300mA Low Power Low Noise
LDO CMOS Voltage Regulator
SE5509
Application Hints
Thermal Considerations
Like any low dropout regulator, SE5509 requires It is important that the thermal limit of the package is
external capacitors to ensure stability. The not exceeded. The SE5509 has built-in thermal
external capacitors must be carefully selected to protection. When the thermal limit is exceeded,
ensure performance.
the IC will enter protection, and VOUT will be pulled
to ground. The power dissipation for a given
application can be calculated as following:
Input Capacitor
An input capacitor of at least 1μF is required.
Ceramic or Tantalum can be used. The value can
be increase without upper limit.
The power dissipation (PD) is
PD = IOUT * [VIN – VOUT
]
Output Capacitor
An output capacitor is required for stability. It must The thermal limit of the package is then limited to
be placed no more than 1 cm away from the VOUT PD(MAX) = [TJ – TA]/ΘJA where TJ is the junction
pin, and connected directly between VOUT and GND temperature, TA is the ambient temperature, and
pins. Electrolytical capacitor is recommended. The ΘJA is around 230°C/W for SE5509. SE5509 is
minimum value is 1μF but may be increase without designed to enter thermal protection at 150°C. For
limit. Ceramic can be used. But the value should not example, if TA is 25°C then the maximum PD is
be more than 2.2μF.
limited to about 0.6W. In other words, if IOUT(MAX)
300mA, then [VIN – VOUT] cannot exceed 2V.
=
Application Diagram
Revision 12/5/2008
Preliminary and all contents are subject to change without prior notice
© Seaward Electronics Inc., 2006. • www.seawardinc.com.cn • Page 5
SEAWARD [ Seaward Electronics Inc. ]
