LP3855EMP-ADJ/NOPB National Semiconductor, LP3855EMP-ADJ/NOPB Datasheet - Page 12

• Manufacturer Part Number: LP3855EMP-ADJ/NOPB
• Description: IC REG LDO 1.5A ADJ SOT223-5
• Manufacturer: National Semiconductor

Specifications of LP3855EMP-ADJ/NOPB

• Regulator Topology: Positive Adjustable
• Voltage - Output: Adjustable
• Voltage - Input: 2.5 ~ 7 V
• Voltage - Dropout (typical): 0.26V @ 1.5A
• Number Of Regulators: 1
• Current - Output: 1.5A (Max)
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: SOT-223 (4 leads + Tab)
• Primary Input Voltage: 7V
• Dropout Voltage Vdo: 240mV
• No. Of Pins: 5
• Output Current: 1.5A
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Limit (min): -
• Other names: LP3855EMP-ADJ; LP3855EMP-ADJTR

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The LP3855-ADJ is available in TO-220 and TO-263 pack-
ages. The thermal resistance depends on amount of copper
area or heat sink, and on air flow. If the maximum allowable
value of θ
age and
needed since the package can dissipate enough heat to sat-
isfy these requirements. If the value for allowable θ
below these 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
as shown in next section for TO263 package.
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
3°C/W for a TO220 package. The value for θ
method of attachment, insulator, etc. θ
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. Figure 3 shows a curve for the
θ
a typical PCB with 1 ounce copper and no solder mask over
the copper area for heat sinking.
HA
JA
FIGURE 3. θ
≤
of TO-263 package for different copper area sizes, using
θ
JA
− θ
JA
≥
calculated above is
60 °C/W for TO-263 package no heatsink is
CH
JA
− θ
CH
vs Copper (1 Ounce) Area for TO-263
JC
.
is the thermal resistance from the case
package
≥
60 °C/W for TO-220 pack-
JC
CH
is the thermal resis-
varies between 1.5°
20074332
CH
JA
will be same
depends on
JC
is about
JA
falls
12
As shown in the figure, increasing the copper area beyond 1
square inch produces very little improvement. The minimum
value for θ
32°C/W.
Figure 4 shows the maximum allowable power dissipation for
TO-263 packages for different ambient temperatures, assum-
ing θ
125°C.
FIGURE 4. Maximum power dissipation vs ambient
JA
is 35°C/W and the maximum junction temperature is
JA
temperature for TO-263 package
for the TO-263 package mounted to a PCB is
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