TMC249 / TMC249A DATA SHEET (V2.09 / 2009-Jul-30)
16
Chopper Principle
Chopper cycle / Using the mixed decay feature
The TMC249 uses a quiet fixed frequency chopper. Both coils are chopped with a phase shift of 180
degrees. The mixed decay option is realized as a self stabilizing system (pat. fi.), by shortening the fast
decay phase, if the ON phase becomes longer. It is advised to enable the mixed decay for each phase
during the second half of each microstepping half-wave, when the current is meant to decrease. This
leads to less motor resonance, especially at medium velocities. With low velocities or during standstill
mixed decay should be switched off. In applications requiring high resolution, or using low inductivity
motors, the mixed decay mode can also be enabled continuously, to reduce the minimum motor
current which can be achieved. When mixed decay mode is continuously on or when using high
inductivity motors at low supply voltage, it is advised to raise the chopper frequency to minimum
36kHz, because the half chopper frequency could become audible under these conditions.
I
I
I
RSENSE
RSENSE
RSENSE
On phase:
Current flows in target
direction
Fast decay phase:
Current flows back into
power supply
Slow decay phase:
Current re-circulation
target current phase A
actual current phase A
on
slow decay
on
fast decay
slow decay
oscillator clock
resp. external clock
mixed decay disabled
mixed decay enabled
When polarity is changed on one bridge, the PWM cycle on that bridge becomes restarted at once.
Fast decay switches off both upper transistors, while enabling the lower transistor opposite to the
selected polarity. Slow decay always enables both lower side transistors.
Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG
TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
