ADAF1080BCPZ datasheet(23/36 Pages) AD

23 / 36 page

Data Sheet

ADAF1080

THEORY OF OPERATION

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Rev. 0 | 23 of 36

Table 14. Truth Table Logic Levels for the PGIA

Gain

GND

VDD

GND

Do not use

VDD

GND

VDD

FLIP COIL AND FLIP COIL DRIVER

The integrated flip coil at the AMR sensors enables the user to set

and reset the magnetic domains of the AMR field sensor to align

the sense field axis in the positive or negative polarity, as described

in the AMR Magnetic Field Sensor section.

This flip coil can be used to:

►

Change the polarity of the AMR sensor enabling electrical-offset

cancellation, including thermal coefficient and lifetime drift

►

Set the sensor to a known state at startup

►

Reset the sensor following a magnetic saturation event

For ease-of-use, the ADAF1080 integrates a flip coil driver. A rising

edge on the FLIP_DRV pin generates a positive current pulse

through the flip coil, setting a positive sensitive polarity on the

sense field axis, and a falling edge generates a negative current

pulse through the flip coil, setting a negative sensitive polarity on

the sense field axis. In Figure 47, the orientation of the sense field

axis is shown with the arrows.

If FLIP_DRV is left floating or connected to VDD, the FLIP_DRV

pin automatically generates at startup a positive-current pulse to

ensure initialization of the sensor with a positive-sensitivity polarity.

Figure 47. The Polarity of the AMR Sensor Sensitivity (Positive Sensitivity

Polarity When FLIP_DRV Set High Shown on the Left, and Negative

Sensitivity Polarity when FLIP_DRV Set Low Shown on the Right)

The output of the sensor after a negative flip edge can be defined

as the following:

VOUTFn=−BSENSE×SDEVICE+VSET2+VOFFSET (2)

where:

BSENSE is the magnetic field vector on the sense field axis of the

ADAF1080.

SDEVICE is the sensitivity of the ADAF1080 due to a magnetic field

on the sense field axis.

VSET is the voltage on the VSET pin.

VOFFSET is the output voltage when BSENSE = 0 mT.

After a positive flip edge, the output of the sensor can be defined as

the following:

VOUTFp=BSENSE×SDEVICE+VSET2+VOFFSET (3)

Equation 2 shows the sensor response after a negative-current

pulse through the flip coil, and Equation 3 shows the sensor

response after a positive-current pulse through the flip coil. VOFFSET

is the electrical output from the device with zero magnetic field

applied as shown in Figure 48

Using Equation 2 and Equation 3, the user can calculate and

remove the electrical offset from the measurement, as described in

the Electrical Offset Cancellation section.

Figure 48. Sensor Response Following a Positive and a Negative Current

Pulse Through the Flip Coil

DIAGNOSTIC COIL

The lead frame of the ADAF1080 can be used to provide a conduc-

tive path such that a known current can be applied at the AMR

magnetic sensor to generate a known magnetic field. The exposed

pad of the ADAF1080 package is fused with Pin 8 and Pin 18. This

conductive path is referred to as the diagnostic coil (see Figure 49).

The diagnostic coil enables the user to generate a known magnetic

field that can verify the sensitivity of the AMR sensor. When a

current (IDIAG) is driven through the diagnostic coil, a magnetic field

(BDIAG) is sensed by the AMR sensor as shown in the following

equation. Ensure that the maximum diagnostic current (IDIAG) does

not exceed 100 mA, and that the time duration of the diagnostic

coil excitation is limited due to thermal considerations. To calculate

the magnetic field detected by the AMR sensor (BDIAG) using the

following equation:

BDIAG= 22.8 μT/100 mA ×IDIAG

(4)

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