STK672-740A-E View Datasheet(PDF) - ON Semiconductor

Part Name

Description

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STK672-740A-E

Thick-Film Hybrid IC 2-phase Stepping Motor Driver

ON Semiconductor 

STK672-740A-E

3. Calculating STK672-740A-E HIC Internal Power Loss

The average internal power loss in each excitation mode of the STK672-740A-E can be calculated from the following

formulas.

Each excitation mode

2-phase excitation mode

2PdAVex=(Vsat+Vdf) × (1/(t1+t2+t3)) ×IOH×t2+(1/(t1+t2+t3)) ×IOH× (Vsat×t1+Vdf×t3)

1-2 Phase excitation mode

1-2PdAVex=(Vsat+Vdf) × (1/(t1+t2+t3)) ×IOH×t2+(1/(t1+t2+t3)) ×IOH× (Vsat×t1+Vdf×t3)

Motor hold mode

HoldPdAVex= (Vsat+Vdf) ×IOH

Vsat: Combined voltage represented by the Ron voltage drop+shunt resistor

Vdf: Combined voltage represented by the MOSFET body diode+shunt resistor

t1, t2, and t3 represent the waveforms shown in the figure below.

t1: Time required for the winding current to reach the set current (IOH)

t2: Time in the constant current control (PWM) region

t3: Time from end of phase input signal until inverse current regeneration is complete

IOH

0A

t1

t2

t3

Motor COM Current Waveform Model

t1= (-L/(R+0.20)) In (1-((R+0.20)/VCC) ×IOH)

t3= (-L/R) In ((VCC+0.20)/(IOH×R+VCC+0.20))

VCC: Motor supply voltage (V)

L: Motor inductance (H)

R: Motor winding resistance (Ω)

IOH: Motor set output current crest value (A)

For Vsat and Vdf, be sure to substitute values from the graphs of Vsat vs. IOH and Vdf vs. IOH while the set current

value is IOH.

Then, determine whether a heat sink is required by comparing with the graph of ΔTc vs. Pd based on the average HIC

power loss calculated.

When designing a heat sink, refer to the section “Thermal design” found on the next page. The average HIC power

loss, PdAV, described above does not have the avalanche’s loss. To include the avalanche’s loss, be sure to add

Equation (2), “STK672-7** Allowable Avalanche Energy Value” to PdAV above. When using this IC without a fin

always check for temperature increases in the set, because the HIC substrate temperature, Tc, varies due to effects of

convection around the HIC.

No. A1136-12/19

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