STK672-532
4. Thermal design
[Operating range in which a heat sink is not used]
Use of a heat sink to lower the operating substrate temperature of the HIC (Hybrid IC) is effective in increasing the
quality of the HIC.
The size of heat sink for the HIC varies depending on the magnitude of the average power loss, PdAV, within the
HIC. The value of PdAV increases as the output current increases. To calculate PdAV, refer to “Calculating Internal
HIC Loss for the STK672-532” in the specification document.
Calculate the internal HIC loss, PdAV, assuming repeat operation such as shown in Figure 1 below, since conduction
during motor rotation and off time both exist during actual motor operations.
I 1
O
Motor phase current
(sink side)
I 2
O
0A
-I 1
O
T1
T3
T2
T0
Figure 1 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
I 1 and I 2: Motor current peak values
O
O
Due to the structure of motor windings, the phase current is a positive and negative current with a pulse form.
Note that figure 1 presents the concepts here, and that the on/off duty of the actual signals will differ.
The hybrid IC internal average power dissipation PdAV can be calculated from the following formula.
PdAV= (T1×P1+T2×P2+T3×0) ÷T0 ---------------------------- (I)
(Here, P1 is the PdAV for I 1 and P2 is the PdAV for I 2)
O
O
If the value calculated using Equation (I) is 1.5W or less, and the ambient temperature, Ta, is 60°C or less, there is no
need to attach a heat sink. Refer to Figure 2 for operating substrate temperature data when no heat sink is used.
[Operating range in which a heat sink is used]
Although a heat sink is attached to lower Tc if PdAV increases, the resulting size can be found using the value of
θc-a in Equation (II) below and the graph depicted in Figure 3.
θc-a= (Tc max-Ta) ÷PdAV ---------------------------- (II)
Tc max: Maximum operating substrate temperature =105°C
Ta: HIC ambient temperature
Although a heat sink can be designed based on equations (I) and (II) above, be sure to mount the HIC in a set and
confirm that the substrate temperature, Tc, is 105°C or less.
The average HIC power loss, PdAV, described above represents the power loss when there is no avalanche operation.
To add the loss during avalanche operations, be sure to add Equation (2), “Allowable STK672-5** Avalanche
Energy Value”, to PdAV.
No. A2111-18/23
SANYO [ SANYO SEMICON DEVICE ]
