MIC5255_06 Datasheet, PDF (11/13 Pages) Micrel Semiconductor – 150mA Low Noise Cap CMOS LDO

Micrel, Inc.
The junction-to-ambient thermal resistance for the
minimum footprint is 235°C/W, from Table 1. The
maximum power dissipation must not be exceeded for
proper operation. Using the output voltage of 3.0V and
an output current of 150mA, the maximum input voltage
can be determined. Because this device is CMOS and
the ground current is typically 100µA over the load
range, the power dissipation contributed by the ground
current is < 1% and can be ignored for this calculation:
315mW = (V_IN – 3.0V) 150mA
315mW = V_IN × 150mA – 450mW
810mW = V_IN × 150mA
V_IN(max) = 5.4V
MIC5255
Therefore, a 3.0V application at 150mA of output current
can accept a maximum input voltage of 5.4V in a SOT-
23-5 package. For a full discussion of heat sinking and
thermal effects on voltage regulators, refer to the “Reg-
ulator Thermals” section of Micrel’s Designing with Low-
Dropout Voltage Regulators handbook.
November 2006
11
M9999-110906