AIC1742
APPLICATION INFORMATION
INPUT-OUTPUT CAPACITORS
Linear regulators require input and output
capacitors to maintain stability. Input capacitor
at 1µF with 1uF aluminum electrolytic or 2.2µF
ceramic output capacitor is recommended. And
it should be selected within the Equivalent
Series Resistance (ESR) range as shown in
the figure 20,21. ESR of ceramic capacitor is
lower and its electrical characteristics
(capacitance and ESR) vary widely over
temperature. In general, tantalum or electric
output capacitor is suggested for heavy load.
Normally, the output capacitor should be 1µF
(aluminum electrolytic) at least and rates for
operating temperature range. Note that it’s
important to check selected manufactures
electrical characteristics (capacitance and ESR)
over temperature.
NOISE BYPASS CAPACITOR
0.01µF bypass capacitor at BP pin reduces
output voltage noise. And the BP pin has to
connect a capacitor to GND.
POWER DISSIPATION
The maximum power dissipation of AIC1742
depends on the thermal resistance of its case
and circuit board, the temperature difference
between the die junction and ambient air, and
the rate of airflow. The rate of temperature rise
is greatly affected by the mounting pad
configuration on the PCB, the board material,
and the ambient temperature. When the IC
mounting with good thermal conductivity is
used, the junction temperature will be low even
when large power dissipation applies.
The power dissipation across the device is
P = I
OUT
(V
IN
-V
OUT
).
The maximum power dissipation is:
P
MAX
=
(T
J
−
T
A
)
(Rθ
JB
+
Rθ
BA
)
Where T
J
-T
A
is the temperature difference
between the die junction and the surrounding
air, Rθ
JB
is the thermal resistance of the
package, and Rθ
BA
is the thermal resistance
through the PCB, copper traces, and other
materials to the surrounding air.
As a general rule, the lower temperature is, the
better reliability of the device is. So the PCB
mounting pad should provide maximum
thermal conductivity to maintain low device
temperature.
GND pin performs a dual function of providing
an electrical connection to ground and
channeling heat away. Therefore, connecting
the GND pin to ground with a large pad or
ground plane would increase the power
dissipation and reduce the device temperature.
10
AIC [ ANALOG INTERGRATIONS CORPORATION ]
