AS5304/AS5306 Integrated Hall IC for linear and off-axis rotary motion detection

Revision 1.5

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7.4

Dynamic Non-Linearity (DNL)

The DNL (dynamic non-linearity) describes the non-linearity of the incremental outputs from one step to the next. In an ideal

system, every change of the incremental outputs would occur after exactly one LSB (e.g. 25µm on AS5304). In practice

however, this step size is not ideal, the output state will change after 1LSB +/-DNL. The DNL must be <+/- ½ LSB to avoid a

missing code. Consequently, the incremental outputs will change when the magnet movement over the IC is

minimum 0.5 LSB and maximum 1.5 LSB’s.

1 LSB + DNL

1 LSB - DNL

1 LSB

lateral magnet movement

37.5 µm

25 µm

12.5 µm

AS5304:

DNL (dynamic non-linearity)

1 LSB + DNL

1 LSB - DNL

1 LSB

lateral magnet movement

22.5 µm

15 µm

7.5 µm

AS5306:

DNL (dynamic non-linearity)

Figure 11:

DNL of AS5304 (left) and AS5306 (right)

8 The AO Output

The Analog Output (AO) provides an analog output voltage that represents the Automatic Gain Control (AGC) of the Hall

sensors signal control loop.

This voltage can be used to monitor the magnetic field strength and hence the gap between magnet and chip surface:

•

Short distance between magnet and IC → strong magnetic field → low loop gain → low AO voltage

•

Long distance between magnet and IC → weak magnetic field → high loop gain → high AO voltage

For ideal operation, the AO voltage should be between 1.0 and 4.0V (typical; see 9.5).

Figure 12:

AO output versus AGC, magnetic field strength, magnet-to-IC gap