MIC22400 Datasheet, PDF (17/19 Pages) Micrel Semiconductor – 4A Integrated Switch Synchronous Buck Regulator with Frequency Programmable up to 4MHz

Micrel, Inc.
• Rθ_JA is a combination of junction to case thermal
resistance (Rθ_JC) and Case-to-Ambient thermal
resistance (Rθ_CA), since thermal resistance of
the solder connection from the ePAD to the PCB
is negligible; Rθ_CA is the thermal resistance of
the ground plane to ambient, so Rθ_JA = Rθ_JC +
Rθ_CA.
VINÆ
VOUT
@3AÈ
1
1.2
1.8
2.5
3.3
3
0.732
0.741
0.825
0.894
–
3.5
0.689
0.691
0.764
0.813
0.817
4
0.672
0.668
0.732
0.776
0.816
4.5
0.668
0.662
0.720
0.762
0.801
5
0.670
0.665
0.720
0.765
0.800
Table 1. Power Dissipation (W) for 4A Output
• T_AMB is the Operating Ambient temperature.
MIC22400
Example:
To calculate the junction temperature for a 50°C
ambient:
T_J = T_AMB+P_DISS . Rθ_JA
T_J = 50 + 0.894 x 45
T_J = 90.2°C
This is below the maximum of 125°C.
February 2008
17
M9999-022108-A