stk672-442b-e Sanyo Semiconductor Corporation, stk672-442b-e Datasheet - Page 14

• Manufacturer Part Number: stk672-442b-e
• Description: 2-phase Stepping Motor Driver
• Manufacturer: Sanyo Semiconductor Corporation

3. STK672-442B-E Allowable Avalanche Energy Value
(1) Allowable Range in Avalanche Mode
When driving a 2-phase stepping motor with constant current chopping using an STK672-4** Series hybrid IC,
the waveforms shown in Figure 1 below result for the output current, I D , and voltage, V DS .
When operations of the MOSFET built into STK672-4** Series ICs is turned off for constant current chopping,
the I D signal falls like the waveform shown in the figure above. At this time, the output voltage, V DS , 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 V DSS . Voltage restriction by
V DSS results in a MOSFET avalanche. During avalanche operations, I D flows and the instantaneous energy at
this time, EAVL1, is represented by Equation (3-1).
During STK672-4** 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 (3-2) used to
find the average power loss, PAVL, during avalanche mode multiplied by the chopping frequency in Equation
(3-1).
For V DSS , IAVL, and tAVL, be sure to actually operate the STK672-4** Series and substitute values when
operations are observed 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 I D , V DSS , and tAVL
waveforms during operation, and then check that the result of calculating Equation (3-2) falls within the
allowable range for avalanche operations.
Figure 1 Output Current, I D , and Voltage, V DS , Waveforms 1 of the STK672-4** Series when Driving a 2-
V DS
I D
EAVL1=V DSS ×IAVL×0.5×tAVL ------------------------------------------- (3-1)
PAVL=V DSS ×IAVL×0.5×tAVL×fc ------------------------------------------- (3-2)
Ex. If V DSS =110V, IAVL=1A, tAVL=0.2μs when using a STK672-442B-E driver, the result is:
PAVL=110×1×0.5×0.2×10
V DSS =110V is a value actually measured using an oscilloscope.
Phase Stepping Motor with Constant Current Chopping
V DSS : V units, IAVL: A units, tAVL: sec units
The coefficient 0.5 in Equation (3-1) is a constant required to convert the IAVL triangle wave to a
square wave.
fc: Hz units (fc is set to the PWM frequency of 50kHz.)
-6
×50×10
STK672-442B-E
3
=0.55W
tAVL: Time of avalanche operations
ITF02557
V DSS : Voltage during avalanche operations
I OH : Motor current peak value
IAVL: Current during avalanche operations
No.A1735-14/24