TMC249 / TMC249A DATA SHEET (V2.02 / Aug 12th, 2005)
9
Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG
Typical winding current values
Current setting
CA3..0 / CB3..0
Percentage of
current
Typical trip voltage of the current sense comparator
(internal reference or analog input voltage of 2V is used)
0000
0%
0 V
(bridge continuously in slow decay condition)
0001
6.7%
23 mV
0010
13.3%
45 mV
...
...
1110
93.3%
317 mV
1111
100%
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).
47K
100nF
AGND
INA
INB
ANN
µC-
PWM
using PWM signal
100K
µC-
Port .2
8 level via R2R-DAC
100K
100K
µC-
Port .1
µC-
Port .0
R1
2 level control
µC-
Port
10nF
Controlling the power down mode via the SPI interface
Standard
function
11
MxA
10
CA3
9
CA2
6
PhA
-0
-
Control
word
function
--
Bit
Enable standby mode and clear
error flags
8
CA1
7
CA0
5
MxB
4
CB3
3
CB2
0
PhB
2
CB1
1
CB0
0
0
00
0
00
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.
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