Datasheet LM1086CT-5.0, LM1086CT-3.3, LM1086CT-2.85, LM1086CSX-5.0, LM1086CSX-2.85 Datasheet (NSC)
...Page 1
LM1086
1.5A Low Dropout Positive Regulators
1.5A Low Dropout Positive Regulators
August 1999
General Description
The LM1086 is a series of low dropout positive voltage regulators with a maximum dropout of 1.5V at 1.5A of load current. It has the same pin-out asNationalSemiconductor’sindustry standard LM317.
The LM1086 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: 2.85V, 3.3V and 5.0V.
The fixed versions integrate the adjust resistors.
The LM1086 circuit includes a zenertrimmedbandgapreference, current limiting and thermal shutdown.
The LM1086 series is available inTO-220andTO-263 packages. D-Pak is available upon special request; contact the
National Semiconductor sales representative in your area.
Connection Diagrams
TO-220
DS100948-2
Top View
Features
n Available in 2.85V, 3.3V, 5V andAdjustable Versions
n Current Limiting and Thermal Protection
n Output Current 1.5A
n Line Regulation 0.015%(typical)
n Load Regulation 0.1%(typical)
Applications
n SCSI-2 Active Terminator
n High Efficiency Linear Regulators
n Battery Charger
n Post Regulation for Switching Supplies
n Constant Current Regulator
n Microprocessor Supply
TO-263
DS100948-4
Top View
Note: D-Pak package also available. Contact National Semiconductor sales
representative in your area.
Basic Functional Diagram, Adjustable Version
DS100948-65
© 1999 National Semiconductor Corporation DS100948 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 LM1086IS-ADJ Rails
LM1086ISX-ADJ Tape and Reel
LM1086IS-2.85 Rails
LM1086ISX-2.85 Tape and Reel
LM1086IS-3.3 Rails
LM1086ISX-3.3 Tape and Reel
LM1086IS-5.0 Rails
LM1086ISX-5.0 Tape and Reel
0˚C to +125˚C LM1086CS-ADJ Rails
LM1086CSX-ADJ Tape and Reel
LM1086CS-2.85 Rails
LM1086CSX-2.85 Tape and Reel
LM1086CS-3.3 Rails
LM1086CSX-3.3 Tape and Reel
LM1086CS-5.0 Rails
LM1086CSX-5.0 Tape and Reel
3-lead TO-220 −40˚C to +125˚C LM1086IT-ADJ Rails
LM1086IT-2.85 Rails
LM1086IT-3.3 Rails
LM1086IT-5.0 Rails
0˚C to +125˚C LM1086CT-ADJ Rails
LM1086CT-2.85 Rails
LM1086CT-3.3 Rails
LM1086CT-5.0 Rails
Note: D-Pak package also available. Contact National Semiconductor sales representative in your area.
TS3B
T03B
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Page 3
Simplified Schematic
DS100948-34
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Page 4
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
Lead Temperature 260˚C, to 10 sec
ESD Tolerance (Note 4) 2000V
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Maximum Input-to-Output Voltage Differential
LM1086-ADJ 29V
LM1086-2.85 27V
LM1086-3.3 27V
LM1086-5.0 25V
Power Dissipation (Note 2) Internally Limited
Junction Temperature (T
)(Note 3) 150˚C
J
Operating Ratings (Note 1)
Junction Temperature Range (T
″C″ Grade
Control Section 0˚C to 125˚C
Output Section 0˚C to 150˚C
″I″ Grade
Control Section −40˚C to 125˚C
Output Section −40˚C to 150˚C
) (Note 3)
J
Storage Temperature Range -65˚C to 150˚C
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
V
OUT
Reference
Voltage
Output Voltage
(Note 7)
LM1086-ADJ
=
10mA, V
I
OUT
10mA ≤I
OUT
(Note 7)
LM1086-2.85
=
0mA, V
I
OUT
0 ≤ I
OUT≤IFULL LOAD
IN−VOUT
≤ I
FULL LOAD
=
5V
IN
, 4.35V≤ VIN≤18V
=
3V
,1.5V ≤ VIN−V
LM1086-3.3
I
OUT
0 ≤ I
=
OUT
0mA, V
≤ I
FULL LOAD
=
5V
IN
, 4.75V ≤ VIN≤18V
LM1086-5.0
∆V
OUT
Line Regulation
(Note 8)
=
0mA, V
I
OUT
0 ≤ I
OUT
LM1086-ADJ
=
10mA, 1.5V≤ (V
I
OUT
≤ I
FULL LOAD
=
8V
IN
, 6.5V ≤ VIN≤20V
IN-VOUT
LM1086-2.85
=
I
OUT
0mA, 4.35V ≤ V
IN
≤ 18V
LM1086-3.3
I
OUT
=
0mA, 4.5V ≤ V
IN
≤ 18V
LM1086-5.0
∆V
OUT
Load Regulation
(Note 8)
=
I
0mA, 6.5V ≤ V
OUT
LM1086-ADJ
(V
IN-VOUT
)=3V, 10mA ≤ I
IN
≤ 20V
LM1086-2.85
=
5V, 0 ≤ I
V
IN
OUT
≤ I
FULL LOAD
LM1086-3.3
=
5V, 0 ≤ I
V
IN
OUT
≤ I
FULL LOAD
LM1086-5.0
Dropout Voltage
(Note 9)
=
8V, 0 ≤ I
V
IN
LM1086-2.85/3.3/5/ADJ
=
1%,I
∆V
REF
≤ I
OUT
FULL LOAD
=
1.5A 1.3 1.5 V
OUT
) ≤ 15V
OUT
≤ I
FULL LOAD
OUT
≤ 15V
Min
(Note
1.238
1.225
2.82
2.79
3.267
3.235
4.950
4.900
Typ
(Note
6)
1.250
1.250
2.85
2.85
3.300
3.300
5.000
5.000
0.015
0.035
0.3
0.6
0.5
1.0
0.5
1.0
0.1
0.2
5)
3
6
3
7
5
10
Max
(Note6)Units
1.262
1.270VV
2.88
2.91
3.333
3.365VV
5.050
5.100VV
0.2
0.2
6
6
10
10
10
10
0.3
0.4
12
20
15
25
20
35
V
V
%
%
mV
mV
mV
mV
mV
mV
%
%
mV
mV
mV
mV
mV
mV
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Page 5
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 LM1086-ADJ
V
IN−VOUT
V
IN−VOUT
=
5V
=
25V
Min
(Note
1.50
0.05
LM1086-2.85
=
8V 1.5 2.7 A
V
IN
LM1086-3.3
=
V
8V 1.5 2.7 A
IN
LM1086-5.0
=
10V 1.5 2.7 A
V
Minimum Load
Current (Note 10)
Quiescent
Current
IN
LM1086-ADJ
=
V
IN−VOUT
25V 5.0 10.0 mA
LM1086-2.85
≤ 18V 5.0 10.0 mA
V
IN
LM1086-3.3
≤ 18V 5.0 10.0 mA
V
IN
LM1086-5.0
≤ 20V 5.0 10.0 mA
V
IN
Thermal
Regulation
Ripple Rejection f
Adjust Pin
=
T
25˚C, 30ms Pulse 0.008 0.04
A
=
120Hz, C
RIPPLE
1.5A
LM1086-2.85, V
LM1086-3.3, V
LM1086-5.0 V
IN
=
25µF Tantalum, I
OUT
=
25µF, (V
ADJ
=
6V 60 72 dB
IN
=
6.3V 60 72 dB
IN
=
8V 60 68 dB
IN−VO
)=3V
OUT
=
LM1086 55 120 µA
Current
Adjust Pin
Current Change
10mA ≤ I
OUT
≤ I
FULL LOAD
, 1.5V ≤ (VIN−V
OUT
) ≤ 15V
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
sipation for the LM1086 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 15W. 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.
Note 10: The minimum output current required to maintain regulation.
)/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
FULL LOAD
, θJA, and TA. The maximum allowable power dissipation at any ambient temperature
J(max)
Curve defines current limit as a function of input-to-output voltage. Note that 15W power dis-
FULL LOAD
Typ
(Note
6)
5)
Max
(Note6)Units
2.7
0.15
60 75 dBLM1086-ADJ, C
0.2 5 µA
0.5
0.3 1.0
1.5/4.0
1.5/4.0
A
A
%
/W
%
%
%
˚C/W
˚C/W
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Typical Performance Characteristics
Dropout Voltage vs
Output Current
Load Regulation vs
Temperature
DS100948-63
Short-Circuit Current vs
Input/Output Difference
DS100948-37
Percent Change in Output Voltage
vs Temperature
DS100948-38
Adjust Pin Current
vs Temperature
DS100948-98
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DS100948-99
Maximum Power Dissipation
vs Temperature
DS100948-42
Page 7
Typical Performance Characteristics (Continued)
Ripple Rejection vs
Frequency (LM1086-Adj.)
Ripple Rejection vs
Frequency (LM1086-5)
DS100948-43
Ripple Rejection vs
Output Current (LM1086-Adj.)
DS100948-44
Ripple Rejection vs
Output Current (LM1086-5)
Line Transient Response
DS100948-45
DS100948-47
DS100948-46
Load Transient Response
DS100948-48
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APPLICATION NOTE
General
Figure 1
LM1086-Adj (excluding protection circuitry) . The topologyis
basically that of the LM317 except for the pass transistor. Instead of a Darlingtion NPN with its two diode voltage drop,
the LM1086 uses a single NPN. This results in alower 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
LM1086 is guaranteed to provide a minimum dropout voltage 1.5V over temperature, at full load.
FIGURE 1. Basic Functional Diagram for the LM1086,
Output Voltage
The LM1086 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 outputvoltage.
The current I
output error . But since it is small (120uAmax), 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 LM1086 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
DS100948-17
FIGURE 2. Basic Adjustable Regulator
DS100948-65
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 beincreased indefinitely to improve
transient response and stability.
Ripple Rejection
Ripple rejection is a function of the open loop gainwithin the
feed-back loop (refer to
Figure 1
and
Figure 2
). The LM1086
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 LM1086 regulates the voltage that appears between its
output and ground pins, or between its output and adjust
pins. In some cases, line resistances canintroduce 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 directlyto the output
terminal on the positive side and directly tied to the ground
terminal on the negative side.
DS100948-18
FIGURE 3. Typical Application using Fixed Output
When the adjustable regulator is used (
performance is obtained with the positive sideof 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 andload 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 LM1086 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 LM1086 regulator,
IN
Figure 4
), the best
DS100948-19
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
.
DS100948-15
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 reducesthe 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 avoltage 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 factoris 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 LM1086 specifies the thermalresistance 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.
DS100948-16
FIGURE 6. Power Dissipation Diagram
Once the device power is determined, the maximum allowable (θ
θ
JA (max)
The LM1086 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
JA
θJA(max, OUTPUT SECTION)=(150˚C for 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 issoldered 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)
)/P
D
J(max)
is 125˚C for the control section, while T
should be calculated separately for each section as
(max, CONTROL SECTION)=(125˚C for T
A(max)
).
=
θ
JA(max)
HA(max)
−(θJC+ θCH)
should be calculated twice as follows:
=
(max, CONTROL SECTION) - (θJC(CON-
θ
=
θ
HA (max)
JA
JA
)
CH
(max, OUTPUT SECTION) - (θJC(OUTPUT
)
CH
can be estimated at 0.2
CH
is calculated for each section, choose the
values to determine the appropri-
HA (max)
can be used to determine the appropriate area
) for each
A(max)
)/P
CH
)/P
D
D
can
-
J
DS100948-64
FIGURE 7. Heat sink thermal Resistance vs Area
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Page 11
Typical Applications
5V to 3.3V, 1.5A Regulator
1.2V to 15V Adjustable Regulator
DS100948-49
DS100948-50
Adjustable@5V
DS100948-53
5V Regulator with Shutdown
DS100948-52
Battery Charger
Regulator with Reference
DS100948-54
DS100948-56
DS100948-55
Adjustable Fixed Regulator
DS100948-57
High Current Lamp Driver Protection
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Page 12
Typical Applications (Continued)
Battery Backup Regulated Supply
DS100948-59
Automatic Light control
Remote Sensing
DS100948-60
Ripple Rejection Enhancement
DS100948-61
DS100948-58
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Page 13
Typical Applications (Continued)
DS100948-51
SCSI-2 Active termination
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Page 14
Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LM1086S-ADJ, LM1086S-3.3, LM1086S-5.0, or LM1086S-12
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3-Lead TO-263 Package
NSC Package Number TS3B
Page 15
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
1.5A Low Dropout Positive Regulators
Order Number LM1086T-ADJ, LM1086T-3.3, LM1086T-5.0, or LM1086T-12
3-Lead TO-220 Package
NSC Package Number T03B
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