TMC246_06 Datasheet, PDF (26/26 Pages) List of Unclassifed Manufacturers – High Current Microstep Stepper Motor Driver with sensorless stall detection, protection / diagnosis and SPI Interface

TMC246 / TMC246A DATA SHEET (V2.03 / Nov. 6th, 2006)
26
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 Trip voltage
(MSB first)
0000xx
0V
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
DAC bit /B1 /B0 /A1 /A0 MDA A5
SPI bit 7
6
5
4
3
2
DAC bit A2 PHA MDB B5 B4 B3
9
8
A4 A3
1
0
B2 PHB
SCK
SCK
TMC236 /
SDI
SDI
TMC239
SDO
CSN
/CS
+V_CC
SRA
110R
4.7nF
opt.
47K 47K
R_S
47K
100K
SDO
C
QD
1/2 74HC74
/OE
C2
/MR
C1
DS1D
/DACA.0
Q0
/DACA.1
Q1
/DACB.0
Q2
/DACB.1
Q3
Q4 _{Free for}
Q5
second
Q6
TMC239
Q7
Q7'
74HC595
Vcc = 5V
Note: Use a 74HC4094
instead of the HC595 to get
rid of the HC74 and inverter
Please see the FAQ document for more application information.
i _{SPI is a trademark of Motorola}
Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG