Datasheet

TMC246 DATA SHEET (V2.02 / Jul. 31st, 2006) 26
Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG
Application Note: Extending the Microstep Resolution
For some applications it might be desired to have a higher microstep resolution, while keeping the
advantages of control via the serial interface. The following schematic shows a solution, which adds
two LSBs by selectively pulling up the SRA / SRB pin by a small voltage difference. Please remark,
that the lower two bits are inverted in the depicted circuit. A full scale sense voltage of 340mV is
assumed. The circuit still takes advantage of completely switching off of the coils when the internal
DAC bits are set to “0000”. This results in the following comparator trip voltages:
Current setting
(MSB first)
Trip voltage
0000xx 0 V
000111 5.8 mV
000110 11.5 mV
000101 17.3 mV
000100 23 mV
...
111101 334.2 mV
111100 340 mV
SPI bit 15 14 13 12 11 10 9 8
DAC bit /B1 /B0 /A1 /A0 MDA A5 A4 A3
SPI bit 7 6 5 4 3 2 1 0
DAC bit A2 PHA MDB B5 B4 B3 B2 PHB
R
S
SRA
TMC236 /
TMC239
110R
4.7nF
opt.
74HC595
C1
Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q7'
/MR
C2
/OE
SCK
SDI
SDO
CSN
+V
CC
DS1D
100K
/CS
SDI
SCK
SDO
Free for
second
TMC239
47K 47K
47K
/DACA.0
/DACA.1
/DACB.0
/DACB.1
Vcc = 5V
1/2 74HC74
C
DQ
Note: Use a 74HC4094
instead of the HC595 to get
rid of the HC74 and inverter
i
SPI is a trademark of Motorola