as2815yu-x ETC-unknow, as2815yu-x Datasheet - Page 3

• Manufacturer Part Number: as2815yu-x
• Description: 1.5a Dropout Voltage Regulator Adjustable Fixed Output,fast Response
• Manufacturer: ETC-unknow

APPLICATION HINTS
The AS2815 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.
Stability
The output capacitor is part of the regulator’s frequency
compensation system. Either a 22µF aluminum electrolytic
capacitor or a 10µF solid tantalum capacitor between the
output terminal and ground guarantees stable operation for all
operating conditions.
However, in order to minimize overshoot and undershoot, and
therefore optimize the design, please refer to the section
‘Ripple Rejection’.
Ripple Rejection
Ripple rejection can be improved by adding a capacitor
between the ADJ pin and ground. When ADJ pin bypassing is
used, the value of the output capacitor required increases to its
maximum (22µF for an aluminum electrolytic capacitor, or
10µF for a solid tantalum capacitor). If the ADJ pin is not
bypass, the value of the output capacitor can be lowered to
100µF for an electrolytic aluminum capacitor or 4.7µF for a
solid tantalum capacitor.
However the value of the ADJ-bypass capacitor should be
chosen with respect to the following equation:
C = 1 / ( 6.28 * F
Where C
equal or larger standard value),
If an ADJ-bypass capacitor is use, the amplitude of the output
ripple will be independent of the output voltage. If an ADJ-
bypass capacitor is not used, the output ripple will be
proportional to the ratio of the output voltage to the reference
voltage:
M = V
Where M = multiplier for the ripple seen when the ADJ pin
is optimally bypassed.
OUT
F
R
V
R
1
/ V
REF
= value of the capacitor in Farads (select an
= ripple frequency in Hz,
= value of resistor R
REF
= Reference Voltage
R
* R
1
)
1
in Ohms.
Reducing parasitic resistance and inductance
One solution to minimize parasitic resistance and inductance is
to connect in parallel capacitors.
improve the transient response of the power supply if your
system requires rapidly changing current load condition.
Thermal Consideration
Although the AS2815 offers some 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. In case
the case has to be electrically isolated, a thermally conductive
spacer can be used. However do not forget to consider its
contribution to thermal resistance.
Assuming:
V
θ
Power dissipation under this condition
P
Junction Temperature
T
For Control & Power Sections
T
121.25°C < T
In both case reliable operation is insured by adequate junction
temperature.
D
J
J
IN
Heatsink Case
= T
= 50 + 7.5*(0.5+6=3) = 121.25°C
= (V
= 10V, V
A
IN
+ P
– V
D
= 6°C/W, θ
* (θ
OUT
OUT
J (max)
) * I
= 5V, I
Case – HS
for Control & Power Sections.
OUT
Heatsink Case
OUT
= 7.5W
+ θ
= 1.5A, T
HS
+ θ
= 0.5°C/W, θ
JC
)
A
This arrangement will
= 50°C/W,
AS2815
Rev. 10/11/00
JC
= 3°C/W