IC-PI datasheet(28/49 Pages) ICHAUS

28 / 49 page

preliminary

iC-PI PROGRAMMABLE 12-BIT

Sin/Cos INTERPOLATION IC WITH RS422 DRIVER

Rev B1, Page 28/48

Offset Calibration CH1, CH2

In order to calibrate the offset, the reference source

must first be selected using VOS12. Two fixed voltages

and two dependent sources are available for this pur-

pose. The fixed voltage sources should be selected for

external sensors which provide stable, self-regulating

signals.

So that photosensors can be operated in optical en-

coders, iC-PI tracks changes in offset voltages via

the signal-dependent source VDC when used in con-

junction with the controlled sensor current source for

LED supply (pin ACO). The VDC potential automati-

cally tracks higher DC photocurrents. To this end, the

center potentials for the VDC offset references can be

adjusted to minimize their AC ripple, using parameters

MP1 for VDC1, and MP2 for VDC2 (refer to the k factor

of Table 28).

The feedback of pin voltage V(ACO) fulfills the same

task as source VDC when MR bridge sensors are sup-

plied by the controlled sensor current source or by sup-

ply VDDS.

VOS12

Addr. 0x05, bit 5:4

Code

Type of source

0x0

Feedback of ACO pin voltage: V(ACO)/20

for supply-dependent differential voltage signals

for Wheatstone sensor bridges

to measure VDDS

0x1, 0x2

Fixed reference: V05 of 500 mV, V025 of 250 mV

for single-ended current or voltage signals

for single-ended or differential stabilized signals

(regulated sensor or waveform generator)

0x3

Self-tracking sources VDC1, VDC2 (125...250 mV)

for differential current signals

for differential voltage signals*

Notes

*) Requires MUX(5:4) = 3 and the sensor’s reference

connected to input X2; refer to Elec. Char. No. 111

for acceptable input voltage).

Table 27: Offset Reference Source CH1, CH2

MP1

Addr. 0x0E, bit 1:0; Addr. 0x0D, bit 7:0

MP2

Addr. 0x0F, bit 5:0; Addr. 0x0E, bit 7:4

Code

VDCi = (1 − k) · VPi + k · VNi

0x000

k = 1/3

0x001

k = 0.3337

...

k = 1/3 + 1/3 · Code/1023

0x200

k = 0.5000 (center setting)

...

0x3FF

k = 2/3

Notes

Adjustment is required only if VOS12 = 0x3

Table 28: VDC Center Potential CH1, CH2

The offset calibration range for CH1 and CH2 is set

using the coarse offset factors OR1 and OR2. Both

sine and cosine signals are then calibrated using the

fine offset factors OF1 and OF2. The calibration target

is reached when the DC component of the differential

signals PCHi to NCHi is zero.

OR1

Addr. 0x10, bit 1:0

OR2

Addr. 0x10, bit 3:2

Code

Range

0x0

0x1

0x2

0x3

x12

Table 29: Coarse Offset Factor CH1, CH2

OF1

Addr. 0x11, bit 6:0; Addr. 0x10, bit 7:4

OF2

Addr. 0x13, bit 2:0; Addr. 0x12, bit 7:0

Code

Factor

0x000

0x001

0.00098

...

+ Code/1023

0x3FF

+ 1

0x400

0x401

−

0.00098

...

−

(Code − 1024)/1023

0x7FF

−

Table 30: Fine Offset Factor CH1, CH2

Phase Correction CH1 to CH2

The phase shift between CH1 and CH2 can be adjusted

using parameter PH12. Following phase calibration,

other calibration parameters may have to be readjusted

(those as amplitude compensation, VDC center poten-

tials and offset voltages).

PH12

Addr. 0x14, bit 5:0; Addr. 0x13, bit 7:4

Code

Correction angle

0x000

0 °

0x001

+ 0.0204 °

...

+ 10.42 ° · Code/511

0x1FF

+ 10.42 °

0x200

0 °

0x201

−

0.0204 °

...

−

10.42 ° · (Code − 512)/511

0x3FF

−

10.42 °

Table 31: Phase Correction CH1 to CH2

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