AMR TECHNOLOGY POWER UP / DOWNAnisotropic magnetoresistance (AMR) makes use of a common An under-voltage lockout circuit monitors the voltage on the material, Permalloy, to act as a magnetometer. Permalloy is an VCC pin. If the VCC voltage is less than the under-voltage alloy containing roughly 80% nickel and 20% iron. The alloy’s threshold the MCA1101 is in an inactive state. Vout and Vref resistance depends on the angle between the magnetization both drive to ground. If the VCC voltage exceeds the under- and the direction of current flow. In a magnetic field, voltage threshold Vout and Vref are released and will drive to magnetization rotates toward the direction of the magnetic field approximately half the VCC supply voltage and an initial and the rotation angle depends on the external field’s magnitude. calibration will commence. Once the initial calibration has Permal oy’s resistance decreases as the direction of completed the MCA1101 becomes active. Vout will slew to magnetization rotates away from the direction in which current indicate the value of current flowing in the IP+/- conductor. flows, and is lowest when the magnetization is perpendicular to Current flow in the IP+/- conductor with a VCC voltage less than the direction of current flow. The resistance changes roughly as the under-voltage threshold will not cause damage to the the square of the cosine of the angle between the magnetization sensor. and the direction of current flow. Permalloy is deposited on a silicon wafer and patterned as a resistive strip. The film’s properties cause it to change resistance in the presence of a
OVERCURRENT DETECTION (OCD)magnetic field. In a current sensor application, two of these resistors are connected in a Wheatstone bridge configuration to The MCA1101 have fast and accurate overcurrent fault permit the measurement of the magnitude of the magnetic field detection circuitry. The overcurrent fault threshold (I FAULTB ) is produced by the current.
user-configurable via an external resistor divider and supports a range of 120% to 200% of the full-scale primary input (IP).
The overcurrent fault threshold (I FAULTB ) is set via a resistor AMR properties are well behaved when the film’s magnetic divider from VCC to ground on the VOC pin. The voltage on the domains are aligned in the same direction. This configuration VOC pin (VVOC), may range from 0 ×VCC to 0.5 ×VCC. ensures high sensitivity, good repeatability, and minimal hysteresis. During fabrication, the film is deposited in a strong For +/-5A parts magnetic field that sets the preferred orientation, or “easy” axis, For VVOC between 0 ×VCC and 0.225 ×VCC the I FAULTB of the magnetization vector in the Permalloy resistors. AMR has threshold level is 1.2×IP. better sensitivity than other methods and reasonably good For V temperature stability. The AMR sensor has sensitivity which is VOC between 0.225 ×VCC and 0.35 ×VCC the I FAULTB approximately a linear function of temperature. threshold level is 1.5×IP.
For VVOC between 0.35 ×VCC and 0.5×VCC the I FAULTB threshold level is 2×IP.
FUNCTIONAL DESCRIPTIONFor +/-20A parts For VVOC between 0 ×VCC and 0.225 ×VCC the I FAULTB Figure 2 provide block diagrams of the fixed gain. The AMR threshold level is 1.2×IP. sensor monitors the magnetic field generated by the current flowing through the U shaped IP+/IP- package lead frame. The For VVOC between 0.225 ×VCC and 0.5 ×VCC the I FAULTB AMR sensor produces a voltage proportional to the magnetic threshold level is 1.5×IP. field created by the positive or negative current in the IP+/IP- current loop while rejecting external magnetic interference. The For +/-50A parts sensor voltage is fed into a differential amplifier whose gain is For VVOC between 0 ×VCC and 0.5 ×VCC the I FAULTB threshold temperature compensated. This is followed by an level is 1.2×IP. instrumentation amplifier output stage that provides a voltage that indicates the current passing through the IP+/IP- pins. To If the input current exceeds the OCD threshold value I FAULTB provide both positive and negative current data the Vout output the output pin FAULTB will transition low and stay low, even if pin is referenced to the Vref output pin. The voltage on the Vref input current drops below the threshold. In order to reset the output is typically one half of the full scale positive and negative range of the Vout current sense output signal. With no current FAULTB output the user needs to bring VOC pin to VCC and flowing in the IP+/IP- pins, the voltage on the Vout output will hold it there for at least THvoc. Once the OCD function is reset typically equal the voltage on the Vref output. Positive IP+/IP- the VOC voltage should return back to its normal operating current causes the voltage on Vout to increase relative to Vref voltage Vvoc. A switch SW1 on Figure 1 can be used for this. while negative IP+/IP- current will cause it to decrease. Other methods are available as well. If OCD function is used, an OCD reset must be applied to the
GAINVOC pin after system power up, to put the OCD function and FAULTB pin in a known state. The sensor resistors are biased by an internal 3.0V reference voltage and the voltage on the Vref output is 1.5V (typical). This arrangement provides a fixed gain and enhanced supply The FAULTB output is active low open drain. A pull-up resistor rejection. The Vout pin drives to approximately 2.8V at full should be connected between FAULTB and VCC. The VCC positive current and 0.3V at full negative current. voltage will determine the high level of FAULTB signal.
FAULTB low output voltage is below 200mV.The value of pull-
up resistor is 2-10kOhm. Phone: 978.965.3200 Fax: 978.965.3201 E-mail:
[email protected] www.aceinna.com Document: 6020-1104-01 Rev C Page 10 of 13
