MIC47050_12 Datasheet, PDF (11/16 Pages) Micrel Semiconductor – 500mA ULDO™ with Low Input and Low Output Voltage

Micrel, Inc.
Power Good (PGOOD)
The Power Good (PGOOD) pin is an open drain output
that goes low when the output voltage (fixed version)
drops below the PGOOD threshold voltage.
The pull-up resistor value should be large enough to
guarantee a proper “low” voltage when the PGOOD pin
pulls low. The PGOOD low voltage is typically 0.1V at
250µA current. A 10kΩ resistor or greater is
recommended when pulling up to 3.3V bias.
If the PGOOD function is not required, the PGOOD pin
may be left unconnected.
Thermal Shutdown
The MIC47050 has an internal over-temperature
protection feature. This feature is for protection only.
The device should never be intentionally operated near
this temperature as this may reduce long term reliability.
The device will turn off when the over-temperature
threshold is exceeded. A 20°C hysteresis is built in to
allow the device to cool before turning back on.
Thermal Considerations
The MIC47050 is designed to provide 0.5A of continuous
current in a very small package. Maximum ambient
operating temperature can be calculated based on the
output current and the voltage drop across the part.
Given that the input voltage is 1.8V, the output voltage is
1.2V and the output current is 0.5A. The actual power
dissipation of the regulator circuit can be determined
using the equation:
  PD  VIN  VOUT  IOUT  VIN  IGND  VBIAS  IBIAS
Because this device is CMOS, the ground current is
insignificant for power dissipation and can be ignored for
this calculation.
  PD  1.8V  1.2V  0.5A  0.3W
To determine the maximum ambient operating
temperature of the package, use the junction-to-ambient
thermal resistance of the device and the following basic
equation:
PD(MAX)

 ^{TJ(MAX)  TA}

 ^Θ_JA



MIC47050
T_J(MAX) = 125°C, the maximum junction temperature of
the die.
θ_JA thermal resistance = 90°C/W.
Table 1 shows junction-to-ambient thermal resistance for
the MIC47050 in the MLF^® or Thin MLF^® package.
Package
θ_JA Recommended
Min. Footprint
6-pin 2mm x 2mm MLF^®
90°C/W
6-pin 2mm x 2mm
Thin MLF^®
90°C/W
Table 1. Thermal Resistance
θ_JC
45°C/W
45°C/W
Substituting P_D for P_D(max) and solving for the ambient
operating temperature will give the maximum operating
conditions for the regulator circuit. The junction-to-
ambient thermal resistance for the minimum footprint is
90°C/W. The maximum power dissipation must not be
exceeded for proper operation. For example, when
operating the MIC47050-1.2YML at an input voltage of
1.8V and a 0.5A load with a minimum footprint layout,
the maximum ambient operating temperature T_A can be
determined as follows:
TA  TJ(MAX)  Θ_JA  PD(MAX)
TA  125C  90C/W  0.3W
TA  98C
Therefore, a 1.2V application with 0.5A of output current
can accept an ambient operating temperature of 98°C in
a 2mm x 2mm MLF^® or Thin MLF^® package.
Thermal Measurements
Measuring the IC’s case temperature is recommended to
insure it is within its operating limits. Although this might
seem like a very elementary task, it is easy to get
erroneous results. The most common mistake is to use
the standard thermal couple that comes with a thermal
meter. This thermal couple wire gauge is large, typically
22 gauge, and behaves like a heatsink, resulting in a
lower case measurement.
Two methods of temperature measurement are using a
smaller thermal couple wire or an infrared thermometer.
If a thermal couple wire is used, it must be constructed
of 36 gauge wire or higher (smaller wire size) to
minimize the wire heat-sinking effect.
April 2012
11
M9999-040312-B