TMC239 DATA SHEET (V1.00 / Apr. 24th, 2003)
9
Copyright © 2002, TRINAMIC Microchips GmbH
counter reaches 3, the bridge remains switched off for 63 PWM cycles and the error flag is read as
“active”. The user can clear the error condition in advance by clearing the error flag. The error counter
is cleared, whenever there are more than 63 PWM cycles without overcurrent. There is one error
counter for each of the low side bridges, and one for the high side. The overcurrent detection is
inactive during the blank pulse time for the corresponding bridge.
The high side comparator detects a short to GND or an overcurrent, whenever the voltage between VS
and VT becomes higher than 0.15 V at any time, except for the blank time period which is logically
ORed for both bridges. Here all transistors become switched off for the rest of the PWM cycle,
because the bridge with the failure is unknown.
The overcurrent flags can be cleared by disabling and re-enabling the chip either via the ENN pin or by
sending a telegram with both current control words set to “0000”. In high side overcurrent conditions
the user can determine which bridge sees the overcurrent, by selectively switching on only one of the
bridges with each polarity (therefore the other bridge should remain programmed to “0000”).
Overtemperature protection and diagnosis
The circuit switches off all output power transistors during an overtemperature condition. The over-
temperature flag should be monitored to detect this condition. The circuit resumes operation after cool
down below the temperature threshold.
Enable pin behavior
During disable conditions the circuit switches off all output power transistors and goes into a low
current shutdown mode. All register contents is cleared to “0”, and all status flags are cleared.
Chopper cycle
The TMC239 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 this 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. The mixed decay mode can also be enabled when output current is near
to zero, to reduce the minimum motor current which can be achieved.
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.
oscillator clock
resp. external clock
actual current phase A
target current phase A
mixed decay disabled
mixed decay enabled
on
slow decay
on
fast decay
slow decay
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