STK672-120-E

No.6042-6/9

• Allowable motor current operating range

The motor current (IOH) must be held within the range corresponding to the area under the curve shown in figure 4.

For example, if the operating substrate temperature Tc is 105

°C, then IOH must be held under IOH = 2.4A, and in

hold mode IOH must be held under IOH = 2.0A.

• Thermal design

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

Thermal design that lowers this hybrid IC’s operating substrate temperature can be effective in improving end product

quality. The size of the heat sink required by this hybrid IC varies with the average power dissipation PD. The value

of PD increases as the output current increases, as shown in figure 5.

Since there are periods when current flows and periods when the current is off during actual motor operation, PD

cannot be determined from the data presented in figure 5. Therefore, we calculate PD assuming that actual motor

operation consists of repetitions of the operation shown in figure 3.

Figure 3 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 3 presents the concepts here, and that the on/off duty of the actual signals will differ.

The hybrid IC internal average power dissipation PD can be calculated from the following formula.

PD = (T1 × P1 + T2 × P2 + T3 × 0) ÷ T0

(I)

(Here, P1 is the PD for IO1 and P2 is the PD for IO2)

If the value calculated in formula (I) above is under 1.5W, then there will be no need to use a heat sink for ambient

temperatures Ta up to 60°C. See figure 6 for operating substrate temperature rise data when a heat sink is not attached.

If a heat sink is to be used, to lower Tc if PD increases, use formula (II) and the graph in figure 7 to determine the size

of the heat sink.

θc - a = (Tc max–Ta) ÷ PD

(II)

Tc max: Maximum operating substrate temperature = 105

°C

Ta: The hybrid IC ambient temperature

While formulas (I) and (II) above are adequate for thermal design, note that figure 5 is merely a single example of one

operating mode for a single motor. For example, while figure 5 shows a 2-phase excitation motor, if 1-2 phase

excitation is used with a 500Hz clock frequency, the drive will be turned off for 25% of the time and the loss PD will be

reduced to 75% of that in figure 5.

It is extremely difficult for calculate the internal average power dissipation PD for all possible end product conditions.

After performing the above rough calculations, always install the hybrid IC in an actual end product and verify that the

substrate temperature Tc does not rise above 105°C.

T1

T2

T0

T3

-IO1

IO2

IO1

Motor phase current

(sink side)