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LM317L
3-Terminal Adjustable Regulator
LM317L 3-Terminal Adjustable Regulator
March 2000
General Description
The LM317L is an adjustable 3-terminal positive voltage
regulator capable of supplying 100mA over a 1.2V to 37V
output range. It is exceptionally easy to use and requires
only two external resistors to set the output voltage. Further,
both line and load regulation are better than standard fixed
regulators.Also, the LM317L is available packaged in a standard TO-92 transistor package which is easy to use.
In addition to higher performance than fixed regulators, the
LM317L offers full overload protection. Included on the chip
are current limit, thermal overload protection and safe area
protection.All overload protection circuitry remains fully functional even if the adjustment terminal is disconnected.
Normally,no capacitors are needed unless the device is situated more than 6 inches from the input filter capacitors in
which case an input bypass is needed. An optional output
capacitor can be added to improve transient response. The
adjustment terminal can be bypassed to achieve very high
ripple rejection ratios which are difficult to achieve with standard 3-terminal regulators.
Besides replacing fixed regulators, the LM317L is useful in a
wide variety of other applications. Since the regulator is
“floating” and sees only the input-to-output differential voltage, supplies of several hundred volts can be regulated as
long as the maximum input-to-output differential is not exceeded.
Also, it makes an especially simple adjustable switching
regulator,a programmable output regulator, or by connecting
a fixed resistor between the adjustment and output, the
LM317L can be used as a precision current regulator. Supplies with electronic shutdown can be achieved by clamping
the adjustment terminal to ground which programs the output to 1.2V where most loads draw little current.
The LM317L is available in a standard TO-92 transistor
package, the SO-8 package, and 6-Bump micro SMD package. The LM317L is rated for operation over a −25˚C to
125˚C range.
Features
n Adjustable output down to 1.2V
n Guaranteed 100 mA output current
n Line regulation typically 0.01%V
n Load regulation typically 0.1%
n Current limit constant with temperature
n Eliminates the need to stock many voltages
n Standard 3-lead transistor package
n 80 dB ripple rejection
n Available in TO-92, SO-8, or 6-Bump micro SMD
package
n Output is short circuit protected
n See AN-1112 for micro SMD considerations
Connection Diagrams
TO-92 Plastic package
DS009064-4
8-Pin SOIC
DS009064-5
Top View
© 2000 National Semiconductor Corporation DS009064 www.national.com
Connection Diagrams (Continued)
LM317L
6-Bump micro SMD
DS009064-49
*
NC = Not Internally connected.
Top View
(Bump Side Down)
Package Part Number Package Marking Media Transport NSC Drawing
TO-92 LM317LZ LM317LZ 1.8k Units per Box Z03A
8-Pin SOIC LM317LM LM317LM Rails M08A
*
6-Bump micro
SMD
Note: The micro SMD package marking is a single digit manufacturing Date Code only.
LM317LIBP – 250 Units Tape and Reel
*
LM317LIBPX – 3k Units Tape and Reel
micro SMD Laser Mark
DS009064-50
BPA06HPA
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LM317L
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Power Dissipation Internally Limited
Storage Temperature −55˚C to +150˚C
Lead Temperature
(Soldering, 4 seconds) 260˚C
Output is Short Circuit Protected
ESD rating to be determined.
Input-Output Voltage Differential 40V
Operating Junction Temperature
Range −40˚C to +125˚C
Electrical Characteristics (Note 2)
Parameter Conditions Min Typ Max Units
Line Regulation T
Load Regulation T
Thermal Regulation T
Adjustment Pin Current 50 100 µA
Adjustment Pin Current 5mA ≤ I
Change 3V ≤ (V
Reference Voltage 3V ≤ (V
Line Regulation 3V ≤ (V
Load Regulation 5mA ≤ I
Temperature Stability T
Minimum Load Current (V
Current Limit 3V ≤ (V
Rms Output Noise, % of V
OUT
Ripple Rejection Ratio V
Long-Term Stability T
Thermal Resistance Z Package 0.4" Leads 180 ˚C/W
Junction to Ambient Z Package 0.125 Leads 160 ˚C/W
Thermal Rating of SO
Package
Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits.
Note 2: Unless otherwise noted, these specifications apply: −25˚C ≤ T
is internally limited, these specifications are applicable for power dissipations up to 625 mW. I
Note 3: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effectsare covered under the specification for thermal regulation.
Note 4: Thermal resistance of the TO-92 package is 180˚C/W junction to ambient with 0.4" leads from a PC board and 160˚C/W junction to ambient with 0.125" lead
length to PC board.
= 25˚C, 3V ≤ (VIN−V
J
= 25˚C, 5mA ≤ I
J
= 25˚C, 10ms Pulse 0.04 0.2 %/W
J
≤ 100mA 0.2 5 µA
L
IN−VOUT
IN−VOUT
5mA ≤ I
OUT
IN−VOUT
OUT
≤ TJ≤ T
MIN
IN−VOUT
3V ≤ (V
IN−VOUT
IN−VOUT
(V
IN−VOUT
OUT
) ≤ 40V, P ≤ 625mW
) ≤ 40V, (Note 4) 1.20 1.25 1.30 V
≤ 100mA, P ≤ 625mW
) ≤ 40V, IL≤ 20mA (Note 3) 0.02 0.07 %/V
≤ 100mA, (Note 3) 0.3 1.5 %
Max
) ≤ 40V 3.5 5 mA
) ≤ 15V 1.5 2.5
) ≤ 13V 100 200 300 mA
) = 40V 25 50 150 mA
) ≤ 40V, IL≤ 20mA (Note 3) 0.01 0.04 %/V
OUT
≤ I
, (Note 3) 0.1 0.5 %
MAX
0.65 %
TJ= 25˚C, 10Hz ≤ f ≤ 10kHz 0.003 %
= 10V, f = 120Hz, C
OUT
C
= 10µF 66 80 dB
ADJ
= 125˚C, 1000 Hours 0.3 1 %
J
= 0 65 dB
ADJ
SO-8 Package 165 ˚C/W
6-Bump micro SMD 290 ˚C/W
165 ˚C/W
≤ 125˚C for the LM317L; VIN−V
j
MAX
is 100 mA.
OUT
= 5V and I
= 40 mA. Although power dissipation
OUT
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Typical Performance Characteristics (Output capacitor = 0µF unless otherwise noted.)
LM317L
Load Regulation
Current Limit
Adjustment Current
Reference Voltage
Temperature Stability
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Dropout Voltage
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Minimum Operating Current
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Typical Performance Characteristics (Output capacitor = 0µF unless otherwise noted.) (Continued)
LM317L
Ripple Rejection
Output Impedance
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Ripple Rejection
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Line Transient Response
Load Transient Response
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Thermal Regulation
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Application Hints
In operation, the LM317L develops a nominal 1.25V refer-
LM317L
ence voltage, V
minal. The reference voltage is impressed across program
resistor R1 and, since the voltage is constant, a constant
current I
then flows through the output set resistor R2, giv-
1
ing an output voltage of
Since the 100µA current from the adjustment terminal represents an error term, the LM317L was designed to minimize
I
and make it very constant with line and load changes.
ADJ
To do this, all quiescent operating current is returned to the
output establishing a minimum load current requirement. If
there is insufficient load on the output, the output will rise.
, between the output and adjustment ter-
REF
tween 500 pF and 5000 pF. A 1µF solid tantalum (or 25µF
aluminum electrolytic) on the output swamps this effect and
insures stability.
Load Regulation
The LM317L is capable of providing extremely good load
regulation but a few precautions are needed to obtain maximum performance. The current set resistor connected between the adjustment terminal and the output terminal (usually 240Ω) should be tied directly to the output 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 15V regulator with
0.05Ω resistance between the regulator and load will have a
load regulation due to line resistance of 0.05Ω xI
. If the set
L
resistor is connected near the load the effective line resistance will be 0.05Ω (1 + R2/R1) or in this case, 11.5 times
worse.
Figure 2
shows the effect of resistance between the regula-
tor and 240Ω set resistor.
With the TO-92 package, it is easy to minimize the resis-
tance from the case to the set resistor,by using two separate
leads to the output pin. The ground of R2 can be returned
near the ground of the load to provide remote ground sensing and improve load regulation.
DS009064-7
FIGURE 1.
External Capacitors
An input bypass capacitor is recommended in case the regulator is more than 6 inches away from the usual large filter
capacitor.A 0.1µF disc or 1µF solid tantalum on the input is
suitable input bypassing for almost all applications. The device is more sensitive to the absence of input bypassing
when adjustment or output capacitors are used, but the
above values will eliminate the possibility of problems.
The adjustment terminal can be bypassed to ground on the
LM317L to improve ripple rejection and noise. This bypass
capacitor prevents ripple and noise from being amplified as
the output voltage is increased. With a 10µF bypass capacitor 80 dB ripple rejection is obtainable at any output level. Increases over 10µF do not appreciably improve the ripple rejection at frequencies above 120Hz. If the bypass capacitor
is used, it is sometimes necessary to include protection diodes to prevent the capacitor from discharging through internal low current paths and damaging the device.
In general, the best type of capacitors to use is solid tantalum.
Solid tantalum capacitors have low impedance even at
high frequencies.
Depending upon capacitor construction, it
takes about 25µF in aluminum electrolytic to equal 1µF solid
tantalum at high frequencies. Ceramic capacitors are also
good at high frequencies; but some types have a large decrease in capacitance at frequencies around 0.5MHz. For
this reason, a 0.01µF disc may seem to work better than a
0.1µF disc as a bypass.
Although the LM317L is stable with no output capacitors, like
any feedback circuit, certain values of external capacitance
can cause excessive ringing. This occurs with values be-
DS009064-8
FIGURE 2. Regulator with Line Resistance
in Output Lead
Thermal Regulation
When power is dissipated in an IC, a temperature gradient
occurs across the IC chip affecting the individual IC circuit
components. With an IC regulator, this gradient can be especially severe since power dissipation is large. Thermal regulation is the effect of these temperature gradients on output
voltage (in percentage output change) per watt of power
change in a specified time. Thermal regulation error is independent of electrical regulation or temperature coefficient,
and occurs within 5ms to 50ms after a change in power dissipation. Thermal regulation depends on IC layout as well as
electrical design. The thermal regulation of a voltage regulator is defined as the percentage change of V
, per watt,
OUT
within the first 10ms after a step of power is applied. The
LM317L specification is 0.2%/W, maximum.
In the Thermal Regulation curve at the bottom of the Typical
Performance Characteristics page, a typical LM317L’s output changes only 7mV (or 0.07% of V
= −10V) when a
OUT
1W pulse is applied for 10 ms. This performance is thus well
inside the specification limit of 0.2%/W x 1W = 0.2% maximum. When the 1W pulse is ended, the thermal regulation
again showsa7mVchange as the gradients across the
LM317L chip die out. Note that the load regulation error of
about 14 mV (0.14%) is additional to the thermal regulation
error.
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