IC-MQ_15 Datasheet, PDF (35/43 Pages) IC-Haus GmbH – Sin/Cos INTERPOLATION IC WITH RS422 DRIVER

iC-MQ PROGRAMMABLE 9-BIT
Sin/Cos INTERPOLATION IC WITH RS422 DRIVER
GENERAL APPLICATION HINTS
Rev F3, Page 35/43
In-circuit Programming Of The EEPROM
Access to the EEPROM is unhindered when the iC-MQ
supply voltage is kept below power down reset thresh-
old VDDoff. In this case an EEPROM which operates
at a supply voltage of 2.5 V and above is required. 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.
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 obtained
determines the minimum signal jitter. Here, the effect
on the transition distance of the A/B output signals is
not always the same but instead dependent on the ab-
solute phase angle of the input signals. The following
gives an example for an interpolation factor of 100, i.e.
400 edges per sine period.
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 transition
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 %.
In a perfect signal conditioning procedure it can be
assumed 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 signals 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 com-
pensate 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
distance 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(90ř + φt)
V(X 6) = 2.5 V − 0.125 Vsin(90ř + φt)
Outputs PA, NA, PB and NB generate a differential A/B
signal with an angle resolution of 4 (an interpolation fac-
tor of 1). When high sine input frequencies are applied
or the resolution is increased, the minimum phase dis-
tance (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 resolution of 200 (an inter-
polation factor of 50) when input frequencies of up to
20 kHz are to be applied.