• Thermal design

[Operating range in which a heat sink is not used]

The STK672-330 package has a structure that uses no screws, and is recommended for use without a heat sink. This

section discusses the safe operating range when no heat sink is used.

In the maximum ratings specifications, Tc max is specified to be 105°C, and when mounted in an actual end product

system, the Tc max value must never be exceeded during operation. Tc can be expressed by formula (A) below, and

thus the range for

∆Tc must be stipulated so that Tc is always under 105°C.

Tc = Ta +

∆Tc (A)

Ta: Hybrid IC (H-IC) ambient temperature,

∆Tc: Temperature increase across the aluminum substrate

As shown in figure 5, the value of

∆Tc increases as the hybrid IC internal average power dissipation P

example shown in the motor current timing chart in figure 2.

operation consists of repetitions of the operation shown in figure 2.

No. 7304-7/11

STK672-330

Figure 2. Motor Current Timing

T1: Motor rotation operation time

T2: Motor hold operation time

T3: Motor current off time

T2 may be reduced, depending on the application.

T0: Single repeated motor operating cycle

IO1 and IO2: Motor current peak values

Due to the structure of motor windings, the phase current is a positive and negative current with a pulse form.

Note that figure 2 presents the concepts here, and that the on/off duty of the actual signals will differ.

(I)

If the value calculated in formula (I) above is under 1.5 W, then from figure 5 we see that operation is allowed up to an

ambient temperature Ta of 60°C.

While the operating range when a heat sink is not used can be determined from formula (I) above, figure 4 is merely a

single example of one operating mode for a single motor.

For example, while figure 4 shows a 2-phase excitation motor, if 1-2 phase excitation is used with a 500-Hz clock

figure 4.

conditions. After performing the above rough calculations, always install the hybrid IC (H-IC) in an actual end product

and verify that the substrate temperature Tc does not rise above 105°C.

Motor phase current

(sink side)

ITF02175