IC-PI datasheet(41/49 Pages) ICHAUS

41 / 49 page

preliminary

iC-PI PROGRAMMABLE 12-BIT

Sin/Cos INTERPOLATION IC WITH RS422 DRIVER

Rev B1, Page 41/48

REVERSE POLARITY PROTECTION

iC-PI is protected against a reversal of the supply volt-

age and has short-circuit-proof, error-tolerant output

drivers. A defective device cable or one wrongly con-

nected is tolerated by iC-PI. All circuitry components

which draw the monitored supply voltage from VDDS

and GNDS are also protected.

The following pins are also reverse polarity protected:

PA, NA, PB, NB, PZ, NZ, ERR, VDD, GND and ACO.

Conditions: This is based on the condition that GNDS

only receives load currents from VDDS. The maximum

voltage difference between GNDS and another pin

should not exceed 6 V (respectively 8 V for pin ERR).

Note: If iC-PI detects reverse polarity on power up,

the line drivers will not be enabled.

If the state of reverse polarity is resolved, iC-PI re-

boots from the EEPROM and enables the line drivers.

APPLICATION NOTES: SIGNAL CONDITIONING

The precise setting of the signal conditioning unit for

correction of the analog input signals is essential 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.

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 VOS12 = 01 (selects V05 of 500 mV) the offset

error can be compensated in increments of 0.5 mV. If

the offset has been compensated for incorrectly by one

step (1 LSB), the absolute angle error would increase

by approx. 0.06° and the transition distance vary by

approximately ± 0.1 %. 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-PI can compensate

for the amplitude ratio in steps of approx. 0.1 % so that

incorrect compensation by 1 LSB would increase the

absolute angle error by approx. 0.06°. The transition

distance would then vary by ± 0.1 %.

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-PI’s

phase correction feature permits a step size of 0.02° so

that incorrect compensation by 1 LSB would increase

the absolute angle error by approx. 0.02°. The transi-

tion distance would then vary by ± 0.03 %.

In a perfect signal conditioning procedure it can be

assumed that the residual error constitutes half a com-

pensation step. With this, in theory iC-PI would achieve

an absolute angle accuracy of approx. 0.03°, with the

transition distance varying by approx. ± 0.05 %. Addi-

tionally, the linearity error of the interpolator must also

be taken into consideration; this increases the absolute

angle error by approx. 0.13° and the variation in tran-

sition distance by approx. 0.5 % (refer to the Electrical

Characteristics No. 302, and 304 for further ratings).

MODE(3:0)

Addr. 0x02; bit 3:0

Code

Operating Mode

Pin PA

Pin NA

Pin PB

Pin NB

Pin PZ

Pin NZ

Pin ERR

0x00

ABZ

A+

A-

B+

B-

Z+

Z-

ERR

0x0E

UVW

A+

B+

Z+

ERR

0x01

Calibration 1

res.

IBN*

PCH0

NCH0

res.

0x02

Calibration 2

PCH1

NCH1

PCH2

NCH2

VDC1

VDC2

res.

0x0B

System Test**

ZIn

TP1

ERR

*) Outputs must be active and not tristate (see note on page 20).

**) Additional parameter settings are required, see page 22, Table 20.

Table 70: Selected operating modes and test signals.

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