stk672-050-e ON Semiconductor, stk672-050-e Datasheet - Page 17

• Manufacturer Part Number: stk672-050-e
• Description: Thick-film Hybrid Ic Unipolar Constant-current Chopper External Excitation Pwm Circuit With Built-in Microstepping Controller Stepping Motor Driver Sine Wave Drive Output Current 3.0a No Heat Sink*
• Manufacturer: ON Semiconductor

θc-a =
<Determining the Size of the Hybrid IC Heat Sink>
Determine θc-a for the heat sink from the average power loss determined in the previous item.
Determine θc-a from the above formula and then size S (in cm
The ambient temperature of the device will vary greatly according to the air flow conditions within the application.
Therefore, always verify that the size of the heat sink is adequate to assure that the Hybrid IC back surface (the
aluminum plate side) will never exceed a Tc max of 105°C, whatever the operating conditions are.
Next we determine the usage conditions with no heat sink by determining the allowable hybrid IC internal average loss
from the thermal resistance of the hybrid IC substrate, namely 18.5°C/W.
For a Tc max of 105°C at an ambient temperature of 50°C
For a Tc max of 105°C at an ambient temperature of 40°C
This hybrid IC can be used with no heat sink as long as it is used at operating conditions below the losses listed above.
(See ΔTc – Pd curve in the graph on page 19.)
<Hybrid IC internal power element (MOSFET) junction temperature calculation>
The junction temperature, Tj, of each device can be determined from the loss Pds in each transistor and the thermal
resistance θj-c.
Here, we determine Pds, the loss for each transistor, by determining Pd EX in each excitation mode.
The steady-state thermal resistance θj-c of a power MOSFET is 5°C/W.
Pds = Pd EX /4
Tj = Tc + θj-c × Pds (°C)
20
16
12
8
4
0
0
No. Fin 23.0 (°C/W)
Tc
Pd
max
2
EX
IC internal average power loss, Pd - W
-
Ta
4
[°C/W]
6
θc-a - Pd
8
θc-a= Tc max -- Ta (°C/W)
Tc max=105°C
10
Pd
12
14
ITF02402
STK672-050-E
16
Tc max: Hybrid IC substrate temperature (°C)
Ta: Application internal temperature (°C)
Pd EX : Hybrid IC internal average loss (W)
2
) of the heat sink from the graphs shown below.
Pd EX =
Pd EX =
1.0
10
2
7
5
3
2
10
No. Fin 23.0 (°C/W)
105
105
18.5
18.5
-
-
2
50
40
Heat sink surface area, S - cm
3
= 2.9W
= 3.5W
5
θc-a - S
7
100
2
2
Vertical
standing type
Natural
convection
air cooling
No.5228-17/19
3
ITF02403
5