ams Datasheet Page 21
[v1-08] 2015-Jan-16 Document Feedback
AS5140H − Detailed Description
LSB Output (Step/Direction Mode)
Output LSB reflects the LSB (least significant bit) of the
programmed incremental resolution (OTP Register Bit Div0,
Div1). Output Dir provides information about the rotational
direction of the magnet, which may be placed above or below
the device (1=clockwise; 0=counter clockwise; top view). Dir is
updated with every LSB change. In both modes (quad A/B,
step/direction), the resolution and the index output are user
programmable. The index pulse indicates the zero position and
is by default one angular step (1LSB) wide. However, it can be
set to three LSBs by programming the Index-bit of the OTP
register accordingly (seeFigure 35).
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 AS5140H 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.
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 27). For example, if 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.