IC-MQ Datasheet, PDF (37/39 Pages) IC-Haus GmbH – PROGRAMMABLE 9-BIT Sin/Cos INTERPOLATION IC WITH RS422 DRIVER

iC-MQ PROGRAMMABLE 9-BIT
Sin/Cos INTERPOLATION IC WITH RS422 DRIVER
APPLICATION HINTS
Rev D4, Page 37/39
In-circuit programming of the EEPROM
Access to the EEPROM is unhindered when the iC-
MQ supply voltage is kept below power down reset
threshold VDDoff. In this case an EEPROM which op-
erates at a supply voltage of 2.5 V and above is re-
quired. If 3.3 V are necessary to power the EEPROM,
iC-MQ’s supply voltage can be raised at a maximum
to power on threshold VDDon; this must occur without
overshooting.
A phase error between the sine and cosine signals
(a deviation in phase shift from the ideal 90°) has the
most marked influence on the absolute angle error at
0°, 90°, 180° and 270°. The greatest effect on the tran-
sition distance is noted at 45°, 135°, 225° and 315°.
iC-MQ’s phase correction feature permits a step size of
0.64° so that incorrect compensation by 1 LSB would
increase the absolute angle error by ca. 0.64°. The
transition distance would then vary by +/- 1.1 %.
The supply voltage provided by pins VDDS and GNDS
can be used to power the EEPROM; shutdown only
occurs with reverse polarity. Here, the load-dependent
voltage drop at both switches must be taken into ac-
count; see Vs(VDDS) and Vs(GNDS) in the Electrical
Characteristics, C01 and C02.
Absolute angle accuracy and edge jitter
The precise setting of the signal conditioning unit for
correction of the analog input signals is crucial to the
result of interpolation; the absolute angle error ob-
tained determines the minimum signal jitter. Here, the
effect on the transition distance of the A/B output sig-
nals is not always the same but instead dependent on
the absolute phase angle of the input signals. The fol-
lowing gives an example for an interpolation factor of
100, i.e. 400 edges per sine period.
In a perfect signal conditioning procedure it can be as-
sumed that the residual error constitutes half a com-
pensation step respectively. With this, in theory iC-
MQ would achieve an absolute angle accuracy of ca.
0.5°, with the transition distance varying by ca. +/-
1.5 %. The linearity error of the interpolator must also
be taken into consideration; this increases the absolute
angle error by ca. 0.12° and the variation in transition
distance by 0.4 %. With ideal, almost static input sig-
nals iC-MQ then obtains an absolute angle accuracy
of 0.62° and a variation in transition distance of under
2 %.
Information on the demo board
The default delivery status of demo board EVAL MQ1D
is such that it expects differential sine/cosine signals at
inputs X3 to X6 with an amplitude of 125 mV, i.e.
The offset error in the cosine signal has the strongest
effect on the absolute angle error at 90° and 270°; at 0°
and 180° its influence on the transition distance is the
most marked. With a range setting of OR1 = OR2 = 00
and VOSSC = 01 the offset error can be compensated
for by an increment of 3.9 mV. If the offset has been
compensated for incorrectly by one step (1 LSB), the
absolute angle error would increase by ca. 0.45° and
the transition distance vary by approximately +/- 0.8 %.
Similar conditions apply to the sine signal, with the sole
difference that the maxima would be shifted by 90°.
An error in amplitude has the strongest effect on the
absolute angle error at 45°, 135°, 225° and 315°; the
biggest change in the transition distance can be ob-
served at 0°, 90°, 180° and 270°. iC-MQ can compen-
sate for the amplitude ratio in steps of 1.5 % so that
incorrect compensation by 1 LSB would increase the
absolute angle error by ca. 0.42°. The transition dis-
tance would then vary by +/- 1.5 %.
V (X 4) = 2.5 V + 0.125 Vsin(ϕt)
V (X 3) = 2.5 V − 0.125 Vsin(ϕt)
V (X 5) = 2.5 V + 0.125 Vsin(90 + ϕt)
V (X 6) = 2.5 V − 0.125 Vsin(90 + ϕt)
Outputs PA, NA, PB and NB generate a differential
A/B signal with an angle resolution of 4 (an interpo-
lation factor of 1). When high sine input frequencies
are applied or the resolution is increased, the mini-
mum phase distance (MTD), short-circuit current limit
(SIK) and driver slew rate (SSR) must be adjusted to
meet requirements. For example, a minimum phase
distance of MTD = 8 should be selected with a resolu-
tion of 200 (an interpolation factor of 50) when input
frequencies of up to 20 kHz are to be applied.