IK1589
Figure 8. Connection for Best Load Regulation
Thermal Considerations
The IK1589 protects itself under overload conditions with internal power and thermal limiting circuitry.
However, for normal continuous load conditions, do not exceed maximum junction temperature ratings. It is
important to consider all sources of thermal resistance from junction-to-ambient. These sources include the
junction-to-case resistance, the case-to-heat sink interface resistance, and the heat sink resistance. Thermal
resistance specifications have been developed to more accurately reflect device temperature and ensure
safe operating temperatures. For example, look at using an IK1589 to generate 2.7A @ 1.2V ±2% from a
3.3V source (3.2V to 3.6V).
Assumptions:
• V
IN
= 3.6V worst case
• V
OUT
= 1.176V worst case
• I
OUT
= 2.7A continuous
• T
A
= 70°C
•
θ
Case-to-Ambient
= 3°C/W (assuming both a heatsink and a thermally conductive material) The power
dissipation in this application is:
P
D
= (V
IN
– V
OUT
) * (I
OUT
) = (3.6 – 1.18) * (2.7) = 6.53W
From the specification table:
T
J
= T
A
+ (P
D
) * (θ
Case-to-Ambient
+
θ
JC
)= 70 + (6.53) * (3 + 3) = 109°C
The junction temperature is below the maximum rating.
Junction-to-case thermal resistance is specified from the IC junction to the bottom of the case directly below
the die. This is the lowest resistance path for heat flow. Proper mounting ensures the best thermal flow from
this area of the package to the heat sink. Use of a thermally conductive material at the case-to-heat sink
interface is recommended. Use a thermally conductive spacer if the case of the device must be electrically
isolated and include its contribution to the total thermal resistance. The case of the IK1589 is directly
connected to the output of the device.
Figure 9. Application Circuit (IK1589)
Rev. 01
IKSEMICON [ IK SEMICON CO., LTD ]
