LT3092
1
Rev. D
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TYPICAL APPLICATION
DESCRIPTION
200mA 2-Terminal
Programmable Current Source
The LT
®
3092 is a programmable 2-terminal current
source. It requires only two resistors to set an output
current between 0.5mA and 200mA. A multitude of analog
techniques lend themselves to actively programming the
output current. The LT3092 is stable without input and
output capacitors, offering high DC and AC impedance. This
feature allows operation in intrinsically safe applications.
The SET pin features 1% initial accuracy and low tem-
perature coefficient. Current regulation is better than
10ppm/V from 1.5V to 40V.
The LT3092 can operate in a 2-terminal current source
configuration in series with signal lines. It is ideal for driv-
ing sensors, remote supplies, and as a precision current
limiter for local supplies.
Internal protection circuitry includes reverse-battery and
reverse-current protection, current limiting and thermal
limiting. The LT3092 is offered in the 8-lead TSOT-23,
3-lead SOT-223 and 8-lead 3mm × 3mm DFN packages.
Adjustable 2-Terminal Current Source
FEATURES
APPLICATIONS
n Programmable 2-Terminal Current Source
n Maximum Output Current: 200mA
n Wide Input Voltage Range: 1.2V to 40V
n Input/Output Capacitors Not Required
n Resistor Ratio Sets Output Current
n Initial Set Pin Current Accuracy: 1%
n Reverse-Voltage Protection
n Reverse-Current Protection
n <0.001%/V Line Regulation Typical
n Current Limit and Thermal Shutdown Protection
n Available in 8-Lead SOT-23, 3-Lead SOT-223 and
8-Lead 3mm × 3mm DFN Packages
n AEC-Q100 Qualified for Automotive Applications
n 2-Terminal Floating Current Source
n GND Referred Current Source
n Variable Current Source
n In-Line Limiter
n Intrinsic Safety Circuits
SET Pin Current vs Temperature
3092 TA01a
IN
SET OUT
+
LT3092
10µA
ROUT
RSET
VIN – VOUT = 1.2V TO 40V
ISOURCE =10µA
R
SET
ROUT
TEMPERATURE (°C)
–50
9.900
SET PIN CURRENT (µA)
9.950
10.000
10.050
–25 025 50 10075 125
10.100
9.925
9.975
10.025
10.075
150
3092 TA01b
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LT3092
2
Rev. D
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PIN CONFIGURATION
ABSOLUTE MAXIMUM RATINGS
IN Pin Voltage Relative to SET, OUT ........................±40V
SET Pin Current (Note 6) ..................................... ±15mA
SET Pin Voltage (Relative to OUT, Note 6) .............. ±10V
Output Short-Circuit Duration .......................... Indefinite
(Note 1) All Voltages Relative to VOUT
TOP VIEW
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 28°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 9) IS OUT, MUST BE SOLDERED TO OUT
ON THE PCB. SEE THE APPLICATIONS INFORMATION SECTION.
5
6
7
8
9
4
3
2
1OUT
OUT
NC
SET
IN
IN
NC
NC
3
2
1
TOP VIEW
TAB IS OUT
IN
OUT
SET
ST PACKAGE
3-LEAD PLASTIC SOT-223
TJMAX = 125°C, θJA = 24°C/W, θJC = 15°C/W
TAB IS OUT, MUST BE SOLDERED TO OUT ON THE PCB.
SEE THE APPLICATIONS INFORMATION SECTION.
NC 1
OUT 2
OUT 3
OUT 4
8 IN
7 IN
6 NC
5 SET
TOP VIEW
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
T
JMAX = 125°C, θJA = 57°C/W, θJC
= 15°C/W
Operating Junction Temperature Range (Notes 2, 8)
E, I Grades ......................................... 40°C to 125°C
MP Grade ........................................... 55°C to 125°C
Storage Temperature Range .................. 65°C to 150°C
Lead Temperature (ST, TS8 Packages Only)
Soldering, 10 sec ..............................................300°C
LT3092
3
Rev. D
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ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3092EDD#PBF LT3092EDD#TRPBF LFJD 8-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
LT3092IDD#PBF LT3092IDD#TRPBF LFJD 8-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
LT3092EST#PBF LT3092EST#TRPBF 3092 3-Lead Plastic SOT-223 –40°C to 125°C
LT3092IST#PBF LT3092IST#TRPBF 3092 3-Lead Plastic SOT-223 –40°C to 125°C
LT3092MPST#PBF LT3092MPST#TRPBF 3092MP 3-Lead Plastic SOT-223 –55°C to 125°C
LT3092ETS8#PBF LT3092ETS8#TRPBF LTFJW 8-Lead Plastic SOT-23 –40°C to 125°C
LT3092ITS8#PBF LT3092ITS8#TRPBF LTFJW 8-Lead Plastic SOT-23 –40°C to 125°C
AUTOMOTIVE PRODUCTS**
LT3092EST#WPBF LT3092EST#WTRPBF 3092 3-Lead Plastic SOT-223 –40°C to 125°C
LT3092IST#WPBF LT3092IST#WTRPBF 3092 3-Lead Plastic SOT-223 –40°C to 125°C
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
**Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These
models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your
local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for
thesemodels.
LT3092
4
Rev. D
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ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Unless otherwise specified, all voltages are with respect to VOUT.
The LT3092E is tested and specified under pulse load conditions such
that TJ @ TA. The LT3092E is 100% tested at TA = 25°C. Performance at
–40°C and 125°C is assured by design, characterization, and correlation
with statistical process controls. The LT3092I is guaranteed to meet all
data sheet specifications over the full –40°C to 125°C operating junction
temperature range. The LT3092MP is 100% tested and guaranteed over
the –55°C to 125°C operating junction temperature range.
Note 3: Minimum load current is equivalent to the quiescent current of
the part. Since all quiescent and drive current is delivered to the output
of the part, the minimum load current is the minimum current required to
maintain regulation.
PARAMETER CONDITIONS MIN TYP MAX UNITS
SET Pin Current ISET VIN = 2V, ILOAD = 1mA
2V ≤ VIN ≤ 40V, 1mA ≤ ILOAD ≤ 200mA
l
9.9
9.8
10
10
10.1
10.2
µA
µA
Offset Voltage (VOUT – VSET) VOS VIN = 2V, ILOAD = 1mA
VIN = 2V, ILOAD = 1mA
l
–2
–4
2
4
mV
mV
Current Regulation (Note 7) ∆ISET
∆VOS
∆ILOAD = 1mA to 200mA
∆ILOAD = 1mA to 200mA
l
–0.1
–0.5
–2
nA
mV
Line Regulation ∆ISET
∆VOS
∆VIN = 2V to 40V, ILOAD = 1mA
∆VIN = 2V to 40V, ILOAD = 1mA
0.03
0.003
0.2
0.010
nA/V
mV/V
Minimum Load Current (Note 3) 2V ≤ VIN ≤ 40V l300 500 µA
Dropout Voltage (Note 4) ILOAD = 10mA
ILOAD = 200mA
l
l
1.22
1.3
1.45
1.65
V
V
Current Limit VIN = 5V, VSET = 0V, VOUT = –0.1V l200 300 mA
Reference Current RMS Output Noise (Note 5) 10Hz ≤ f ≤ 100kHz 0.7 nARMS
Ripple Rejection f = 120Hz, VRIPPLE = 0.5VP-P, ILOAD = 0.1A,
CSET = 0.1µF, COUT = 2.2µF
f = 10kHz
f = 1MHz
90
75
20
dB
dB
dB
Thermal Regulation ISET 10ms Pulse 0.003 %/W
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TJ = 25°C. (Note 2)
Note 4: For the LT3092, dropout is specified as the minimum input-to-
output voltage differential required supplying a given output current.
Note 5: Adding a small capacitor across the reference current resistor
lowers output noise. Adding this capacitor bypasses the resistor shot noise
and reference current noise (see the Applications Information section).
Note 6: Diodes with series 1k resistors clamp the SET pin to the OUT pin.
These diodes and resistors only carry current under transient overloads.
Note 7: Current regulation is Kelvin-sensed at the package.
Note 8: This IC includes overtemperature protection that protects the
device during momentary overload conditions. Junction temperature
exceeds the maximum operating junction temperature when
overtemperature protection is active. Continuous operation above the
specified maximum operating junction temperature may impair device
reliability.
LT3092
5
Rev. D
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TEMPERATURE (°C)
–50
–2.0
OFFSET VOLTAGE (mV)
–1.0
0.0
1.0
–25 025 50 10075 125
2.0
–1.5
–0.5
0.5
1.5
150
3092 G03
INPUT-TO-OUTPUT VOLTAGE (V)
0
–1.00
OFFSET VOLTAGE (mV)
–0.50
0
0.50
510 15 20 3025 35
1.00
–0.75
–0.25
0.25
0.75
40
3092 G05
IOUT = 1mA
TEMPERATURE (°C)
–50
9.900
SET PIN CURRENT (µA)
9.925
9.975
10.000
10.025
10.100
10.075
050 75
3092 G01
9.950
10.050
–25 25 100 125 150
SET PIN CURRENT DISTRIBUTION (µA)
10.20
3092 G02
9.90 10 10.10
9.80
N = 1326
VOS DISTRIBUTION (mV)
2
3092 G04
–1 01
–2
N = 1326
LOAD CURRENT (mA)
0
–400
OFFSET VOLTAGE (µV)
–350
–250
–200
–150
100
–50
100
3092 G06
–300
0
50
–100
50 150 200
TYPICAL PERFORMANCE CHARACTERISTICS
Offset Voltage Distribution Offset Voltage
Offset Voltage Current Regulation
SET Pin Current SET Pin Current Distribution Offset Voltage (VOUT – VSET)
TEMPERATURE (°C)
–50
–80
WITH LOAD (nA)
–70
–50
–40
–30
–10
050 75
3092 G07
–60
0
10
–20
–25 25 100 125 150
∆IOUT = 1mA TO 200mA
VIN – VOUT = 3V
LT3092
6
Rev. D
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TEMPERATURE (°C)
–50
0
MINIMUM OUTPUT CURRENT (µA)
200
300
400
600
050 75
3092 G08
100
500
–25 25 100 125 150
T
J
= –55°C
T
J
= 25°C
T
J
= 125°C
LOAD CURRENT (mA)
0
25
50
75
100
125
150
175
200
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
DROPOUT VOLTAGE (V
IN
– V
OUT
) (V)
3092 G09
I
LOAD
= 200mA
I
LOAD
= 10mA
TEMPERATURE (°C)
–50
–25
0
25
50
75
100
125
150
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
DROPOUT VOLTAGE (V
IN
– V
OUT
) (V)
3092 G10
INPUT-TO-OUTPUT DIFFERENTIAL VOLTAGE (V)
0
0
CURRENT LIMIT (mA)
100
200
300
246 8 10
400
50
150
250
350
3092 G11
TJ = 25°C
TEMPERATURE (°C)
–50
0
CURRENT LIMIT (mA)
50
150
200
250
500
350
050 75
3092 G12
100
400
450
300
–25 25 100 125 150
VIN = 7V
VOUT = 0V
TYPICAL PERFORMANCE CHARACTERISTICS
Current Limit
Line Transient Response Line Transient Response
Dropout Voltage Dropout Voltage
Current Limit
Minimum Output Current
TIME (µs)
0
3092 G13
0
INPUT VOLTAGE (V)
OUTPUT CURRENT
DEVIATION (mA)
8
20 40 60
4
6
–1.0
0
–0.5
0.5
1.0
1.5
2
10 30 80 100
50 70 90
1mA CURRENT SOURCE
CONFIGURATION
TIME (µs)
10
3092 G14
0
INPUT VOLTAGE (V)
OUTPUT CURRENT
DEVIATION (mA)
8
20 40 60
4
6
–10
0
–5
5
10
2
10 30 80 100
50 70 90
10mA CURRENT SOURCE
CONFIGURATION
LT3092
7
Rev. D
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RTEST (Ω)
0
OUTPUT VOLTAGE (mV)
800
700
600
500
400
300
200
100
0
3092 G17
20001000
VIN = 36V
VIN = 5V
SET PIN = 0V
VIN VOUT
RTEST
FREQUENCY (Hz)
0.01
REFERENCE CURRENT
NOISE SPECTRAL DENSITY (pA/√Hz)
100
10k 100k10010 1k
3092 G19
1
0.1
10
TYPICAL PERFORMANCE CHARACTERISTICS
Residual Output for Less Than
Minimum Output Current Output Impedance
Noise Spectral Density
Turn-On ResponseTurn-On Response
FREQUENCY (Hz)
OUTPUT IMPEDANCE (Ω)
100 1k 10k 100k 1M 10M10
100
1k
100M
10M
10
1
1G
100k
10k
1M
3092 G18
ISOURCE = 100mA
ISOURCE =
10mA
ISOURCE = 1mA
VRSET = 100mV
TIME (µs)
8
3092 G15
0
INPUT VOLTAGE (V)
OUTPUT
CURRENT (mA)
6
10 20 30
2
4
0
0.5
1.0
0
515 40 50
25 35 45
1mA CURRENT SOURCE
CONFIGURATION
TIME (µs)
8
3092 G16
0
INPUT VOLTAGE (V)
OUTPUT
CURRENT (mA)
6
10 20 30
2
4
0
5
10
15
0
515 40 50
25 35 45
10mA CURRENT SOURCE
CONFIGURATION
LT3092
8
Rev. D
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PIN FUNCTIONS
(DD/ST/TS8)
IN (Pins 7, 8/Pin 3/Pins 7, 8): Input. This pin supplies
power to bias internal circuitry and supply output load
current. For the device to operate properly and regulate,
the voltage on this pin must be 1.2V to 1.4V above the OUT
pin (depending on output load current—see the dropout
voltage specifications in the Electrical Characteristics
table).
NC (Pins 3, 5, 6/NA/Pins 1, 6): No Connection. These
pins have no connection to internal circuitry and may be
tied to IN, OUT, GND or floated.
OUT (Pins 1, 2/Pin 2/Pins 2, 3, 4): Output. This is the
power output of the device. The minimum current source
value to which the LT3092 can be set is 0.5mA or the
device will not regulate.
SET (Pin 4/Pin 1/Pin 5): Set. This pin is the error ampli-
fier’s noninverting input and also sets the operating bias
point of the circuit. A fixed 10μA current source flows out
of this pin. Two resistors program IOUT as a function of
the resistor ratio relative to 10μA. Output current range
is 0.5mA to the maximum rated 200mA level.
Exposed Pad/Tab (Pin 9/Tab/NA): Output. The Exposed
Pad of the DFN package and the Tab of the SOT-223
package are tied internally to OUT. Tie them directly to
the OUT pins (Pins 1, 2/Pin 2) at the PCB. The amount
of copper area and planes connected to OUT determine
the effective thermal resistance of the packages (see the
Applications Information section).
BLOCK DIAGRAM
+
IN
SET OUT
10µA
3092 BD
LT3092
9
Rev. D
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Introduction
The LT3092 is a versatile IC that operates as a 2-terminal
programmable current source with the addition of only
two external resistors; no external bypass capacitors are
needed for stability.
The LT3092 is easy to use and has all the protection fea-
tures expected in high performance products. Included
are reverse-voltage protection, reverse-current protec
-
tion, short-circuit protection and thermal shutdown with
hysteresis.
The LT3092 operates with or without input and output
capacitors. The simplest current source application
requires only two discrete resistors to set a constant
output current up to 200mA. A variety of analog tech-
niques lend themselves to regulating and varying the cur-
rent source value.
The device utilizes a precision “0” TC 10μA reference cur-
rent source to program output current. This 10µA cur-
rent source connects to the noninverting input of a power
operational amplifier. The power operational amplifier pro-
vides a low impedance buffered output of the voltage on
the noninverting input.
Many application areas exist in which operation without
input and output capacitors is advantageous. A few of
these applications include sensitive circuits that cannot
endure surge currents under fault or overload conditions
and intrinsic safety applications in which safety regula-
tions limit energy storage devices that may spark or arc.
Programming Output Current in 2-Terminal
Current Source Mode
Setting the LT3092 to operate as a 2-terminal current
source is a simple matter. The 10µA reference current
from the SET pin is used with one resistor to generate
a small voltage, usually in the range of 100mV to 1V
(200mV is a level that will help reject offset voltage, line
regulation, and other errors without being excessively
large). This voltage is then applied across a second resis-
tor that connects from OUT to the first resistor. Figure1
shows connections and formulas to calculate a basic cur-
rent source configuration.
APPLICATIONS INFORMATION
With a 10μA current source generating the reference
that gains up to set output current, leakage paths to or
from the SET pin can create errors in the reference and
output currents. High quality insulation should be used
(e.g., Teflon, Kel-F). The cleaning of all insulating surfaces
to remove fluxes and other residues may be required.
Surface coating may be necessary to provide a moisture
barrier in high humidity environments.
Minimize board leakage by encircling the SET pin and
circuitry with a guard ring operated at a potential close
to itself; tie the guard ring to the OUT pin. Guarding
both sides of the circuit board is required. Bulk leakage
reduction depends on the guard ring width. Ten nanoam-
peres of leakage into or out of the SET pin and its asso-
ciated circuitry creates a 0.1% reference current error.
Leakages of this magnitude, coupled with other sources
of leakage, can cause significant offset voltage and refer-
ence current drift, especially over the possible operating
temperature range.
Figure1. Using the LT3092 as a Current Source
I
OUT
0.5mA
VSET =10µA RSET
IOUT =VSET
ROUT
+10µA
=10µA RSET
ROUT
+10µA
IN
SET OUT
+
LT3092
10µA
IOUT
VSET RSET
3092 F01
+
ROUT
Selecting RSET and ROUT
In Figure1, both resistors RSET and ROUT program the
value of the output current. The question now arises: the
ratio of these resistors is known, but what value should
each resistor be?
The first resistor to select is RSET. The value selected
should generate enough voltage to minimize the error
caused by the offset between the SET and OUT pins. A
reasonable starting level is 200mV of voltage across RSET
(RSET equal to 20k). Resultant errors due to offset volt-
age are a few percent. The lower the voltage across RSET
becomes, the higher the error term due to the offset.
LT3092
10
Rev. D
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APPLICATIONS INFORMATION
and inductive components and may be complex distrib-
uted networks. In addition, the current source’s value will
differ between applications and its connection may be
GND referenced, power supply referenced or floating in
a signal line path. Analog Devices strongly recommends
that stability be tested in situ for any LT3092 application.
In LT3092 applications with long wires or PCB traces, the
inductive reactance may cause instability. In some cases,
adding series resistance to the input and output lines (as
shown in Figure2) may sufficiently dampen these pos-
sible high-Q lines and provide stability. The user must
evaluate the required resistor values against the design’s
headroom constraints. In general, operation at low out-
put current levels (< 5mA) automatically requires higher
values of programming resistors and may provide the
necessary damping without additional series impedance.
If the line impedances in series with the LT3092 are com-
plex enough such that series damping resistors are not
sufficient, a frequency compensation network may be
necessary. Several options may be considered.
From this point, selecting ROUT is easy, as it is a straight-
forward calculation from RSET. Take note, however, resis-
tor errors must be accounted for as well. While larger
voltage drops across RSET minimize the error due to off-
set, they also increase the required operating headroom.
Obtaining the best temperature coefficient does not
require the use of expensive resistors with low ppm tem-
perature coefficients. Instead, since the output current of
the LT3092 is determined by the ratio of RSET to ROUT,
those resistors should have matching temperature char-
acteristics. Less expensive resistors made from the same
material will provide matching temperature coefficients.
See resistor manufacturers’ data sheets for more details.
Stability and Frequency Compensation
The LT3092 does not require input or output capacitors
for stability in many current-source applications. Clean,
tight PCB layouts provide a low reactance, well controlled
operating environment for the LT3092 without requiring
capacitors to frequency-compensate the circuit. The front
page Typical Application circuit illustrates the simplicity
of using the LT3092.
Some current source applications will use a capacitor
connected in parallel with the SET pin resistor to lower
the current source’s noise. This capacitor also provides a
soft-start function for the current source. This capacitor
connection is depicted in Figure7 (see the Quieting the
Noise section).
When operating with a capacitor across the SET pin resis-
tor, external compensation is usually required to maintain
stability and compensate for the introduced pole. The fol-
lowing paragraphs discuss methods for stabilizing the
LT3092 for either this capacitance or other complex
impedances that may be presented to the device. Analog
Devices strongly recommends testing stability in situ with
final components before beginning production.
Although the LT3092s design strives to be stable without
any capacitors over a wide variety of operating conditions,
it is not possible to test for all possible combinations of
input and output impedances that the LT3092 will encoun-
ter. These impedances may include resistive, capacitive
Figure2. Adding Series Resistor Decouples
and Dampens Long Line Reactances
IN
SET OUT
+
LT3092
10µA
RSET ROUT
RSERIES
RSERIES
LONG LINE
REACTANCE/INDUCTANCE
3092 F02
LONG LINE
REACTANCE/INDUCTANCE
LT3092
11
Rev. D
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APPLICATIONS INFORMATION
Figure3 depicts the simplest frequency compensation
network as a single capacitor connected across the two
terminals of the current source. In this case, either a
capacitor with a value less than 1000pF, or greater than
1µF (ESR < 0.5Ω), may stabilize the circuit. Some applica-
tions may use the small value capacitor to stand off DC
voltage, but allow the transfer of data down a signal line.
For some applications, this capacitance range may be
unacceptable or present a design constraint. One circuit
example typifying this is an “intrinsically-safe” circuit in
which an overload or fault condition potentially allows
the capacitors stored energy to create a spark or arc.
For applications in which a single capacitor is unaccept-
able, Figure3 alternately shows a series RC network con-
nected across the two terminals of the current source.
This network has two benefits. First, it limits the potential
discharge current of the capacitor under a fault condi-
tion, preventing sparks or arcs. Second, it bridges the gap
between the upper bound of 1000pF for small capacitors
to the lower bound of 1µF for large capacitors such that
almost any value capacitor can be used. This allows the
user greater flexibility for frequency compensating the
loop and fine tuning the RC network for complex imped-
ance networks. In many instances, a series RC network
is the best solution for stabilizing the application circuit.
Typical resistor values will range from 100Ω to about 5k,
especially for capacitor values in between 1000pF and
1µF. Once again, Analog Devices strongly recommends
Figure4. Input and/or Output Capacitors May
Be Used for Compensation
testing stability in situ for any LT3092 application across
all operating conditions, especially ones that present
complex impedance networks at the input and output of
the current source.
If an application refers the bottom of the LT3092 current
source to GND, it may be necessary to bypass the top
of the current source with a capacitor to GND. In some
cases, this capacitor may already exist and no additional
capacitance is required. For example, if the LT3092 was
used as a variable current source on the output of a power
supply, the output bypass capacitance would suffice to
provide LT3092 stability. Other applications may require
the addition of a bypass capacitor. Once again, the same
capacitor value requirements previously mentioned apply
in that an upper bound of 1000pF exists for small values
of capacitance, and a lower bound of 1µF (ESR < 0.5Ω)
exists for large value capacitors. A series RC network may
also be used as necessary, and depends on the applica-
tion requirements.
In some extreme cases, capacitors or series RC networks
may be required on both the LT3092s input and output to
stabilize the circuit. Figure4 depicts a general application
using input and output capacitor networks, rather than
an input-to-output capacitor. As the input of the current
source tends to be high impedance, placing a capacitor
on the input does not have the same effect as placing a
capacitor on the lower impedance output, and the same
3092 F04
IN
SET OUT
+
LT3092
10µA
IOUT
RSET ROUT
COUT OR
VIN
COUT
ROUT
CIN
RIN
Figure3. Compensation From Input to
Output of Current Source Provides Stability
3092 F03
IN
SET OUT
+
LT3092
10µA CCOMP OR
RSET ROUT
RCOMP
CCOMP
LT3092
12
Rev. D
For more information www.analog.com
APPLICATIONS INFORMATION
restrictions do not apply. Capacitors in the range of 0.1µF
to 1µF usually provide sufficient bypassing on the input,
and the value of input capacitance may be increased with-
out limit.
If an application uses GND referred capacitors on the
input or output (particularly the input), pay attention to
the length of the lines powering and returning ground
from the circuit. In the case where long power supply and
return lines are coupled with low ESR input capacitors,
application-specific voltage spikes, oscillations and reli-
ability concerns may be seen. This is not an issue with
LT3092 stability, but rather the low ESR capacitor form-
ing a high-Q resonant tank circuit with the inductance of
the input wires. Adding series resistance with the input
of the LT3092, or with the input capacitor, often solves
this. Resistor values of 0.1Ω to 1Ω are often sufficient to
dampen this resonance.
Give extra consideration to the use of ceramic capacitors.
Ceramic capacitors are manufactured with a variety of
dielectrics, each with different behavior across tempera-
ture and applied voltage. The most common dielectrics
used are specified with EIA temperature characteristic
codes of Z5U, Y5V, X5R and X7R. The Z5U and Y5V
dielectrics are good for providing high capacitances in
a small package, but they tend to have strong voltage
and temperature coefficients as shown in Figure5 and
Figure6. When used with a 5V regulator, a 16V 10μF Y5V
capacitor can exhibit an effective value as low as 1μF to
2μF for the DC bias voltage applied and over the operating
temperature range. The X5R and X7R dielectrics result in
more stable characteristics and are more suitable for use
as the output capacitor. The X7R type has better stability
across temperature, while the X5R is less expensive and
is available in higher values. Care still must be exercised
when using X5R and X7R capacitors; the X5R and X7R
codes only specify operating temperature range and maxi-
mum capacitance change over temperature. Capacitance
change due to DC bias with X5R and X7R capacitors is
better than Y5V and Z5U capacitors, but can still be sig-
nificant enough to drop capacitor values below appro-
priate levels. Capacitor DC bias characteristics tend to
improve as component case size increases, but expected
capacitance at operating voltage should be verified.
Voltage and temperature coefficients are not the only
sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress. In a
ceramic capacitor the stress can be induced by vibrations
in the system or thermal transients.
DC BIAS VOLTAGE (V)
CHANGE IN VALUE (%)
3092 F05
20
0
–20
–40
–60
–80
–100 04810
2 6 12 14
X5R
Y5V
16
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
Figure5. Ceramic Capacitor DC Bias Characteristics
TEMPERATURE (°C)
–50
40
20
0
–20
–40
–60
–80
–100 25 75
3092 F06
–25 0 50 100 125
Y5V
CHANGE IN VALUE (%)
X5R
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
Figure6. Ceramic Capacitor Temperature Characteristics
LT3092
13
Rev. D
For more information www.analog.com
APPLICATIONS INFORMATION
Quieting the Noise
When a reduction in the noise of the current source is
desired, a small capacitor can be placed across RSET
(CSET in Figure7). Normally, the 10µA reference cur-
rent source generates noise current levels of 2.7pA/√Hz
(0.7nARMS over the 10Hz to 100kHz bandwidth). The SET
pin resistor generates a spot noise equal to i
n
= 4kT/R (k
= Boltzmann’s constant, 1.38 • 10–23J/°K, and T is abso-
lute temperature) which is RMS-summed with the noise
generated by the 10µA reference current source. Placing
a CSET capacitor across RSET (as shown in Figure7)
bypasses this noise current. Note that this noise reduction
capacitor increases start-up time as a factor of the time
constant formed by RSET CSET. When using a capacitor
across the SET pin resistor, the external pole introduced
usually requires compensation to maintain stability. See
the Stability and Frequency Compensation section for
detailed descriptions on compensating LT3092 circuits.
A curve in the Typical Performance Characteristics section
depicts noise spectral density for the reference current
over a 10Hz to 100kHz bandwidth.
Paralleling Devices
Obtain higher output current by paralleling multiple
LT3092s together. The simplest application is to run two
current sources side by side and tie their inputs together
and their outputs together, as shown in
Figure8
. This
allows the sum of the current sources to deliver more out-
put current than a single device is capable of delivering.
Another method of paralleling devices requires fewer
components and helps to share power between devices.
Tie the individual SET pins together and tie the individual
IN pins together. Connect the outputs in common using
small pieces of PC trace as ballast resistors to promote
equal current sharing. PC trace resistance in milliohms/
inch is shown in Table1. Ballasting requires only a tiny
area on the PCB.
Table1. PC Board Trace Resistance
WEIGHT (oz) 10mil WIDTH 20mil WIDTH
1 54.3 27.1
2 27.1 13.6
Trace resistance is measured in mΩ/in
The worst-case room temperature offset, only ±2mV be-
tween the SET pin and the OUT pin, allows the use of very
small ballast resistors.
As shown in Figure9, each LT3092 has a small 40mΩ
ballast resistor, which at full output current gives better
than 80% equalized sharing of the current. The external
resistance of 40mΩ (20mΩ for the two devices in paral-
lel) only adds about 8mV of output voltage compliance at
an output of 0.4A. Of course, paralleling more than two
LT3092s yields even higher output current. Spreading the
device on the PC board also spreads the heat. Series input
resistors can further spread the heat if the input-to-output
difference is high.
Thermal Considerations
The LT3092s internal power and thermal limiting circuitry
protects itself under overload conditions. For continuous
normal load conditions, do not exceed the 125°C maxi-
mum junction temperature. Carefully consider all sources
of thermal resistance from junction-to-ambient. This
includes (but is not limited to) junction-to-case, case-
to-heat sink interface, heat sink resistance or circuit
Figure7. Adding CSET Lowers Current Noise
3092 F07
IN
SET OUT
+
LT3092
10µA CCOMP OR
RSET ROUT
RCOMP
CCOMP
CSET
LT3092
14
Rev. D
For more information www.analog.com
APPLICATIONS INFORMATION
board-to-ambient as the application dictates. Consider
all additional, adjacent heat generating sources in proxim-
ity on the PCB.
Surface mount packages provide the necessary heat
sinking by using the heat spreading capabilities of the
PC board, copper traces and planes. Surface mount heat
sinks, plated through-holes and solder filled vias can also
spread the heat generated by power devices.
Junction-to-case thermal resistance is specified from the
IC junction to the bottom of the case directly, or the bot-
tom of the pin most directly, in the heat path. This is the
lowest thermal resistance path for heat flow. Only proper
device mounting ensures the best possible thermal flow
from this area of the package to the heat sinking material.
Note that the Exposed Pad of the DFN package and the
Tab of the SOT-223 package are electrically connected
to the output (VOUT).
The following tables list thermal resistance as a function
of copper areas in a fixed board size. All measurements
were taken in still air on a four-layer FR-4 board with 1oz
solid internal planes and 2oz external trace planes with a
total finished board thickness of 1.6mm.
PCB layers, copper weight, board layout and thermal vias
affect the resultant thermal resistance. Please reference
JEDEC standard JESD51-7 for further information on high
thermal conductivity test boards. Achieving low thermal
resistance necessitates attention to detail and careful
Figure8. Connect Two LT3092s for Higher Current
Figure9. Parallel Devices
3092 F08
1.33Ω 1.33Ω
300Ω 300Ω
IOUT
IOUT, 300mA
+
LT3092
10µA 10µA
+
LT3092
20k20k
IN IN
SET SETOUTOUTOUTOUT
3092 F09
I
OUT
IOUT, 400mA
+
LT3092
10µA
+
LT3092
10µA
R
2.5Ω
Rx
50k
40mΩ*
40mΩ*
*40mΩ PC BOARD TRACE
1V
IN IN
SET SET
Rx=
V
IN MAX
()
R
90%
LT3092
15
Rev. D
For more information www.analog.com
layout. Demo circuit 1531A’s board layout using multiple
inner VOUT planes and multiple thermal vias achieves
28°C/W performance for the DFN package.
Table2. DD Package, 8-Lead DFN
COPPER AREA THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE* BACKSIDE BOARD AREA
2500mm22500mm22500mm225°C/W
1000mm22500mm22500mm225°C/W
225mm22500mm22500mm228°C/W
100mm22500mm22500mm232°C/W
*Device is mounted on topside
Table3. TS8 Package, 8-Lead SOT-23
COPPER AREA THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE* BACKSIDE BOARD AREA
2500mm22500mm22500mm254°C/W
1000mm22500mm22500mm254°C/W
225mm22500mm22500mm257°C/W
100mm22500mm22500mm263°C/W
*Device is mounted on topside
Table4. ST Package, 3-Lead SOT-223
COPPER AREA THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE* BACKSIDE BOARD AREA
2500mm22500mm22500mm220°C/W
1000mm22500mm22500mm220°C/W
225mm22500mm22500mm224°C/W
100mm22500mm22500mm229°C/W
*Device is mounted on topside
For further information on thermal resistance and using thermal information,
refer to JEDEC standard JESD51, notably JESD51-12.
Calculating Junction Temperature
Example: Given an industrial factory application with an
input voltage of 15V ±10%, an output voltage of 12V ±5%,
an output current of 200mA and a maximum ambient
temperature of 50°C, what would be the maximum junc-
tion temperature for a DFN package?
The total circuit power equals:
PTOTAL = (VIN – VOUT)(IOUT)
The SET pin current is negligible and can be ignored.
VIN(MAX CONTINUOUS) = 16.5 (15V + 10%)
VOUT(MIN CONTINUOUS) = 11.4V (12V – 5%)
IOUT = 200mA
Power dissipation under these conditions equals:
PTOTAL = (16.5 – 11.4V)(200mA) = 1.02W
Junction temperature equals:
TJ = TA + PTOTALθJA
TJ = 50°C + (1.02W • 30°C/W) = 80.6°C
In this example, the junction temperature is below the
maximum rating, ensuring reliable operation.
Protection Features
The LT3092 incorporates several protection features ideal
for battery-powered circuits, among other applications.
In addition to normal circuit protection features such as
current limiting and thermal limiting, the LT3092 protects
itself against reverse-input voltages, reverse-output volt-
ages, and reverse OUT-to-SET pin voltages.
Current limit protection and thermal overload protection
protect the IC against output current overload conditions.
For normal operation, do not exceed a junction temper-
ature of 125°C. The thermal shutdown circuits typical
temperature threshold is 165°C and has about 5°C of
hysteresis.
The LT3092’s IN pin withstands ±40V voltages with
respect to the SET and OUT pins. Reverse-current flow,
if OUT is greater than IN, is less than 1mA (typically under
100µA), protecting the LT3092 and sensitive loads.
Clamping diodes and 1k limiting resistors protect the
LT3092’s SET pin relative to the OUT pin voltage. These
protection components typically only carry current under
transient overload conditions. These devices are sized to
handle ±10V differential voltages and ±15mA crosspin
current flow without concern.
APPLICATIONS INFORMATION
LT3092
16
Rev. D
For more information www.analog.com
TYPICAL APPLICATIONS
Paralleling Current Sources for Higher Current
High Voltage Current Source
IOUT =10µA R2
R1+R4
R3
3092 TA02
IN
SET OUT
+
LT3092
10µA
R1R2
IN
SET OUT
+
LT3092
10µA
R3R4
IOUT
3092 TA03
IN
SET OUT
+
LT3092
10µA
R1
40mΩ
R2
40.2k
IN
SET OUT
+
LT3092
10µA
R3
40mΩ
R4
400mA
3092 TA04
IN
SET OUT
+
LT3092
10µA
R3
R4
20k
+
D1
35V
IOUT
100mA
IN
SET OUT
+
LT3092
10µA
R1
R2
20k
200mV
D2
35V
IOUT 0.5mA
IOUT =200mV
R1
3092 TA05
IN
SET
OUT
+
LT3092
10µA
R1
Rx
R2
20k
IOUT
100mA
V
MAX =V
IN VOUT
( )
MAX
Rx=V
MAX
200mV
R1 90%
Paralleling LT3092s with Ballast Resistor
Decreasing Power Dissipation in LT3092 100mA Current Source
3092 TA06
IN
SET
OUT
+
LT3092
10µA
R1
C1
R2
20k
IOUT
100mA
LIMIT dV
dt
90% IOUT
C1
Capacitor Adds Stability, But Limits Slew Rate
LT3092
17
Rev. D
For more information www.analog.com
TYPICAL APPLICATIONS
3092 TA07
IN
SET OUT
+
LT3092
10µA
IOUT
VIN
LOAD
MURATA
NCP15WF104F03RC
1% 100k
49.9k 49.9Ω
3092 TA08
IN
SET OUT
+
LT3092
10µA
IOUT = 0.5mA TO
100mA
DAC OUTPUT
0V TO 1V 10Ω
3092 TA09
IN
SET OUT
LT3092
10µA
1mA
OUTPUT
INPUT
V+
100Ω10k
+
3092 TA11
IN
SET OUT
+
LT3092
10µA
200mA
VIN
OPTO-FET
100k 4.99Ω
NEC PS 7801-1A
3092 TA10
IN
SET OUT
+
LT3092
10µA
IOUT
200mA
VIN
LOAD
VN2222LL
20k
ON OFF
Pulsed Current Source, Load to Ground
Fully Floating Current Source Switches
From 200mA to Quiescent Current
DAC Controlled Current Source
Remote Temperature Sensor Active Load
LT3092
18
Rev. D
For more information www.analog.com
TYPICAL APPLICATIONS
3092 TA12
IN
SET
20k
OUT
LT3092
10µA
IOUT
VIN
LOAD
ON
OFF
+
+
LT3092
10µA
3092 TA13
IOUT
ISET
IOUT IOUT
20k RV
IOUT
=02
.
Pulsed Current Source, Load to VIN 2-Terminal AC Current Limiter
Voltage Clamp
3092 TA14
IN
SET
OUT
+
LT3092
10µA
10k
10k
10k VOUT
VIN
VIN – VOUT = 11V TRIP POINT
100k
10V
4.99Ω
2N3906
2N3904 3092 TA15
IN
SET OUT
+
LT3092
10µA
124Ω
0.1%
10mA
IOUT
LT1634-1.25
High Accuracy Current Source
LT3092
19
Rev. D
For more information www.analog.com
TYPICAL APPLICATIONS
3092 TA16
IN
SET OUT
+
LT3092
VIN
VN2222LL*
10µA
4.99Ω
*CURRENT FOLDBACK CIRCUIT LIMITS
THE LT3092 POWER DISSIPATION
IOUT = 200mA, IF VIN – VOUT < 12V
= 100mA, IF VIN – VOUT > 12V
VOUT
100k*
10k*
100k
10V*
2-Level Current Source
More Efficient Current Source
+
3092 TA17
IN
SET OUT
LT3092
BOOST
SW
BIAS
FB
VIN
VIN
SHDN
LT3470A
ZVP3306F
GND
10µA
C3
47µF
36V
1k
1nF
IOUT
20k
100Ω
0.22µF
33µH
+
LT3092
20
Rev. D
For more information www.analog.com
PACKAGE DESCRIPTION
3.00 ±0.10
(4 SIDES)
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON TOP AND BOTTOM OF PACKAGE
0.40 ±0.10
BOTTOM VIEW—EXPOSED PAD
1.65 ±0.10
(2 SIDES)
0.75 ±0.05
R = 0.125
TYP
2.38 ±0.10
14
85
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
0.00 – 0.05
(DD8) DFN 0509 REV C
0.25 ±0.05
2.38 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
1.65 ±0.05
(2 SIDES)2.10 ±0.05
0.50
BSC
0.70 ±0.05
3.5 ±0.05
PACKAGE
OUTLINE
0.25 ±0.05
0.50 BSC
DD Package
8-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698 Rev C)
LT3092
21
Rev. D
For more information www.analog.com
PACKAGE DESCRIPTION
.114 – .124
(2.90 – 3.15)
.248 – .264
(6.30 – 6.71)
.130 – .146
(3.30 – 3.71)
.264 – .287
(6.70 – 7.30)
.0905
(2.30)
BSC
.033 – .041
(0.84 – 1.04)
.181
(4.60)
BSC
.024 – .033
(0.60 – 0.84)
.071
(1.80)
MAX
10°
MAX
.012
(0.31)
MIN
.0008 – .0040
(0.0203 – 0.1016)
10° – 16°
.010 – .014
(0.25 – 0.36)
10° – 16°
RECOMMENDED SOLDER PAD LAYOUT
ST3 (SOT-233) 0502
.129 MAX
.059 MAX
.059 MAX
.181 MAX
.039 MAX
.248 BSC
.090
BSC
ST Package
3-Lead Plastic SOT-223
(Reference LTC DWG # 05-08-1630)
LT3092
22
Rev. D
For more information www.analog.com
PACKAGE DESCRIPTION
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.22 – 0.36
8 PLCS (NOTE 3)
DATUM ‘A’
0.09 – 0.20
(NOTE 3)
TS8 TSOT-23 0710 REV A
2.90 BSC
(NOTE 4)
0.65 BSC
1.95 BSC
0.80 – 0.90
1.00 MAX 0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
PIN ONE ID
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
0.40
MAX
0.65
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637 Rev A)
LT3092
23
Rev. D
For more information www.analog.com
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
B 12/09 Update Order Information. 2
C 02/17 Update Dropout Voltage graphs.
Amended Application Circuit connection.
6
1, 8, 9, 10, 11,
13, 14, 16, 17,
18, 19, 24
D 08/20 Added AEC-Q100 Qualified for Automotive Applications to Features.
Added #W options for 3-Lead SOT.
Removed lead finished options.
Changed current source mode IOUT formula.
1
3
3
9
(Revision history begins at Rev B)
LT3092
24
Rev. D
For more information www.analog.com
ANALOG DEVICES, INC. 2009-2020
www.analog.com
08/20
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Stable with 2.2µF Ceramic Capacitors, DFN-8, MS8 Packages
LTC3025 300mA Micropower VLDO Linear
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1.1A, Parallelable, Low Noise,
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300mV Dropout Voltage (2-Supply Operation), Low Noise: 40µVRMS, VIN: 1.2V to 36V,
VOUT : 0V to 35.7V, Current-Based Reference with 1-Resistor VOUT Set; Directly Parallelable
(No Op Amp Required), Stable with Ceramic Caps, TO-220, SOT-223, MSOP-8 and
3mm × 3mm DFN-8 Packages; LT3080-1 Version Has Integrated Internal Ballast Resistor
LT3085 500mA, Parallelable, Low Noise, Low
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275mV Dropout Voltage (2-Supply Operation), Low Noise: 40µVRMS, VIN: 1.2V to 36V,
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(No Op Amp Required), Stable with Ceramic Caps, MSOP-8 and 2mm × 3mm DFN-6 Packages
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LT6106 Low Cost, 36V High Side Current
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36V (44V Max) Current Sense, Dynamic Range of 2000:1, 106dB of PSRR
LT6107 High Temperature High Side Current
Sense Amp in SOT-23
36V (44V Max) Current Sense, Dynamic Range of 2000:1, 106dB of PSRR, –55 to 150°C
(MP-Grade)
Current Limiter for Remote Power
3092 TA19
IN
SET OUT
+
LT3092
10µA
4.99Ω
VOUT
VIN
100k
ADJUST LIMIT
LDO
TYPICAL APPLICATIONS
USB LED Driver
3092 TA18
IN
SET OUT
+
LT3092
10µA
200mA LED
USB
20k