STK672-210-E

No. 7464-6/10

Thermal Design

The size of the heat sink required for the STK672-210-E depends on the output current IOH (A), the electrical

characteristics of the motor, the excitation mode, and the basic drive frequency.

The thermal resistance (

θc-a) of the required heat sink can be determined from the following formula.

(°C/W)

Tc max: The STK672-210-E substrate temperature (°C)

Ta: The STK672-210-E ambient temperature (°C)

Pd: The average internal power dissipation in the STK672-210-E (W)

For example, the required area for a heat sink made from 2mm thick aluminum can be determined from the graph at the

right below. Note that the ambient temperature is greatly influenced by the ventilation and air flow patterns within the

application. This means that the size of the heat sink must be determined with care so that the STK672-210-E back

surface (aluminum substrate) temperature Tc in the mounted state never exceeds, under any conditions that might occur,

the temperature Tc = 105

°C.

STK672-210-E Average Internal Power Dissipation Pd

Of the devices that contribute to the STK672-210-E average internal power supply, the devices with the largest power

dissipation are the current control devices, the diodes that handle the regenerative current, the current detection resistor,

and the predriver circuit.

The following presents formulas for calculating the power dissipation for the different excitation (drive) modes.

2 phase excitation mode

Pd2EX = (Vsat + Vdf) × 0.5 × CLOCK × IOH × t2 + 0.5 × CLOCK × IOH × (Vsat × t1 + Vdf × t3)

1-2 phase excitation mode

Pd1-2EX = (Vsat + Vdf) × 0.25 × CLOCK × IOH × t2 + 0.25 × CLOCK × IOH × (Vsat × t1 + Vdf × t3)

Motor hold mode

PdHOLDEX = (Vsat + Vdf) × IOH

Vsat: Ron voltage drop + shunt resistor combined voltage

Vdf: FET internal diode + shunt resistor combined voltage

CLOCK: Input clock (shows clock in the timing charts on page 4)

Figure 1 Motor COM current waveform model

Pd

Ta

-

max

Tc

a

-

c

=

θ

IOH

0A

t1

t2

t3

ITF01880

04

8

12

16

20

2

6

10

14

18

IC internal average power dissipation, Pd - W

θc-a - Pd

0

8

12

16

20

4

ITF01881

10

23

5

7

100

1000

23

5

7

θc-a - S

1.0

5

7

2

3

10

100

5

7

2

3

No Fin

23.0[°C/W]

Tc max=105°C

40°C

50°C

60°C

No Fin

23.0[°C/W]

Mounted vertically

Convection cooling

2mm

thick

Al pla

te (w

ith n

o surf

ace fi

nish)

(With

a flat

black

surfa

ce fin

ish)

θc-a=

(°C/W)

Tc max--Ta

Pd