AMC2576
APPLICATION INFORMATION (contd.)
Feedback Connection
For fixed output voltage version, the FB (feedback) pin must be connected to V
OUT
. For the adjustable version, it is
important to place the output voltage ratio resistors near AMC2576 as possible in order to minimize the noise
introduction.
ENABLE
It is required that the ENABLE must
not
be left open. For normal operation, connect this pin to a “LOW” voltage
(typically, below 1.6V). On the other hand, for standby mode, connect this pin with a “HIGH” voltage. This pin can
be safely pulled up to +V
IN
without a resistor in series with it.
Grounding
To maintain output voltage stability, the power ground connections must be low-impedance. For the 5-lead TO-220
and TO-263 style package, both the tab and pin 3 are ground and either connection may be used.
Heat Sink and Thermal Consideration
Although the AMC2576 requires only a small heat sink for most cases, the following thermal consideration is
important for all operation. With the package thermal resistances
θ
JA
and
θ
JC
, total power dissipation can be estimated
as follows:
P
D
= (V
IN
×
I
Q
)+(V
OUT
/ V
IN
)(I
LOAD
×
V
SAT
);
When no heat sink is used, the junction temperature rise can be determined by the following:
∆T
J
= P
D
× θ
JA
;
With the ambient temperature, the actual junction temperature will be:
T
J
=
∆T
J
+T
A
;
If the actual operating junction temperature is out of the safe operating junction temperature (typically 125°C), then a
heat sink is required. When using a heat sink, the junction temperature rise will be reduced by the following:
∆T
J
= P
D
×
(θ
JC
+
θ
interface
+
θ
Heat sink
);
As one can see from the above, it is important to choose an heat sink with adequate size and thermal resistance, such
that to maintain the regulator’s junction temperature below the maximum operating temperature.
Copyright
©
2006 ADDtek Corp.
10
DD007_E
--
DECEMBER 2006
ADDTEK [ ADDTEK CORP ]
