STK672-543-E

No. A2113-13/22

2. Calculating STK672-543-E HIC Internal Power Loss

The average internal power loss in each excitation mode of the STK672-543-E can be calculated from the following

formulas.

Each excitation mode

2-phase excitation mode

2PdAVex= (Vsat+Vdf)

×0.5×CLOCK×IOH×t2+0.5×CLOCK×IOH× (Vsat×t1+Vdf×t3)

1-2 phase excitation mode

1-2PdAVex= (Vsat+Vdf)

×0.25×CLOCK×IOH×t2+0.25×CLOCK×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

CLOCK: Input CLOCK (CLOCK pin signal frequency)

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

Motor COM Current Waveform Model

t1= (-L/(R+0.28)) ln (1-((R+0.28)/VCC) ×IOH)

t3= (-L/R) ln ((VCC+0.28)/(IOH×R+VCC+0.28))

VCC: Motor supply voltage (V)

L: Motor inductance (H)

R: Motor winding resistance (

Ω)

IOH: Motor set output current crest value (A)

Relationship of CLOCK, t1, t2, and t3 in each excitation mode

2-phase excitation mode: t2= (2/CLOCK) - (t1+t3)

1-2 phase excitation mode: t2= (3/CLOCK) -t1

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 “STK672-543-E 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), “STK672-5** 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.

IOH

0A

t1

t2

t3