FEDL5401A-02
OKI Semiconductor
ML5401A
Figure 4: Load regulation precaution
6)
Thermal Management
When an integrated circuit operates with an appreciable current, its junction temperature is elevated. It is
important to quantify its thermal limits in order to achieve acceptable performance and reliability. This limit is
determined by summing the individual parts consisting of a series of temperature rises from the semiconductor
junction to the operating environment. A one-dimensional steady-state model of conduction heat transfer is
demonstrated in Figure 5. The heat generated at the device junction flows through the die to the die attach pad,
through the lead frame to the surrounding case material, to the printed circuit board, and eventually to the
ambient environment. Below is a list of variables that may affect the thermal resistance.
Θ
JC
(Component Variables)
Leadframe Size & Material
No. of Conduction Pins
Die Size
Die Attach Material
Molding Compound Size and Material
Θ
CA
(Application Variables)
Mounting Pad Size, Material & Location
PCB Size & Material
Traces Length, Width & thickness
Ambient Temperature
Figure 5: Cross-sectional view of Integrated Circuit Mounted on a printed circuit board.
Note that the case temperature is measured at the point where the leads contact with the mounting pad surface
The ML5401A regulator has internal thermal shutdown to protect the device from over-heating. Under all possible
operating conditions, the junction temperature of the ML5401A must be within the range of 0°C to 125°C.
The power dissipated by the regulator, P
D
, is:
P
D
= (V
IN
-V
OUT
)*I
L
+ V
dd
*I
dd,
Thus: T
J
(max) = P
D
*
θ
JA
+ T
A
(max)
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