However, the inductance of the field probe
is low while its core material is in saturation (the horizontal
part of the hysteresis curve) and is high at the vertical part
of the hysteresis curve. The resulting inductance and the
series resistance determine the output voltage and current
versus time performance characteristic.
Without external magnetic influence, the duty cycle is
exactly 50% because of the inherent symmetry of the
magnetic hysteresis; the probe inductor is driven from −B
saturation through the high inductance range to +B
saturation and back again in a time-symmetric manner
(see Figure 2b).
If the core material is magnetized in one direction, a long
and a short charge time result because the probe current
through the inductors generates a field that either
subtracts or adds to the flux in the probe core, either driving
the probe core out of saturation or further into saturation
(see Figure 2c). The current into the probe is limited by the
voltage drops across the probe driver resistors.
The DRV401 continuously monitors the logic magnetic flux
polarity state. In the case of distortion noise and excessive
overload that could fully saturate the probe, the overload
control circuit recovers the probe loop. During an overload
condition, the probe oscillation frequency increases to
approximately 1.6MHz until limited by the internal timing
control.
In an overload condition, the compensation current (I_COMP)
driver cannot deliver enough current into the sensor
secondary winding, and the magnetic flux in the sensor
main core becomes uncompensated.
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