概述
数据手册
替代型号LT3085EMS8E#PBF 概述
暂无描述 稳压芯片
LT3085EMS8E#PBF 数据手册
通过下载LT3085EMS8E#PBF数据手册来全面了解它。这个PDF文档包含了所有必要的细节，如产品概述、功能特性、引脚定义、引脚排列图等信息。
PDF下载LT3085
Adjustable 500mA Single
Resistor Low Dropout
Regulator
FEATURES
DESCRIPTION
The LT®3085 is a 500mA low dropout linear regulator that
can be paralleled to increase output current or spread
heat on surface mounted boards. Designed as a precision
current source and voltage follower, this new regulator
finds use in many applications requiring high current,
adjustability to zero, and no heat sink. The device also
brings out the collector of the pass transistor to allow
low dropout operation—down to 275mV—when used
with a second supply.
n
Outputs May be Paralleled for Higher Current and
Heat Spreading
n
Output Current: 500mA
n
Single Resistor Programs Output Voltage
n
1% Initial Accuracy of SET Pin Current
n
Output Adjustable to 0V
n
Current Limit Constant with Temperature
n
Low Output Noise: 40μV
(10Hz to 100kHz)
RMS
n
n
n
n
n
n
n
Wide Input Voltage Range: 1.2V to 36V
Low Dropout Voltage: 275mV
A key feature of the LT3085 is the capability to supply a
wide output voltage range. By using a reference current
throughasingleresistor,theoutputvoltageisprogrammed
to any level between zero and 36V. The LT3085 is stable
with 2.2μF of capacitance on the output, and the IC uses
small ceramic capacitors that do not require additional
ESR as is common with other regulators.
< 1mV Load Regulation
< 0.001%/ V Line Regulation
Minimum Load Current: 0.5mA
Stable with Minimum 2.2μF Ceramic Capacitor
Current Limit with Foldback and Overtemperature
Protected
n
8-Lead MSOP, and 6-Lead 2mm × 3mm DFN Packages
Internal protection circuitry includes current limiting
and thermal limiting. The LT3085 is offered in the 8-lead
MSOP and a low profile (0.75mm) 6-lead 2mm × 3mm
DFNpackage(bothwithanExposedPadforbetterthermal
characteristics).
APPLICATIONS
n
High Current All Surface Mount Supply
n
High Efficiency Linear Regulator
n
Post Regulator for Switching Supplies
Low Parts Count Variable Voltage Supply
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and VLDO
and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
n
n
Low Output Voltage Power Supplies
TYPICAL APPLICATION
Variable Output Voltage 500mA Supply
N = 1676
IN
LT3085
V
IN
1.2V TO 36V
V
CONTROL
+
–
1μF
OUT
V
OUT
SET
2.2μF
R
V
SET
= R
• 10μA
SET
OUT
10.00
SET PIN CURRENT DISTRIBUTION (μA)
9.80
9.90
10.10
10.20
3085 TA01a
3085 TA01b
3085fb
1
LT3085
(Note 1) All Voltages Relative to VOUT
ABSOLUTE MAXIMUM RATINGS
V
Pin Voltage..................................... 40V, –0.3V
Operating Junction Temperature Range (Notes 2, 10)
E, I Grade........................................... –40°C to 125°C
MP Grade........................................... –55°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
CONTROL
IN Pin Voltage ................................................ 40V, –0.3V
SET Pin Current (Note 7) .................................... ±15mA
SET Pin Voltage (Relative to OUT) ..........................±10V
Output Short-Circuit Duration .......................... Indefinite
MS8E Package Only.......................................... 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
6
5
4
IN
IN
V
OUT
OUT
SET
1
2
3
OUT
OUT
OUT
SET
1
2
3
4
8 IN
7 IN
6 NC
5 V
7
9
CONTROL
CONTROL
MS8E PACKAGE
8-LEAD PLASTIC MSOP
DCB PACKAGE
6-LEAD (2mm s 3mm) PLASTIC DFN
T
JMAX
= 125°C, θ = 60°C/W, θ = 10°C/W
JA JC
EXPOSED PAD (PIN 9) IS OUT, MUST BE SOLDERED TO V
ON PCB
OUT
T
= 125°C, θ = 73°C/W, θ = 10.6°C/W
JA JC
JMAX
SEE THE APPLICATIONS INFORMATION SECTION
EXPOSED PAD (PIN 7) IS OUT, MUST BE SOLDERED TO V
ON PCB
OUT
SEE THE APPLICATIONS INFORMATION SECTION
ORDER INFORMATION
LEAD FREE FINISH
LT3085EDCB#PBF
LT3085EMS8E#PBF
LT3085IDCB#PBF
LT3085IMS8E#PBF
LT3085MPMS8E#PBF
LEAD BASED FINISH
LT3085EDCB
TAPE AND REEL
PART MARKING*
LDQQ
PACKAGE DESCRIPTION
6-Lead (2mm × 3mm) Plastic DFN
8-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–55°C to 125°C
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–55°C to 125°C
LT3085EDCB#TRPBF
LT3085EMS8E#TRPBF
LT3085IDCB#TRPBF
LT3085IMS8E#TRPBF
LTDQP
LDQQ
6-Lead (2mm × 3mm) Plastic DFN
8-Lead Plastic MSOP
LTDQP
LT3085MPMS8E#TRPBF LTDWQ
8-Lead Plastic MSOP
TAPE AND REEL
LT3085EDCB#TR
LT3085EMS8E#TR
LT3085IDCB#TR
LT3085IMS8E#TR
LT3085MPMS8E#TR
PART MARKING*
PACKAGE DESCRIPTION
6-Lead (2mm × 3mm) Plastic DFN
8-Lead Plastic MSOP
LDQQ
LT3085EMS8E
LTDQP
LDQQ
LT3085IDCB
6-Lead (2mm × 3mm) Plastic DFN
8-Lead Plastic MSOP
LT3085IMS8E
LTDQP
LTDWQ
LT3085MPMS8E
8-Lead Plastic MSOP
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
3085fb
2
LT3085
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C (Note 2).
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
SET Pin Current
I
V
V
= 1V, V
≥ 1V, V
= 2V, I
= 1mA, T = 25°C
LOAD
9.9
9.8
10
10
10.1
10.2
μA
μA
SET
IN
IN
CONTROL
CONTROL
LOAD
J
l
l
l
≥ 2V, 1mA ≤ I
≤ 500mA (Note 9)
Output Offset Voltage (V
– V
)
SET
V
V
V
= 1V, V
= 1V, V
= 2V, I
= 2V, I
= 1mA, T = 25°C
–1.5
–3
1.5
3
mV
mV
OUT
OS
IN
IN
CONTROL
CONTROL
LOAD
LOAD
J
= 1mA
ΔI
ΔI
= 1mA to 500mA
= 1mA to 500mA (Note 8)
–0.1
–0.6
nA
mV
Load Regulation
ΔI
LOAD
LOAD
SET
–1
ΔV
OS
ΔV = 1V to 36V, ΔV
IN
= 2V to 36V, I
= 2V to 36V, I
= 1mA
= 1mA
0.1
0.003
0.5
nA/V
mV/V
Line Regulation
ΔI
IN
CONTROL
CONTROL
LOAD
LOAD
SET
OS
ΔV = 1V to 36V, ΔV
ΔV
l
l
Minimum Load Current (Notes 3, 9)
V
IN
V
IN
= V
= V
= 10V
= 36V
300
500
1
μA
mA
CONTROL
CONTROL
V
V
V
Dropout Voltage (Note 4)
I
I
= 100mA
= 500mA
1.2
V
V
CONTROL
LOAD
LOAD
l
1.35
1.6
l
l
Dropout Voltage (Note 4)
I
I
= 100mA
= 500mA
85
275
150
450
mV
mV
IN
LOAD
LOAD
l
l
Pin Current (Note 5)
I
I
= 100mA
= 500mA
3
8
6
15
mA
mA
CONTROL
LOAD
LOAD
l
Current Limit (Note 9)
Error Amplifier RMS Output Noise (Note 6)
V
= 5V, V
= 5V, V = 0V, V
= –0.1V
500
650
33
mA
IN
CONTROL
SET
OUT
I
= 500mA, 10Hz ≤ f ≤ 100kHz, C
= 10μF, C = 0.1μF
μV
nA
LOAD
OUT
SET
RMS
RMS
Reference Current RMS Output Noise (Note 6) 10Hz ≤ f≤ 100kHz
0.7
Ripple Rejection
f = 120Hz, V
f=10kHz
= 0.5V , I
= 0.1A, C = 0.1μF, C = 2.2μF
90
75
20
dB
dB
dB
RIPPLE
P-P LOAD
SET
OUT
f=1MHz
Thermal Regulation, I
10ms Pulse
0.003
%/W
SET
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 5. The V
pin current is the drive current required for the
CONTROL
output transistor. This current will track output current with roughly a 1:60
ratio. The minimum value is equal to the quiescent current of the device.
Note 6. Output noise is lowered by adding a small capacitor across the
voltage setting resistor. Adding this capacitor bypasses the voltage setting
resistor shot noise and reference current noise; output noise is then equal
to error amplifier noise (see Applications Information section).
Note 2. Unless otherwise specified, all voltages are with respect to V
.
OUT
The LT3085 is tested and specified under pulse load conditions such that
T ≅ T . The LT3085E is 100% tested at T = 25°C. Performance of the
J
A
A
LT3085E over the full –40°C to 125°C operating junction temperature
range is assured by design, characterization, and correlation with
statistical process controls. The LT3085I regulators are guaranteed
over the full –40°C to 125°C operating junction temperature range. The
LT3085 (MP grade) 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.
Note 7. The SET pin is clamped to the output with diodes through 1k
resistors. These resistors and diodes will only carry current under
transient overloads.
Note 8. Load regulation is Kelvin sensed at the package.
Note 9. Current limit includes foldback protection circuitry. Current limit
decreases at higher input-to-output differential voltages. See the Typical
Performance Characteristics graphs for more information.
Note 10. This IC includes over-temperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
when over-temperature protection is active. Continuous operation above
the specified maximum operating junction temperature may impair device
reliability.
Note 4. For the LT3085, dropout is caused by either minimum control
voltage (V
) or minimum input voltage (V ). Both parameters are
CONTROL
IN
specified with respect to the output voltage. The specifications represent
the minimum input-to-output differential voltage required to maintain
regulation.
3085fb
3
LT3085
TYPICAL PERFORMANCE CHARACTERISTICS
Set Pin Current
Set Pin Current Distribution
Offset Voltage (VOUT – VSET
)
10.20
10.15
10.10
10.05
10.00
9.95
2.0
1.5
N = 1676
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
9.90
9.85
9.80
10.00
SET PIN CURRENT DISTRIBUTION (μA)
9.80
9.90
10.10
10.20
50 75
TEMPERATURE (°C)
50 75
TEMPERATURE (°C)
–50 –25
0
25
100 125 150
–50 –25
0
25
100 125 150
3085 G02
3085 G01
3085 G03
Offset Voltage Distribution
Offset Voltage
Offset Voltage
1.00
0.75
0.50
0.25
0.25
0
I
= 1mA
LOAD
N = 1676
T
= 25°C
J
–0.25
–0.50
T
= 125°C
J
0
–0.75
–1.00
–0.25
–0.50
–0.75
–1.00
–1.25
–1.50
–1.75
6
12
24
0
30
36
18
0
50 100 150 200 250 300 350 400 450 500
0
–2
–1
1
2
INPUT-TO-OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
V
DISTRIBUTION (mV)
OS
3085 G05
3085 G06
3085 G04
Dropout Voltage
Minimum Load Current
Load Regulation
(Minimum IN Voltage)
0
–0.1
–0.2
–0.3
–0.4
–0.5
–0.6
–0.7
–0.8
20
400
350
300
250
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
ΔI
IN
= 1mA TO 500mA
OUT
LOAD
V
– V
= 36V
IN, CONTROL
OUT
V
– V
= 2V
10
T
= 125°C
J
0
CHANGE IN REFERENCE CURRENT
–10
–20
–30
–40
–50
–60
200
150
V
– V
= 1.5V
IN, CONTROL
OUT
T
J
= 25°C
(V
– V
)
SET
OUT
100
50
0
CHANGE IN OFFSET VOLTAGE
50 75
25
TEMPERATURE (°C)
–50 –25
0
100 125 150
50 75
25
TEMPERATURE (°C)
0
50 100 150 200 250 300 350 400 450 500
–50 –25
0
100 125 150
LOAD CURRENT (mA)
3085 G07
3085 G09
3085 G08
3085fb
4
LT3085
TYPICAL PERFORMANCE CHARACTERISTICS
Dropout Voltage
(Minimum IN Voltage)
Dropout Voltage (Minimum
Dropout Voltage (Minimum
VCONTROL Pin Voltage)
V
CONTROL Pin Voltage)
1.6
1.4
1.2
1.0
400
350
300
250
200
150
100
50
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
I
= 500mA
LOAD
T
= –50°C
J
I
= 500mA
LOAD
I
= 100mA
LOAD
T
= 125°C
J
0.8
0.6
T
= 25°C
J
I
= 100mA
LOAD
25
0.4
0.2
0
0
0
50 100 150 200 250 300 350 400 450 500
50 75
–50 –25
0
100 125 150
50 75
TEMPERATURE (°C)
–50 –25
0
25
100 125 150
LOAD CURRENT (mA)
TEMPERATURE (°C)
3085 G11
3085 G10
3085 G12
Current Limit
Current Limit
Load Transient Response
700
600
500
400
300
200
100
60
40
20
700
600
500
400
300
200
V
C
V
= 1.5V
OUT
SET
IN
T
= 25°C
J
= 0.1μF
= V
CONTROL
= 3V
V
V
= 7V
IN
OUT
0
–20
–40
200
100
= 0V
C
= 10μF CERAMIC
OUT
C
= 2.2μF CERAMIC
OUT
100
0
0
0
0
5
10 15 20 25 30 35 40
0
20 40
120 140 160 180
200
60 80 100
50 75
25
TEMPERATURE (°C)
–50 –25
0
100 125 150
INPUT-TO-OUTPUT DIFFERENTIAL (V)
TIME (μs)
3085 G14
3085 G15
3085 G13
Load Transient Response
Line Transient Response
Turn-On Response
100
50
150
100
1.5
1
C
= 10μF CERAMIC
OUT
C
R
SET
R
= 2.2μF
50
0
OUT
0
0.5
0
CERAMIC
V
= 1.5V
= 10mA
= 2.2μF
OUT
= 100k
= 0
–50
SET
I
LOAD
C
C
OUT
= 2Ω
–50
–100
500
250
0
–100
8
LOAD
CERAMIC
= 0.1μF
CERAMIC
C
= 2.2μF CERAMIC
OUT
C
SET
6
4
6
4
V
V
C
= V
= 3V
CONTROL
IN
= 1.5V
OUT
SET
= 0.1μF
2
0
2
0
0
10 20 30 40 50 60 70 80 90 100
0
10 20 30 40 50 60 70 80 90 100
0
2
4
6
8
10 12 14 16 18 20
TIME (μs)
TIME (μs)
TIME (μs)
3085 G17
3085 G16
3085 G18
3085fb
5
LT3085
TYPICAL PERFORMANCE CHARACTERISTICS
Residual Output Voltage with
Less Than Minimum Load
VCONTROL Pin Current
VCONTROL Pin Current
8
7
6
5
4
3
2
1
0
800
700
600
500
400
300
200
100
0
20
18
16
14
12
10
8
V
V
= V
= V
= 2V
CONTROL
OUT
T
= –50°C
IN
IN
J
SET PIN = 0V
= 1V
V
IN
= 20V
V
IN
V
OUT
R
TEST
T
= 25°C
J
I
= 500mA
LOAD
T
= 125°C
J
V
= 10V
IN
DEVICE IN
CURRENT LIMIT
V
= 5V
IN
6
4
2
I
= 1mA
12
LOAD
6
0
0
0.1
0.2
0.3
0.4
0.5
0
1k
2k
0
18
24
30
36
INPUT-TO-OUTPUT DIFFERENTIAL (V)
LOAD CURRENT (A)
R
(Ω)
TEST
3085 G20
3085 G21
3085 G19
Ripple Rejection - Dual Supply
- VCONTROL Pin
Ripple Rejection - Dual Supply
- IN Pin
Ripple Rejection - Single Supply
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
I
= 100mA
I
= 100mA
LOAD
LOAD
I
= 100mA
LOAD
I
= 500mA
LOAD
I
= 500mA
LOAD
I
= 500mA
LOAD
V
V
= V
+ 1V
OUT (NOMINAL)
IN
OUT (NOMINAL)
V
V
= V
+2V
CONTROL
IN
= V
+2V
CONTROL
RIPPLE = 50mV
= V
+2V
V
= V
= V
P–P
+2V
OUT (NOMINAL)
CONTROL
RIPPLE = 50mV
OUT (NOMINAL)
P–P
IN
CONTROL
P–P
RIPPLE = 50mV
C
C
= 2.2μF CERAMIC
= 0.1μF CERAMIC
OUT
SET
C
C
= 2.2μF CERAMIC
= 0.1μF CERAMIC
C
C
= 2.2μF CERAMIC
= 0.1μF CERAMIC
OUT
SET
OUT
SET
10
100
1k
10k
100k
1M
10
100
1k
10k
100k
1M
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
3085 G22
3085 G23
3085 G24
Ripple Rejection (120Hz)
Noise Spectral Density
Output Voltage Noise
85
84
83
82
81
80
79
78
77
10k
1k
1k
V
OUT
100
100μV/DIV
100
10
1
10
3085 G27
TIME 1ms/DIV
V
R
C
= 1V
OUT
SET
SET
= 100k
= O.1μF
= 10μF
= 0.5A
SINGLE SUPPLY OPERATION
V
= V
+2V
1.0
0.1
IN
OUT (NOMINAL)
C
I
RIPPLE = 50mV , f = 120Hz
OUT
LOAD
P–P
I
= 0.1A
LOAD
C
= 2.2μF, C
= 0.1μF
SET
OUT
–50 –25
0
25 50 75 100 125 150
FREQUENCY (Hz)
3085 G25
10
100
1k
10k
100k
FREQUENCY (Hz)
3085 G26
3085fb
6
LT3085
TYPICAL PERFORMANCE CHARACTERISTICS
Error Amplifier Gain and Phase
Ripple Rejection - SET Pin Current
150
135
120
105
90
21
18
15
12
9
216
144
72
I
= 500mA
LOAD
C
= 0.1μF
SET
= 0
0
–72
–144
–216
–288
–360
–432
–504
I
= 100mA
LOAD
75
C
6
SET
I
= 500mA
LOAD
60
3
45
0
30
R
IN
= 100k
SET
–3
–6
–9
V
= V
= V
P–P
+2V
OUT (NOMINAL)
CONTROL
I
= 100mA
100k
LOAD
15
RIPPLE = 50mV
0
10
100
1k
10k
1M
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
FREQUENCY (Hz)
3085 G29
3085 G28
PIN FUNCTIONS
(DCB/MS8E)
V
(Pin 4/Pin 5): This pin is the supply pin for the
rises with frequency, so include a bypass capacitor in
battery-powered circuits. A bypass capacitor in the range
of 1μF to 10μF suffices.
CONTROL
control circuitry of the device. The current flow into this
pin is about 1.7% of the output current. For the device to
regulate, this voltage must be more than 1.2V to 1.35V
NC (NA/Pin 6): No Connection. The No Connect pin has
greater than the output voltage (see V
Dropout
CONTROL
no connection to internal circuitry and may be tied to V ,
IN
Voltage in the Electrical Characteristics table and graphs
in the Typical Performance Characteristics). The LT3085
V
, V , GND, or floated.
CONTROL OUT
OUT (Pins 1, 2/Pins 1, 2, 3): This is the power output
of the device. There must be a minimum load current of
1mA or the output may not regulate. A minimum 2.2μF
output capacitor is required for stability.
requires a bypass capacitor at V
if more than six
CONTROL
inchesawayfromthemaininputfiltercapacitor.Theoutput
impedance of a battery rises with frequency, so include
a bypass capacitor in battery-powered circuits. A bypass
capacitor in the range of 1μF to 10μF suffices.
SET(Pin3/Pin4):Thispinisthenon-invertinginputtothe
error amplifier and the regulation set point for the device.
A fixed current of 10μA flows out of this pin through a
singleexternalresistor,whichprogramstheoutputvoltage
of the device. Output voltage range is zero to the absolute
maximumratedoutputvoltage.Transientperformancecan
be improved and output noise can be decreased by adding
a small capacitor from the SET pin to ground.
IN (Pins 5, 6/Pins 7, 8): This is the collector to the power
device of the LT3085. The output load current is supplied
through this pin. For the device to regulate, the voltage at
this pin must be more than 0.1V to 0.5V greater than the
output voltage (see V Dropout Voltage in the Electrical
IN
Characteristics table and graphs in the Typical Perfor-
mance Characteristics). The LT3085 requires a bypass
capacitor at IN if more than six inches away from the main
input filter capacitor. The output impedance of a battery
Exposed Pad (Pin 7/Pin 9): OUT. Tie directly to Pins 1, 2/
Pins 2, 3 directly at the PCB.
3085fb
7
LT3085
BLOCK DIAGRAM
IN
V
CONTROL
10μA
+
–
3085 BD
SET
OUT
APPLICATIONS INFORMATION
The LT3085 regulator is easy to use and has all the pro-
tection features expected in high performance regulators.
Included are short-circuit protection and safe operating
area protection, as well as thermal shutdown.
What is not so obvious from this architecture are the ben-
efitsofusingatrueinternalcurrentsourceasthereference
asopposedtoabootstrappedreferenceinolderregulators.
A true current source allows the regulator to have gain
and frequency response independent of the impedance on
the positive input. Older adjustable regulators, such as the
LT1086, have a change in loop gain with output voltage
as well as bandwidth changes when the adjustment pin
is bypassed to ground. For the LT3085, the loop gain is
unchanged by changing the output voltage or bypassing.
Output regulation is not fixed at a percentage of the output
voltage but is a fixed fraction of millivolts. Use of a true
current source allows all the gain in the buffer amplifier
to provide regulation and none of that gain is needed to
amplify up the reference to a higher output voltage.
TheLT3085isespeciallywellsuitedtoapplicationsneeding
multiple rails. The new architecture adjusts down to zero
with a single resistor, handling modern low voltage digital
IC’saswellasallowingeasyparalleloperationandthermal
managementwithoutheatsinks.Adjustingto“zero”output
allows shutting off the powered circuitry and when the
input is pre-regulated – such as a 5V or 3.3V input supply
– external resistors can help spread the heat.
Aprecision“0”TC10μAinternalcurrentsourceisconnected
to the non-inverting input of a power operational amplifier.
Thepoweroperationalamplifierprovidesalowimpedance
buffered output to the voltage on the non-inverting input.
A single resistor from the non-inverting input to ground
sets the output voltage and if this resistor is set to zero,
zero output results. As can be seen, any output voltage
can be obtained from zero up to the maximum defined by
the input power supply.
The LT3085 has the collector of the output transistor
connectedtoaseparatepinfromthecontrolinput.Sincethe
dropoutonthecollector(INpin)isonly275mV,twosupplies
can be used to power the LT3085 to reduce dissipation: a
higher voltage supply for the control circuitry and a lower
voltagesupplyforthecollector.Thisincreasesefficiencyand
reduces dissipation. To further spread the heat, a resistor
can be inserted in series with the collector to move some
of the heat out of the IC and spread it on the PC board.
3085fb
8
LT3085
APPLICATIONS INFORMATION
The LT3085 can be operated in two modes. Three terminal
mode has the control pin connected to the power input pin
whichgivesalimitationof1.35Vdropout.Alternatively,the
“control” pin can be tied to a higher voltage and the power
IN pin to a lower voltage giving 275mV dropout on the
IN pin and minimizing the power dissipation. This allows
With the low level current used to generate the reference
voltage, leakage paths to or from the SET pin can create
errors in the reference and output voltages. High quality
insulation should be used (e.g., Teflon, Kel-F); cleaning
of all insulating surfaces to remove fluxes and other resi-
dues will probably be required. Surface coating may be
necessary to provide a moisture barrier in high humidity
environments.
for a 500mA supply regulating from 2.5V to 1.8V
or
IN
OUT
1.8V to 1.2V
with low dissipation.
IN
OUT
Setting Output Voltage
Table 1. 1% Resistors for Common Output Voltages
V
R
SET
OUT
The LT3085 generates a 10μA reference current that flows
out of the SET pin. Connecting a resistor from SET to
ground generates a voltage that becomes the reference
point for the error amplifier (see Figure 1). The reference
voltage is a straight multiplication of the SET pin current
and the value of the resistor. Any voltage can be generated
and there is no minimum output voltage for the regulator.
Table 1 lists many common output voltages and standard
1% resistor values used to generate that output voltage.
A minimum load current of 1mA is required to maintain
regulation regardless of output voltage. For true zero
voltage output operation, this 1mA load current must be
returned to a negative supply voltage.
1V
100k
121k
150k
182k
249k
332k
499k
1.2V
1.5V
1.8V
2.5V
3.3V
5V
Board leakage can be minimized by encircling the SET
pin and circuitry with a guardring operated at a potential
close to itself; the guardring should be tied to the OUT pin.
Guarding both sides of the circuit board is required. Bulk
leakage reduction depends on the guard ring width. Ten
nanoamperes of leakage into or out of the SET pin and
associated circuitry creates a 0.1% error in the reference
voltage. Leakages of this magnitude, coupled with other
sourcesofleakage,cancausesignificantoffsetvoltageand
reference drift, especially over a wide temperature range.
IN
LT3085
V
CONTROL
10μA
+
–
+
+
V
V
CONTROL
IN
OUT
V
C
OUT
SET
R
If guardring techniques are used, this bootstraps any
stray capacitance at the SET pin. Since the SET pin is
a high impedance node, unwanted signals may couple
into the SET pin and cause erratic behavior. This will
be most noticeable when operating with minimum
output capacitors at full load current. The easiest way
to remedy this is to bypass the SET pin with a small
amount of capacitance from SET to ground, 10pF to
20pF is sufficient.
OUT
C
SET
SET
3085 F01
V
= R • 10μA
SET
OUT
Figure 1. Basic Adjustable Regulator
3085fb
9
LT3085
APPLICATIONS INFORMATION
Input Capacitance and Stability
As power supply impedance does vary, the amount of
capacitance needed to stabilize your application will also
vary. Extra capacitance placed directly on the output of
the power supply requires an order of magnitude more
capacitanceasopposedtoplacingextracapacitanceclose
to the LT3085.
The LT3085 is designed to be stable with a minimum
capacitance of 1μF at each input pin. Ceramic capacitors
with low ESR are available for use to bypass these pins,
but in cases where long wires connect the LT3085 inputs
to a power supply (and also from ground of the LT3085
circuitry back to power supply ground), this causes insta-
bilities. This happens due to the wire inductance forming
an LC tank circuit with the input capacitor and not as a
result of instability on the LT3085.
Using series resistance between the power supply and
the input of the LT3085 also stabilizes the application.
As little as 0.1Ω to 0.5Ω, often less, is all that is needed
to provide damping in the circuit. If the extra impedance
between the power supply and the input is unacceptable,
placing the resistors in series with the capacitors will pro-
vide damping to prevent the LC resonance from causing
full-blown oscillation.
The self-inductance, or isolated inductance, of a wire is
directly proportional to its length. The diameter does not
have a major influence on its self-inductance. As an ex-
ample, the self-inductance of a 2-AWG isolated wire with a
diameterof0.26in.isapproximatelyhalftheself-inductance
of a 30-AWG wire with a diameter of 0.01in. One foot of
30-AWG wire has 465nH of self-inductance.
Stability and Output Capacitance
The LT3085 requires an output capacitor for stability. It
is designed to be stable with most low ESR capacitors
(typically ceramic, tantalum or low ESR electrolytic). A
minimum output capacitor of 2.2μF with an ESR of 0.5Ω
or less is recommended to prevent oscillations. Larger
values of output capacitance decrease peak deviations
and provide improved transient response for larger load
current changes. Bypass capacitors, used to decouple
individual components powered by the LT3085, increase
the effective output capacitor value.
The overall self-inductance of a wire is reduced in one of
two ways. One is to divide the current flowing towards
the LT3085 between two parallel conductors. In this
case, the farther apart the wires are from each other, the
more the self-inductance is reduced, up to a 50% reduc-
tion when placed a few inches apart. Splitting the wires
basically connects two equal inductors in parallel, but
placing them in close proximity gives the wires mutual
inductance adding to the self-inductance. The second
and most effective way to reduce overall inductance is to
place both forward- and return-current conductors (the
wire for the input and the wire for ground) in very close
proximity. Two 30-AWG wires separated by only 0.02in.
used as forward- and return-current conductors reduce
the overall self-inductance to approximately one-fifth that
of a single isolated wire.
Forimprovementintransientperformance,placeacapaci-
tor across the voltage setting resistor. Capacitors up to
1μF can be used. This bypass capacitor reduces system
noise as well, but start-up time is proportional to the time
constant of the voltage setting resistor (R in Figure 1)
SET
and SET pin bypass capacitor.
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior across
temperature and applied voltage. The most common
dielectrics used are specified with EIA temperature
characteristiccodesofZ5U,Y5V,X5RandX7R.TheZ5Uand
Y5V dielectrics are good for providing high capacitances
If the LT3085 is powered by a battery mounted in close
proximity on the same circuit board, a 2.2μF input capaci-
tor is sufficient for stability. When powering from distant
supplies, use a larger input capacitor based on a guide-
line of 1μF plus another 1μF per 8 inches of wire length.
3085fb
10
LT3085
APPLICATIONS INFORMATION
in a small package, but they tend to have strong voltage
and temperature coefficients as shown in Figures 2
and 3. 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
acrosstemperature, whiletheX5Rislessexpensiveandis
availableinhighervalues.Carestillmustbeexercisedwhen
using X5R and X7R capacitors; the X5R and X7R codes
only specify operating temperature range and maximum
capacitancechangeovertemperature.Capacitancechange
due to DC bias with X5R and X7R capacitors is better than
Y5VandZ5Ucapacitors,butcanstillbesignificantenough
todropcapacitorvaluesbelowappropriatelevels.Capacitor
DC bias characteristics tend to improve as component
casesizeincreases, butexpectedcapacitanceatoperating
voltage should be verified.
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress,
ceramic capacitor the stress can be induced by vibrations
in the system or thermal transients.
Paralleling Devices
LT3085’s may be paralleled with other LT308X devices to
obtainhigheroutputcurrent.TheSETpinsaretiedtogether
and the IN pins are tied together. This is the same whether
it’s in three terminal mode or has separate input supplies.
The outputs are connected in common using a small piece
of PC trace as a ballast resistor to equalize the currents.
PC trace resistance in milliohms/inch is shown in Table
1. Only a tiny area is needed for ballasting.
Table 1. PC Board Trace Resistance
WEIGHT (oz)
10 mil WIDTH
54.3
20 mil WIDTH
27.1
1
2
27.1
13.6
Trace resistance is measured in mΩ/in
Voltage and temperature coefficients are not the only
sources of problems. Some ceramic capacitors have a
40
20
20
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
0
X5R
0
X5R
–20
–40
–60
–20
Y5V
–40
–60
–80
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
Y5V
–80
–100
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
–100
0
8
12 14
2
4
6
10
16
3085 F03
DC BIAS VOLTAGE (V)
Figure 3. Ceramic Capacitor Temperature Characteristics
3085 F02
Figure 2. Ceramic Capacitor DC Bias Characteristics
3085fb
11
LT3085
APPLICATIONS INFORMATION
The worst-case offset between the SET pin and the output
of only 1.5mV allows very small ballast resistors to be
used. As shown in Figure 4, the two devices have a small
10mΩ and 20mΩ ballast resistors, which at full output
current gives better than 80% equalized sharing of the
current. The external resistance of 20mΩ (6.6mΩ for the
two devices in parallel) only adds about 10mV of output
regulation drop at an output of 1.5A. Even with an output
voltage as low as 1V, this only adds 1% to the regulation.
Of course, more than two LT308X’s can be paralleled for
even higher output current. They are spread out on the
PC board, spreading the heat. Input resistors can further
spread the heat if the input-to-output difference is high.
The first test was done with approximately 1.6V
input- to-output and 0.5A per device. This gave a 800mW
dissipation in each device and a 1A output current. The
temperature rise above ambient is approximately 28°C
and both devices were within plus or minus 1°C. Both the
thermal and electrical sharing of these devices is excel-
lent. The thermograph in Figure 5 shows the temperature
distribution between these devices and the PC board
reaches ambient temperature within about a half an inch
from the devices.
The power is then increased with 3.4V across each device.
Thisgives1.7wattsdissipationineachdeviceandadevice
temperature of about 90°C, about 65°C above ambient
as shown in Figure 6. Again, the temperature matching
Thermal Performance
In this example, two LT3085 2mm × 3mm DFN devices
are mounted on a 1oz copper 4-layer PC board. They are
placed approximately 1.5 inches apart and the board is
mounted vertically for convection cooling. Two tests were
set up to measure the cooling performance and current
sharing of these devices.
V
IN
LT3080
V
CONTROL
+
–
10mΩ
OUT
Figure 5. Temperature Rise at 800mW Dissipation
SET
V
IN
LT3085
V
IN
4.8V TO 28V
V
CONTROL
+
–
1μF
20mΩ
V
3.3V
1.5A
OUT
OUT
SET
165k
10μF
3085 F04
Figure 4. Parallel Devices
Figure 6. Temperature Rise at 1.7W Dissipation
3085fb
12
LT3085
APPLICATIONS INFORMATION
between the devices is within 2°C, showing excellent
tracking between the devices. The board temperature has
reached approximately 40°C within about 0.75 inches of
each device.
The LT3085 uses a unity-gain follower from the SET pin
to drive the output, and there is no requirement to use
a resistor to set the output voltage. Use a high accuracy
voltage reference placed at the SET pin to remove the er-
rors in output voltage due to reference current tolerance
and resistor tolerance. Active driving of the SET pin is
acceptable; the limitations are the creativity and ingenuity
of the circuit designer.
While90°Cisanacceptableoperatingtemperatureforthese
devices, this is in 25°C ambient. For higher ambients, the
temperaturemustbecontrolledtopreventdevicetempera-
ture from exceeding 125°C. A 3-meter-per-second airflow
across the devices will decrease the device temperature
about 20°C providing a margin for higher operating ambi-
ent temperatures.
Oneproblemthatanormallinearregulatorseeswithrefer-
ence voltage noise is that noise is gained up along with the
output when using a resistor divider to operate at levels
higherthanthenormalreferencevoltage.WiththeLT3085,
the unity-gain follower presents no gain whatsoever from
the SET pin to the output, so noise figures do not increase
accordingly. Error amplifier noise is typically 100nV/√Hz
Both at low power and relatively high power levels de-
vices can be paralleled for higher output current. Current
sharing and thermal sharing is excellent, showing that
acceptable operation can be had while keeping the peak
temperatures below excessive operating temperatures on
a board. This technique allows higher operating current
linear regulation to be used in systems where it could
never be used before.
(33μV
over the 10Hz to 100kHz bandwidth); this is
RMS
another factor that is RMS summed in to give a final noise
figure for the regulator.
Curves in the Typical Performance Characteristics show
noise spectral density and peak-to-peak noise character-
istics for both the reference current and error amplifier
over the 10Hz to 100kHz bandwidth.
Quieting the Noise
The LT3085 offers numerous advantages when it comes
to dealing with noise. There are several sources of noise
in a linear regulator. The most critical noise source for any
LDO is the reference; from there, the noise contribution
from the error amplifier must be considered, and the gain
created by using a resistor divider cannot be forgotten.
Overload Recovery
LikemanyICpowerregulators,theLT3085hassafeoperat-
ing area (SOA) protection. The SOA protection decreases
current limit as the input-to-output voltage increases and
keeps the power dissipation at safe levels for all values
of input-to-output voltage. The LT3085 provides some
output current at all values of input-to-output voltage up
to the device breakdown. See the Current Limit curve in
the Typical Performance Characteristics.
Traditional low noise regulators bring the voltage refer-
ence out to an external pin (usually through a large value
resistor) to allow for bypassing and noise reduction of
reference noise. The LT3085 does not use a traditional
voltage reference like other linear regulators, but instead
uses a reference current. That current operates with typi-
When power is first turned on, the input voltage rises and
the output follows the input, allowing the regulator to start
intoveryheavyloads. Duringstart-up, astheinputvoltage
is rising, the input-to-output voltage differential is small,
allowing the regulator to supply large output currents.
With a high input voltage, a problem can occur wherein
removal of an output short will not allow the output volt-
age to recover. Other regulators, such as the LT1085 and
LT1764A, also exhibit this phenomenon so it is not unique
to the LT3085.
cal noise current levels of 2.3pA/√Hz (0.7nA
over the
RMS
10Hz to 100kHz bandwidth). The voltage noise of this is
equal to the noise current multiplied by the resistor value.
The resistor generates spot noise equal to√4kTR (k =
-23
Boltzmann’s constant, 1.38 • 10 J/°K, and T is absolute
temperature) which is RMS summed with the reference
current noise. To lower reference noise, the voltage set-
ting resistor may be bypassed with a capacitor, though
this causes start-up time to increase as a factor of the RC
time constant.
3085fb
13
LT3085
APPLICATIONS INFORMATION
The problem occurs with a heavy output load when the
input voltage is high and the output voltage is low. Com-
mon situations are immediately after the removal of a
short circuit. The load line for such a load may intersect
the output current curve at two points. If this happens,
there are two stable operating points for the regulator.
With this double intersection, the input power supply may
need to be cycled down to zero and brought up again to
make the output recover.
On the LT3085, internal resistors and diodes limit current
paths on the SET pin. Even with bypass capacitors on the
SET pin, no protection diode is needed to ensure device
safety under short-circuit conditions. The SET pin handles
10V (either transient or DC) with respect to OUT without
any device degradation.
Internal parasitic diodes exist between OUT and the two
inputs.Negativeinputvoltagesaretransferredtotheoutput
and may damage sensitive loads. Reverse-biasing either
input to OUT will turn on these parasitic diodes and allow
current flow. This current flow will bias internal nodes
of the LT3085 to levels that possibly cause errors when
suddenly returning to normal operating conditions and
expecting the device to start and operate. Prediction of
results of a bias fault is impossible, immediate return to
normal operating conditions can be just as difficult after
a bias fault. Suffice it to say that extra wait time, power
cycling, or protection diodes may be needed to allow the
LT3085 to return to a normal operating mode as quickly
as possible.
Load Regulation
BecausetheLT3085isafloatingdevice(thereisnoground
pin on the part, all quiescent and drive current is delivered
to the load), it is not possible to provide true remote load
sensing. Load regulation will be limited by the resistance
of the connections between the regulator and the load.
The data sheet specification for load regulation is Kelvin
sensed at the pins of the package. Negative side sensing
is a true Kelvin connection, with the bottom of the voltage
setting resistor returned to the negative side of the load
(seeFigure7).Connectedasshown,systemloadregulation
will be the sum of the LT3085 load regulation and the
parasitic line resistance multiplied by the output current.
It is important to keep the positive connection between
the regulator and load as short as possible and use large
wire or PC board traces.
Protection diodes are not otherwise needed between
the OUT pin and IN pin. The internal diodes can handle
microsecond surge currents of up to 50A. Even with
large output capacitors, obtaining surge currents of those
magnitudesisdifficultinnormaloperation.Onlywithlarge
output capacitors, such as 1000μF to 5000μF, and with
IN instantaneously shorted to ground will damage occur.
A crowbar circuit at IN is capable of generating those
levels of currents, and then protection diodes from OUT
to IN are recommended. Normal power supply cycling or
system “hot plugging and unplugging” does not do any
damage.
Internal Parasitic Diodes and Protection Diodes
Innormaloperation,theLT3085doesnotrequireprotection
diodes. Older three-terminal regulators require protection
diodesbetweentheVOUTpinandtheinputpinorbetween
the ADJ pin and the VOUT pin to prevent die overstress.
A protection diode between OUT and V
is usually
CONTROL
CONTROL
IN
LT3085
not needed. The internal parasitic diode on V
of
V
CONTROL
the LT3085 handles microsecond surge currents of 1A to
10A. Again, this only occurs when using crowbar circuits
PARASITIC
+
–
RESISTANCE
with large value output capacitors. Since the V
CONTROL
R
P
R
P
R
P
OUT
pin is usually a low current supply, this is unlikely. Still,
LOAD
R
SET
SET
a protection diode is recommended if V can be
CONTROL
instantaneously shorted to ground. Normal power supply
cycling or system “hot plugging and unplugging” does
not do any damage.
3085 F07
Figure 7. Connections for Best Load Regulation
3085fb
14
LT3085
APPLICATIONS INFORMATION
IftheLT3085isconfiguredasathree-terminal(singlesupply)
provide better performance than found in these tables.
For example, a 4-layer, 1 ounce copper PCB board with
5 thermal vias from the DFN or MSOP exposed backside
regulatorwithINandV
shortedtogether,theinternal
CONTROL
diode of the IN pin will protect the V
pin.
CONTROL
pad to inner layers (connected to V ) achieves 40°C/W
OUT
Like any other regulator, exceeding the maximum input-
to-output differential causes internal transistors to break
down and then none of the internal protection circuitry
is functional.
thermal resistance. Demo circuit 1401A’s board layout
achieves this 40°C/W performance. This is approximately
a 45% improvement over the numbers shown in Tables
2 and 3.
Thermal Considerations
Table 2. MSE Package, 8-Lead MSOP
COPPER AREA
The LT3085 has internal power and thermal limiting cir-
cuitry designed to protect it under overload conditions.
For continuous normal load conditions, maximum junc-
tion temperature must not be exceeded. It is important
to give consideration to all sources of thermal resistance
from junction to ambient. This includes junction-to-case,
case-to-heat sink interface, heat sink resistance or circuit
board-to-ambient as the application dictates. Additional
heat sources nearby must also be considered.
THERMAL RESISTANCE
TOPSIDE* BACKSIDE BOARD AREA
(JUNCTION-TO-AMBIENT)
2
2
2
2
2
2
2
2
2
2500mm
1000mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
55°C/W
2
57°C/W
2
225mm
100mm
60°C/W
2
65°C/W
*Device is mounted on topside
Table 3. DCB Package, 6-Lead DFN
COPPER AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Surface mount heat sinks and
plated through-holes can also be used to spread the heat
generated by power devices. Boards specified in thermal
resistance tables have no vias on plated through-holes
from topside to backside.
TOPSIDE* BACKSIDE BOARD AREA
2
2
2
2
2
2
2
2
2
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
68°C/W
70°C/W
73°C/W
78°C/W
2
1000mm
2
225mm
100mm
2
*Device is mounted on topside
For future information on the thermal resistance and using thermal
information, refer to JEDEC standard JESD51, notably JESD51-12.
Junction-to-case thermal resistance is specified from
the IC junction to the bottom of the case directly below
the die. This is the lowest resistance path for heat flow.
Proper mounting is required to ensure the best possible
thermal flow from this area of the package to the heat
sinkingmaterial.NotethattheExposedPadiselectrically
connected to the output.
Calculating Junction Temperature
Example: Given an output voltage of 0.9V, a V
CONTROL
voltage of 3.3V 10%, an IN voltage of 1.5V 5%, output
current range from 1mA to 0.5A and a maximum ambi-
ent temperature of 50°C, what will the maximum junction
2
temperature be for the DFN package on a 2500mm board
with topside copper area of 500mm ?
The following tables list thermal resistance for several
different copper areas given a fixed board size. All mea-
surements were taken in still air on two-sided 1/16” FR-4
board with one ounce copper.
2
The power in the drive circuit equals:
P
= (V
– V )(I
)
DRIVE
CONTROL
OUT CONTROL
PCB layers, copper weight, board layout and thermal vias
affect the resultant thermal resistance. Although Tables
2 and 3 provide thermal resistance numbers for 2-layer
board with 1 ounce copper, modern multi-layer PCBs
where I
is equal to I /60. I
is a function
canbefound
CONTROL
ofoutputcurrent. AcurveofI
OUT
CONTROL
vsI
CONTROL
OUT
in the Typical Performance Characteristics curves.
3085fb
15
LT3085
APPLICATIONS INFORMATION
The power in the output transistor equals:
Reducing Power Dissipation
P
= (V – V )(I )
OUT OUT
In some applications it may be necessary to reduce
the power dissipation in the LT3085 package without
sacrificing output current capability. Two techniques are
available. The first technique, illustrated in Figure 8, em-
ploys a resistor in series with the regulator’s input. The
voltagedropacrossRS decreasestheLT3085’sIN-to-OUT
differential voltage and correspondingly decreases the
LT3085’s power dissipation.
OUTPUT
IN
The total power equals:
= P + P
OUTPUT
P
TOTAL
DRIVE
The current delivered to the SET pin is negligible and can
be ignored.
V
V
V
= 3.630V (3.3V + 10%)
CONTROL(MAX CONTINUOUS)
= 1.575V (1.5V + 5%)
IN(MAX CONTINUOUS)
V
IN
V
C1
CONTROL
LT3085
= 0.9V, I
= 0.5A, T = 50°C
A
R
S
OUT
OUT
IN
V
IN
a
Power dissipation under these conditions is equal to:
= (V – V )(I
P
)
OUT CONTROL
DRIVE
CONTROL
+
–
IOUT
60
0.5A
60
ICONTROL
=
=
= 8.3mA
OUT
V
OUT
C2
SET
P
P
P
= (3.630V – 0.9V)(8.3mA) = 23mW
DRIVE
3085 F08
R
SET
= (V – V )(I )
OUT OUT
OUTPUT
OUTPUT
IN
= (1.575V – 0.9V)(0.5A) = 337mW
Figure 8. Reducing Power Dissipation Using a Series Resistor
Total Power Dissipation = 360mW
Junction Temperature will be equal to:
As an example, assume: V = V
= 5V, V
= 3.3V
IN
CONTROL
OUT
andI
=0.5A.UsetheformulasfromtheCalculating
OUT(MAX)
T = T + P
• θ (approximated using tables)
JA
J
A
TOTAL
Junction Temperature section previously discussed.
T = 50°C + 360mW • 73°C/W = 76°C
J
Inthiscase,thejunctiontemperatureisbelowthemaximum
rating, ensuring reliable operation.
3085fb
16
LT3085
APPLICATIONS INFORMATION
WithoutseriesresistorR ,powerdissipationintheLT3085
Calculating R yields:
S
P
equals:
5.5V –3.2V
RP =
= 7.30Ω
0.5A
60
315mA
PTOTAL = 5V –3.3V •
+ 5V –3.3V •0.5A
(
)
(
)
(5% Standard value = 7.Ω)
= 0.86W
The maximum total power dissipation is (5.5V – 3.2V) •
0.5A = 1.2W. However the LT3085 supplies only:
If the voltage differential (V ) across the NPN pass
transistor is chosen as 0.5V, then R equals:
DIFF
S
5.5V –3.2V
0.5A –
= 0.193A
7.5Ω
Therefore, the LT3085’s power dissipation is only:
= (5.5V – 3.2V) • 0.193A = 0.44W
5V –3.3V −0.5V
RS =
= 2.4Ω
0.5A
Power dissipation in the LT3085 now equals:
P
DIS
0.5A
60
R dissipates 0.71W of power. As with the first technique,
P
PTOTAL = 5V –3.3V •
+ 0.5V •0.5A = 0.26W
(
)
(
)
choose appropriate wattage resistors to handle and dis-
sipate the power properly. With this configuration, the
LT3085 supplies only 0.36A. Therefore, load current can
increase by 0.3A to 0.143A while keeping the LT3085 in
its normal operating range.
TheLT3085’spowerdissipationisnowonly30%compared
to no series resistor. R dissipates 0.6W of power. Choose
S
appropriate wattage resistors to handle and dissipate the
power properly.
V
IN
The second technique for reducing power dissipation,
shown in Figure 9, uses a resistor in parallel with the
LT3085. This resistor provides a parallel path for current
flow, reducing the current flowing through the LT3085.
This technique works well if input voltage is reasonably
constant and output load current changes are small. This
technique also increases the maximum available output
current at the expense of minimum load requirements.
V
C1
CONTROL
LT3085
IN
R
P
+
–
OUT
V
OUT
C2
SET
3085 F09
R
SET
As an example, assume: V = V
= 5V, V
OUT(MAX)
=
IN
CONTROL
= 3.2V, I
IN(MAX)
= 0.5A and
5.5V, V
= 3.3V, V
OUT
OUT(MIN)
I
= 0.35A. Also, assuming that R carries no more
Figure 9. Reducing Power Dissipation Using a Parallel Resistor
OUT(MIN)
P
than 90% of I
= 630mA.
OUT(MIN)
3085fb
17
LT3085
TYPICAL APPLICATIONS
Higher Output Current
MJ4502
V
IN
6V
50Ω
IN
LT3085
V
CONTROL
+
100μF
+
–
1μF
V
3.3V
5A
OUT
OUT
+
SET
4.7μF
100μF
332k
3085 TA02
Current Source
IN
LT3085
V
IN
10V
V
CONTROL
1μF
+
–
2Ω
OUT
I
OUT
0A TO 0.5A
0.5W
SET
4.7μF
100k
3085 TA03
Power Oscillator
IN
LT3085
V
IN
V
CONTROL
+
–
V
OUT
OUT
400Hz
4VAC
P-P
10μF
SET
6.3V, 150mA
LIGHT BULB #47
47nF
2.21k
4.7μF
20Ω
8.45k
8.45k
499k
220n
47nF
121Ω
3085 TA22
3085fb
18
LT3085
TYPICAL APPLICATIONS
Adding Shutdown
Low Dropout Voltage LED Driver
V
IN
IN
LT3085
V
V
IN
C1
CONTROL
100mA
D1
LT3085
IN
V
CONTROL
+
–
+
–
OUT
V
OUT
3085 TA04
SET
R1
OUT
Q1
Q2*
VN2222LL
ON OFF
SET
R1
24.9k
VN2222LL
R2
2.49Ω
SHUTDOWN
3085 TA05
*Q2 INSURES ZERO OUTPUT
IN THE ABSENCE OF ANY
OUTPUT LOAD.
Using a Lower Value SET Resistor
V
IN
LT3085
IN
12V
V
CONTROL
+
–
C1
1μF
OUT
V
OUT
0.5V TO 10V
SET
R1
49.9k
1%
V
= 0.5V + 1mA • R
SET
OUT
R2
499Ω
1%
C
1mA
OUT
4.7μF
R
SET
10k
3085 TA06
3085fb
19
LT3085
TYPICAL APPLICATIONS
Adding Soft-Start
IN
LT3085
V
IN
4.8V to 28V
V
CONTROL
+
–
D1
C1
1μF
1N4148
V
3.3V
0.5A
OUT
OUT
SET
R1
C
OUT
C2
0.01μF
4.7μF
332k
3085 TA07
Coincident Tracking
IN
LT3085
V
CONTROL
IN
LT3085
+
–
V
V
OUT3
CONTROL
OUT
5V
IN
LT3085
0.5A
V
IN
+
–
SET
7V TO 28V
169k
V
V
3.3V
0.5A
CONTROL
OUT2
4.7μF
OUT
3085 TA08
+
–
SET
R2
C3
4.7μF
C1
1.5μF
80.6k
V
2.5V
0.5A
OUT1
OUT
SET
R1
249k
C2
4.7μF
3085fb
20
LT3085
TYPICAL APPLICATIONS
Lab Supply
IN
LT3085
IN
LT3085
V
IN
12V TO 18V
V
V
CONTROL
CONTROL
+
–
+
–
+
1Ω
15μF
0.25W
OUT
50k
OUT
V
OUT
0V TO 10V
SET
SET
R4
+
+
15μF
4.7μF
100μF
1M
0A TO 0.5A
3085 TA09
High Voltage Regulator
6.1V
10k
V
IN
50V
1N4148
IN
LT3085
BUZ11
V
CONTROL
+
+
–
10μF
V
OUT
OUT
0.5A
V
OUT
V
OUT
= 20V
= 10μA • R
SET
+
4.7μF
SET
R
SET
15μF
2M
3085 TA10
Ramp Generator
IN
LT3085
V
IN
5V
V
CONTROL
+
–
1μF
OUT
V
OUT
SET
1μF
4.7μF
VN2222LL
VN2222LL
3085 TA12
3085fb
21
LT3085
TYPICAL APPLICATIONS
Reference Buffer
IN
LT3085
V
IN
V
CONTROL
+
–
OUT
V
OUT
*
INPUT
OUTPUT
C2
SET
4.7μF
LT1019
C1
1μF
3085 TA11
GND
*MIN LOAD 0.5mA
Ground Clamp
IN
LT3085
V
V
IN
EXT
V
CONTROL
20Ω
+
–
OUT
1μF
V
OUT
SET
1N4148
4.7μF
5k
3085 TA13
Boosting Fixed Output Regulators
IN
LT3085
V
CONTROL
+
–
OUT
20mΩ
SET
20mΩ
42Ω*
3.3V
2A
OUT
LT1963-3.3
5V
10μF
47μF
3085 TA20
33k
*4mV DROP ENSURES LT3085 IS
OFF WITH NO LOAD
MULTIPLE LT3085’S CAN BE USED
3085fb
22
LT3085
TYPICAL APPLICATIONS
Low Voltage, High Current Adjustable High Efficiency Regulator*
0.47μH
10k
PV
SV
SW
IN
+
100μF
×2
†
2.7V TO 5.5V
I
IN
LT3085
IN
TH
+
12.1k
294k
100μF
×2
470pF
LTC3414
R
2.2MEG 100k
1000pF
T
2N3906
V
CONTROL
PGOOD
RUN/SS
+
–
V
FB
OUT
20mΩ
78.7k
124k
SYNC/MODE
SGND PGND
SET
IN
LT3085
V
CONTROL
+
–
*DIFFERENTIAL VOLTAGE ON LT3085
IS 0.6V SET BY THE V OF THE 2N3906 PNP.
BE
OUT
20mΩ
†
0V TO 4V
2A
†
MAXIMUM OUTPUT VOLTAGE IS 1.5V
BELOW INPUT VOLTAGE
SET
IN
LT3085
V
CONTROL
+
–
OUT
20mΩ
SET
IN
LT3085
V
CONTROL
+
–
OUT
20mΩ
3085 TA18
SET
+
100μF
100k
3085fb
23
LT3085
TYPICAL APPLICATIONS
Adjustable High Efficiency Regulator*
CMDSH-4E
†
V
BOOST
SW
4.5V TO 25V
IN
10μF
1μF
LT3493
0.1μF
10μH
100k
IN
LT3085
SHDN
TP0610L
68μF
0.1μF
V
MBRM140
CONTROL
200k
+
–
FB
GND
†
OUT
0V TO 10V
0.5A
4.7μF
10k
3085 TA19
SET
1MEG
*DIFFERENTIAL VOLTAGE ON LT3085
10k
≈ 1.4V SET BY THE TPO610L P-CHANNEL THRESHOLD.
†
MAXIMUM OUTPUT VOLTAGE IS 2V
BELOW INPUT VOLTAGE
2 Terminal Current Source
C
COMP
*
IN
LT3085
V
CONTROL
+
–
R1
OUT
SET
100k
1V
R1
I
=
OUT
3085 TA21
*C
COMP
R1 ≤ 10Ω 10μF
R1 ≥ 10Ω 2.2μF
3085fb
24
LT3085
PACKAGE DESCRIPTION
DCB Package
6-Lead Plastic DFN (2mm × 3mm)
(Reference LTC DWG # 05-08-1715 Rev A)
0.70 p 0.05
1.65 p 0.05
3.55 p 0.05
(2 SIDES)
2.15 p 0.05
PACKAGE
OUTLINE
0.25 p 0.05
0.50 BSC
1.35 p 0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
TYP
2.00 p 0.10
(2 SIDES)
0.40 p 0.10
R = 0.05
TYP
4
6
3.00 p 0.10 1.65 p 0.10
(2 SIDES)
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
PIN 1 NOTCH
R0.20 OR 0.25
s 45° CHAMFER
(DCB6) DFN 0405
3
1
0.25 p 0.05
0.50 BSC
0.75 p 0.05
0.200 REF
1.35 p 0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
0.00 – 0.05
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (TBD)
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 THE
TOP AND BOTTOM OF PACKAGE
3085fb
25
LT3085
PACKAGE DESCRIPTION
MS8E Package
8-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1662 Rev F)
BOTTOM VIEW OF
EXPOSED PAD OPTION
1.88
(.074)
1.68
1
0.29
REF
0.889 p 0.127
(.035 p .005)
1.88 p 0.102
(.074 p .004)
(.066)
0.05 REF
DETAIL “B”
5.23
(.206)
MIN
3.20 – 3.45
1.68 p 0.102
(.066 p .004)
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
(.126 – .136)
DETAIL “B”
8
NO MEASUREMENT PURPOSE
3.00 p 0.102
0.52
(.0205)
REF
(.118 p .004)
(NOTE 3)
0.65
(.0256)
BSC
0.42 p 0.038
(.0165 p .0015)
TYP
8
7 6
5
RECOMMENDED SOLDER PAD LAYOUT
3.00 p 0.102
(.118 p .004)
(NOTE 4)
4.90 p 0.152
(.193 p .006)
DETAIL “A”
0o – 6o TYP
0.254
(.010)
GAUGE PLANE
1
2
3
4
0.53 p 0.152
(.021 p .006)
1.10
(.043)
MAX
0.86
(.034)
REF
DETAIL “A”
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.1016 p 0.0508
(.004 p .002)
0.65
(.0256)
BSC
MSOP (MS8E) 0210 REV F
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD
SHALL NOT EXCEED 0.254mm (.010") PER SIDE.
3085fb
26
LT3085
REVISION HISTORY (Revision history begins at Rev B)
REV
DATE
DESCRIPTION
PAGE NUMBER
B
6/10
Updated trademarks
1
Revised Conditions in Electrical Characteristics table
3
6
Changed I
value on curve G27 in Typical Performance Characteristics section
LOAD
Revised Figure 1
9
Added 200k resistor to drawing 3085 TA19 in Typical Applications section
Updated Package Description drawings
24
25, 26
3085fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
27
LT3085
TYPICAL APPLICATION
Paralleling Regulators
IN
LT3080
V
CONTROL
+
–
10mΩ
OUT
SET
IN
LT3085
V
IN
4.8V TO 36V
V
CONTROL
+
–
20mΩ
V
3.3V
1.5A
OUT
OUT
1μF
SET
165k
10μF
3085 TA14
RELATED PARTS
PART NUMBER
LDOs
DESCRIPTION
COMMENTS
LT1086
LT1763
LT3021
1.5A Low Dropout Regulator
500mA, Low Noise LDO
500mA VLDO Regulator
Fixed 2.85V, 3.3V, 3.6V, 5V and 12V Output
300mV Dropout Voltage, Low Noise = 20μV
, V : 1.8V to 20V, SO-8 Package
RMS IN
V : 0.9V to 10V, Dropout Voltage = 190mV, V
= 200mV, 5mm × 5mm DFN-16,
IN
ADJ
SO-8 Packages
LT3080
1.1A, Parallelable, Low Noise,
Low Dropout Linear Regulator
300mV Dropout Voltage (2-Supply Operation), Low Noise = 40μV
OUT
(No Op Amp Required), Stable with Ceramic Capacitors, TO-220, SOT-223, MSOP and
3mm × 3mm DFN Packages
, V : 1.2V to 36V,
RMS IN
V
: 0V to 35.7V, Current-Based Reference with 1-Resistor V
Set, Directly Parallelable
OUT
LT3080-1
Parallelable 1.1A Adjustable Single 300mV Dropout Voltage (2-Supply Operation), Low Noise = 40μV
, V : 1.2V to 36V,
RMS IN
Resistor Low Dropout Regulator
(with Internal Ballast R)
V
: 0V to 35.7V, Current-Based Reference with 1-Resistor V
Set, Directly Parallelable
OUT
OUT
(No Op Amp Required), Stable with Ceramic Capacitors, TO-220, SOT-223, MSOP and
3mm × 3mm DFN Packages. LT3080-1 Version Has Integrated Ballast Resistor
LT1963A
LT1965
1.5A Low Noise, Fast Transient
Response LDO
1.1A Low Noise LDO
340mV Dropout Voltage, Low Noise = 40μV
and SO-8 Packages
290mV Dropout Voltage, Low Noise = 40μV
, V : 2.5V to 20V, TO-220, DD, SOT-223
RMS IN
, V : 1.8V to 20V, V : 1.2V to 19.5V,
RMS IN OUT
Stable with Ceramic Caps TO-220, DDPak, MSOP and 3mm × 3mm DFN Packages
V : 1.14V to 3.5V (Boost Enabled), 1.14V to 5.5V (with External 5V), V = 0.1V,
LTC®3026
1.5A Low Input Voltage VLDOTM
Regulator
IN
DO
I = 950μA, Stable with 10μF Ceramic Capacitors, 10-Lead MSOP and DFN Packages
Q
Switching Regulators
LT1976
High Voltage, 1.5A Step-Down
Switching Regulator
f = 200kHz, I = 100μA, TSSOP-16E Package
Q
LTC3414
4A (I ), 4MHz Synchronous
95% Efficiency, V : 2.25V to 5.5V, V
= 0.8V, TSSOP Package
OUT(MIN)
OUT
IN
Step-Down DC/DC Converter
LTC3406/LTC3406B 600mA (I ), 1.5MHz Synchronous 95% Efficiency, V : 2.5V to 5.5V, V
= 0.6V, I = 20μA, I < 1μA,
Q SD
OUT
IN
OUT(MIN)
OUT(MIN)
Step-Down DC/DC Converter
ThinSOTTM Package
LTC3411
1.25A (I ), 4MHz Synchronous
95% Efficiency, V : 2.5V to 5.5V, V
= 0.8V, I = 60μA, I < 1μA, 10-Lead MS or
Q SD
OUT
IN
Step-Down DC/DC Converter
DFN Packages
3085fb
LT 0610 REV B • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
28
●
●
© LINEAR TECHNOLOGY CORPORATION 2008
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LT3085EMS8E#PBF CAD模型
引脚图
封装焊盘图
LT3085EMS8E#PBF 替代型号
| 型号 | 制造商 | 描述 | 替代类型 | 文档 |
| LT3085EMS8E#TRPBF | Linear | 暂无描述 | 功能相似 |
|
| LT3085IMS8E#PBF | Linear | LT3085 - Adjustable 500mA Single Resistor Low Dropout Regulator; Package: MSOP; Pins: 8; T | 功能相似 |
|
LT3085EMS8E#PBF 相关器件
| 型号 | 制造商 | 描述 | 价格 | 文档 |
| LT3085EMS8E#TR | Linear | IC VREG 0 V-36 V ADJUSTABLE POSITIVE LDO REGULATOR, 0.45 V DROPOUT, PDSO8, PLASTIC, MSOP-8, Adjustable Positive Single Output LDO Regulator | 获取价格 |
|
| LT3085EMS8E#TRPBF | Linear | 暂无描述 | 获取价格 |
|
| LT3085EMS8E-PBF | Linear | Adjustable 500mA Single Resistor Low Dropout Regulator | 获取价格 |
|
| LT3085EMS8E-TR | Linear | Adjustable 500mA Single Resistor Low Dropout Regulator | 获取价格 |
|
| LT3085EMS8E-TRPBF | Linear | Adjustable 500mA Single Resistor Low Dropout Regulator | 获取价格 |
|
| LT3085IDCB | Linear | Adjustable 500mA Single Resistor Low Dropout Regulator | 获取价格 |
|
| LT3085IDCB#PBF | Linear | LT3085 - Adjustable 500mA Single Resistor Low Dropout Regulator; Package: DFN; Pins: 6; Temperature Range: -40&deg;C to 85&deg;C | 获取价格 |
|
| LT3085IDCB#TR | Linear | 暂无描述 | 获取价格 |
|
| LT3085IDCB#TRMPBF | Linear | LT3085 - Adjustable 500mA Single Resistor Low Dropout Regulator; Package: DFN; Pins: 6; Temperature Range: -40&deg;C to 85&deg;C | 获取价格 |
|
| LT3085IDCB#TRPBF | Linear | LT3085 - Adjustable 500mA Single Resistor Low Dropout Regulator; Package: DFN; Pins: 6; Temperature Range: -40&deg;C to 85&deg;C | 获取价格 |
|
LT3085EMS8E#PBF 相关文章
Bourns 密封通孔金属陶瓷微调电位计产品选型手册(英文版)
- 2024-09-20
- 5
Bourns 精密环境传感器产品选型手册(英文版)
- 2024-09-20
- 8
Bourns POWrTher 负温度系数(NTC)热敏电阻手册 (英文版)
- 2024-09-20
- 8
Bourns GMOV 混合过压保护组件产品选型手册(英文版)
- 2024-09-20
- 6
