iC-TW8 16-BIT SIN/COS INTERPOLATOR
Pin Configuration Mode
Jan 9, 2013 Page PC7/15
Connecting the ABZ Outputs
Power-Up Sequence
In pin configuration mode, the iC-TW8 provides
industry-standard quadrature incremental outputs
at OUTA (pin 18) and OUTB (pin 17). If an index
sensor is connected to the ZERO inputs of the iC-
TW8, a Z output synchronous with the AB out-
puts is also available on OUTZ (pin 16). These
outputs can be directly connected to an encoder
counter such as the iC-TW9.
After power-up, the iC-TW8’s POR circuit monitors
the supply voltage and waits until it has reached the
appropriate threshold (as determined by the xRST
connections). The iC-TW8 then starts up using the
internal oscillator (even if a crystal or external clock
source is connected) and executes its start-up cycle as
outlined below.
1. Read parameter values from EEPROM.
2. Set proper clock source and frequency.
Alternatively, the ABZ outputs can be connected
to a differential line driver (such as the iC-HD7 or
iC-HX) as shown in Figure 10. When using a line
driver it is especially important to isolate the iC-
TW8 from external switching noise using a regu-
lator, as shown.
3. Read configuration inputs and enable signal
path.
4. Wait for all analog circuitry to settle.
5. Clear all faults.
24V
regulator
3.3V
regulator
5V
6. Start ABZ output generation.
If any faults are detected during the start-up cycle, the
iC-TW8 does not enable the AB outputs but goes into
an idle state with the FAULT output (pin 20) asserted
(low).
line driver
AVDD
DVDD
VCC
VB1
VB2
VB3
A1
The amount of time the iC-TW8 waits for the analog
circuitry to settle (twait) depends on the clock fre-
quency as shown by the formula below.
OUTA
OUTB
OUTZ
E1
E3
E5
A2
A3
A4
AVSS/DVSS
GNDx
A5
A6
1048
twait[ms]
iC-TW8
iC-HX
fclock[MHz]
Figure 10: Line Driver Connection
For example, using a 32 MHz crystal, the iC-TW8
waits 33 ms for the analog circuitry to settle.
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