AS5040 datasheet(7/28 Pages) AMSCO

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AS5040 10-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER

Revision 1.6, 03-Oct-06

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Page 7 of 28

5.2.1

Incremental Power-up Lock Option

After power-up, the incremental outputs can optionally be

locked or unlocked, depending on the status of the CSn

pin:

CSn = low at power-up:

CSn has an internal pull-up resistor and must be

externally pulled low (Rext

≤ 5kΩ). If Csn is low at

power-up, the incremental outputs (A, B, Index) will

be high until the internal offset compensation is

finished.

This unique state (A=B=Index = high) may be used

as an indicator for the external controller to shorten

the waiting time at power-up. Instead of waiting for

the specified maximum power up-time (0), the

controller can start requesting data from the AS5040

as soon as the state (A=B=Index = high) is cleared.

CSn = high or open at power-up:

In this mode, the incremental outputs (A, B, Index)

will remain at logic high state, until CSn goes low or

a low pulse is applied at CSn. This mode allows

intentional disabling of the incremental outputs until

for example the system microcontroller is ready to

receive data.

5.3

Incremental Output Hysteresis

To avoid flickering incremental outputs at a stationary

magnet position, a hysteresis is introduced.

In case of a rotational direction change, the incremental

outputs have a hysteresis of 2 LSB.

Regardless of the programmed incremental resolution,

the hysteresis of 2 LSB always corresponds to the

highest resolution of 10 bit. In absolute terms, the

hysteresis is set to 0.704 degrees for all resolutions.

For constant rotational directions, every magnet position

change is indicated at the incremental outputs (see

Figure 8). If for example the magnet turns clockwise from

position „x+3“ to „x+4“, the incremental output would

also indicate this position accordingly.

A change of the magnet’s rotational direction back to

position „x+3“ means, that the incremental output still

remains unchanged for the duration of 2 LSB, until

position „x+2“ is reached. Following this direction, the

incremental outputs will again be updated with every

change of the magnet position.

Figure 8: Hysteresis window for incremental outputs

Pulse Width Modulation (PWM)

Output

The AS5040 provides a pulse width modulated output

(PWM), whose duty cycle is proportional to the measured

angle:

() 1

1025 −

⋅

off

Position

The PWM frequency is internally trimmed to an accuracy

±5% (±10% over full temperature range). This

tolerance can be cancelled by measuring the complete

duty cycle as shown above.

1/fPWM

Angle

359.65 deg

(Pos 1023)

0 deg

(Pos 0)

1µs

1025µs

PWMIN

PWMAX

1024µs

Figure 9: PWM output signal

Magnet Position

Hysteresis:

0.7°

X+2

Incremental

Output

Indication

Clockwise Direction

Counterclockwise Direction

X+4

X+2

X+4 X+5

X+3

X+1

X+3

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