TMC249 / TMC249A DATA SHEET (V2.10 / 2011-Aug-10)
12
Typical motor coil current values
Current setting Percentage of Typical trip voltage of the current sense comparator
current
(internal reference or analog input voltage of 2V is used)
CA3..0 / CB3..0
0000
0001
0010
...
0%
0 V
(bridge continuously in slow decay condition)
6.7%
13.3%
...
23 mV
45 mV
1110
1111
93.3%
100%
317 mV
340 mV
The current values correspond to a standard 4 Bit DAC, where 100%=15/16. The contents of all
registers is cleared to “0” on power-on reset or disable via the ENN pin, bringing the IC to a low power
standby mode. All SPI inputs have Schmitt-Trigger function.
Base current control via INA and INB in SPI mode
In SPI mode, the IC can use an external reference voltage for each DAC. This allows the adaptation to
different motors. This mode is enabled by tying pin ANN to GND. A 2.0V input voltage gives full scale
current of 100%. In this case, the typical trip voltage of the current sense comparator is determined by
the input voltage and the DAC current setting (see table above) as follows:
VTRIP,A = 0.17 VINA “percentage SPI current setting A”
VTRIP,B = 0.17 VINB “percentage SPI current setting B”
A maximum of 3.0V VIN is possible. Multiply the percentage of base current setting and the DAC table
to get the overall coil current. It is advised to operate at a high base current setting, to reduce the
effects of noise voltages. This feature allows a high resolution setting of the required motor current
using an external DAC or PWM-DAC (see schematic for examples).
using PWM signal
8 level via R2R-DAC
2 level control
INA
INB
µC-
PWM
µC-
Port .2
47K
100K
100K
100K
R1
100nF
µC-
Port .1
10nF
AGND
ANN
µC-
Port .0
µC-
Port
Controlling the power down mode via the SPI interface
Bit
11
10
9
8
7
6
5
4
3
2
1
0
Standard
function
Control
word
MxA CA3 CA2 CA1 CA0 PhA MxB CB3 CB2 CB1 CB0 PhB
-
0
0
0
0
-
-
0
0
0
0
-
function
Enable standby mode and
clear error flags
Programming current value “0000” for both coils at a time clears the overcurrent flags and switches the
TMC249 into a low current standby mode with coils switched off.
Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG
TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
