AS1358 / AS1359
Datasheet - Application Information
9.3 Power Dissipation
Maximum power dissipation (PD) of the LDO is the sum of the power dissipated by the internal series MOSFET and the quiescent current
required to bias the internal voltage reference and the internal error amplifier, and is calculated as:
PDMAXSeriespass = ILOADMAXVINMAX – VOUTMIN Watts
Internal power dissipation as a result of the bias current for the internal voltage reference and the error amplifier is calculated as:
PDMAXBias = VINMAXIQ Watts
(EQ 3)
(EQ 4)
(EQ 5)
Total LDO power dissipation is calculated as:
PDMAXTotal = PDMAXSeriespass + PDMAXBias Watts
9.4 Junction Temperature
Under all operating conditions, the maximum junction temperature should not be allowed to exceed 125ºC (unless the data sheet specifically
allows). Limiting the maximum junction temperature requires knowledge of the heat path from junction to case (JCºC/W fixed by the IC
manufacturer), and adjustment of the case to ambient heat path (CAºC/W) by manipulation of the PCB copper area adjacent to the IC position.
Figure 20. Package Physical Arrangements
SOTxx Package
Chip
Bond Wire
Package
Lead Frame
PCB
Figure 21. Steady State Heat Flow Equivalent Circuit
Junction
TJ°C
Package
TC°C
PCB/Heatsink
TS°C
Ambient
TA°C
RJC
RCS
RSA
Chip
Power
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