LP3882ES-1.2 National Semiconductor, LP3882ES-1.2 Datasheet - Page 9

• Manufacturer Part Number: LP3882ES-1.2
• Description: 1.5A Fast-Response Ultra Low Dropout Linear
• Manufacturer: National Semiconductor

Application Hints
UNDER VOLTAGE LOCKOUT
The bias voltage is monitored by a circuit which prevents the
regulator output from turning on if the bias voltage is below
approximately 4V.
SHUTDOWN OPERATION
Pulling down the shutdown (S/D) pin will turn-off the regula-
tor. Pin S/D must be actively terminated through a pull-up
resistor (10 kΩ to 100 kΩ) for a proper operation. If this pin
is driven from a source that actively pulls high and low (such
as a CMOS rail to rail comparator), the pull-up resistor is not
required. This pin must be tied to Vin if not used.
POWER DISSIPATION/HEATSINKING
A heatsink may be required depending on the maximum
power dissipation and maximum ambient temperature of the
application. Under all possible conditions, the junction tem-
perature must be within the range specified under operating
conditions. The total power dissipation of the device is given
by:
P
where I
The maximum allowable temperature rise (T
on the maximum ambient temperature (T
cation, and the maximum allowable junction temperature
(T
T
The maximum allowable value for junction to ambient Ther-
mal Resistance, θ
θ
These parts are available in TO-220 and TO-263 packages.
The thermal resistance depends on amount of copper area
or heat sink, and on air flow. If the maximum allowable value
of θ
and ≥ 60 ˚C/W for TO-263 package no heatsink is needed
since the package can dissipate enough heat to satisfy these
requirements. If the value for allowable θ
limits, a heat sink is required.
HEATSINKING TO-220 PACKAGE
The thermal resistance of a TO220 package can be reduced
by attaching it to a heat sink or a copper plane on a PC
board. If a copper plane is to be used, the values of θ
be same as shown in next section for TO263 package.
JA
Rmax
D
Jmax
= (V
JA
= T
):
= T
calculated above is ≥ 60 ˚C/W for TO-220 package
GND
Rmax
IN
−V
Jmax
is the operating ground current of the device.
OUT
/ P
− T
D
)I
OUT
Amax
JA
, can be calculated using the formula:
+ (V
IN
)I
GND
(Continued)
JA
Amax
falls below these
Rmax
) of the appli-
) depends
JA
will
9
The heatsink to be used in the application should have a
heatsink to ambient thermal resistance,
θ
In this equation, θ
to the surface of the heat sink and θ
tance from the junction to the surface of the case. θ
about 3˚C/W for a TO220 package. The value for θ
pends on method of attachment, insulator, etc. θ
between 1.5˚C/W to 2.5˚C/W. If the exact value is unknown,
2˚C/W can be assumed.
HEATSINKING TO-263 PACKAGE
The TO-263 package uses the copper plane on the PCB as
a heatsink. The tab of these packages are soldered to the
copper plane for heat sinking. The graph below shows a
curve for the θ
sizes, using a typical PCB with 1 ounce copper and no solder
mask over the copper area for heat sinking.
HA
FIGURE 1. θ
≤ θ
JA
− θ
CH
JA
JA
− θ
of TO-263 package for different copper area
CH
vs Copper (1 Ounce) Area for TO-263
JC
is the thermal resistance from the case
.
package
JC
is the thermal resis-
20063225
www.national.com
CH
CH
varies
JC
de-
is