TMC249 / TMC249A DATA SHEET (V2.09 / 2009-Jul-30)
29
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
000111
000110
000101
000100
...
0 V
5.8 mV
11.5 mV
17.3 mV
23 mV
111101
111100
334.2 mV
340 mV
SPI bit
DAC bit
SPI bit
15
/B1
7
14
/B0
6
13
/A1
5
12
/A0
4
11
MDA
3
10
A5
2
9
A4
1
8
A3
0
DAC bit
A2
PHA MDB
B5
B4
B3
B2
PHB
SCK
SDI
SCK
SDI
TMC236 /
TMC239
SDO
CSN
SRA
110R
4.7nF
opt.
47K
47K
RS
/CS
47K
+VCC
100K
/OE
C2
/MR
C1
/DACA.0
DS1D
Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q7'
/DACA.1
/DACB.0
/DACB.1
Free for
second
TMC239
74HC595
Vcc = 5V
C
Note: Use a 74HC4094
SDO
Q
D
instead of the HC595 to get
rid of the HC74 and inverter
1/2 74HC74
Please see the FAQ document for more application information.
Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG
TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
