LT3990IMSE-5#TRPBF [Linear]
LT3990 - 62V, 350mA Step-Down Regulator with 2.5µA Quiescent Current and Integrated Diodes; Package: MSOP; Pins: 16; Temperature Range: -40°C to 85°C;
| 型号： | LT3990IMSE-5#TRPBF |
| 厂家： | 
Linear |
| 描述： | LT3990 - 62V, 350mA Step-Down Regulator with 2.5µA Quiescent Current and Integrated Diodes; Package: MSOP; Pins: 16; Temperature Range: -40°C to 85°C 开关 光电二极管 |
| 文件： | 总22页 (文件大小：296K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3990/LT3990-3.3/LT3990-5
62V, 350mA Step-Down
Regulator with 2.5µA
Quiescent Current and
Integrated Diodes
FEATURES
DESCRIPTION
Low Ripple Burst Mode® Operation
The LT®3990 is an adjustable frequency monolithic buck
switching regulator that accepts a wide input voltage
range up to 62V, and consumes only 2.5µA of quiescent
current. A high efficiency switch is included on the die
along with the catch diode, boost diode, and the neces-
saryoscillator, controlandlogiccircuitry. LowrippleBurst
Mode operation maintains high efficiency at low output
currents while keeping the output ripple below 5mV in a
typical application. Current mode topology is used for fast
transient response and good loop stability. A catch diode
current limit provides protection against shorted outputs
and overvoltage conditions. An accurate programmable
undervoltage lockout feature is available, producing a low
shutdowncurrentof0.7µA.Apowergoodflagsignalswhen
n
2.5µA I at 12V to 3.3V
Q
IN
OUT
Output Ripple < 5mV
P-P
n
n
n
n
n
Wide Input Voltage Range: 4.2V to 62V Operating
Adjustable Switching Frequency: 200kHz to 2.2MHz
Integrated Boost and Catch Diodes
350mA Output Current
Fixed Output Voltages: 3.3V, 5V
2µA I at 12V
Q
IN
n
n
Accurate Programmable Undervoltage Lockout
FMEA Fault Tolerant (MSOP Package)
OutputStaysatorBelowRegulationVoltageDuring
Adjacent Pin Short or When a Pin is Left Floating
n
n
n
n
Low Shutdown Current: I = 0.7µA
Q
Internal Sense Limits Catch Diode Current
Power Good Flag
Small, Thermally Enhanced 16-Pin MSOP
and (3mm × 3mm) DFN Packages
V
reaches90%oftheprogrammedoutputvoltage.The
OUT
LT3990 is available in small, thermally enhanced 16-pin
MSOP and 3mm × 3mm DFN packages.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
APPLICATIONS
n
Automotive Battery Regulation
n
Power for Portable Products
n
Industrial Supplies
TYPICAL APPLICATION
Power Loss
1000
V
= 12V
IN
5V Step-Down Converter
100
10
V
IN
6.5V TO 62V
0.22µF
33µH
V
BOOST
LT3990-5
EN/UVLO SW
IN
V
OUT
5V
OFF ON
1
350mA
PG
BD
0.1
RT
V
OUT
22µF
2.2µF
GND
374k
f = 400kHz
0.01
3990 TA01a
0.001 0.01
0.1
1
10
100
LOAD CURRENT (mA)
3990 TA01b
3990fa
1
LT3990/LT3990-3.3/LT3990-5
(Note 1)
ABSOLUTE MAXIMUM RATINGS
V , EN/UVLO Voltage...............................................62V
Operating Junction Temperature Range (Note 2)
LT3990E/LT3990E-X........................... –40°C to 125°C
LT3990I/LT3990I-X ............................ –40°C to 125°C
LT3990H/LT3990H-X.......................... –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
IN
BOOST Pin Voltage ...................................................75V
BOOST Pin Above SW Pin.........................................30V
FB/V , RT Voltage....................................................6V
OUT
PG, BD Voltage .........................................................30V
MS Only............................................................ 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
1
2
3
4
5
6
7
8
FB/V
FB/V
*
*
16 RT
OUT
OUT
15 NC
14 PG
13 BD
12 NC
11 BOOST
10 NC
FB
1
2
3
4
5
10 RT
NC
EN/UVLO
9
8
7
6
PG
EN/UVLO
NC
17
GND
11
GND
V
IN
BD
V
IN
GND
GND
BOOST
SW
NC
GND
9
SW
MSE PACKAGE
16-LEAD PLASTIC MSOP
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
θ
= 40°C/W, θ = 10°C/W
JC
JA
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
θ
= 45°C/W, θ = 10°C/W
JC
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
JA
*FB FOR LT3990, V
FOR LT3990-3.3, LT3990-5
OUT
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
LFWJ
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3990EDD#PBF
LT3990EDD#TRPBF
LT3990IDD#TRPBF
LT3990EMSE#TRPBF
LT3990IMSE#TRPBF
LT3990HMSE#TRPBF
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
10-Lead (3mm × 3mm) Plastic DFN
10-Lead (3mm × 3mm) Plastic DFN
16-Lead Plastic MSOP
LT3990IDD#PBF
LFWJ
LT3990EMSE#PBF
LT3990IMSE#PBF
3990
3990
16-Lead Plastic MSOP
LT3990HMSE#PBF
LT3990EMSE-3.3#PBF
LT3990IMSE-3.3#PBF
LT3990HMSE-3.3#PBF
LT3990EMSE-5#PBF
LT3990IMSE-5#PBF
LT3990HMSE-5#PBF
3990
16-Lead Plastic MSOP
LT3990EMSE-3.3#TRPBF 399033
LT3990IMSE-3.3#TRPBF 399033
LT3990HMSE-3.3#TRPBF 399033
16-Lead Plastic MSOP
16-Lead Plastic MSOP
16-Lead Plastic MSOP
LT3990EMSE-5#TRPBF
LT3990IMSE-5#TRPBF
LT3990HMSE-5#TRPBF
39905
39905
39905
16-Lead Plastic MSOP
16-Lead Plastic MSOP
16-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.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
3990fa
2
LT3990/LT3990-3.3/LT3990-5
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VBD = 3.3V unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
Minimum Input Voltage
Quiescent Current from V
4
4.2
V
V
V
V
Low
High
High
0.7
1.9
1.2
2.8
4
µA
µA
µA
IN
EN/UVLO
EN/UVLO
EN/UVLO
l
l
l
LT3990 Feedback Voltage
1.195
1.185
1.21
1.21
1.225
1.235
V
V
LT3990-3.3 Output Voltage
LT3990-5 Output Voltage
3.26
3.234
3.3
3.3
3.34
3.366
V
V
4.94
4.9
5
5
5.06
5.1
V
V
l
l
LT3990 FB Pin Bias Current (Note 3)
FB/Output Voltage Line Regulation
Switching Frequency
0.1
20
nA
4.2V < V < 40V
0.0002
0.01
%/V
IN
R = 41.2k, V = 6V
1.84
672
168
2.3
840
210
2.76
1008
252
MHz
kHz
kHz
T
T
T
IN
IN
IN
R = 158k, V = 6V
R = 768k, V = 6V
Switch Current Limit
V
V
= 5V, V = 0V
535
360
700
450
210
0.05
725
0.05
900
0.02
1.4
865
540
mA
mA
mV
µA
mV
µA
mV
µA
V
IN
FB
Catch Schottky Current Limit
= 5V
IN
Switch V
I
SW
= 200mA
CESAT
Switch Leakage Current
2
2
Catch Schottky Forward Voltage
Catch Schottky Reverse Leakage
Boost Schottky Forward Voltage
Boost Schottky Reverse Leakage
Minimum Boost Voltage (Note 4)
BOOST Pin Current
I
= 100mA, V = V = NC
IN BD
SCH
V
SW
= 12V
I
= 50mA, V = NC, V
= 0V
SCH
IN
BOOST
V
V
= 12V
2
1.8
12
REVERSE
l
l
= 5V
IN
I
= 200mA, V
= 15V
BOOST
8.5
mA
nA
V
SW
EN/UVLO Pin Current
V
= 12V
1
30
EN/UVLO
EN/UVLO Voltage Threshold
EN/UVLO Voltage Hysteresis
PG Threshold Offset from Feedback Voltage
PG Hysteresis as % of Output Voltage
PG Leakage
EN/UVLO Rising, V ≥ 4.2V
1.14
6.5
1.19
35
1.28
IN
mV
%
V
FB
Rising
10
13.5
1
1.0
%
V
V
= 3V
0.01
80
µA
µA
ns
PG
PG
l
l
PG Sink Current
= 0.4V
30
Minimum Switch On-Time
Minimum Switch Off-Time
115
100
V
IN
= 10V
160
ns
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 3: Bias current flows into the FB pin.
Note 4: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.
Note 2: The LT3990E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization, and correlation with statistical process controls. The
LT3990I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3990H is guaranteed over the full –40°C to
150°C operating junction temperature range. High junction temperatures
degrade operating lifetimes. Operating lifetime is derated at junction
temperatures greater than 125°C.
3990fa
3
LT3990/LT3990-3.3/LT3990-5
T = 25°C, unless otherwise noted.
A
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency, VOUT = 3.3V
Efficiency, VOUT = 5V
LT3990 Feedback Voltage
1.220
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
V
= 12V
IN
V
= 24V
IN
V
= 24V
IN
1.215
1.210
V
= 12V
IN
V
= 36V
V
= 36V
IN
IN
V
= 48V
IN
V
= 48V
IN
1.205
1.200
1.195
FRONT PAGE APPLICATION
V
= 3.3V
OUT
R1 = 1M
R2 = 576k
FRONT PAGE APPLICATION
10 100
LOAD CURRENT (mA)
50
TEMPERATURE (°C)
–50 –25
0
25
75 100 125 150
0.01
0.1
1
10
100
0.01
0.1
1
LOAD CURRENT (mA)
3990 G01
3990 G02
3990 G03
LT3990-3.3 Output Voltage
LT3990-5 Output Voltage
No-Load Supply Current
3.32
4.0
3.5
3.0
2.5
5.04
FRONT PAGE APPLICATION
V
= 3.3V
OUT
R1 = 1M
3.31
3.30
5.02
5.00
R2 = 576k
LT3990-3.3
3.29
3.28
3.27
4.98
4.96
4.94
2.0
1.5
50
TEMPERATURE (°C)
–50 –25
0
25
75 100 125 150
50
TEMPERATURE (°C)
5
25
35
45
55
–50 –25
0
25
75 100 125 150
15
INPUT VOLTAGE (V)
3990 G04
3990 G06
3990 G05
No-Load Supply Current
Maximum Load Current
Maximum Load Current
650
600
550
500
450
400
350
15
650
600
550
500
450
400
350
FRONT PAGE APPLICATION
FRONT PAGE APPLICATION
FRONT PAGE APPLICATION
V
= 3.3V
V
= 5V
V
V
= 12V
OUT
OUT
IN
OUT
= 3.3V
12
9
TYPICAL
R1 = 1M
TYPICAL
R2 = 576k
MINIMUM
MINIMUM
6
3
0
50
–50 –25
0
25
75 100 125 150
5
15
25
35
45
55
5
15
25
35
45
55
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
TEMPERATURE (°C)
3990 G07
3990 G08
3990 G09
3990fa
4
LT3990/LT3990-3.3/LT3990-5
T = 25°C, unless otherwise noted.
A
TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Load Current
Load Regulation
Switch Current Limit
0.25
0.20
0.15
0.10
0.05
0
800
700
600
500
400
300
200
100
0
H-GRADE
LIMITED BY CURRENT LIMIT
SWITCH PEAK
CURRENT LIMIT
600
500
LIMITED BY MAXIMUM
JUNCTION TEMPERATURE
θ
JA
= 45°C/W
–0.05
–0.10
–0.15
–0.20
400
300
200
CATCH DIODE VALLEY CURRENT LIMIT
FRONT PAGE APPLICATION
V
V
= 12V
OUT
IN
FRONT PAGE APPLICATION
REFERENCED FROM V
= 5V
AT 100mA LOAD
OUT
75 100
50
100
200 250 300 350
–50 –25
0
25 50
125 150
0
150
0
20
40
60
80
100
TEMPERATURE (°C)
DUTY CYCLE (%)
LOAD CURRENT (mA)
3990 G10
3990 G11
3990 G12
Minimum
Switch On-Time/Switch Off-Time
Switch Current Limit
Switching Frequency
250
225
200
175
150
125
100
75
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
900
800
700
600
500
400
300
LOAD CURRENT = 175mA
SWITCH PEAK CURRENT LIMIT
MINIMUM ON-TIME
MINIMUM OFF-TIME
CATCH DIODE VALLEY CURRENT LIMIT
50
25
0
75 100
–50 –25
0
25 50
125 150
–50
0
25 50 75 100 125 150
TEMPERATURE (°C)
125
100
–25
–50
50
–25
0
25
75
150
TEMPERATURE (°C)
TEMPERATURE (°C)
3990 G13
3990 G14
3990 G15
Switch VCESAT (ISW = 200mA)
vs Temperature
BOOST Pin Current
Switch VCESAT
300
250
200
150
600
500
21
18
15
12
9
400
300
200
100
0
6
3
0
100
200
300
500
0
400
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
0
100
200
300
400
500
SWITCH CURRENT (mA)
SWITCH CURRENT (mA)
3990 G18
3990 G16
3990 G17
3990fa
5
LT3990/LT3990-3.3/LT3990-5
T = 25°C, unless otherwise noted.
A
TYPICAL PERFORMANCE CHARACTERISTICS
Minimum Input Voltage,
OUT = 3.3V
Minimum Input Voltage,
VOUT = 5V
Boost Diode Forward Voltage
V
5.0
4.5
4.0
3.5
3.0
2.5
6.5
6.0
5.5
5.0
4.5
4.0
1.2
1.0
FRONT PAGE APPLICATION
= 3.3V
FRONT PAGE APPLICATION
f = 600kHz
V
OUT
TO START
TO RUN
TO START
0.8
0.6
TO RUN
0.4
0.2
0
–50°C
25°C
125°C
150°C
0
50 100 150 200 250 300 350
LOAD CURRENT (mA)
0
50 100 150 200 250 300 350
LOAD CURRENT (mA)
0
50
100
150
200
BOOST DIODE CURRENT (mA)
3990 G19
3990 G20
3990 G21
Catch Diode Forward Voltage
Catch Diode Leakage
Power Good Threshold
15
92
91
90
89
1.0
0.8
0.6
0.4
0.2
0
V
= 12V
R
12
8
6
3
0
–50°C
25°C
125°C
150°C
88
50
TEMPERATURE (°C)
–50 –25
0
25
75 100 125 150
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
100
200
300
0
400
CATCH DIODE CURRENT (mA)
3990 G23
3990 G24
3990 G22
Transient Load Response; Load
Current is Stepped from 10mA
(Burst Mode Operation) to 110mA
Transient Load Response; Load
Current is Stepped from 100mA
to 200mA
EN/UVLO Threshold
1.240
1.215
1.190
1.165
V
V
OUT
OUT
100mV/DIV
100mV/DIV
I
I
L
L
100mA/DIV
100mA/DIV
3990 G26
3990 G27
100µs/DIV
100µs/DIV
FRONT PAGE APPLICATION
FRONT PAGE APPLICATION
V
V
= 12V
OUT
V
V
= 12V
OUT
IN
IN
= 5V
= 5V
1.140
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3990 G25
3990fa
6
LT3990/LT3990-3.3/LT3990-5
T = 25°C, unless otherwise noted.
A
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Waveforms,
Burst Mode Operation
Switching Waveforms, Full
Frequency Continuous Operation
V
V
SW
5V/DIV
SW
5V/DIV
I
I
L
L
100mA/DIV
200mA/DIV
V
V
OUT
OUT
5mV/DIV
5mV/DIV
3990 G28
3990 G29
2µs/DIV
1µs/DIV
FRONT PAGE APPLICATION
FRONT PAGE APPLICATION
V
IN
V
= 12V
V
IN
V
= 12V
= 5V
= 10mA
= 5V
= 350mA
OUT
LOAD
OUT
LOAD
I
I
f = 600kHz
f = 600kHz
PIN FUNCTIONS (DFN, MSOP)
FB (Pin 1/Pins 1, 2 LT3990 Only): The LT3990 regulates
the FB pin to 1.21V. Connect the feedback resistor divider
tap to this pin. The two FB pins on the MSE package are
connected internally and provide a redundant path for the
feedback divider. Tie the divider to both pins.
GND (Pins 4, 5, Exposed Pad Pin 11/Pin 8, Exposed
Pad Pin 17): Ground. The exposed pad must be soldered
to the PCB.
SW (Pin 6/Pin 9): The SW pin is the output of an internal
power switch. Connect this pin to the inductor.
V
(Pins 1, 2, LT3990-X Only): The LT3990-3.3 and
OUT
BOOST (Pin 7/Pin 11): This pin is used to provide a drive
voltage,higherthantheinputvoltage,totheinternalbipolar
NPN power switch.
LT3990-5 regulate the V
pin to 3.3V and 5V, respec-
OUT
tively. This pin connects to the internal feedback divider
that programs the fixed output voltage. The two V pins
are connected internally and provide a redundant path to
the output. Tie the output to both pins.
OUT
BD (Pin 8/Pin 13): This pin connects to the anode of the
boost diode. This pin also supplies current to the LT3990’s
internal regulator when BD is above 3.2V.
EN/UVLO (Pin 2/Pin 4): The part is in shutdown when this
pin is low and active when this pin is high. The threshold
voltage is 1.19V going up with 35mV of hysteresis. Tie to
PG (Pin 9/Pin 14): The PG pin is the open-drain output of
an internal comparator. PG remains low until the FB pin
is within 10% of the final regulation voltage. PG is valid
V ifshutdownfeatureisnotused.TheEN/UVLOthreshold
IN
when V is above 4.2V and EN/UVLO is high.
is accurate only when V is above 4.2V. If V is lower
IN
IN
IN
than 4.2V, ground EN/UVLO to place the part in shutdown.
RT (Pin 10/Pin 16): A resistor is tied between RT and
ground to set the switching frequency.
V
(Pin 3/Pin 6): The V pin supplies current to the
IN
IN
LT3990’sinternalcircuitryandtotheinternalpowerswitch.
NC (Pins 3, 5, 7, 10, 12, 15, MSOP Only): No Connects.
Thesepinsarenotconnectedtointernalcircuitryandmust
be left floating to ensure fault tolerance.
This pin must be locally bypassed.
3990fa
7
LT3990/LT3990-3.3/LT3990-5
BLOCK DIAGRAM
V
IN
V
IN
C1
INTERNAL 1.21V REF
SHDN
–
+
BD
1.19V
+
–
EN/UVLO
D
BOOST
SLOPE COMP
BOOST
SWITCH LATCH
R
Q
S
RT
PG
OSCILLATOR
C3
200kHz TO 2.2MHz
R
T
L1
C2
1.09V
+
–
+
SW
V
OUT
V
C
Burst Mode
DETECT
ERROR
AMP
D
CATCH
–
R2
R1
LT3990-X
ONLY*
LT3990
ONLY
FB
V
OUT
GND
R2
R1
3990 BD
*LT3990-3.3: R1 = 12.65M, R2 = 7.35M
LT3990-5: R1 = 15.15M, R2 = 4.85M
3990fa
8
LT3990/LT3990-3.3/LT3990-5
OPERATION
The LT3990 is a constant frequency, current mode step-
down regulator. An oscillator, with frequency set by RT,
sets an RS flip-flop, turning on the internal power switch.
An amplifier and comparator monitor the current flowing
If the EN/UVLO pin is low, the LT3990 is shut down and
draws 0.7µA from the input. When the EN/UVLO pin ex-
ceeds 1.19V, the switching regulator will become active.
The switch driver operates from either V or from the
IN
between the V and SW pins, turning the switch off when
IN
BOOST pin. An external capacitor is used to generate a
voltage at the BOOST pin that is higher than the input
supply. This allows the driver to fully saturate the internal
bipolar NPN power switch for efficient operation.
this current reaches a level determined by the voltage at
V (see Block Diagram). An error amplifier measures the
C
output voltage through an external resistor divider tied to
the FB pin and servos the V node. If the error amplifier’s
C
To further optimize efficiency, the LT3990 automatically
switches to Burst Mode operation in light load situations.
Between bursts, all circuitry associated with controlling
the output switch is shut down reducing the input supply
current to 1.8µA.
output increases, more current is delivered to the output;
if it decreases, less current is delivered.
Anothercomparatormonitorsthecurrentflowingthrough
thecatchdiodeandreducestheoperatingfrequencywhen
the current exceeds the 450mA bottom current limit. This
foldback in frequency helps to control the output current
in fault conditions such as a shorted output with high
input voltage. Maximum deliverable current to the output
is therefore limited by both switch current limit and catch
diode current limit.
The LT3990 contains a power good comparator which
trips when the FB pin is at 90% of its regulated value. The
PG output is an open-drain transistor that is off when the
output is in regulation, allowing an external resistor to pull
the PG pin high. Power good is valid when the LT3990 is
enabled and V is above 4.2V.
IN
An internal regulator provides power to the control cir-
cuitry. The bias regulator normally draws power from
the V pin, but if the BD pin is connected to an external
IN
voltage higher than 3.2V, bias power will be drawn from
theexternalsource(typicallytheregulatedoutputvoltage).
This improves efficiency.
3990fa
9
LT3990/LT3990-3.3/LT3990-5
APPLICATIONS INFORMATION
FB Resistor Network
where V is the typical input voltage, V
is the output
IN
OUT
voltage, V is the integrated catch diode drop (~0.7V),
D
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis-
tors according to:
and V is the internal switch drop (~0.5V at max load).
SW
This equation shows that slower switching frequency is
necessary to accommodate high V /V
ratio.
IN OUT
V
1.21
OUT
Lower frequency also allows a lower dropout voltage.
The input voltage range depends on the switching fre-
quency because the LT3990 switch has finite minimum
on and off times. The switch can turn off for a minimum
of ~160ns but the minimum on-time is a strong function
of temperature. Use the minimum switch on-time curve
(see Typical Performance Characteristics) to design for
an application’s maximum temperature, while adding
about 30% for part-to-part variation. The minimum and
maximum duty cycles that can be achieved taking these
on and off times into account are:
R1= R2
–1
Reference designators refer to the Block Diagram. Note
that choosing larger resistors will decrease the quiescent
current of the application circuit.
Setting the Switching Frequency
The LT3990 uses a constant frequency PWM architecture
thatcanbeprogrammedtoswitchfrom200kHzto2.2MHz
by using a resistor tied from the RT pin to ground. A table
showing the necessary R value for a desired switching
T
DC
DC
= f • t
SW ON(MIN)
MIN
frequency is in Table 1.
= 1 – f • t
MAX
SW OFF(MIN)
Table 1. Switching Frequency vs RT Value
where f is the switching frequency, the t is the
ON(MIN)
SWITCHING FREQUENCY (MHz)
R VALUE (kΩ)
T
SW
minimumswitchon-time,andthet
istheminimum
0.2
0.3
0.4
0.5
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
787
511
374
287
232
169
127
102
84.5
69.8
59
OFF(MIN)
switch off-time (~160ns). These equations show that
duty cycle range increases when switching frequency is
decreased.
A good choice of switching frequency should allow ad-
equate input voltage range (see next section) and keep
the inductor and capacitor values small.
51.1
44.2
Input Voltage Range
The minimum input voltage is determined by either the
LT3990’s minimum operating voltage of 4.2V or by its
maximum duty cycle (as explained in previous section).
The minimum input voltage due to duty cycle is:
Operating Frequency Trade-Offs
Selectionoftheoperatingfrequencyisatrade-offbetween
efficiency, componentsize, minimumdropoutvoltageand
maximum input voltage. The advantage of high frequency
operationisthatsmallerinductorandcapacitorvaluesmay
be used. The disadvantages are lower efficiency, lower
maximum input voltage, and higher dropout voltage. The
VOUT + VD
1– fSW •tOFF(MIN)
V
=
– VD + VSW
IN(MIN)
where V
is the minimum input voltage, V
D
is the
SW
SW
IN(MIN)
OUT
highest acceptable switching frequency (f
given application can be calculated as follows:
) for a
SW(MAX)
output voltage, V is the catch diode drop (~0.7V), V
is the internal switch drop (~0.5V at max load), f is
the switching frequency (set by RT), and t
VOUT + VD
is the
OFF(MIN)
fSW(MAX)
=
minimumswitchoff-time(160ns).Notethathigherswitch-
ing frequency will increase the minimum input voltage.
tON(MIN) V – V + VD
(
)
IN
SW
3990fa
10
LT3990/LT3990-3.3/LT3990-5
APPLICATIONS INFORMATION
If a lower dropout voltage is desired, a lower switching
frequency should be used.
where V is the voltage drop of the catch diode (~0.7V),
D
L is in µH and f is in MHz. The inductor’s RMS current
SW
rating must be greater than the maximum load current
and its saturation current should be about 30% higher.
For robust operation in fault conditions (start-up or short
circuit) and high input voltage (>30V), the saturation
current should be above 800mA. To keep the efficiency
high, the series resistance (DCR) should be less than
0.1Ω, and the core material should be intended for high
frequency applications. Table 2 lists several vendors and
suitable types.
The highest allowed V during normal operation
IN(OP-MAX)
be calculated by the following equation:
IN
(V
) is limited by minimum duty cycle and can
VOUT + VD
fSW •tON(MIN)
V
=
– VD + VSW
IN(OP-MAX)
where t
is the minimum switch on-time.
ON(MIN)
However, the circuit will tolerate inputs up to the absolute
This simple design guide will not always result in the
optimum inductor selection for a given application. As a
general rule, lower output voltages and higher switching
frequency will require smaller inductor values. If the ap-
plication requires less than 350mA load current, then a
lesser inductor value may be acceptable. This allows use
of a physically smaller inductor, or one with a lower DCR
resulting in higher efficiency. There are several graphs in
theTypicalPerformanceCharacteristicssectionofthisdata
sheet that show the maximum load current as a function
of input voltage for several popular output voltages. Low
inductance may result in discontinuous mode operation,
which is acceptable but reduces maximum load current.
For details of maximum output current and discontinu-
ous mode operation, see Linear Technology Application
maximumratingsoftheV andBOOSTpins,regardlessof
IN
chosenswitchingfrequency.Duringsuchtransientswhere
V ishigherthanV
IN
,theswitchingfrequencywill
IN(OP-MAX)
be reduced below the programmed frequency to prevent
damage to the part. The output voltage ripple and inductor
current ripple may also be higher than in typical operation,
however the output will still be in regulation.
Inductor Selection
For a given input and output voltage, the inductor value
and switching frequency will determine the ripple current.
The ripple current increases with higher V or V
and
IN
OUT
decreases with higher inductance and faster switching
frequency. A good starting point for selecting the induc-
tor value is:
Note 44.Finally,fordutycyclesgreaterthan50%(V /V
OUT IN
VOUT + VD
> 0.5), there is a minimum inductance required to avoid
subharmonic oscillations. See Application Note 19.
L = 3
fSW
Table 2. Inductor Vendors
Input Capacitor
VENDOR
Coilcraft
Sumida
URL
Bypass the input of the LT3990 circuit with a ceramic
capacitor of X7R or X5R type. Y5V types have poor
performance over temperature and applied voltage, and
should not be used. A 1µF to 4.7µF ceramic capacitor
is adequate to bypass the LT3990 and will easily handle
the ripple current. Note that larger input capacitance
is required when a lower switching frequency is used
www.coilcraft.com
www.sumida.com
www.tokoam.com
www.we-online.com
www.cooperet.com
www.murata.com
Toko
Würth Elektronik
Coiltronics
Murata
3990fa
11
LT3990/LT3990-3.3/LT3990-5
APPLICATIONS INFORMATION
(due to longer on-times). If the input power source has
high impedance, or there is significant inductance due to
long wires or cables, additional bulk capacitance may be
necessary. This can be provided with a low performance
electrolytic capacitor.
the output ripple, so low impedance (at the switching
frequency) is important. The output ripple decreases with
increasing output capacitance, down to approximately
1mV. See Figure 1. Note that a larger phase lead capacitor
should be used with a large output capacitor.
18
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple
attheLT3990andtoforcethisveryhighfrequencyswitch-
ing current into a tight local loop, minimizing EMI. A 1µF
capacitor is capable of this task, but only if it is placed
closetotheLT3990(seethePCBLayoutsection).Asecond
precautionregardingtheceramicinputcapacitorconcerns
themaximuminputvoltageratingoftheLT3990.Aceramic
input capacitor combined with trace or cable inductance
forms a high quality (under damped) tank circuit. If the
LT3990 circuit is plugged into a live supply, the input volt-
agecanringtotwiceitsnominalvalue, possiblyexceeding
theLT3990’svoltagerating.Thissituationiseasilyavoided
(see the Hot Plugging Safely section).
FRONT PAGE APPLICATION
f = 600kHz
16
C
= 47pF FOR C
≥ 47µF
LEAD
OUT
14
12
10
8
6
4
V
= 24V
60
IN
2
V
= 12V
IN
0
0
80
100
20
40
C
(µF)
OUT
3990 F01
Figure 1. Worst-Case Output Ripple Across Full Load Range
When choosing a capacitor, look carefully through the
data sheet to find out what the actual capacitance is under
operating conditions (applied voltage and temperature).
A physically larger capacitor or one with a higher voltage
rating may be required. Table 3 lists several capacitor
vendors.
Output Capacitor and Output Ripple
The output capacitor has two essential functions. It stores
energy in order to satisfy transient loads and stabilize the
LT3990’s control loop. Ceramic capacitors have very low
equivalent series resistance (ESR) and provide the best
ripple performance. A good starting value is:
Table 3. Recommended Ceramic Capacitor Vendors
MANUFACTURER
AVX
WEBSITE
50
VOUT •fSW
www.avxcorp.com
www.murata.com
www.t-yuden.com
www.vishay.com
www.tdk.com
COUT
=
Murata
Taiyo Yuden
Vishay Siliconix
TDK
where f is in MHz and C
is the recommended output
OUT
SW
capacitance in μF. Use X5R or X7R types. This choice will
provide low output ripple and good transient response.
Transientperformancecanbeimprovedwithahighervalue
capacitorifcombinedwithaphaseleadcapacitor(typically
22pF) between the output and the feedback pin. A lower
value of output capacitor can be used to save space and
cost but transient performance will suffer.
Ceramic Capacitors
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
whenusedwiththeLT3990duetotheirpiezoelectricnature.
When in Burst Mode operation, the LT3990’s switching
frequency depends on the load current, and at very light
loads the LT3990 can excite the ceramic capacitor at audio
frequencies, generating audible noise. Since the LT3990
The second function is that the output capacitor, along
with the inductor, filters the square wave generated by the
LT3990toproducetheDCoutput. Inthisroleitdetermines
3990fa
12
LT3990/LT3990-3.3/LT3990-5
APPLICATIONS INFORMATION
500
operates at a lower current limit during Burst Mode op-
eration, the noise is typically very quiet to a casual ear. If
this is unacceptable, use a high performance tantalum or
electrolytic capacitor at the output.
FRONT PAGE APPLICATION
400
300
200
100
0
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LT3990. As pre-
viously mentioned, a ceramic input capacitor combined
with trace or cable inductance forms a high quality (under
damped)tankcircuit. IftheLT3990circuitispluggedintoa
live supply, the input voltage can ring to twice its nominal
value,possiblyexceedingtheLT3990’srating.Thissituation
is easily avoided (see the Hot Plugging Safely section).
0
50 100 150 200 250 300 350
LOAD CURRENT (mA)
3990 F03
Figure 3. Switching Frequency in Burst Mode Operation
Low Ripple Burst Mode Operation
At higher output loads (above ~35mA for the front page
application) the LT3990 will be running at the frequency
To enhance efficiency at light loads, the LT3990 operates
inlowrippleBurstModeoperationwhichkeepstheoutput
capacitor charged to the proper voltage while minimizing
the input quiescent current. During Burst Mode opera-
tion, the LT3990 delivers single cycle bursts of current to
the output capacitor followed by sleep periods where the
output power is delivered to the load by the output capaci-
tor. Because the LT3990 delivers power to the output with
single, low current pulses, the output ripple is kept below
5mV for a typical application. See Figure 2.
programmed by the R resistor, and will be operating in
T
standard PWM mode. The transition between PWM and
low ripple Burst Mode is seamless, and will not disturb
the output voltage.
BOOST and BD Pin Considerations
CapacitorC3andtheinternalboostSchottkydiode(seethe
Block Diagram) are used to generate a boost voltage that
is higher than the input voltage. In most cases a 0.22µF
capacitor will work well. Figure 4 shows two ways to ar-
range the boost circuit. The BOOST pin must be more than
1.9V above the SW pin for best efficiency. For outputs of
2.2V and above, the standard circuit (Figure 4a) is best.
For outputs between 2.2V and 2.5V, use a 0.47µF boost
capacitor. For output voltages below 2.2V, the boost diode
can be tied to the input (Figure 4b), or to another external
supply greater than 2.2V. However, the circuit in Figure 4a
is more efficient because the BOOST pin current and BD
pin quiescent current come from a lower voltage source.
Also, be sure that the maximum voltage ratings of the
BOOST and BD pins are not exceeded.
Astheloadcurrentdecreasestowardsanoloadcondition,
the percentage of time that the LT3990 operates in sleep
mode increases and the average input current is greatly
reduced resulting inhigh efficiencyevenatvery lowloads.
Note that during Burst Mode operation, the switching
frequency will be lower than the programmed switching
frequency. See Figure 3.
V
SW
5V/DIV
I
L
100mA/DIV
V
OUT
5mV/DIV
The minimum operating voltage of an LT3990 application
is limited by the minimum input voltage (4.2V) and by the
maximum duty cycle as outlined in a previous section. For
proper start-up, the minimum input voltage is also limited
by the boost circuit. If the input voltage is ramped slowly,
the boost capacitor may not be fully charged. Because
3990 G28
2µs/DIV
FRONT PAGE APPLICATION
V
V
= 12V
IN
= 5V
OUT
LOAD
I
= 10mA
f = 600kHz
Figure 2. Burst Mode Operation
3990fa
13
LT3990/LT3990-3.3/LT3990-5
APPLICATIONS INFORMATION
V
OUT
5.0
4.5
4.0
3.5
3.0
2.5
FRONT PAGE APPLICATION
= 3.3V
V
OUT
BD
V
V
IN
BOOST
LT3990
IN
C3
TO START
TO RUN
SW
GND
(4a) For V
≥ 2.2V
OUT
BD
0
50 100 150 200 250 300 350
LOAD CURRENT (mA)
V
V
IN
BOOST
LT3990
IN
C3
6.5
6.0
5.5
5.0
4.5
4.0
V
FRONT PAGE APPLICATION
OUT
SW
OUT
V
= 5V, f = 600kHz
GND
TO START
3990 F04
(4b) For V
< 2.2V; V < 30V
IN
OUT
TO RUN
Figure 4. Two Circuits for Generating the Boost Voltage
the boost capacitor is charged with the energy stored
in the inductor, the circuit will rely on some minimum
load current to get the boost circuit running properly.
This minimum load will depend on input and output volt-
ages, and on the arrangement of the boost circuit. The
minimum load generally goes to zero once the circuit has
started. Figure 5 shows a plot of minimum load to start
and to run as a function of input voltage. In many cases
the discharged output capacitor will present a load to the
switcher, which will allow it to start. The plots show the
0
50 100 150 200 250 300 350
3990 F05
LOAD CURRENT (mA)
Figure 5. The Minimum Input Voltage Depends on
Output Voltage, Load Current and Boost Circuit
source resistance. A switching regulator draws constant
power from the source, so source current increases as
source voltage drops. This looks like a negative resistance
loadtothesourceandcancausethesourcetocurrentlimit
or latch low under low source voltage conditions. UVLO
prevents the regulator from operating at source voltages
where the problems might occur. The UVLO threshold can
be adjusted by setting the values R3 and R4 such that they
satisfy the following equation:
worst-case situation where V is ramping very slowly.
IN
For lower start-up voltage, the boost diode can be tied to
V ; however, this restricts the input range to one-half of
IN
the absolute maximum rating of the BOOST pin.
Enable and Undervoltage Lockout
The LT3990 is in shutdown when the EN/UVLO pin is low
and active when the pin is high. The rising threshold of the
EN/UVLO comparator is 1.19V, with a 35mV hysteresis.
This threshold is accurate when V is above 4.2V. If V
is lower than 4.2V, tie EN/UVLO pin to GND to place the
R3+ R4
VUVLO
=
•1.19V
R4
IN
IN
where switching should not start until V is above V
Note that due to the comparator’s hysteresis, switching
will not stop until the input falls slightly below V
Undervoltage lockout is functional only when V
greater than 5V.
.
UVLO
IN
part in shutdown.
.
UVLO
is
Figure 6 shows how to add undervoltage lockout (UVLO)
to the LT3990. Typically, UVLO is used in situations where
the input supply is current limited, or has a relatively high
UVLO
3990fa
14
LT3990/LT3990-3.3/LT3990-5
APPLICATIONS INFORMATION
LT3990
D4
BD
BOOST
LT3990
EN/UVLO SW
V
V
IN
IN
V
V
IN
IN
R3
R4
1.19V
EN/UVLO
+
–
SHDN
V
OUT
GND
FB
3990 F06
+
BACKUP
Figure 6. Undervoltage Lockoout
3990 F07
Shorted and Reversed Input Protection
Figure 7. Diode D4 Prevents a Shorted Input from Discharging a
Backup Battery Tied to the Output. It Also Protects the Circuit from
a Reversed Input. The LT3990 Runs Only when the Input Is Present
If the inductor is chosen so that it won’t saturate exces-
sively, a LT3990 buck regulator will tolerate a shorted
output. There is another situation to consider in systems
where the output will be held high when the input to the
LT3990 is absent. This may occur in battery charging ap-
plications or in battery backup systems where a battery
or some other supply is diode ORed with the LT3990’s
GND
GND
1
2
3
4
5
10
9
EN/UVLO
PG
output. If the V pin is allowed to float and the EN/UVLO
V
8
IN
IN
7
pin is held high (either by a logic signal or because it is
6
tied to V ), then the LT3990’s internal circuitry will pull
IN
its quiescent current through its SW pin. This is fine if the
system can tolerate a few µA in this state. If the EN/UVLO
pin is grounded, the SW pin current will drop to 0.7µA.
V
GND
OUT
3990 F08
However, if the V pin is grounded while the output is held
VIAS TO LOCAL GROUND PLANE
VIAS TO V
IN
OUT
high, regardless of EN/UVLO, parasitic diodes inside the
LT3990 can pull current from the output through the SW
Figure 8. A Good PCB Layout Ensures Proper, Low EMI Operation
pin and the V pin. Figure 7 shows a circuit that will run
IN
only when the input voltage is present and that protects
output capacitor, should be placed on the same side of
the circuit board, and their connections should be made
on that layer. Place a local, unbroken ground plane below
these components. The SW and BOOST nodes should be
as small as possible. Finally, keep the FB nodes small so
that the ground traces will shield them from the SW and
BOOST nodes. The exposed pad on the bottom must be
soldered to ground so that the pad acts as a heat sink. To
keep thermal resistance low, extend the ground plane as
much as possible, and add thermal vias under and near
the LT3990 to additional ground planes within the circuit
board and on the bottom side.
against a shorted or reversed input.
PCB Layout
For proper operation and minimum EMI, care must
be taken during printed circuit board layout. Figure 8
shows the recommended component placement with
trace, ground plane and via locations. Note that large,
switched currents flow in the LT3990’s V and SW pins,
IN
the internal catch diode and the input capacitor. The loop
formed by these components should be as small as pos-
sible. These components, along with the inductor and
3990fa
15
LT3990/LT3990-3.3/LT3990-5
APPLICATIONS INFORMATION
Hot Plugging Safely
Power dissipation within the LT3990 can be estimated by
calculatingthetotalpowerlossfromanefficiencymeasure-
ment and subtracting inductor loss. The die temperature
is calculated by multiplying the LT3990 power dissipation
by the thermal resistance from junction to ambient.
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LT3990 circuits. However, these ca-
pacitors can cause problems if the LT3990 is plugged into
a live supply. The low loss ceramic capacitor, combined
with stray inductance in series with the power source,
forms an under damped tank circuit, and the voltage at
Finally, be aware that at high ambient temperatures the
internalSchottkydiodewillhavesignificantleakagecurrent
(see Typical Performance Characteristics) increasing the
quiescent current of the LT3990 converter.
the V pin of the LT3990 can ring to twice the nominal
IN
input voltage, possibly exceeding the LT3990’s rating and
damaging the part. If the input supply is poorly controlled
or the user will be plugging the LT3990 into an energized
supply, the input network should be designed to prevent
thisovershoot.SeeLinearTechnologyApplicationNote 88
for a complete discussion.
Fault Tolerance
The LT3990 regulator in the MSOP package is designed to
tolerate single fault conditions. Shorting any two adjacent
pins together or leaving any one single pin floating does
not raise V
above the programmed value or cause
OUT
damage to the part.
High Temperature Considerations
The NC pins are not connected to internal circuitry and
must be left floating to ensure fault tolerance.
For higher ambient temperatures, care should be taken in
the layout of the PCB to ensure good heat sinking of the
LT3990. The exposed pad on the bottom must be soldered
to a ground plane. This ground should be tied to large
copper layers below with thermal vias; these layers will
spreadtheheatdissipatedbytheLT3990.Placingadditional
vias can reduce thermal resistance further. The maximum
loadcurrentshouldbederatedastheambienttemperature
approaches the maximum junction rating.
Other Linear Technology Publications
Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 100
shows how to generate a bipolar output supply using a
buck regulator.
3990fa
16
LT3990/LT3990-3.3/LT3990-5
TYPICAL APPLICATIONS
3.3V Step-Down Converter
5V Step-Down Converter
V
V
IN
6.5V TO 62V
IN
4.2V TO 62V
C3
0.22µF
C3
0.22µF
V
BOOST
LT3990
EN/UVLO SW
V
BOOST
LT3990
EN/UVLO SW
IN
IN
L1
L1
33µH
33µH
V
V
OUT
OUT
3.3V
5V
OFF ON
OFF ON
350mA
350mA
PG
PG
BD
BD
R1
R1
22pF
22pF
1M
1M
C1
2.2µF
C1
2.2µF
C2
22µF
C2
22µF
RT
FB
RT
FB
GND
GND
R2
576k
R2
316k
374k
f = 400kHz
374k
f = 400kHz
3990 TA02
3990 TA03
3.3V Step-Down Converter
5V Step-Down Converter
V
V
IN
6.5V TO 62V
IN
4.2V TO 62V
0.22µF
33µH
0.22µF
33µH
V
BOOST
V
BOOST
LT3990-5
EN/UVLO SW
IN
IN
LT3990-3.3
V
V
OUT
OUT
3.3V
5V
OFF ON
EN/UVLO SW
OFF ON
350mA
350mA
PG
PG
BD
BD
RT
V
OUT
RT
V
OUT
22µF
22µF
2.2µF
2.2µF
GND
GND
374k
f = 400kHz
374k
f = 400kHz
3990 TA10
3990 TA11
2.5V Step-Down Converter
1.8V Step-Down Converter
V
V
IN
4.2V TO 30V
IN
4.2V TO 62V
C3
0.47µF
C3
0.22µF
V
BOOST
LT3990
EN/UVLO SW
V
BOOST
LT3990
IN
IN
L1
L1
22µH
33µH
V
V
OUT
OUT
2.5V
1.8V
OFF ON
OFF ON
EN/UVLO SW
350mA
350mA
PG
BD
PG
BD
R1
R1
47pF
47pF
1M
487k
C1
2.2µF
C1
2.2µF
C2
47µF
C2
47µF
RT
FB
RT
FB
GND
GND
R2
931k
R2
1M
511k
f = 300kHz
374k
3990 TA04
3990 TA05
f = 400kHz
3990fa
17
LT3990/LT3990-3.3/LT3990-5
TYPICAL APPLICATIONS
12V Step-Down Converter
5V, 2MHz Step-Down Converter
V
V
IN
IN
8.5V TO 16V
TRANSIENTS
TO 62V
15V TO 62V
C3
C3
0.1µF
0.1µF
V
BOOST
LT3990
EN/ULVO SW
IN
L1
33µH
V
BOOST
LT3990
EN/UVLO SW
IN
L1
10µH
V
OUT
V
12V
OFF ON
OUT
5V
OFF ON
350mA
PG
BD
350mA
R1
PG
BD
22pF
R1
1M
22pF
C1
2.2µF
C2
22µF
RT
FB
1M
C1
1µF
C2
10µF
RT
FB
GND
R2
113k
127k
f = 1MHz
GND
R2
316k
51.1k
f = 2MHz
3990 TA06
3990 TA07
5V Step-Down Converter with Undervoltage Lockout
V
IN
kΩ
6.5V TO 62V
+
–
0.22µF
33µH
V
BOOST
LT3990
EN/UVLO SW
IN
5.6M
V
OUT
5V
350mA
PG
BD
1.3M
2.2µF
22pF
1M
RT
FB
22µF
GND
316k
374k
f = 400kHz
3990 TA08a
Input Current During Start-Up
Start-Up from High Impedance Input Source
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
UVLO PROGRAMMED TO 6.5V
INPUT CURRENT
DROPOUT
V
IN
5V/DIV
CONDITIONS
FRONT PAGE
APPLICATION
V
OUT
2V/DIV
FRONT PAGE
APPLICATION
WITH UVLO
PROGRAMMED
TO 6.5V
3990 TA08c
5ms/DIV
FRONT PAGE APPLICATION
V
V
= 12V
OUT
IN
= 5V
1k INPUT SOURCE RESISTANCE
2.5mA LOAD
–0.5
0
2
6
8
10
12
4
INPUT VOLTAGE (V)
3990 TA08b
3990fa
18
LT3990/LT3990-3.3/LT3990-5
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699 Rev C)
0.70 ±0.05
3.55 ±0.05
2.15 ±0.05 (2 SIDES)
1.65 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.125
0.40 ± 0.10
TYP
6
10
3.00 ±0.10
(4 SIDES)
1.65 ± 0.10
(2 SIDES)
PIN 1 NOTCH
R = 0.20 OR
PIN 1
TOP MARK
(SEE NOTE 6)
0.35 × 45°
CHAMFER
(DD) DFN REV C 0310
5
1
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
0.200 REF
2.38 ±0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
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
3990fa
19
LT3990/LT3990-3.3/LT3990-5
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
MSE Package
16-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1667 Rev E)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 ±0.102
(.112 ±.004)
2.845 ±0.102
(.112 ±.004)
0.889 ±0.127
(.035 ±.005)
1
8
0.35
REF
5.23
(.206)
MIN
1.651 ±0.102
(.065 ±.004)
1.651 ±0.102
(.065 ±.004)
3.20 – 3.45
(.126 – .136)
0.12 REF
DETAIL “B”
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
DETAIL “B”
16
9
0.305 ±0.038
0.50
(.0197)
BSC
NO MEASUREMENT PURPOSE
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
(.0120 ±.0015)
TYP
0.280 ±0.076
(.011 ±.003)
RECOMMENDED SOLDER PAD LAYOUT
16151413121110
9
REF
DETAIL “A”
0.254
(.010)
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
0° – 6° TYP
4.90 ±0.152
(.193 ±.006)
GAUGE PLANE
0.53 ±0.152
(.021 ±.006)
1 2 3 4 5 6 7 8
DETAIL “A”
0.86
(.034)
REF
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.1016 ±0.0508
(.004 ±.002)
MSOP (MSE16) 0911 REV E
0.50
(.0197)
BSC
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 INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL
NOT EXCEED 0.254mm (.010") PER SIDE.
3990fa
20
LT3990/LT3990-3.3/LT3990-5
REVISION HISTORY (Revision history begins at Rev B)
REV
DATE
DESCRIPTION
PAGE NUMBER
B
08/12 Title, Features, Typical Application clarified to add fixed output versions
Clarified Absolute Maximum Ratings, added H-grade option
Clarified pinout for fixed voltage options, clarified Ordering Information for fixed output and H-grades
Clarified Electrical Characteristics table
1
2
2
3
Clarified Typical Performance Characteristics
4, 6
7, 8
14, 15
17
Clarified Pin Functions and Block Diagram
Clarified EN/UVLO text and formula
Clarified Typical Applications
3990fa
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.
21
LT3990/LT3990-3.3/LT3990-5
TYPICAL APPLICATION
1.21V Step-Down Converter
V
IN
4.2V TO 30V
C3
0.22µF
V
BOOST
LT3990
EN/UVLO SW
IN
L1
15µH
V
OUT
1.2V
OFF ON
350mA
BD
PG
RT
FB
C1
2.2µF
C2
47µF
GND
374k
3990 TA09
f = 400kHz
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT3970/LT3970-3.3/ 40V, 350mA, 2.2MHz High Efficiency Micropower Step-Down DC/DC V : 4.2V to 40V, V
= 1.21V, I = 2.5µA, I < 1µA,
Q SD
IN
OUT(MIN)
LT3970-5
Converter with I = 2.5µA
3mm × 2mm DFN-10, MSOP-10
Q
LT3971
38V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC
V : 4.3V to 38V, V = 1.2V, I = 2.8µA, I < 1µA,
IN
OUT(MIN)
Q
SD
Converter with I = 2.8µA
3mm × 3mm DFN-10, MSOPE-10
Q
LT3991
LT3682
55V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC
V : 4.3V to 55V, V = 1.2V, I = 2.8µA, I < 1µA,
IN
OUT(MIN)
Q
SD
Converter with I = 2.8µA
3mm × 3mm DFN-10, MSOPE-10
Q
36V, 60V
, 1A, 2.2MHz High Efficiency Micropower Step-Down
V : 3.6V to 36V, V = 0.8V, I = 75µA, I < 1µA,
MAX
IN
OUT(MIN)
Q
SD
DC/DC Converter
3mm × 3mm DFN-12
3990fa
LT 0812 REV A • PRINTED IN USA
22 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
LINEAR TECHNOLOGY CORPORATION 2010
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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