AS2715
APPLICATION HINTS
will guarantee stability over load. A tantalum capacitor is
recommended for a fast load transient response.
The AS2715 incorporates protection against over-current
faults, reversed load insertion, over temperature operation, and
positive and negative transient voltage. However, the use of
an output capacitor is required in order to insure the stability
and the performances.
If the power source has high AC impedance, a 0.1µF capacitor
between input & ground is recommended. This capacitor
should have good characteristics up to 250 kHz.
Thermal Consideration
Minimum Load Current
Although the AS2715 offers limiting circuitry for overload
conditions, it is necessary not to exceed the maximum junction
temperature, and therefore to be careful about thermal
resistance. The heat flow will follow the lowest resistance
path, which is the Junction-to-case thermal resistance. In
order to insure the best thermal flow of the component, a
proper mounting is required. Note that the case of the device
is electrically connected to the output. The
To ensure a proper behavior of the regulator at light load, a
minimum load of 5mA for AS2715 is required.
VOUT
VIN
case has to be electrically isolated, a thermally conductive
spacer can be used. However do not forget to consider its
contribution to thermal resistance.
AS2715
Assuming:
VIN = 10V, VOUT = 5V, IOUT = 1.5A, TA = 50°C/W,
θHeatsink Case= 6°C/W, θHeatsink Case = 0.5°C/W, θ JC = 3°C/W
Power dissipation under this condition
PD = (VIN – VOUT) * IOUT = 7.5W
Fig.1 Basic Fixed Output Regulator
Junction Temperature
TJ = TA + PD * (θCase – HS + θ HS θ JC
)
For the Control Section
TJ = 50 + 7.5*(0.5 + 6=3) = 121.25°C
121.25°C < TJ (max) for the Control & Power Sections.
In both case reliable operation is insured by adequate junction
temperature.
Capacitor Requirements
The output capacitor is needed for stability and to minimize
the output noise. The required value of the capacitor varies
with the load. However, a minimum value of 10µF Aluminum
Rev. 10/11/00
SIPEX [ SIPEX CORPORATION ]
