Datasheet LM1084ISX-12, LM1084IS-ADJ, LM1084IS-5.0, LM1084IS-12, LM1084IT-ADJ Datasheet (NSC)
...Page 1
LM1084
5A Low Dropout Positive Regulators
LM1084 5A Low Dropout Positive Regulators
September 1999
General Description
The LM1084 is a series of low dropout voltage positive regulators with a maximum dropout of 1.5V at 5A of load current.
It has thesamepin-out as National Semiconductor’s industry
standard LM317.
The LM1084 is available in an adjustable version, which can
set the output voltage with only two external resistors. It is
also available in three fixed voltages: 3.3V, 5.0V and 12.0V.
The fixed versions intergrate the adjust resistors.
The LM1084 circuit includes a zener trimmed bandgap reference, current limiting and thermal shutdown.
The LM1084 series is available in TO-220 and TO-263 packages.
Connection Diagrams
TO-220
DS100946-36
Top View
Features
n Available in 3.3V, 5.0V, 12V and Adjustable Versions
n Current Limiting and Thermal Protection
n Output Current 5A
n Industrial Temperature Range −40˚C to 125˚C
n Line Regulation 0.015%(typical)
n Load Regulation 0.1%(typical)
Applications
n Post Regulator for Switching DC/DC Conveter
n High Efficiency Linear Regulators
n Battery Charger
TO-263
DS100946-35
Top View
Basic Functional Diagram, Adjustable Version
DS100946-65
© 1999 National Semiconductor Corporation DS100946 www.national.com
Page 2
Ordering Information
Package Temperature Range Part Number Transport Media NSC Drawing
3-lead TO-263 −40˚C to +125˚C LM1084IS-ADJ Rails
LM1084ISX-ADJ Tape and Reel
LM1084IS-12 Rails
LM1084ISX-12 Tape and Reel
LM1084IS-3.3 Rails
LM1084ISX-3.3 Tape and Reel
LM1084IS-5.0 Rails
LM1084ISX-5.0 Tape and Reel
3-lead TO-220 −40˚C to + 125˚C LM1084IT-ADJ Rails
LM1084IT-12 Rails
LM1084IT-3.3 Rails
LM1084IT-5.0 Rails
Simplified Schematic
TS3B
T03B
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DS100946-34
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.
Junction Temperature (T
)(Note 3) 150˚C
J
Storage Temperature Range -65˚C to 150˚C
Lead Temperature 260˚C, to 10 sec
ESD Tolerance (Note 4) 2000V
Maximum Input to Output Voltage Differential
LM1084-ADJ 29V
LM1084-12 18V
LM1084-3.3 27V
LM1084-5.0 25V
Operating Ratings (Note 1)
Junction Temperature Range (T
Control Section −40˚C to 125˚C
Output Section −40˚C to 150˚C
) (Note 3)
J
Power Dissipation (Note 2) Internally Limited
Electrical Characteristics
Typicals and limits appearing in normal type apply for TJ= 25˚C. Limits appearing in Boldface type apply over the entire
junction temperature range for operation.
Symbol Parameter Conditions
V
REF
Reference
Voltage
LM1084-ADJ
=
10mA, V
I
OUT
10mA ≤I
OUT
25V
IN−VOUT
≤ I
FULL LOAD
=
3V
,1.5V ≤ (VIN−V
(Note 7)
V
OUT
Output Voltage
(Note 7)
LM1084-3.3
=
0mA, V
I
OUT
0 ≤ I
OUT≤IFULL LOAD
=
8V
IN
, 4.8V≤ VIN≤15V
LM1084-5.0
I
OUT
0 ≤ I
=
OUT
0mA, V
≤ I
FULL LOAD
=
8V
IN
, 6.5V ≤ VIN≤ 20V
LM1084-12
∆V
OUT
Line Regulation
(Note 8)
=
I
0mA, V
OUT
0 ≤ I
OUT
LM1084-ADJ
=
10mA, 1.5V≤ (V
I
OUT
≤ I
FULL LOAD
=
15V
IN
, 13.5V ≤ VIN≤ 25V
IN-VOUT
LM1084-3.3
I
OUT
=
0mA, 4.8V ≤ V
IN
≤ 15V
LM1084-5.0
I
OUT
=
0mA, 6.5V ≤ V
IN
≤ 20V
LM1084-12
∆V
OUT
Load Regulation
(Note 8)
=
I
0mA, 13.5V ≤ V
OUT
LM1084-ADJ
(V
IN-VOUT
)=3V, 10mA ≤ I
IN
≤ 25V
OUT
LM1084-3.3
=
5V, 0 ≤ I
V
IN
OUT
≤ I
FULL LOAD
LM1084-5.0
=
8V, 0 ≤ I
V
IN
OUT
≤ I
FULL LOAD
LM1084-12
Dropout Voltage
(Note 9)
=
15V, 0 ≤ I
V
IN
LM1084-3.3/5/12/ADJ
=
1%,I
∆V
REF
≤ I
OUT
FULL LOAD
=
5A 1.3 1.5 V
OUT
) ≤ 15V
≤ I
FULL LOAD
OUT
) ≤
Min
(Note
6)
1.238
1.225
3.270
3.235
4.950
4.900
11.880
11.760
Typ
(Note
5)
1.250
1.250
3.300
3.300
5.000
5.000
12.000
12.000
0.015
0.035
0.5
1.0
0.5
1.0
1.0
2.0
0.1
0.2
3
7
5
10
12
24
Max
(Note6)Units
1.262
1.270
3.330
3.365
5.050
5.100
12.120
12.240VV
0.2
0.2
6
6
10
10
25
25
0.3
0.4
15
20
20
35
36
72
V
V
V
V
V
V
%
%
mV
mV
mV
mV
mV
mV
%
%
mV
mV
mV
mV
mV
mV
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Page 4
Electrical Characteristics (Continued)
Typicals and limits appearing in normal type apply for TJ= 25˚C. Limits appearing in Boldface type apply over the entire
junction temperature range for operation.
Symbol Parameter Conditions
I
LIMIT
Current Limit LM1084-ADJ
V
IN−VOUT
V
IN−VOUT
=
5V
=
25V
Min
(Note
6)
5.5
0.3
LM1084-3.3
=
8V 5.5 8.0 A
V
IN
LM1084-5.0
=
V
10V 5.5 8.0 A
IN
LM1084-12
=
17V 5.5 8.0 A
V
Minimum Load
Current (Note
10)
Quiescent
Current
IN
LM1084-ADJ
=
V
IN−VOUT
25V
LM1084-3.3
=
18V 5.0 10.0 mA
V
IN
LM1084-5.0
≤ 20V 5.0 10.0 mA
V
IN
LM1084-12
≤ 25V 5.0 10.0 mA
V
IN
Thermal
Regulation
Ripple Rejection f
Adjust Pin
=
T
25˚C, 30ms Pulse 0.003 0.015
A
=
120Hz,=C
RIPPLE
=
5A
LM1084-3.3, V
LM1084-5.0, V
LM1084-12 V
ADJ
IN
IN
=
IN
=
25µF Tantalum, I
OUT
,=25µF, (VIN−VO)=3V
=
6.3V 60 72 dB
=
8V 60 68 dB
OUT
60 75 dBLM1084-ADJ, C
15V 54 60 dB
LM1084 55 120 µA
Current
Adjust Pin
Current Change
10mA ≤ I
1.5V ≤ V
≤ I
OUT
IN−VOUT
FULL LOAD
≤ 25V
,
Temperature
Stability
Long Term
Stability
RMS Output
=
T
125˚C, 1000Hrs
A
10Hz ≤ f≤ 10kHz 0.003
Noise
OUT
)
3-Lead TO-263: Control Section/Output Section
3-Lead TO-220: Control Section/Output Section
(%of V
Thermal
Resistance
Junction-to-Case
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 specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.
Note 2: Power dissipation is kept in a safe range by current limiting circuitry. Refer to Overload Recovery in Application Notes.
Note 3: The maximum power dissipation is a function of T
=(T
is P
D
Note 4: For testing purposes, ESD was applied using human body model, 1.5kΩ in series with 100pF.
Note 5: Typical Values represent the most likely parametric norm.
Note 6: All limits are guaranteed by testing or statistical analysis.
Note 7: I
dissipation for the LM1084 is only achievable over a limited range of input-to-output voltage.
Note 8: Load and line regulation are measured at constant junction temperature, and are guaranteed up to the maximum power dissipation of 30W. Power dissipa-
tion is determined by the input/output differential and the output current. Guaranteed maximum power dissipation will not be available over the full input/output range.
Note 9: Dropout voltage is specified over the full output current range of the device.
)/θJA. All numbers apply for packages soldered directly into a PC board. Refer to Thermal Considerations in the Application Notes.
J(max)–TA
is defined in the current limit curves. The I
FULLLOAD
, θJA, and TA. The maximum allowable power dissipation at any ambient temperature
J(max)
Curve defines the current limit as a function of input-to-output voltage. Note that 30W power
FULLLOAD
Typ
(Note
5)
Max
(Note6)Units
8.0
0.6
5 10.0 mA
0.2 5 µA
0.5
0.3 1.0
0.65/2.7
0.65/2.7
˚C/W
˚C/W
A
A
%
/W
%
%
%
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Electrical Characteristics (Continued)
Note 10: The minimum output current required to maintain regulation.
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Typical Performance Characteristics
Dropout Voltage (VIN−V
Load Regulation
OUT
DS100946-63
DS100946-38
)
Short-Circuit Current
DS100946-71
LM1084-ADJ Ripple Rejection
DS100946-43
LM1084-ADJ Ripple Rejection vs Current
DS100946-90
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Temperature Stability
DS100946-25
Page 7
Typical Performance Characteristics (Continued)
Adjust Pin Current
DS100946-26
LM1084-ADJ LineTransient Response
DS100946-70
LM1084-ADJ Load Transient Response
DS100946-69
Maximum Power Dissipation
DS100946-68
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Page 8
APPLICATION NOTE
General
Figure 1
LM1084-Adj (excluding protection circuitry) . The topology is
basically that of the LM317 except for the pass transistor. Instead of a Darlingtion NPN with its two diode voltage drop,
the LM1084 uses a single NPN. This results in a lower dropout voltage. The structure of the pass transistor is also
known as a quasi LDO. The advantage a quasi LDO over a
PNP LDO is its inherently lower quiescent current. The
LM1084 is guaranteed to provide a minimum dropout voltage 1.5V over temperature, at full load.
FIGURE 1. Basic Functional Diagram for the LM1084,
Output Voltage
The LM1084 adjustable version develops at 1.25V reference
voltage, (V
As shown in figure 2, this voltage is applied across resistor
R1 to generate a constant current I1. This constant current
then flows through R2. The resulting voltage drop across R2
adds to the reference voltage to sets the desired output voltage.
The current I
output error . But since it is small (120uA max), it becomes
negligible when R1 is in the 100Ω range.
For fixed voltage devices, R1 and R2 are integrated inside
the devices.
Stability Consideration
Stability consideration primarily concern the phase response
of the feedback loop. In order for stable operation, the loop
must maintain negative feedback. The LM1084 requires a
certain amount series resistance with capacitive loads. This
series resistance introduces a zero within the loop to in-
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shows a basic functional diagram for the
excluding Protection circuitry
), between the output and the adjust terminal.
REF
from the adjustment terminal introduces an
ADJ
DS100946-17
FIGURE 2. Basic Adjustable Regulator
DS100946-65
crease phase margin and thus increase stability. The equivalent series resistance (ESR) of solid tantalum or aluminum
electrolytic capacitors is used to provide the appropriate zero
(approximately 500 kHz).
The Aluminum electrolytic are less expensive than tantalums, but their ESR varies exponentially at cold temperatures; therefore requiring close examination when choosing
the desired transient response over temperature. Tantalums
are a convenient choice because their ESR varies less than
2:1 over temperature.
The recommended load/decoupling capacitance is a 10uF
tantalum or a 50uF aluminum. These values will assure stability for the majority of applications.
The adjustable versions allows an additional capacitor to be
used at the ADJ pin to increase ripple rejection. If this is done
the output capacitor should be increased to 22uF for tantalums or to 150uF for aluminum.
Capacitors other than tantalum or aluminum can be used at
the adjust pin and the input pin. A 10uF capacitor is a reasonable value at the input. See Ripple Rejection section regarding the value for the adjust pin capacitor.
It is desirable to have large output capacitance for applications that entail large changes in load current (microprocessors for example). The higher the capacitance, the larger the
available charge per demand. It is also desirable to provide
low ESR to reduce the change in output voltage:
∆V=∆I x ESR
It is common practice to use several tantalum and ceramic
capacitors in parallel to reduce this change in the output voltage by reducing the overall ESR.
Output capacitance can be increased indefinitely to improve
transient response and stability.
Ripple Rejection
Ripple rejection is a function of the open loop gain within the
feed-back loop (refer to
Figure 1
and
Figure 2
). The LM1084
exhibits 75dB of ripple rejection (typ.). When adjusted for
voltages higher than V
function of adjustment gain: (1+R1/R2) or V
fore a 5V adjustment decreases ripple rejection by a factor of
, the ripple rejection decreases as
REF
O/VREF
. There-
four (−12dB); Output ripple increases as adjustment voltage
increases.
However, the adjustable version allows this degradation of
ripple rejection to be compensated. The adjust terminal can
be bypassed to ground with a capacitor (C
ance of the C
desired ripple frequency. This bypass capacitor prevents
should be equal to or less than R1 at the
ADJ
). The imped-
ADJ
ripple from being amplified as the output voltage is increased.
*
f
RIPPLE
*
C
) ≤ R
ADJ
1
1/(2π
Load Regulation
The LM1084 regulates the voltage that appears between its
output and ground pins, or between its output and adjust
pins. In some cases, line resistances can introduce errors to
the voltage across the load. To obtain the best load regulation, a few precautions are needed.
Figure 3
regulator.Rt1 and Rt2 are the line resistances. V
than the V
resistances. In this case, the load regulation seen at the
R
shows a typical application using a fixed output
by the sum of the voltage drops along the line
OUT
would be degraded from the data sheet specification.
LOAD
LOAD
is less
Page 9
APPLICATION NOTE (Continued)
To improve this, the load should be tied directly to the output
terminal on the positive side and directly tied to the ground
terminal on the negative side.
DS100946-18
FIGURE 3. Typical Application using Fixed Output
When the adjustable regulator is used (
performance is obtained with the positive side of the resistor
R1 tied directly to the output terminal of the regulator rather
than near the load. This eliminates line drops from appearing
effectively in series with the reference and degrading regulation. For example, a 5V regulator with 0.05Ω resistance between the regulator and load will have a load regulation due
to line resistance of 0.05Ω xI
near the load the effective line resistance will be 0.05Ω (1 +
R2/R1) or in this case, it is 4 times worse. In addition, the
ground side of the resistor R2 can be returned near the
ground of the load to provide remote ground sensing and improve load regulation.
FIGURE 4. Best Load Regulation using Adjustable
3.0 Protection Diodes
Under normal operation, the LM1084 regulator does not
need any protection diode. With the adjustable device, the
internal resistance between the adjustment and output terminals limits the current. No diode is needed to divert the current around the regulator even with a capacitor on the adjustment terminal. The adjust pin can take a transient signal of
±
25V with respect to the output voltage without damaging
the device.
When an output capacitor is connected to a regulator and
the input is shorted, the output capacitor will discharge into
the output of the regulator. The discharge current depends
on the value of the capacitor, the output voltage of the regulator, and rate of decrease of V
the internal diode between the output and input pins can
Regulator
.IfR1(=125Ω) is connected
L
Output Regulator
. In the LM1084 regulator,
IN
Figure 4
), the best
DS100946-19
withstand microsecond surge currents of 10A to 20A. With
an extremely large output capacitor (≥1000 µf), and with input instantaneously shorted to ground, the regulator could
be damaged. In this case, an external diode is recommended between the output and input pins to protect the
regulator, shown in
Figure 5
.
DS100946-15
FIGURE 5. Regulator with Protection Diode
Overload Recovery
Overload recovery refers to regulator’s ability to recover from
a short circuited output. A key factor in the recovery process
is the current limiting used to protect the output from drawing
too much power. The current limiting circuit reduces the output current as the input to output differential increases. Refer
to short circuit curve in the curve section.
During normal start-up, the input to output differential is
small since the output follows the input. But, if the output is
shorted, then the recovery involves a large input to output
differential. Sometimes during this condition the current limiting circuit is slow in recovering. If the limited current is too
low to develop a voltage at the output, the voltage will stabilize at a lower level. Under these conditions it may be necessary to recycle the power of the regulator in order to get the
smaller differential voltage and thus adequate start up conditions. Refer to curve section for the short circuit current vs.
input differential voltage.
Thermal Considerations
ICs heats up when in operation, and power consumption is
one factor in how hot it gets. The other factor is how well the
heat is dissipated. Heat dissipation is predictable by knowing
the thermal resistance between the IC and ambient (θ
Thermal resistance has units of temperature per power
JA
(C/W). The higher the thermal resistance, the hotter the IC.
The LM1084 specifies the thermal resistance for each pack-
age as junction to case (θ
tance to ambient (θ
added, one for case to heat-sink (θ
to ambient (θ
as follows:
=
T
T
J
). The junction temperature can be predicted
HA
A+PD(θJC
). In order to get the total resis-
JC
), two other thermal resistance must be
JA
+ θCH+ θHA)=TA+PDθ
) and one for heatsink
CH
JA
TJis junction temperature, TAis ambient temperature, and
P
is the power consumption of the device. Device power
D
consumption is calculated as follows:
=
I
I
IN
L+IG
=
P
(V
D
IN−VOUT)IL+VINIG
).
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Page 10
APPLICATION NOTE (Continued)
Figure 6
shows the voltages and currents which are present
in the circuit.
DS100946-16
FIGURE 6. Power Dissipation Diagram
Once the devices power is determined, the maximum allowable (θ
θ
JA (max)
The LM1084 has different temperature specifications for two
different sections of the IC: the control section and the output
section. The Electrical Characteristics table shows the junction to case thermal resistances for each of these sections,
while the maximum junction temperatures (T
section is listed in the Absolute Maximum section of the
datasheet. T
(max)
θ
JA (max)
follows:
θ
(max, CONTROL SECTION)=(125˚C - T
JA
θJA(max, OUTPUT SECTION)=(150˚C - T
The required heat sink is determined by calculating its required thermal resistance (θ
θ
HA (max)
(θ
HA (max)
(θ
HA (max)
TROL SECTION) + θ
(θ
HA (max)
SECTION) + θ
If thermal compound is used, θ
C/W. If the case is soldered to the heat sink, then a θ
be estimated as 0 C/W.
After, θ
lower of the two θ
ate heat sink.
If PC board copper is going to be used as a heat sink, then
Figure 7
(size) of copper foil required.
) is calculated as:
JA (max)
=
T
R(max)/PD
J(max)
is 150˚C for the output section.
=
T
J(max)−TA(max)/PD
J(max)
is 125˚C for the control section, while T
should be calculated separately for each section as
A(max)
A(max))PD
).
=
θ
JA (max)
HA (max)
−(θJC+ θCH)
) should also be calculated twice as follows:
)=θJA(max, CONTROL SECTION) - (θJC(CON-
)
CH
)=θJA(max, OUTPUT SECTION) - (θJC(OUTPUT
)
CH
is calculated for each section, choose the
HA (max)
HA (max)
can be estimated at 0.2
CH
values to determine the appropri-
can be used to determine the appropriate area
) for each
)/P
D
can
CH
-
J
DS100946-64
FIGURE 7. Heat sink thermal Resistance vs Area
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Page 11
Typical Applications
5V to 3.3V, 5A Regulator
1.2V to 15V Adjustable Regulator
DS100946-67
DS100946-50
Adjustable@5V
DS100946-53
5V Regulator with Shutdown
DS100946-52
Battery Charger
Regulator with Reference
DS100946-54
DS100946-56
DS100946-55
Adjustable Fixed Regulator
DS100946-57
High Current Lamp Driver Protection
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Page 12
Typical Applications (Continued)
Battery Backup Regulated Supply
Automatic Light control
DS100946-59
DS100946-61
Remote Sensing
DS100946-60
Ripple Rejection Enhancement
DS100946-62
Generating Negative Supply voltage
DS100946-58
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Page 13
Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LM1084S-ADJ, LM1084S-3.3, LM1084S-5.0, or LM1084S-12
3-Lead TO-263 Package
NSC Package Number TS3B
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Page 14
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
LM1084 5A Low Dropout Positive Regulators
Order Number LM1084T-ADJ, LM1084T-3.3, LM1084T-5.0, or LM1084T-12
3-Lead TO-220 Package
NSC Package Number T03B
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