The LM3411isalowpowerfixed-voltage(3.3Vor5.0V)precision shunt regulator designed specifically fordrivinganoptoisolator to provide feedback isolation in a switching regulator.
The LM3411 circuitry includes an internally compensated op
amp, a bandgap reference, NPN output transistor, and voltage setting resistors.
A trimmed precision bandgap reference with temperature
drift curvature correction, provides a guaranteed 1%precision over theoperatingtemperature range (A grade version).
The amplifier’s inverting input is externally accessible for
loop frequency compensation when used as part of a larger
servo system. The output is an open-emitter NPN transistor
capable of driving up to 15 mA of load current.
Because of its small die size, the LM3411 has been made
available in the sub-miniature 5-lead SOT23-5 surface
mount package. This package is ideal for use in space critical applications.
Although its main application is to provide a precision output
voltage (no trimming required) and maintain very good regulation in isolated DC/DC converters, it can also be used with
other types of voltage regulators or power semiconductors to
provide a precision output voltage without precision resistors
or trimming.
Features
n Fixed voltages of 3.3V and 5.0V with initial tolerance of
±
1%for standard grade and±0.5%for A grade
n Custom voltages available (3V–17V)
n Wide output current range, 20 µA–15 mA
n Low temperature coefficient
n Available in 5-lead SOT23-5 surface mount package
(tape and reel)
Applications
n Secondary controller for isolated DC/DC PWM switching
regulators systems
n Use with LDO regulator for high-precision fixed output
regulators
n Precision monitoring applications
n Use with many types of regulators to increase precision
and improve performance
LM3411 Precision Secondary Regulator/Driver
December 1999
Typical Application and Functional Diagram
DS011987-1
Basic Isolated DC/DC Converter
DS011987-2
LM3411 Functional Diagram
SIMPLE SWITCHER™is a tradmark of National Semiconductor Corporation.
*No internal connection, but should be soldered to PC board for best heat
transfer.
Five Lead Surface Mount Package Marking
and Order Information (SOT23-5)
The small SOT23-5 package allows only 4 alphanumeric characters to identify the product. The table below contains the field information marked on the package.
Grade
3.3VA (Prime)LM3411AM5-3.3D00A1000 unit increments on tape and reel
3.3VA (Prime)LM3411AM5X-3.3D00A3000 unit increments on tape and reel
3.3VB (Standard)LM3411M5-3.3D00B1000 unit increments on tape and reel
3.3VB (Standard)LM3411M5X-3.3D00B3000 unit increments on tape and reel
5.0VA (Prime)LM3411AM5-5.0D01A1000 unit increments on tape and reel
5.0VA (Prime)LM3411AM5X-5.0D01A3000 unit increments on tape and reel
5.0VB (Standard)LM3411M5-5.0D01B1000 unit increments on tape and reel
5.0VB (Standard)LM3411M5X-5.0D01B3000 unit increments on tape and reel
The first letter “D” identifies the part as a Driver, the next two numbers indicate the voltage, “00” for 3.3V part and “01” for a 5V
part. The fourth letter indicates the grade, “B” for standard grade, “A” for the prime grade.
The SOT23-5 surface mount package is only available on tape in quantities increments of 250 on tape and reel (indicated by the
letters “M5” in the part number), or in quantities increments of 3000 on tape and reel (indicated by the letters “M5X” in the part
number).
Order InformationPackage
Marking
FIGURE 1. SOT23-5 Marking and Order Information
Supplied as
www.national.com2
Page 3
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Voltage V(IN)20V
Output Current20 mA
Junction Temperature150˚C
Storage Temperature−65˚C to +150˚C
Lead Temperature
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 do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the 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: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
bient thermal resistance), and T
given in the Absolute Maximum Ratings, whichever is lower. The typical thermal resistance (θ
for the M5 package.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 4: Typical numbers are at 25˚C and represent the most likely parametric norm.
Note 5: Limits are 100%production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control
(SQC) methods. The limits are used to calculate National’s Averaging Outgoing Level (AOQL).
Note 6: Actual test is done using equivalent current sink instead of a resistor load.
Note 7: V
Note 8: See Applications and Curves sections for information on this resistor.
SAT
=
V(IN) − V
(ambient temperature). The maximum allowable power dissipation at any temperature is (P
A
, when the voltage at the IN pin is forced 100 mV above the nominal regulating voltage (V
OUT
=
25˚C, and those with boldface type apply over full Operating Tempera-
J
REG,VOUT
=
1.5V.
(Note 4)LimitLimit(Limits)
(Note 5)(Note 5)
=
5mA5V
5.025/5.0505.050/5.100V(max)
4.975/4.9504.950/4.900V(min)
=
5mA
=
5mA85µA
±
0.5/±1
±1/±
2
110/115125/150µA(max)
≤ 1 mA3.3mA/mV
OUT
1.5/0.751.0/0.5mA/mV(min)
≤ 15 mA6.0mA/mV
OUT
3.3/2.02.5/1.7mA/mV(min)
≤ V
OUT
− 1.2V (−1.3)1000V/V
REG
250Ω (Note 6)750/350650/300V/V(min)
≤ V
OUT
− 1.2V (−1.3)3500V/V
REG
2kΩ1500/9001000/700V/V(min)
+100 mV1.0V
REG
=
15 mA1.2/1.31.2/1.3V(max)
−100 mV0.1µA
REG
=
0V0.5/1.00.5/1.0µA(max)
7070kΩ(min)
=
1 mA, 10 Hz ≤ f ≤ 10 kHz80µV
(maximum junction temperature), θJA(junction to am-
Jmax
) when soldered to a printed circuit board is approximately 306˚C/W
JA
REG
Dmax
).
=
T
Jmax−TA
)/θJAor the number
%
(max)
RMS
www.national.com4
Page 5
Typical Performance Characteristics
LM3411
Normalized
Temperature Drift
Circuit Used for Bode Plots
Bold Plot
DS011987-30
DS011987-8
Quiescent Current
Bode Plot
Response Time
for 3.3V Version
=
(C
0 pF)
C
DS011987-31
DS011987-33
Output Saturation
Voltage (V)
SAT
Bode Plot
Response Time
for 3.3V Version
=
(C
10 nF)
C
DS011987-32
DS011987-34
DS011987-44
Circuit Used for Response Time
DS011987-11
Response Time
for 5V Version
=
(C
0 pF)
C
DS011987-35
DS011987-37
Response Time
for 5V Version
=
(C
10 nF)
C
DS011987-36
DS011987-38
www.national.com5
Page 6
Typical Performance Characteristics (Continued)
LM3411
Tempco of Internal
Feedback Resistor (Rf)
Regulation Voltage
Change vs
Output Current
Regulation Voltage vs
Output Voltage and
Load Resistance
Regulation Voltage vs
Output Voltage and
Load Resistance
DS011987-39
DS011987-42
DS011987-40
DS011987-41
www.national.com6
Page 7
Product Description
The LM3411 is a shunt regulator specifically designed to be
the reference and control section in an overall feedback loop
of a regulated power supply. The regulated output voltage is
sensed between the IN pin and GROUND pin of the LM3411.
If the voltage at the IN pin is less than the LM3411 regulating
voltage (V
age at the IN pin approaches the V
begins sourcing current. This current is then used to drive a
), the OUT pin sources no current. As the volt-
REG
voltage, the OUT pin
REG
feedback device, (opto-coupler) or a power device, (linear
regulator, switching regulator, etc.) which servos the output
voltage to be the same value as V
REG
.
In some applications, (even under normal operating conditions) the voltage on the IN pin can be forced above the
V
voltage. In these instances, the maximum voltage ap-
REG
plied to the IN pin should not exceed 20V.In addition, an external resistor may be required on the OUT pin to limit the
maximum current to 20 mA.
Compensation
The inverting input of the error amplifier is brought out to allow overall closed-loop compensation. In many of the applications circuits shown here, compensation is provided by a
single capacitor connected from the compensation pin to the
out pin of the LM3411. The capacitor values shown in the
schematics are adequate under most conditions, but they
can be increased or decreased depending on the desired
loop response. Applying a load pulse to the output of a regulator circuit and observing the resultant output voltage response is a easy method of determining the stability of the
control loop. Analyzing more complex feedback loops requires additional information.
The formula for AC gain at a frequency (f) is as follows;
where Rf≈ 52 kΩ for the 3.3V part, and Rf≈ 94 kΩ for the 5V
part.
The resistor (R
on the die. Since this resistor value will affect the phase mar-
) in the formula is an internal resistor located
f
gin, the worst case maximum and minimum values are important when analyzing closed loop stability. The minimum
and maximum room temperature values of this resistor are
specified in the Electrical Characteristics section of this data
sheet, and a curve showing the temperature coefficient is
shown in the curves section. In the applications shown here,
the worst case phase margin occurs with minimum values of
R
.
f
Test Circuit
The test circuit shown in
and verify various LM3411 parameters. Test conditions are
set by forcing the appropriate voltage at the V
point and selecting the appropriate R
the Electrical Characteristics section. Use a DVM at the
“measure” test points to read the data.
Figure 2
can be used to measure
or I
L
OUT
as specified in
OUT
Set test
LM3411
FIGURE 2. LM3411 Test Circuit
DS011987-14
www.national.com7
Page 8
Applications Information
LM3411
DS011987-15
FIGURE 3. Isolated 250 mA Flyback Switching Regulator
FIGURE 4. Isolated 1.5A Flyback Switching Regulator Using a LM2577
The LM3411 regulator/driver provides the reference and
feedback drive functions in a regulated power supply. It can
also be used together with many different types of regulators, (both linear and switching) as well as other power semiconductor devices to add precision and improve regulation
specifications. Output voltage tolerances better than 0.5
%
are possible without using trim pots or precision resistors.
One of the main applications of the LM3411 is to drive an
opto-isolator to provide feedback signal isolation in a switching regulator circuit. For low current applications, (up to 250
mA) the circuit shown in
Figure 3
provides good regulation
and complete input/output electrical isolation.
For an input voltage of 15V,this circuit can provide an output
of either 3.3V or 5V with a load current up to 250 mA with excellent regulation characteristics. With the part values
shown, this circuit operates at 80 kHz., and can be synchronized to a clock or an additional LM3578. (See LM1578 data
sheet for additional information.)
www.national.com8
DS011987-16
An isolated DC/DC flyback converter capable of higher output current is shown in
LM2577 SIMPLE SWITCHER
Figure 4
. This circuit utilizes the
™
voltage regulator for the
Pulse Width Modulation (PWM), power switch and protection
functions, while the LM3411 provides the voltage reference,
gain and opto coupler drive functions. In this circuit, the reference and error amplifier in the LM2577 are not used (note
that the feedback pin is grounded). The gain is provided by
the LM3411. Since the voltage reference is located on the
secondary side of the transformer, this circuit provides very
good regulation specifications.
The output of a switching regulator typically will contain a
small ripple voltage at the switching frequency and may also
contain voltage transients. These transient voltage spikes
can be sensed by the LM3411 and could give an incorrect
regulation voltage. An RC filter consisting of a 1Ω resistor
and a 100 nF capacitor will filter these transients and minimize this problem. The 1Ω resistor should be located on the
ground side of the LM3411, and the capacitor should be
physically located near the package.
Page 9
Applications Information (Continued)
FIGURE 5. Precision 1A Buck Regulator
LM3411
DS011987-17
FIGURE 6. Negative Input, Negative or Positive Output Flyback Regulator
Improved output voltage tolerance and regulation specifications are possible by combining the LM3411Awithone of the
SIMPLE SWITCHER buck regulator IC’s, such as the
LM2574, LM2575, or LM2576. The circuit shown in
can provide a 5V,±0.5%Output (1%over the operating temperature range) without using any trim-pots or precision resistors. Typical line regulation numbers area1mVchange
on the output for a 8V–18V change on the input, and load
regulation of 1 mV with a load change from 100 mA–1A.
A DC-DC flyback converter that accepts a negative input
voltage, and delivers either a positive or negative output is
shown in
Figure 6
as the LM2574, LM2575, or LM2576, depending on how
much output current is needed) operating in a flyback configuration. The LM3411 provides the reference and the required level shifting circuitry needed to make the circuit work
correctly.
A unique feature of this circuit is the ability to ground either
the high or low side of the output, thus generating either a
negative or a positive output voltage. Although no isolation is
. The circuit utilizes a buck regulator (such
Figure 5
DS011987-18
provided, with the addition of an opto-isolator and related
components, this circuit could provide input/output isolation.
Combining a LM3411A-5.0with a 1A low dropout linear regulator results in a 5V
ture range) regulator with excellent regulation specifications,
with no trimming or 1%resistors needed.
An added benefit of this circuit (and also true of many of the
other circuits shown here) is the high-side and low-side remote output voltage sensing feature. Sensing the output
voltage at the load eliminates the voltage drops associated
with wire resistance, thus providing near perfect load regulation.
A 5V, 1A regulator circuit featuring low dropout, very good
regulation specifications, self protection features and allows
output voltage sensing is shown in
used is a LM2941 adjustable low dropout positive regulator,
which also features an ON/OFF pin to provide a shutdown
feature.
±
0.5%(1%over the operating tempera-
Figure 7
. The regulator
www.national.com9
Page 10
Applications Information (Continued)
LM3411
FIGURE 7. Precision 5V 1A Low Dropout Regulator
FIGURE 8. 3.3V 0.5A Low Dropout Regulator
Figure 8
The circuit in
using the LM3411-3.3 and several discrete components.
shows a 3.3V low dropout regulator
DS011987-20
DS011987-19
This circuit is capable of excellent performance with both the
dropout voltage and the ground pin current specifications improved over the LM2941/LM3411 circuit.
The standard LM317 three terminal adjustable regulator circuit can greatly benefit by adding a LM3411. Performance is
increased and features are added. The circuit shown in
ure 9
provides much improved line and load regulation,
Fig-
lower temperature drift, and full remote output voltage sensing on both the high and low side. In addition, a precise current limit or constant current feature is simple to add.
Current limit protection in most IC regulators is mainly to protect the IC from gross over-current conditions which could
otherwise fuse bonding wires or blow IC metalization, therefore not much precision is needed for the actual current limit
values. Current limit tolerances can sometimes vary from
±
10%to as high as +300%over manufacturing and temperature variations. Often critical circuitry requires a much
tighter control over the amount of current the power supply
can deliver. For example, a power supply may be needed
that can deliver 100%of its design current, but can still limit
the maximum current to 110%to protect critical circuitry from
high current fault conditions.
The circuit in
that is better than
Figure 9
can provide a current limit accuracy
±
4%, over all possible variations, in addition to having excellent line, load and temperature
specifications.
FIGURE 9. Precision Positive Voltage Regulator with Accurate Current Limit
Like the positive regulators, the performance of negative adjustable regulators can also be improved by adding the
LM3411. Output voltages of either 3.3V or 5V at currents up
to 1.5A (3A when using a LM333) are possible. Adding two
www.national.com10
DS011987-21
resistors to the circuit in
Figure 10
limit feature as shown in
±
of
4%over manufacturing and temperature variations are
adds the precision current
Figure 11
. Current limit tolerances
possible with this circuit.
Page 11
Applications Information (Continued)
DS011987-22
FIGURE 10. Precision Negative Voltage Regulator
DS011987-23
FIGURE 11. Precision Negative Voltage
Regulator with Accurate Current Limit
Figure 12
Asimple 5V supply monitor circuit is shown in
ing the LM3411’s voltage reference, op-amp (as a comparator) and output driver,this circuit provides a LED indication of
the presence of the 5V supply.
. Us-
DS011987-25
FIGURE 13.±50 mV External Trim
The LM3411 is guaranteed to drive a 15 mA load, but if more
current is needed, a NPN boost transistor can be added. The
circuit shown in
Figure 14
is a shunt regulator capable of pro-
viding excellent regulation over a very wide range of current.
DS011987-26
FIGURE 14. 250 mA Shunt Regulator
Perhaps one of the simplest applications for the LM3411 is
the voltage detector circuit shown in
Figure 15
is low when the input voltage is less than V
V(IN) pin rises above V
internal NPN output resistor.
, the OUT pin is pulled high by the
REG
. The OUT pin
. When the
REG
LM3411
DS011987-24
FIGURE 12. 4.7V Power ON Detector with Hysteresis
±
The LM3411 initial room temperature tolerance is
±
0.5%for the “A” grade part. If a tighter tolerance is needed,
a trim scheme is shown in
±
mately
1%adjustment range of the regulation voltage
(V
).
REG
Figure 13
that provides approxi-
1%and
DS011987-27
FIGURE 15. Voltage Detector
Also an overvoltage detector, the crowbar circuit shown in
Figure 16
is normally located at the output of a power supply
to protect the load from an overvoltage condition should the
power supply fail with an input/output short.
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
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.
labeling, can be reasonably expected to result in a
significant injury to the user.
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.