LP3961EMP-5.0 National Semiconductor, LP3961EMP-5.0 Datasheet - Page 13

• Manufacturer Part Number: LP3961EMP-5.0
• Description: IC,VOLT REGULATOR,FIXED,+5V,CMOS,SOT-223-4,4PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LP3961EMP-5.0

• Rohs Compliant: NO

Applications Information
Dropout Voltage
The dropout voltage of a regulator is defined as the minimum
input-to-output differential required to stay within 2% of the
output voltage. The LP3961/LP3964 use an internal MOS-
FET with an Rds(on) of 240m (typically). For CMOS LDOs,
the dropout voltage is the product of the load current and the
Rds(on) of the internal MOSFET.
Reverse Current Path
The internal MOSFET in LP3961and LP3964 has an inher-
ent parasitic diode. During normal operation, the input volt-
age is higher than the output voltage and the parasitic diode
is reverse biased. However, if the output is pulled above the
input in an application, then current flows from the output to
the input as the parasitic diode gets forward biased. The out-
put can be pulled above the input as long as the current in
the parasitic diode is limited to 200mA continuous and 1A
peak.
Maximum Output Current Capability
LP3961 and LP3964 can deliver a continuous current of
800mA over the full operating temperature range. A heatsink
may be required depending on the maximum power dissipa-
tion and maximum ambient temperature of the application.
Under all possible conditions, the junction temperature must
be within the range specified under operating conditions.
The total power dissipation of the device is given by:
P
where I
(specified under Electrical Characteristics).
The maximum allowable temperature rise (T
on the maximum ambient temperature (T
cation, and the maximum allowable junction temperature(T
max
T
The maximum allowable value for junction to ambient Ther-
mal Resistance,
LP3961 and LP3964 are available in TO-220, TO-263, and
SOT-223 packages. The thermal resistance depends on
amount of copper area or heat sink, and on air flow. If the
maximum allowable value of
˚C/W for TO-220 package, 60 ˚C/W for TO-263 package,
and
needed since the package can dissipate enough heat to sat-
isfy these requirements. If the value for allowable
below these limits, a heat sink is required.
Heatsinking TO-220 Packages
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
be same as shown in next section for TO263 package.
The heatsink to be used in the application should have a
heatsink to ambient thermal resistance,
In this equation,
tion to the surface of the heat sink and
sistance from the junction to the surface of the case.
about 3˚C/W for a TO220 package. The value for
JA
HA
Rmax
D
):
= (V
= T
= T
JA
Rmax
GND
140 ˚C/W for SOT-223 package, no heatsink is
IN
−
−V
Jmax
OUT
is the operating ground current of the device
CH
/ P
− T
D
−
)I
OUT
CH
Amax
JA
JC
, can be calculated using the formula:
is the thermal resistance from the junc-
+ (V
.
IN
)I
GND
JA
calculated above is
JC
Amax
is the thermal re-
(Continued)
Rmax
) of the appli-
) depends
JA
CH
JA
JC
falls
de-
will
60
is
J -
13
pends on method of attachment, insulator, etc.
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 and SOT-223 Packages
The TO-263 and SOT223 packages use the copper plane on
the PCB as a heatsink. The tab of these packages are sol-
dered to the copper plane for heat sinking. Figure 3 shows a
curve for the
sizes, using a typical PCB with 1 ounce copper and no solder
mask over the copper area for heat sinking.
As shown in the figure, increasing the copper area beyond 1
square inch produces very little improvement. The minimum
value for
32˚C/W.
Figure 4 shows the maximum allowable power dissipation
for TO-263 packages for different ambient temperatures, as-
suming
ture is 125˚C.
Figure 5 shows a curve for the
different copper area sizes, using a typical PCB with 1 ounce
copper and no solder mask over the copper area for heat
sinking.
FIGURE 3.
FIGURE 4. Maximum power dissipation vs ambient
JA
JA
is 35˚C/W and the maximum junction tempera-
temperature for TO-263 package
JA
for the TO-263 packag mounted to a PCB is
JA
of TO-263 package for different copper area
vs Copper(1 Ounce) Area for TO-263
package
JA
of SOT-223 package for
DS101129-32
DS101129-33
www.national.com
CH
varies