iC-TW2 8-BIT SIN/COS INTERPOLATION IC
WITH INTEGRATED EEPROM
Rev D3, Page 19/30
CONFIGURATION DEPENDENCIES
The following paragraph describes dependencies be- Always use the highest accuracy possible to still satisfy
tween several chip configuration settings and system finput
performance. It is vital to understand the implication of
.
system parameters to be able to tune the iC-TW2 for 4. Determine fosc. Selecting the slowest fosc possible
full performance. It is especially important to correctly lowers power consumption and improves jitter perfor-
program register FREQ(6:0), since this directly affects mance.
accuracy and maximum allowed input frequency.
Clock tuning
Selecting configuration parameters
1. Observe fosc/32 on pin A_U during calibra-
Follow the outlined procedure below to select the tion mode 2.
proper configuration. Refer to Table 22 for reference.
2. Use CLOCK(4:0) to tune the oscillator to the desired
1. Determine the maximum input frequency finput as re- fcal frequency. (fpinA = fosc/32)
quired by the application.
3. Be aware that the oscillator can have as much
2. Calculate fcore based on finput and interpolation rate as 20 % frequency variation over the operating tem-
INTER(7:0).
perature range (-40 °C to 125 °C). The oscillator runs
slower at higher temperatures. To guarantee perfor-
3. Select fsystem based on the accuracy requirement. mance at 125 °C it is necessary to tune the oscillator
See Table 21. Accuracy is a function of interpolation to typ. 12 % higher frequency at room temperature of
and frequency (registers INTER(7:0) and FREQ(6:0)). 25 °C.
INTER(7:0)
129 to 256; 0
65 to 128
FREQ(6:0)
Accuracy Mode
High accuracy
Medium accuracy
High accuracy
Low accuracy
Theoretical Absolute Accuracy
0 to 127
±2.8°
±5.6°
±2.8 °
±11.2°
±5.6°
±2.8°
0
1 to 127
1 to 64
0
1
Medium accuracy
High accuracy
2 to 127
Table 21: Accuracy modes
Description
Parameter / Condition
Requirement or relationship
Control bit
Oscillator frequency
fosc [Hz]
<30 MHz, when VDD = 5 V
<25 MHz, when VDD = 3.3 V
CLOCK(4:0)
System Clock
fsystem [Hz]
fsystem = fosc, if CLKDIV = 0
fsystem = fosc/2, if CLKDIV = 1
CLKDIV
Core Clock
fcore [Hz]
ffront [Hz]
fcore = fsystem / (1 + FREQ(6:0))
FREQ(6:0)
Max front-end input
frequency
ffront = fsystem / 256, if High Accuracy
ffront = fsystem / 128, if Medium Accuracy
ffront = fsystem / 64, if Low Accuracy
FREQ(6:0)
INTER(7:0)
Max back-end frequency fback [Hz]
fback = fcore / INTER(7:0)
INTER(7:0)
Max iC-TW2 input
frequency
finput [Hz]
finput = min(ffront, fback)
Min A/B edge separation tedge
tedge = 1 / fcore
A/B edge granularity
Hysteresis
tgran
tgran = 1 / fsystem
±(HYST(1:0) x 1.4 °), if High Accuracy
HYST(1:0)
±(HYST(1:0) x 2.8 °) if Medium or Low Accuracy
SIN/COS to A/B output
latency
tlatency [µs]
10 / fsystem [MHz] + 0.2, if no filter
18 / fsystem [MHz] + 0.2, if 8 sample average
26 / fsystem [MHz] + 0.2, if 16 sample average
FILTER(1:0)
Table 22: Configuration dependencies
ICHAUS [ IC-HAUS GMBH ]
