LM2937-3.3 [NSC]
400mA and 500mA Voltage Regulators; 400毫安提供最大500mA电流稳压器
| 型号： | LM2937-3.3 |
| 厂家： | 
National Semiconductor |
| 描述： | 400mA and 500mA Voltage Regulators |
| 文件： | 总11页 (文件大小：303K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
February 1998
LM2937-2.5, LM2937-3.3
400mA and 500mA Voltage Regulators
two-battery jumps and up to +60V/−50V load dump tran-
sients. Familiar regulator features such as short circuit and
thermal shutdown protection are also built in.
General Description
The LM2937-2.5 and LM2937-3.3 are positive voltage regu-
lators capable of supplying up to 500 mA of load current.
Both regulators are ideal for converting a common 5V logic
supply, or higher input supply voltage, to the lower 2.5V and
3.3V supplies to power VLSI ASIC’s and microcontrollers.
Special circuitry has been incorporated to minimize the qui-
escent current to typically only 10 mA with a full 500 mA load
current when the input to output voltage differential is greater
than 5V.
Features
n Fully specified for operation over −40˚C to +125˚C
n Output current in excess of 500 mA (400mA for
SOT-223 package)
n Output trimmed for 5% tolerance under all operating
conditions
n Wide output capacitor ESR range, 0.01Ω up to 5Ω
n Internal short circuit and thermal overload protection
n Reverse battery protection
n 60V input transient protection
n Mirror image insertion protection
The LM2937 requires an output bypass capacitor for stabil-
ity. As with most regulators utilizing a PNP pass transistor,
the ESR of this capacitor remains a critical design param-
eter, but the LM2937-2.5 and LM2937-3.3 include special
compensation circuitry that relaxes ESR requirements. The
LM2937 is stable for all ESR ratings less than 5Ω. This al-
lows the use of low ESR chip capacitors.
The regulators are also suited for automotive applications,
with built in protection from reverse battery connections,
Connection Diagram and Ordering Information
TO-220 Plastic Package
SOT-223 Plastic Package
DS100113-24
DS100113-25
Front View
Front View
Order Number LM2937ET-2.5, LM2937ET-3.3,
Order Number LM2937IMP-2.5, LM2937IMP-3.3,
See NS Package Number MA04A
See NS Package Number T03B
TO-263 Surface-Mount Package
DS100113-27
Side View
DS100113-26
Top View
Order Number LM2937ES-2.5, LM2937ES-3.3,
See NS Package Number TS3B
© 1998 National Semiconductor Corporation
DS100113
www.national.com
Connection Diagram and Ordering Information (Continued)
Temperature
Range
Output Voltage
NSC
Package
Drawing
TS3B
Package
2.5
3.3
−40˚C ≤ TA ≤ 125˚C
−40˚C ≤ TA ≤ 85˚C
LM2937ES-2.5
LM2937ET-2.5
LM2937IMP-2.5
L68B
LM2937ES-3.3
LM2937ET-3.3
LM2937IMP-3.3
L69B
TO-263
TO-220
T03B
MA04A
SOT-223
SOT-223 Package
Markings
The small physical size of the SOT-223 package does not allow sufficient space to provide the complete device part number. The actual devices will be labeled with
the package markings shown.
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2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
TO-263 (10 seconds)
SOT-223 (Vapor Phase, 60 seconds)
SOT-223 (Infrared, 15 seconds)
ESD Susceptibility (Note 3)
230˚C
215˚C
220˚C
2 kV
Input Voltage
Operating Conditions(Note 1)
Continuous
26V
60V
Transient (t ≤ 100 ms)
Temperature Range (Note 2)
Internal Power Dissipation (Note 2)
Maximum Junction Temperature
Storage Temperature Range
Lead Temperature Soldering
TO-220 (10 seconds)
Internally Limited
150˚C
LM2937ES, LM2937ET
−40˚C ≤ TA ≤ 125˚C
−65˚C to +150˚C
LM2937IMP
−40˚C ≤ TA ≤ 85˚C
Input Voltage Range
4.75V to 26V
260˚C
Electrical Characteristics(Note 4)
=
=
=
VIN VNOM + 5V, IOUTmax 500 mA for the TO-220 and TO-263 packages, IOUTmax 400mA for the SOT-223 package, COUT
=
10 µF unless otherwise indicated. Boldface limits apply over the entire operating temperature range, of the indicated
=
=
device, all other specifications are for TA TJ 25˚C.
Output Voltage (VOUT
)
2.5V
3.3V
Units
Parameter
Output Voltage
Conditions
Typ
Limit
2.42
2.38
2.56
2.62
25
Typ
Limit
3.20
3.14
3.40
3.46
33
5 mA ≤ IOUT ≤ IOUTmax
V (Min)
V(Min)
2.5
3.3
V(Max)
V(Max)
mV(Max)
Line Regulation(Note 5)
4.75V ≤ VIN ≤ 26V,
7.5
9.9
=
IOUT 5 mA
Load Regulation
5 mA ≤ IOUT ≤ IOUTmax
7V ≤ VIN ≤ 26V,
2.5
2
25
10
3.3
2
33
10
mV(Max)
mA(Max)
Quiescent Current
=
IOUT 5 mA
=
VIN (VOUT + 5V),
10
20
10
20
mA(Max)
=
IOUT IOUTmax
=
=
VIN 5V, IOUT IOUTmax
66
75
100125
66
99
100125
mA(Max)
µVrms
Output Noise
10 Hz–100 kHz,
=
Voltage
IOUT 5 mA
Long Term Stability
Short-Circuit Current
Peak Line Transient
Voltage
1000 Hrs.
10
1.0
75
13.2
1.0
75
mV
0.6
60
0.6
60
A(Min)
V(Min)
=
<
tf 100 ms, RL 100Ω
Maximum Operational
Input Voltage
26
26
V(Min)
V(Min)
V(Min)
=
Reverse DC
VOUT ≥ −0.6V, RL 100Ω
−30
−75
−15
−50
−30
−75
−15
−50
Input Voltage
=
<
tr 1 ms, RL 100Ω
Reverse Transient
Input Voltage
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
outside of its rated Operating Conditions.
=
Note 2: The maximum allowable power dissipation at any ambient temperature is P
(125 − T )/θ , where 125 is the maximum junction temperature for op-
JA
MAX
A
eration, T is the ambient temperature, and θ is the junction-to-ambient thermal resistance. If this dissipation is exceeded, the die temperature will rise above 125˚C
JA
A
and the electrical specifications do not apply. If the die temperature rises above 150˚C, the regulator will go into thermal shutdown. The junction-to-ambient thermal
resistance θ is 65˚C/W, for the TO-220 package, 73˚C/W for the TO-263 package, and 174˚C/W for the SOT-223 package. When used with a heatsink, θ is the
J
A
J
A
sum of the device junction-to-case thermal resistance θ of 3˚C/W and the heatsink case-to-ambient thermal resistance. If the TO-263 or SOT-223 packages are
JC
used, the thermal resistance can be reduced by increasing the P.C. board copper area thermally connected to the package (see Application Hints for more information
on heatsinking).
Note 3: ESD rating is based on the human body model, 100 pF discharged through 1.5 kΩ.
=
Note 4: Typicals are at T
25˚C and represent the most likely parametric norm.
J
Note 5: The minimum input voltage required for proper biasing of these regulators is 4.75V. Below this level the outputs will fall out of regulation. This effect is not
the normal dropout characteristic where the output falls out of regulation due to the PNP pass transistor entering saturation. If a value for worst case effective input
to output dropout voltage is required in a specification, the values should be 2.37V maximum for the LM2937-2.5 and 1.6V maximum for the LM2937-3.3.
3
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Typical Performance Characteristics
Output Voltage vs
Temperature (2.5V)
Output Voltage vs
Temperature (3.3V)
Quiescent Current vs
Output Current (2.5V)
DS100113-2
DS100113-3
DS100113-4
Quiescent Current vs
Output Current (3.3V)
Quiescent Current vs
Input Voltage (2.5V)
Quiescent Current vs
Input Voltage (3.3V)
DS100113-5
DS100113-6
DS100113-7
Line Transient Response
Ripple Rejection
Load Transient Response
DS100113-9
DS100113-10
DS100113-8
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4
Typical Performance Characteristics (Continued)
Output Impedance
Maximum Power
Dissipation (TO-220)
Maximum Power Dissipation
(TO-263) (Note 2)
DS100113-11
DS100113-12
DS100113-13
Low Voltage Behavior (2.5V)
Low Voltage Behavior (3.3)
DS100113-14
DS100113-15
Output at Voltage
Extremes
Output Capacitor ESR
Peak Output Current
DS100113-17
DS100113-18
DS100113-16
Typical Application
DS100113-1
* Required if the regulator is located more than 3 inches from the power supply filter capacitors.
*
*
Required for stability. C must be at least 10 µF (over the full expected operating temperature range) and located as close as possible to the regulator. The
out
equivalent series resistance, ESR, of this capacitor may be as high as 3Ω.
5
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Application Hints
The figure below shows the voltages and currents which are
present in the circuit, as well as the formula for calculating
the power dissipated in the regulator:
EXTERNAL CAPACITORS
The output capacitor is critical to maintaining regulator stabil-
ity, and must meet the required conditions for both ESR
(Equivalent Series Resistance) and minimum amount of ca-
pacitance.
MINIMUM CAPACITANCE:
The minimum output capacitance required to maintain stabil-
ity is 10 µF (this value may be increased without limit).
Larger values of output capacitance will give improved tran-
sient response.
ESR LIMITS:
DS100113-19
The ESR of the output capacitor will cause loop instability if
it is too high or too low. The acceptable range of ESR plotted
versus load current is shown in the graph below. It is essen-
tial that the output capacitor meet these requirements,
or oscillations can result.
=
=
÷
I
G
(V − V
IN OUT
I
P
I
IN
L
) I + (V ) I
IN G
D
L
FIGURE 2. Power Dissipation Diagram
The next parameter which must be calculated is the maxi-
mum allowable temperature rise, TR (max). This is calcu-
lated by using the formula:
Output Capacitor ESR
=
TR (max) TJ(max) − TA (max)
where: TJ (max) is the maximum allowable junction tem-
perature, which is 125˚C for commercial
grade parts.
TA (max) is the maximum ambient temperature
which will be encountered in the applica-
tion.
Using the calculated values for TR(max) and PD, the maxi-
mum allowable value for the junction-to-ambient thermal re-
sistance, θ(J−A), can now be found:
=
θ(J−A) TR (max)/PD
DS100113-17
IMPORTANT: If the maximum allowable value for θ(J−A) is
found to be ≥ 53˚C/W for the TO-220 package, ≥ 80˚C/W for
the TO-263 package, or ≥174˚C/W for the SOT-223 pack-
age, no heatsink is needed since the package alone will dis-
sipate enough heat to satisfy these requirements.
FIGURE 1. ESR Limits
It is important to note that for most capacitors, ESR is speci-
fied only at room temperature. However, the designer must
ensure that the ESR will stay inside the limits shown over the
entire operating temperature range for the design.
If the calculated value for θ(J−A)falls below these limits, a
heatsink is required.
For aluminum electrolytic capacitors, ESR will increase by
about 30X as the temperature is reduced from 25˚C to
−40˚C. This type of capacitor is not well-suited for low tem-
perature operation.
HEATSINKING TO-220 PACKAGE PARTS
The TO-220 can be attached to a typical heatsink, or se-
cured to a copper plane on a PC board. If a copper plane is
to be used, the values of θ(J−A) will be the same as shown in
the next section for the TO-263.
Solid tantalum capacitors have a more stable ESR over tem-
perature, but are more expensive than aluminum electrolyt-
ics. A cost-effective approach sometimes used is to parallel
an aluminum electrolytic with a solid Tantalum, with the total
capacitance split about 75/25% with the Aluminum being the
larger value.
If a manufactured heatsink is to be selected, the value of
heatsink-to-ambient thermal resistance, θ(H−A), must first be
calculated:
=
θ(H−A) θ(J−A) − θ(C−H) − θ(J−C)
If two capacitors are paralleled, the effective ESR is the par-
allel of the two individual values. The “flatter” ESR of the Tan-
talum will keep the effective ESR from rising as quickly at low
temperatures.
Where: θ(J−C) is defined as the thermal resistance from
the junction to the surface of the case. A
value of 3˚C/W can be assumed for θ(J−C)
for this calculation.
HEATSINKING
θ(C−H)
is defined as the thermal resistance be-
tween the case and the surface of the heat-
sink. The value of θ(C−H) will vary from
about 1.5˚C/W to about 2.5˚C/W (depend-
ing on method of attachment, insulator,
etc.). If the exact value is unknown, 2˚C/W
A heatsink may be required depending on the maximum
power dissipation and maximum ambient temperature of the
application. Under all possible operating conditions, the junc-
tion temperature must be within the range specified under
Absolute Maximum Ratings.
should be assumed for θ(C−H)
.
To determine if a heatsink is required, the power dissipated
by the regulator, PD, must be calculated.
When a value for θ(H−A) is found using the equation shown,
a heatsink must be selected that has a value that is less than
or equal to this number.
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6
θ(H−A) is specified numerically by the heatsink manufacturer
in the catalog, or shown in a curve that plots temperature rise
vs power dissipation for the heatsink.
HEATSINKING TO-263 AND SOT-223 PACKAGE PARTS
Both the TO-263 (“S”) and SOT-223 (“MP”) packages use a
copper plane on the PCB and the PCB itself as a heatsink.
To optimize the heat sinking ability of the plane and PCB,
solder the tab of the package to the plane.
Figure 3 shows for the TO-263 the measured values of θ(J−A)
for different copper area sizes using a typical PCB with 1
ounce copper and no solder mask over the copper area used
for heatsinking.
DS100113-22
FIGURE 5. θ(J−A) vs Copper (2 ounce) Area for the
SOT-223 Package
DS100113-20
FIGURE 3. θ(J−A) vs Copper (1 ounce) Area for the
TO-263 Package
As shown in the figure, increasing the copper area beyond 1
square inch produces very little improvement. It should also
be observed that the minimum value of θ(J−A) for the TO-263
package mounted to a PCB is 32˚C/W.
DS100113-23
FIGURE 6. Maximum Power Dissipation vs TAMB for
the SOT-223 Package
As a design aid, Figure 4 shows the maximum allowable
power dissipation compared to ambient temperature for the
TO-263 device (assuming θ(J−A) is 35˚C/W and the maxi-
mum junction temperature is 125˚C).
Please see AN1028 for power enhancement techniques to
be used with the SOT-223 package.
SOT-223 SOLDERING RECOMMENDATIONS
It is not recommended to use hand soldering or wave solder-
ing to attach the small SOT-223 package to a printed circuit
board. The excessive temperatures involved may cause
package cracking.
Either vapor phase or infrared reflow techniques are pre-
ferred soldering attachment methods for the SOT-223 pack-
age.
DS100113-21
FIGURE 4. Maximum Power Dissipation vs TAMB for
the TO-263 Package
Figure 5 and Figure 6 show the information for the SOT-223
package. Figure 6 assumes a θ(J−A) of 74˚C/W for 1 ounce
copper and 51˚C/W for 2 ounce copper and a maximum
junction temperature of 125˚C.
7
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Physical Dimensions inches (millimeters) unless otherwise noted
Plastic Package
Order Number LM2937ET-2.5,
LM2937ET-3.3,
NS Package Number T03B
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8
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
TO-263 3-Lead Plastic Surface Mount Package
Order Number LM2937ES-2.5, LM2937ES-3.3,
NS Package Number TS3B
9
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
SOT-223 3-Lead Plastic Surface Mount Package
Order Number LM2937IMP-2.5, LM2937IMP-3.3,
NS Package Number MA04A
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VICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMI-
CONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or sys-
tems which, (a) are intended for surgical implant into
the body, or (b) support or sustain life, and whose fail-
ure 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 in any component of a life support
device or system whose failure to perform can be rea-
sonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
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