TMC248-LA DATASHEET (Rev. 1.01 / 2013-MAR-26)
23
7.5 Blank Time
The TMC248 uses a digital blanking pulse for the current chopper comparators. This prevents current
spikes, which can occur during switching action due to capacitive loading, from terminating the
chopper cycle.
The lowest possible blanking time gives the best results for microstepping. A long blank time leads to
a long minimum turn-on time, thus giving an increased lower limit for the current.
Please remark, that the blank time should cover both, switch-off time of the lower side transistors
and turn-on time of the upper side transistors plus some time for the current to settle. Thus the
complete switching duration should never exceed 1.5µs. With slow external power stages it will
become necessary to add additional RC-filtering for the sense resistor inputs.
The TMC248 allows adapting the blank time to the load conditions and to the selected slope in four
steps:
BLANK TIME SETTINGS
BL2
BL1
Typical blank time
Remarks
GND
GND
VCC
VCC
GND
VCC
GND
VCC
0.6 µs
0.9 µs
1.2 µs
1.5 µs
Very short. Will require good filtering on SRA and SRB.
Works well in good low inductivity layouts.
Default for most applications.
May be used with slow bridges or high sense resistor trace
inductivity.
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