IC-TW2_13 Datasheet, PDF (17/28 Pages) IC-Haus GmbH – 8-BIT SIN/COS INTERPOLATION IC

iC-TW2 8-BIT SIN/COS INTERPOLATION IC
WITH INTEGRATED EEPROM
CONFIGURATION DEPENDENCIES
Rev E2, Page 17/28
This section describes the dependencies between the
chip configuration and the system’s performance. It is
vital to understand the implication of system parame-
ters to be able to tune the iC-TW2 for full performance.
It is especially important to correctly program regis-
ter FREQ(6:0), since this directly affects accuracy and
maximum allowed input frequency.
Selecting configuration parameters
To select a proper configuration follow the outlined pro-
cedure below. Refer to Table 26 for reference.
1. Determine the maximum input frequency f_in()max as
required by the application.
2. Calculate f_core based on f_in()max and resolution
INTER(7:0).
3. Select f_system based on the accuracy requirements.
Accuracy is a function of resolution INTER(7:0) and
clock scaling FREQ(6:0). Always use the highest ac-
curacy possible to still satisfy f_in()max.
4. Determine f_osc. Selecting the slowest possible f_osc
lowers power consumption and improves jitter perfor-
mance.
INTER(7:0) FREQ(6:0)
129 to 256; 0
65 to 128
1 to 64
0 to 127
0
1 to 127
0
1
2 to 127
Accuracy
Mode
High accuracy
Medium acc.
High accuracy
Low accuracy
Medium acc.
High accuracy
Theoretical
Absolute
Accuracy
±2.8°
±5.6°
±2.8 °
±11.2°
±5.6°
±2.8°
Table 21: Accuracy modes
CLKDIV
Code
0
1
Note
Addr. 0x0B; bit 1
R/W
Function (defaults to eeprom setting)
f_system = fosc
f_system = fosc / 2
It is recommended to use the divider when support
for high input frequencies is not required.
Table 22: Master clock divider
FREQ(6:0)
Code
0x00
...
0x7F
Addr. 0x05; bit 6:0
Clock scaling (defaults to eeprom setting)
fcore = f_system
fcore = f_system / (1 + FREQ(6:0))
fcore = f_system / 128
R/W
Table 23: Clock scaling
Clock tuning
1. Observe f_osc/32 on pin A_U during calibra-
tion mode 2.
2. Use CLOCK(4:0) to tune the oscillator to the desired
f_cal frequency. (f_pinA = f_osc/32)
3. Be aware that the oscillator can have as much
as 20 % frequency variation over the operating tem-
perature range (-40 °C to 125 °C). The oscillator runs
slower at higher temperatures. To guarantee perfor-
mance at 125 °C it is necessary to tune the oscillator
to typ. 12 % higher frequency at room temperature of
25 °C.
Accuracy modes
The converter resolution INTER(7:0) in conjunction
with the clock scaling FREQ(6:0) define iC-TW2’s ac-
curacy mode. Based on the selected accuracy mode
other system parameters are defined as shown in Ta-
ble 26.
HYST(1:0)
Code
00
01
10
11
Addr. 0x06; bit 1:0
R/W
Function (defaults to eeprom setting)
High accuracy
Medium / low accuracy
no hysteresis
no hysteresis
±1.4 °
±2.8 °
±2.81 °
±5.6 °
±5.63 °´
±11.3 °
Table 24: Hysteresis control
FILTER(1:0)
Addr. 0x06; bit 3:2
R/W
Code
Function (defaults to eeprom setting)
00
filter disabled
01
Average of 8 samples
10
Average of 16 samples
11
undefined
Notes
It is recommended to enable the filter in almost all
cases as it removes loop instability noise. However,
enabling the filter increases the Sin/Cos input to
A/B output latency (see Table 26 for details).
Table 25: Datapath filter control