LP3875ES-ADJ [NSC]

1.5A Fast Ultra Low Dropout Linear Regulators; 1.5A快速超低压降线性稳压器
LP3875ES-ADJ
型号: LP3875ES-ADJ
厂家: National Semiconductor    National Semiconductor
描述:

1.5A Fast Ultra Low Dropout Linear Regulators
1.5A快速超低压降线性稳压器

稳压器
文件: 总15页 (文件大小:692K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
July 2005  
LP3875-ADJ  
1.5A Fast Ultra Low Dropout Linear Regulators  
General Description  
Features  
n Ultra low dropout voltage  
n Low ground pin current  
The LP3875-ADJ fast ultra low-dropout linear regulators op-  
erate from a +2.5V to +7.0V input supply. These ultra low  
dropout linear regulators respond very quickly to step  
changes in load, which makes them suitable for low voltage  
microprocessor applications. The LP3875-ADJ is developed  
on a CMOS process which allows low quiescent current  
operation independent of output load current. This CMOS  
process also allows the LP3875-ADJ to operate under ex-  
tremely low dropout conditions.  
n Load regulation of 0.06%  
n 10nA quiescent current in shutdown mode  
n Guaranteed output current of 1.5A DC  
n Available in TO-263, TO-220 and SOT-223 packages  
n Minimum output capacitor requirements  
n Overtemperature/overcurrent protection  
n −40˚C to +125˚C junction temperature range  
Dropout Voltage: Ultra low dropout voltage; typically 38mV  
at 150mA load current and 380mV at 1.5A load current.  
Applications  
Ground Pin Current: Typically 6mA at 1.5A load current.  
n Microprocessor power supplies  
n GTL, GTL+, BTL, and SSTL bus terminators  
n Power supplies for DSPs  
n SCSI terminator  
Shutdown Mode: Typically 10nA quiescent current when  
the shutdown pin is pulled low.  
Adjustable Output Voltage: The output voltage may be  
programmed via two external resistors.  
n Post regulators  
n High efficiency linear regulators  
n Battery chargers  
n Other battery powered applications  
Typical Application Circuit  
20074645  
*See Application Hints  
© 2005 National Semiconductor Corporation  
DS200746  
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Connection Diagrams  
20074605  
20074606  
Top View  
Top View  
TO220-5 Package  
Bent, Staggered Leads  
TO263-5 Package  
20074681  
Top View  
SOT223-5 Package  
Pin Description for TO220-5 and TO263-5 Packages  
LP3875-ADJ  
Pin #  
Name  
SD  
Function  
1
2
3
4
5
Shutdown  
VIN  
Input Supply  
Ground  
GND  
VOUT  
ADJ  
Output Voltage  
Set Output Voltage  
Pin Description for SOT223-5 Package  
LP3875-ADJ  
Shutdown  
Pin #  
Name  
Function  
1
2
3
4
5
SD  
VIN  
Input Supply  
Output Voltage  
Set Output Voltage  
Ground  
VOUT  
ADJ  
GND  
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2
Ordering Information  
20074631  
Package Type Designator is "T" for TO220 package, "S" for TO263 package, and "MP" for SOT-223 package.  
TABLE 1. Package Marking and Ordering Information  
Description  
Output  
Voltage  
Order Number  
LP3875EMP-ADJ  
LP3875EMPX-ADJ  
(Current,  
Option)  
Package Type  
SOT223-5  
Package Marking  
LHSB  
Supplied As:  
ADJ  
1.5A, Adj  
1000 Units on Tape  
and Reel  
ADJ  
1.5A, Adj  
SOT223-5  
LHSB  
2000 Units on Tape  
and Reel  
ADJ  
ADJ  
ADJ  
LP3875ES-ADJ  
LP3875ESX-ADJ  
LP3875ET-ADJ  
1.5A, Adj  
1.5A, Adj  
1.5A, Adj  
TO263-5  
TO263-5  
TO220-5  
LP3875ES-ADJ  
LP3875ES-ADJ  
LP3875ET-ADJ  
Rail  
Tape and Reel  
Rail  
3
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Block Diagram  
LP3875-ADJ  
20074629  
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4
Absolute Maximum Ratings (Note 1)  
IOUT (Survival)  
Short Circuit Protected  
If Military/Aerospace specified devices are required,  
please contact the National Semiconductor Sales Office/  
Distributors for availability and specifications.  
Operating Ratings  
Input Supply Voltage (Operating),  
(Note 10)  
Storage Temperature Range  
Lead Temperature  
−65˚C to +150˚C  
2.5V to 7.0V  
(Soldering, 5 sec.)  
260˚C  
2 kV  
Shutdown Input Voltage  
(Operating)  
ESD Rating (Note 3)  
Power Dissipation (Note 2)  
Input Supply Voltage (Survival)  
Shutdown Input Voltage  
(Survival)  
−0.3V to 7.0V  
1.5A  
Internally Limited  
−0.3V to +7.5V  
Maximum Operating Current (DC)  
Operating Junction Temp. Range  
−40˚C to +125˚C  
−0.3V to +7.5V  
−0.3V to +6.0V  
Output Voltage (Survival), (Note  
6), (Note 7)  
Electrical Characteristics  
LP3875-ADJ  
Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range.  
Unless otherwise specified: VIN = VO(NOM) + 1V, IL = 10 mA, COUT = 10µF, VSD = 2V.  
Symbol  
Parameter  
Conditions  
Typ  
LP3875-ADJ  
Units  
(Note 4)  
(Note 5)  
Min  
Max  
1.234  
1.253  
VOUT +1V VIN 7V  
10 mA IL 1.5A  
1.198  
VADJ  
Adjust Pin Voltage  
1.216  
10  
V
1.180  
VOUT +1V VIN7V  
10 mA IL 1.5A  
IADJ  
Adjust Pin Input Current  
100  
nA  
%
VOL  
Output Voltage Line  
Regulation (Note 8)  
Output Voltage Load  
Regulation  
VOUT +1V VIN 7.0V  
0.02  
0.06  
0.06  
0.12  
VO/ IOUT  
10 mA IL 1.5A  
%
(Note 8)  
VIN - VOUT  
IL = 150 mA  
IL = 1.5A  
38  
380  
5
50  
60  
450  
550  
9
Dropout Voltage  
(Note 9)  
mV  
mA  
IL = 150 mA  
IL = 1.5A  
10  
14  
15  
10  
50  
Ground Pin Current In  
Normal Operation Mode  
IGND  
6
IGND  
Ground Pin Current In  
Shutdown Mode  
VSD 0.3V  
0.01  
1.8  
3.2  
µA  
A
-40˚C TJ 85˚C  
VO VO(NOM) - 4%  
IO(PK)  
Peak Output Current  
Short Circuit Protection  
ISC Short Circuit Current  
A
5
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Electrical Characteristics  
LP3875-ADJ (Continued)  
Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range.  
Unless otherwise specified: VIN = VO(NOM) + 1V, IL = 10 mA, COUT = 10µF, VSD = 2V.  
Symbol  
Parameter  
Conditions  
Typ  
LP3875-ADJ  
Units  
(Note 4)  
(Note 5)  
Min  
Max  
0.3  
Shutdown Input  
Output = High  
VIN  
0
2
VSDT  
Shutdown Threshold  
V
Output = Low  
IL = 1.5A  
TdOFF  
TdON  
Turn-off delay  
Turn-on delay  
SD Input Current  
20  
25  
1
µs  
µs  
nA  
IL = 1.5A  
ISD  
VSD = VIN  
AC Parameters  
VIN = VOUT + 1V  
COUT = 10uF  
73  
57  
VOUT = 3.3V, f = 120Hz  
VIN = VOUT + 0.5V  
COUT = 10uF  
PSRR  
Ripple Rejection  
dB  
VOUT = 3.3V, f = 120Hz  
f = 120Hz  
ρn(l/f)  
Output Noise Density  
Output Noise Voltage  
0.8  
µV  
BW = 10Hz – 100kHz  
VOUT = 2.5V  
150  
en  
µV (rms)  
BW = 300Hz – 300kHz  
VOUT = 2.5V  
100  
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for which the device is  
intended to be functional, but does not guarantee specific performance limits. For guaranteed specifications and test conditions, see Electrical Characteristics. The  
guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed  
test conditions.  
Note 2: At elevated temperatures, devices must be derated based on package thermal resistance. The devices in TO220 package must be derated at θ = 50˚C/W  
jA  
2
(with 0.5in , 1oz. copper area), junction-to-ambient (with no heat sink). The devices in the TO263 surface-mount package must be derated at θ = 60˚C/W (with  
0.5in , 1oz. copper area), junction-to-ambient. The SOT-223 package must be derated at θ = 90˚C/W (with 0.5in , 1oz. copper area), junction-to-ambient.  
jA  
2
2
jA  
Note 3: The human body model is a 100pF capacitor discharged through a 1.5kresistor into each pin.  
Note 4: Typical numbers are at 25˚C and represent the most likely parametric norm.  
Note 5: Limits are guaranteed by testing, design, or statistical correlation.  
Note 6: If used in a dual-supply system where the regulator load is returned to a negative supply, the output must be diode-clamped to ground.  
Note 7: The output PMOS structure contains a diode between the V and V  
terminals. This diode is normally reverse biased. This diode will get forward biased  
OUT  
IN  
if the voltage at the output terminal is forced to be higher than the voltage at the input terminal. This diode can typically withstand 200mA of DC current and 1Amp  
of peak current.  
Note 8: Output voltage line regulation is defined as the change in output voltage from the nominal value due to change in the input line voltage. Output voltage load  
regulation is defined as the change in output voltage from the nominal value due to change in load current.  
Note 9: Dropout voltage is defined as the minimum input to output differential voltage at which the output drops 2% below the nominal value. Dropout voltage  
specification applies only to output voltages of 2.5V and above. For output voltages below 2.5V, the drop-out voltage is nothing but the input to output differential,  
since the minimum input voltage is 2.5V.  
Note 10: The minimum operating value for V is equal to either [V  
+ V  
] or 2.5V, whichever is greater.  
DROPOUT  
IN  
OUT(NOM)  
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6
Typical Performance Characteristics Unless otherwise specified: TJ = 25˚C, COUT = 10µF,  
CIN = 10µF, S/D pin is tied to VIN, VOUT = 2.5V, VIN = VO(NOM) + 1V, IL = 10mA  
Ground Current vs Output Voltage  
Dropout Voltage vs Output Load Current  
IL = 1.5A  
20074660  
20074654  
Shutdown IQ vs Junction Temperature  
DC Load Reg. vs Junction Temperature  
20074655  
20074658  
DC Line Regulation vs Temperature  
Noise vs Frequency  
20074661  
20074659  
7
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Typical Performance Characteristics Unless otherwise specified: TJ = 25˚C, COUT = 10µF,  
CIN = 10µF, S/D pin is tied to VIN, VOUT = 2.5V, VIN = VO(NOM) + 1V, IL = 10mA (Continued)  
Load Transient Response  
CIN = COUT = 10µF, OSCON  
Load Transient Response  
CIN = COUT = 100µF, OSCON  
20074677  
20074676  
Load Transient Response  
Load Transient Response  
CIN = COUT = 100µF, POSCAP  
CIN = COUT = 10µF, TANTALUM  
20074678  
20074679  
Load Transient Response  
CIN = COUT = 100µF, TANTALUM  
20074680  
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8
Application Hints  
SETTING THE OUTPUT VOLTAGE  
Fz = 45,000 = 1 / ( 2 x π x R1 x CFF )  
The output voltage is set using the resistors R1 and R2 (see  
Typical Application Circuit). The output is also dependent on  
the reference voltage (typically 1.216V) which is measured  
at the ADJ pin. The output voltage is given by the equation:  
A good quality ceramic with X5R or X7R dielectric should be  
used for this capacitor.  
SELECTING A CAPACITOR  
It is important to note that capacitance tolerance and varia-  
tion with temperature must be taken into consideration when  
selecting a capacitor so that the minimum required amount  
of capacitance is provided over the full operating tempera-  
ture range. In general, a good Tantalum capacitor will show  
very little capacitance variation with temperature, but a ce-  
ramic may not be as good (depending on dielectric type).  
Aluminum electrolytics also typically have large temperature  
variation of capacitance value.  
VOUT = VADJ x ( 1 + R1 / R2)  
This equation does not include errors due to the bias current  
flowing in the ADJ pin which is typically about 10 nA. This  
error term is negligible for most applications. If R1 is  
>
100k, a small error may be introduced by the ADJ bias  
current.  
The tolerance of the external resistors used contributes a  
significant error to the output voltage accuracy, with 1%  
resistors typically adding a total error of approximately 1.4%  
to the output voltage (this error is in addition to the tolerance  
of the reference voltage at VADJ).  
Equally important to consider is a capacitor’s ESR change  
with temperature: this is not an issue with ceramics, as their  
ESR is extremely low. However, it is very important in Tan-  
talum and aluminum electrolytic capacitors. Both show in-  
creasing ESR at colder temperatures, but the increase in  
aluminum electrolytic capacitors is so severe they may not  
be feasible for some applications (see Capacitor Character-  
istics Section).  
EXTERNAL CAPACITORS  
Like any low-dropout regulator, external capacitors are re-  
quired to assure stability. These capacitors must be correctly  
selected for proper performance.  
INPUT CAPACITOR: An input capacitor of at least 10µF is  
required. Ceramic Ceramic, Tantalum, or Electrolytic capaci-  
tors may be used, and capacitance may be increased with-  
out limit  
CAPACITOR CHARACTERISTICS  
CERAMIC: For values of capacitance in the 10 to 100 µF  
range, ceramics are usually larger and more costly than  
tantalums but give superior AC performance for bypassing  
high frequency noise because of very low ESR (typically less  
than 10 m). However, some dielectric types do not have  
good capacitance characteristics as a function of voltage  
and temperature.  
OUTPUT CAPACITOR: An output capacitor is required for  
loop stability. It must be located less than 1 cm from the  
device and connected directly to the output and ground pins  
using traces which have no other currents flowing through  
them (see PCB Layout section).  
The minimum value of output capacitance that can be used  
for stable full-load operation is 10µF, but it may be increased  
without limit. The output capacitor must have an ESR value  
as shown in the stable region of the curve below. Tantalum  
capacitors are recommended for the output capacitor.  
Z5U and Y5V dielectric ceramics have capacitance that  
drops severely with applied voltage. A typical Z5U or Y5V  
capacitor can lose 60% of its rated capacitance with half of  
the rated voltage applied to it. The Z5U and Y5V also exhibit  
a severe temperature effect, losing more than 50% of nomi-  
nal capacitance at high and low limits of the temperature  
range.  
ESR Curve  
X7R and X5R dielectric ceramic capacitors are strongly rec-  
ommended if ceramics are used, as they typically maintain a  
capacitance range within 20% of nominal over full operat-  
ing ratings of temperature and voltage. Of course, they are  
typically larger and more costly than Z5U/Y5U types for a  
given voltage and capacitance.  
TANTALUM: Solid Tantalum capacitors are recommended  
for use on the output because their typical ESR is very close  
to the ideal value required for loop compensation. They also  
work well as input capacitors if selected to meet the ESR  
requirements previously listed.  
Tantalums also have good temperature stability: a good  
quality Tantalum will typically show a capacitance value that  
varies less than 10-15% across the full temperature range of  
125˚C to −40˚C. ESR will vary only about 2X going from the  
high to low temperature limits.  
20074670  
The increasing ESR at lower temperatures can cause oscil-  
lations when marginal quality capacitors are used (if the ESR  
of the capacitor is near the upper limit of the stability range at  
room temperature).  
CFF (Feed Forward Capacitor)  
The capacitor CFF is required to add phase lead and help  
improve loop compensation. The correct amount of capaci-  
tance depends on the value selected for R1 (see Typical  
Application Circuit). The capacitor should be selected such  
that the zero frequency as given by the equation shown  
below is approximately 45 kHz:  
ALUMINUM: This capacitor type offers the most capaci-  
tance for the money. The disadvantages are that they are  
larger in physical size, not widely available in surface mount,  
and have poor AC performance (especially at higher fre-  
quencies) due to higher ESR and ESL.  
9
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recommended that some inductance be placed between the  
output capacitor and the load, and good RF bypass capaci-  
tors be placed directly across the load.  
Application Hints (Continued)  
Compared by size, the ESR of an aluminum electrolytic is  
higher than either Tantalum or ceramic, and it also varies  
greatly with temperature. A typical aluminum electrolytic can  
exhibit an ESR increase of as much as 50X when going from  
25˚C down to −40˚C.  
PCB layout is also critical in high noise environments, since  
RFI/EMI is easily radiated directly into PC traces. Noisy  
circuitry should be isolated from "clean" circuits where pos-  
sible, and grounded through a separate path. At MHz fre-  
quencies, ground planes begin to look inductive and RFI/  
EMI can cause ground bounce across the ground plane.  
It should also be noted that many aluminum electrolytics only  
specify impedance at a frequency of 120 Hz, which indicates  
they have poor high frequency performance. Only aluminum  
electrolytics that have an impedance specified at a higher  
frequency (between 20 kHz and 100 kHz) should be used for  
the LP387X. Derating must be applied to the manufacturer’s  
ESR specification, since it is typically only valid at room  
temperature.  
In multi-layer PCB applications, care should be taken in  
layout so that noisy power and ground planes do not radiate  
directly into adjacent layers which carry analog power and  
ground.  
OUTPUT NOISE  
Any applications using aluminum electrolytics should be  
thoroughly tested at the lowest ambient operating tempera-  
ture where ESR is maximum.  
Noise is specified in two ways-  
Spot Noise or Output noise density is the RMS sum of all  
noise sources, measured at the regulator output, at a spe-  
cific frequency (measured with a 1Hz bandwidth). This type  
of noise is usually plotted on a curve as a function of fre-  
quency.  
PCB LAYOUT  
Good PC layout practices must be used or instability can be  
induced because of ground loops and voltage drops. The  
input and output capacitors must be directly connected to the  
input, output, and ground pins of the LP387X using traces  
which do not have other currents flowing in them (Kelvin  
connect).  
Total output Noise or Broad-band noise is the RMS sum  
of spot noise over a specified bandwidth, usually several  
decades of frequencies.  
Attention should be paid to the units of measurement. Spot  
noise is measured in units µV/ Hz or nV/ Hz and total output  
noise is measured in µV(rms).  
The best way to do this is to lay out CIN and COUT near the  
device with short traces to the VIN, VOUT, and ground pins.  
The regulator ground pin should be connected to the exter-  
nal circuit ground so that the regulator and its capacitors  
have a "single point ground".  
The primary source of noise in low-dropout regulators is the  
internal reference. In CMOS regulators, noise has a low  
frequency component and a high frequency component,  
which depend strongly on the silicon area and quiescent  
current. Noise can be reduced in two ways: by increasing the  
transistor area or by increasing the current drawn by the  
internal reference. Increasing the area will decrease the  
chance of fitting the die into a smaller package. Increasing  
the current drawn by the internal reference increases the  
total supply current (ground pin current). Using an optimized  
trade-off of ground pin current and die size, LP3875-ADJ  
achieves low noise performance and low quiescent current  
operation.  
It should be noted that stability problems have been seen in  
applications where "vias" to an internal ground plane were  
used at the ground points of the IC and the input and output  
capacitors. This was caused by varying ground potentials at  
these nodes resulting from current flowing through the  
ground plane. Using a single point ground technique for the  
regulator and it’s capacitors fixed the problem.  
Since high current flows through the traces going into VIN  
and coming from VOUT, Kelvin connect the capacitor leads to  
these pins so there is no voltage drop in series with the input  
and output capacitors.  
The total output noise specification for LP3875-ADJ is pre-  
sented in the Electrical Characteristics table. The Output  
noise density at different frequencies is represented by a  
curve under typical performance characteristics.  
RFI/EMI SUSCEPTIBILITY  
RFI (radio frequency interference) and EMI (electromagnetic  
interference) can degrade any integrated circuit’s perfor-  
mance because of the small dimensions of the geometries  
inside the device. In applications where circuit sources are  
present which generate signals with significant high fre-  
SHORT-CIRCUIT PROTECTION  
The LP3875-ADJ is short circuit protected and in the event of  
a peak over-current condition, the short-circuit control loop  
will rapidly drive the output PMOS pass element off. Once  
the power pass element shuts down, the control loop will  
rapidly cycle the output on and off until the average power  
dissipation causes the thermal shutdown circuit to respond  
to servo the on/off cycling to a lower frequency. Please refer  
to the section on thermal information for power dissipation  
calculations.  
>
quency energy content ( 1 MHz), care must be taken to  
ensure that this does not affect the IC regulator.  
If RFI/EMI noise is present on the input side of the regulator  
(such as applications where the input source comes from the  
output of a switching regulator), good ceramic bypass ca-  
pacitors must be used at the input pin of the IC.  
If a load is connected to the IC output which switches at high  
speed (such as a clock), the high-frequency current pulses  
required by the load must be supplied by the capacitors on  
the IC output. Since the bandwidth of the regulator loop is  
less than 100 kHz, the control circuitry cannot respond to  
load changes above that frequency. The means the effective  
output impedance of the IC at frequencies above 100 kHz is  
determined only by the output capacitor(s).  
SHUTDOWN OPERATION  
A CMOS Logic level signal at the shutdown ( SD) pin will  
turn-off the regulator. Pin SD must be actively terminated  
through a 10kpull-up resistor 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.  
In applications where the load is switching at high speed, the  
output of the IC may need RF isolation from the load. It is  
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10  
HEATSINKING TO-263 PACKAGE  
Application Hints (Continued)  
DROPOUT VOLTAGE  
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 1 shows a curve for the  
The dropout voltage of a regulator is defined as the minimum  
input-to-output differential required to stay within 2% of the  
nominal output voltage. For CMOS LDOs, the dropout volt-  
age is the product of the load current and the Rds(on) of the  
internal MOSFET.  
θ
JA of TO-263 package for different copper area sizes, using  
a typical PCB with 1 ounce copper and no solder mask over  
the copper area for heat sinking.  
REVERSE CURRENT PATH  
The internal MOSFET in the LP3875-ADJ has an inherent  
parasitic diode. During normal operation, the input voltage 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  
output can be pulled above the input as long as the current  
in the parasitic diode is limited to 200mA continuous and 1A  
peak.  
POWER DISSIPATION/HEATSINKING  
20074632  
The LP3875-ADJ can deliver a continuous current of 1.5A  
over the full operating temperature range. A heatsink may be  
required depending on the maximum power dissipation 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:  
FIGURE 1. θJA vs Copper (1 Ounce) Area for TO-263  
package  
As shown in the figure, increasing the copper area beyond 1  
square inch produces very little improvement. The minimum  
value for θJA for the TO-263 package mounted to a PCB is  
32˚C/W.  
PD = (VIN−VOUT)IOUT+ (VIN)IGND  
where IGND is the operating ground current of the device  
(specified under Electrical Characteristics).  
Figure 2 shows the maximum allowable power dissipation  
for TO-263 packages for different ambient temperatures,  
assuming θJA is 35˚C/W and the maximum junction tempera-  
ture is 125˚C.  
The maximum allowable temperature rise (TRmax) depends  
on the maximum ambient temperature (TAmax) of the appli-  
cation, and the maximum allowable junction temperature  
(TJmax):  
TRmax = TJmax− TAmax  
The maximum allowable value for junction to ambient Ther-  
mal Resistance, θJA, can be calculated using the formula:  
θJA = TRmax / PD  
The LP3875-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 θJA calculated above is 60 ˚C/W for TO-220  
package 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 θJA falls  
below these limits, a heat sink is required.  
20074633  
HEATSINKING TO-220 PACKAGE  
FIGURE 2. Maximum power dissipation vs ambient  
temperature for TO-263 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 θJA will  
be same as shown in next section for TO263 package.  
HEATSINKING SOT223-5 PACKAGE  
The heatsink to be used in the application should have a  
heatsink to ambient thermal resistance,  
Figure 3 shows a curve for the θJA of SOT-223 package for  
different copper area sizes, using a typical PCB with 1 ounce  
copper and no solder mask over the copper area for heat  
sinking.  
θHA≤ θJA θCH θJC  
.
In this equation, θCH is the thermal resistance from the case  
to the surface of the heat sink and θJC is the thermal resis-  
tance from the junction to the surface of the case. θJC is  
about 3˚C/W for a TO220 package. The value for θCH de-  
pends on method of attachment, insulator, etc. θCH varies  
between 1.5˚C/W to 2.5˚C/W. If the exact value is unknown,  
2˚C/W can be assumed.  
11  
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Application Hints (Continued)  
20074683  
FIGURE 4. SCENARIO A, θJA = 148˚C/W  
20074682  
FIGURE 3. θJA vs Copper(1 Ounce) Area for SOT-223  
package  
The following figures show different layout scenarios for  
SOT-223 package.  
20074684  
FIGURE 5. SCENARIO B, θJA = 125˚C/W  
www.national.com  
12  
Physical Dimensions inches (millimeters) unless otherwise noted  
TO220 5-lead, Molded, Stagger Bend Package (TO220-5)  
NS Package Number T05D  
For Order Numbers, refer to the “Ordering Information” section of this document.  
13  
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)  
TO263 5-Lead, Molded, Surface Mount Package (TO263-5)  
NS Package Number TS5B  
For Order Numbers, refer to the “Ordering Information” section of this document.  
www.national.com  
14  
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)  
SOT223, 5-Lead, Molded, Surface Mount Package (SOT223-5)  
NS Package Number MP05A  
For Order Numbers, refer to the “Ordering Information” section of this document.  
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves  
the right at any time without notice to change said circuitry and specifications.  
For the most current product information visit us at www.national.com.  
LIFE SUPPORT POLICY  
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS  
WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR  
CORPORATION. As used herein:  
1. Life support devices or systems are devices or systems  
which, (a) are intended for surgical implant into the body, or  
(b) support or sustain life, and whose failure to perform when  
properly used in accordance with instructions for use  
provided in the labeling, can be reasonably expected to result  
in a significant injury to the user.  
2. A critical component is any component of a life support  
device or system whose failure to perform can be reasonably  
expected to cause the failure of the life support device or  
system, or to affect its safety or effectiveness.  
BANNED SUBSTANCE COMPLIANCE  
National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products  
Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain  
no ‘‘Banned Substances’’ as defined in CSP-9-111S2.  
Leadfree products are RoHS compliant.  
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