Data Sheet

ADA4570

THEORY OF OPERATION

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Rev. 0 | 10 of 14

As shown in the Figure 1, the ADA4570 contains all the necessary

peripherals for AMR angle sensing of a magnetic field in the x-y

plane of the sensor.

The bridge driver provides the voltage supply to the AMR sensor.

The sensitivity of AMR sensor is temperature dependent, and the

bridge driver is designed to provide a supply voltage that compen-

sates for the temperature dependence (see Figure 17).

Figure 17. Temperature Compensated Bridge Driver

The ADA4570 consists of two dies that are connected internally by

bond wires, the AMR sensor and an application specific IC (ASIC)

that incorporates the electronics required to condition the output

signals. A broken bond wire detection system was implemented

in the ASIC that detects if any of the bond wires between the

AMR bridge and ASIC become detached or broken. Note that when

a broken bond wire is detected, the VSIN and VCOS differential

signal outputs are forced low.

Electromagnetic interference (EMI) filters are implemented at the

AMR sensor outputs to prevent unwanted noise and interference

from appearing in the signal band of the input to the instrumentation

amplifier.

The architecture of the instrumentation amplifier consists of pre-

cision, low noise, zero drift amplifiers that feature a proprietary

chopping technique. This chopping technique offers a low input

offset voltage as well as a low input offset voltage drift. The zero

drift design also features chopping ripple suppression circuitry that

removes glitches and other artifacts caused by chopping.

Offset voltage errors caused by common-mode voltage swings

and power supply variations are also corrected by the chopping

technique, resulting in a very high dc common-mode rejection ratio.

The amplifiers feature a low broadband noise of 33 nV/√Hz and

no 1/f noise component. These features are ideal for amplification

of the low level AMR bridge signals for high precision sensing

applications.

The differential amplifier outputs, VSIN and VCOS, are capable

of driving the inputs of an external ADC without requiring any

additional signal conditioning, as shown in Figure 18.

Figure 18. Typical Application Diagram