AS1117
Maximum Junction Temperature range:
APPLICATION NOTES EXTERNAL
CAPACITOR
TJ = Tambient (max) + PD* thermal resistance (Junction-to-
ambient)
To ensure the stability of the AS1117 an output capacitor of
at least 10µF (tantalum)or 50µF (aluminum) is required. The
value may change based on the application requirements on
the output load or temperature range. The capacitor
equivalent series resistance (ESR) will effect the AS1117
stability. The value of ESR can vary from the type of
capacitor used in the applications. The recommended value
for ESR is 0.5Ω. The output capacitance could increase in
size to above the minimum value. The larger value of output
capacitance as high as 100µF can improve the load transient
response.
Maximum Junction temperature must not exceed the 125°C.
50 X 50 mm
35 X 17 mm
SOLDERING METHODS
The AS1117 SOT-223 package is designed to be compatible
with infrared reflow or vapor-phase reflow soldering
techniques. During soldering the non-active or mildly active
fluxes may be used. The AS1117 die is attached to the
heatsink lead which exits opposite the input, output, and
ground pins.
16 X 10 mm
Hand soldering and wave soldering should be avoided since
these methods can cause damage to the device with excessive
Fig. 1. Substrate Layout for SOT-223
thermal gradients on the package.
The SOT-223
recommended soldering method are as follows: vapor phase
reflow and infrared reflow with the component preheated to
within 65°C of the soldering temperature range.
THERMAL CHARACTERISTICS
The thermal resistance of AS1117 is 15°C/W from junction
to tab and 31 °C/W from tab to ambient for a total of 46
°C/W from junction to ambient. The AS1117 features the
internal thermal limiting to protect the device during
overload conditions. Special care needs to be taken during
continuos load conditions the maximum junction temperature
does not exceed 125 °C.
Taking the FR-4 printed circuit board and 1/16 thick with 1
ounce copper foil as an experiment (fig.1 & fig.2), the PCB
material is effective at transmitting heat with the tab attached
to the pad area and a ground plane layer on the backside of
the substrate. Refer to table 1 for the results of the
experiment.
The thermal interaction from other components in the
application can effect the thermal resistance of the AS1117.
The actual thermal resistance can be determined with
experimentation. AS1117 power dissipation is calculated as
follows:
PD = (VIN - VOUT)(IOUT
)
Rev. 10/6/00
SIPEX [ SIPEX CORPORATION ]
