STK672-401C-E Datasheet, PDF (15/19 Pages) Sanyo Semicon Device – Thick-Film Hybrid IC 2-phase Stepping Motor Driver

STK672-401C-E
4. STK672-401C-E Allowable Avalanche Energy Value
(1) Allowable Range in Avalanche Mode
When driving a 2-phase stepping motor with constant current chopping using an STK672-401C-E hybrid IC, the
waveforms shown in Figure 1 below result for the output current, ID, and voltage, VDS.
VDSS: Voltage during avalanche operations
VDS
IOH: Motor current peak value
IAVL: Current during avalanche operations
ID
tAVL: Time of avalanche operations
ITF02557
Figure 1 Output Current, ID, and Voltage, VDS, Waveforms 1 of the STK672-400 Series when Driving a
2-Phase Stepping Motor with Constant Current Chopping
When operations of the MOSFET built into STK672-400 Series ICs is turned off for constant current chopping,
the ID signal falls like the waveform shown in the figure above. At this time, the output voltage, VDS, suddenly
rises due to electromagnetic induction generated by the motor coil.
In the case of voltage that rises suddenly, voltage is restricted by the MOSFET VDSS. Voltage restriction by
VDSS results in a MOSFET avalanche. During avalanche operations, ID flows and the instantaneous energy at
this time, EAVL1, is represented by Equation (4-1).
EAVL1=VDSS×IAVL×0.5×tAVL ------------------------------------------- (4-1)
VDSS: V units, IAVL: A units, tAVL: sec units
The coefficient 0.5 in Equation (4-1) is a constant required to convert the IAVL triangle wave to a
square wave.
During STK672-400 Series operations, the waveforms in the figure above repeat due to the constant current
chopping operation. The allowable avalanche energy, EAVL, is therefore represented by Equation (4-2) used to
find the average power loss, PAVL, during avalanche mode multiplied by the chopping frequency in Equation
(4-1).
PAVL=VDSS×IAVL×0.5×tAVL×fc ------------------------------------------- (4-2)
fc: Hz units (fc is set to the PWM frequency of 62.5kHz.)
For VDSS, IAVL, and tAVL, be sure to actually operate the STK672-400 Series and substitute values when
operations are observed using an oscilloscope.
Ex. If VDSS=110V, IAVL=0.8A, tAVL=0.2μs when using a STK672-401C-E driver, the result is:
PAVL=110×0.8×0.5×0.2×10^-6×62.5×10³=0.55W
VDSS=110V is a value actually measured using an oscilloscope.
The allowable loss range for the allowable avalanche energy value, PAVL, is shown in the graph in Figure 3.
When examining the avalanche energy, be sure to actually drive a motor and observe the ID, VDSS, and tAVL
waveforms during operation, and then check that the result of calculating Equation (4-2) falls within the
allowable range for avalanche operations.
No.A2137-15/19