LINER LT3990IMSTRPBF 60v, 350ma step-down regulator with 2.5î¼a quiescent current and integrated diode Datasheet

Electrical Specifications Subject to Change
LT3990
60V, 350mA Step-Down
Regulator with 2.5µA
Quiescent Current and
Integrated Diodes
FEATURES
DESCRIPTION
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The LT®3990 is an adjustable frequency monolithic buck
switching regulator that accepts a wide input voltage
range up to 60V, 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 necessary oscillator, control and logic circuitry. Low ripple Burst
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 enable pin with accurate
threshold is available, producing a low shutdown current
of 0.7μA. A power good flag signals when VOUT reaches
90% of the programmed output voltage. The LT3990 is
available in small 10-pin MSOP and 3mm × 2mm DFN
packages.
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n
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Low Ripple Burst Mode® Operation
2.5μA IQ at 12VIN to 3.3VOUT
Output Ripple < 5mVP-P
Wide Input Voltage Range: 4.2V to 60V Operating
Adjustable Switching Frequency: 200kHz to 2.2MHz
Integrated Boost and Catch Diodes
350mA Output Current
Accurate 1V Enable Pin Threshold
Low Shutdown Current: IQ = 0.7μA
Internal Sense Limits Catch Diode Current
Power Good Flag
Output Voltage: 1.21V to 25V
Internal Compensation
Small 10-Pin MSOP and (3mm × 2mm) DFN Packages
APPLICATIONS
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Automotive Battery Regulation
Power for Portable Products
Industrial Supplies
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.
TYPICAL APPLICATION
5V Step-Down Converter
Efficiency
90
VIN = 12V
VIN
6V TO 60V
0.22μF
LT3990
OFF ON
22μH
EN
PG
SW
RT
FB
226k
f = 600kHz
VOUT
5V
350mA
BD
22pF
2.2μF
80
BOOST
GND
1M
22μF
316k
3990 TA01a
EFFICIENCY (%)
VIN
70
60
50
40
30
0.01
0.1
1
10
LOAD CURRENT (mA)
100
3990 TA01b
3990p
1
LT3990
ABSOLUTE MAXIMUM RATINGS (Note 1)
VIN, EN Voltage .........................................................60V
BOOST Pin Voltage ...................................................75V
BOOST Pin Above SW Pin.........................................30V
FB, RT Voltage.............................................................6V
PG, BD Voltage .........................................................30V
Operating Junction Temperature Range (Note 2)
LT3990E ............................................. –40°C to 125°C
LT3990I .............................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
MS Only ............................................................ 300°C
PIN CONFIGURATION
TOP VIEW
FB 1
10 RT
EN 2
9
PG
8
BD
GND 4
7
BOOST
GND 5
6
SW
VIN 3
11
TOP VIEW
FB
EN
VIN
GND
GND
10
9
8
7
6
1
2
3
4
5
RT
PG
BD
BOOST
SW
MS PACKAGE
10-LEAD PLASTIC MSOP
DDB PACKAGE
10-LEAD (3mm s 2mm) PLASTIC DFN
θJA = 100°C/W
θJA = 76°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3990EDDB#PBF
LT3990EDDB#TRPBF
LFCZ
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3990IDDB#PBF
LT3990IDDB#TRPBF
LFCZ
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3990EMS#PBF
LT3990EMS#TRPBF
LTFDB
10-Lead Plastic MSOP
–40°C to 125°C
LT3990IMS#PBF
LT3990IMS#TRPBF
LTFDB
10-Lead Plastic MSOP
–40°C to 125°C
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/
3990p
2
LT3990
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
l
Minimum Input Voltage
Quiescent Current from VIN
VEN Low
VEN High
VEN High
l
Feedback Voltage
l
1.195
1.185
l
TYP
MAX
4
4.2
V
0.7
1.7
0.98
2.7
3.5
μA
μA
μA
1.21
1.21
1.225
1.235
V
V
0.1
20
nA
0.0002
0.01
%/V
1.76
640
160
2.25
800
200
2.64
960
240
MHz
kHz
kHz
VIN = 5V, VFB = 0V
535
700
865
mA
VIN = 5V
350
400
500
mA
FB Pin Bias Current (Note 3)
FB Voltage Line Regulation
4.2V < VIN < 60V
Switching Frequency
RT = 41.2k, VIN = 6V
RT = 158k, VIN = 6V
RT = 768k, VIN = 6V
Switch Current Limit
Catch Schottky Current Limit
Switch VCESAT
ISW = 200mA
300
Switch Leakage Current
0.05
ISCH = 100mA, VIN = VBD = NC
650
Catch Schottky Reverse Leakage
VSW = 12V
0.05
Boost Schottky Forward Voltage
ISCH = 50mA, VIN = NC, VBOOST = 0V
875
Boost Schottky Reverse Leakage
VREVERSE = 12V
Catch Schottky Forward Voltage
l
Minimum Boost Voltage (Note 4)
VIN = 5V
BOOST Pin Current
ISW = 200mA, VBOOST = 15V
EN Pin Current
VEN = 12V
EN Voltage Threshold
EN Rising, VIN ≥ 4.2V
l
0.95
EN Voltage Hysteresis
PG Threshold Offset from Feedback Voltage
PG Sink Current
VFB Rising
80
2
VPG = 3V
2
VPG = 0.4V
VIN = 10V
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: 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.
l
40
μA
mV
0.02
2
1.4
1.8
5.5
8
mA
1
30
nA
1
1.05
V
120
0.01
l
μA
mV
μA
V
mV
160
12
Minimum Switch On-Time
Minimum Switch Off-Time
mV
30
PG Hysteresis
PG Leakage
UNITS
mV
mV
1
μA
80
μA
90
ns
100
160
ns
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.
3990p
3
LT3990
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Efficiency, VOUT = 3.3V
Efficiency, VOUT = 5V
VFB vs Temperature
90
90
1.220
FRONT PAGE APPLICATION
80
VIN = 12V
EFFICIENCY (%)
VIN = 36V
60
50
FRONT PAGE APPLICATION
VOUT = 3.3V
R1 = 1M
R2 = 576k
40
30
0.01
0.1
1
10
LOAD CURRENT (mA)
70
1.210
VIN = 36V
60
1.205
50
1.200
40
30
0.01
100
0.1
1
10
LOAD CURRENT (mA)
No-Load Supply Current
3.0
2.5
2.0
12
SUPPLY CURRENT (μA)
SUPPLY CURRENT (µA)
3.5
Maximum Load Current
550
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 3.3V
R1 = 1M
R2 = 576k
9
6
FRONT PAGE APPLICATION
VOUT = 3.3V
TYPICAL
500
MINIMUM
450
400
3
1.5
1.0
5
10
25
30
15
20
INPUT VOLTAGE (V)
35
0
–50 –25
40
0
Maximum Load Current
500
LOAD CURRENT (mA)
TYPICAL
500
MINIMUM
450
400
5
10
15
20
25
30
INPUT VOLTAGE (V)
35
40
3990 G07
30
15
20
25
INPUT VOLTAGE (V)
300
35
40
Load Regulation
0.20
0.15
LIMITED BY CURRENT LIMIT
400
LIMITED BY MAXIMUM
JUNCTION TEMPERATURE;
QJA = 76°C/W
200
100
350
10
3990 G06
600
FRONT PAGE APPLICATION
VOUT = 5V
550
5
3990 G05
Maximum Load Current
600
350
25 50
75 100 125 150
TEMPERATURE (°C)
3990 G04
LOAD CURRENT (mA)
25 50
75 100 125 150
TEMPERATURE (°C)
3990 G03
No-Load Supply Current
15
FRONT PAGE APPLICATION
VOUT = 3.3V
R1 = 1M
R2 = 576k
0
3990 G02
3990 G01
4.0
1.195
–50 –25
100
LOAD REGULATION (%)
EFFICIENCY (%)
70
1.215
VIN = 12V
VIN = 24V
VFB (V)
VIN = 24V
LOAD CURRENT (mA)
80
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
0.10
0.05
0
–0.05
–0.10
–0.15 FRONT PAGE APPLICATION
REFERENCED FROM VOUT AT 100mA LOAD
–0.20
50
100 150 200 250 300 350
0
LOAD CURRENT (mA)
3990 G08
3990 G09
3990p
4
LT3990
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Switch Current Limit
Switch Current Limit
800
Switching Frequency
2.4
800
2.2
600
500
CATCH DIODE VALLEY CURRENT LIMIT
400
300
700
2.0
1.8
FREQUENCY (MHz)
SWITCH PEAK
CURRENT LIMIT
SWITCH CURRENT LIMIT (mA)
SWITCH CURRENT LIMIT (mA)
SWITCH PEAK CURRENT LIMIT
700
600
500
CATCH DIODE VALLEY CURRENT LIMIT
400
1.6
1.4
1.2
1.0
0.8
0.6
300
0.4
0.2
200
0
20
40
60
DUTY CYCLE (%)
200
–50 –25
100
80
0
3990 G10
3990 G12
Switch VCESAT (ISW = 200mA)
vs Temperature
Switch VCESAT
350
LOAD CURRENT = 175mA
500
160
140
MINIMUM OFF-TIME
120
100
80
MINIMUM ON-TIME
60
SWITCH VCESAT (mV)
400
SWITCH VCESAT (mV)
300
250
40
300
200
100
20
0
200
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
5.0
14
6.5
4.5
INPUT VOLTAGE (V)
6
4
300
400
200
SWITCH CURRENT (mA)
500
Minimum Input Voltage,
VOUT = 5V
FRONT PAGE APPLICATION
VOUT = 3.3V
12
8
100
3990 G15
Minimum Input Voltage,
VOUT = 3.3V
BOOST Pin Current
10
0
3990 G14
3990 G13
FRONT PAGE APPLICATION
VOUT = 5V
6.0
INPUT VOLTAGE (V)
SWITCH ON-TIME/SWITCH OFF-TIME (ns)
25 50 75 100 125 150
TEMPERATURE (°C)
180
0
–50 –25
BOOST PIN CURRENT (mA)
0
3990 G11
Minimum
Switch On-Time/Switch Off-Time
200
0
–50 –25
25 50 75 100 125 150
TEMPERATURE (oC)
TO START
4.0
TO RUN
3.5
3.0
TO START
5.5
TO RUN
5.0
4.5
2
0
0
100
200
300
400
SWITCH CURRENT (mA)
500
3990 G16
2.5
0
50
100 150 200 250
LOAD CURRENT (mA)
300
350
3990 G17
4.0
0
50
100 150 200 250
LOAD CURRENT (mA)
300
350
3990 G17
3990p
5
LT3990
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Boost Diode Forward Voltage
Catch Diode Forward Voltage
CATCH DIODE VF (V)
BOOST DIODE VF (V)
1.0
0.8
0.6
0.4
–50°C
25°C
125°C
150°C
0.2
0
0
50
100
150
BOOST DIODE CURRENT (mA)
20
0.8
16
0.6
0.4
–50°C
25°C
125°C
150°C
0.2
0
200
100
300
200
CATCH DIODE CURRENT (mA)
0
3990 G19
400
VR = 12V
12
8
4
0
–50 –25
0
25 50
75 100 125 150
TEMPERATURE (°C)
3990 G20
Power Good Threshold
3990 G21
Transient Load Response; Load
Current is Stepped from 10mA
(Burst Mode Operation) to 110mA
EN Threshold
1.050
THRESHOLD VOLTAGE (V)
92
91
THRESHOLD (%)
Catch Diode Leakage
1.0
CATCH DIODE LEAKAGE (μA)
1.2
90
89
88
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1.025
VOUT
100mV/DIV
1.000
IL
100mA/DIV
100μs/DIV
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
0.975
0.950
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3990 G22
3990 G23
Transient Load Response; Load
Current is Stepped from 100mA
to 200mA
VOUT
100mV/DIV
IL
100mA/DIV
100μs/DIV
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
3990 G25
3990 G24
Switching Waveforms,
Burst Mode Operation
Switching Waveforms, Full
Frequency Continuous Operation
VSW
5V/DIV
VSW
5mV/DIV
IL
100mA/DIV
IL
200mA/DIV
VOUT
5mV/DIV
VOUT
5mV/DIV
2μs/DIV
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
ILOAD = 10mA
3990 G26
1μs/DIV
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
ILOAD = 350mA
3990 G27
3990p
6
LT3990
PIN FUNCTIONS
FB (Pin 1): The LT3990 regulates the FB pin to 1.21V. Connect the feedback resistor divider tap to this pin.
EN (Pin 2): The part is in shutdown when this pin is low
and active when this pin is high. The hysteretic threshold
voltage is 1V going up and 0.97V going down. Tie to VIN
if shutdown feature is not used. The EN threshold is accurate only when VIN is above 4.2V. If VIN is lower than
4.2V, ground EN to place the part in shutdown.
VIN (Pin 3): The VIN pin supplies current to the LT3990’s
internal circuitry and to the internal power switch. This
pin must be locally bypassed.
BOOST (Pin 7): This pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar
NPN power switch.
BD (Pin 8): 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.
PG (Pin 9): 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 when
VIN is above 4.2V and EN is high.
GND (Pins 4, 5): Ground.
RT (Pin 10): A resistor is tied between RT and ground to
set the switching frequency.
SW (Pin 6): The SW pin is the output of an internal power
switch. Connect this pin to the inductor.
Exposed Pad (Pin 11, DFN Only): Ground. Must be soldered to PCB.
BLOCK DIAGRAM
3
VIN
C1
VIN
INTERNAL 1.21V REF
1V
2
EN
–
+
8
+
SHDN
–
BD
DBOOST
SLOPE COMP
BOOST
SWITCH LATCH
7
R
10
RT
9
RT
PG
OSCILLATOR
200kHz TO 2.2MHz
+
+
1.09V
ERROR
AMP
–
–
GND
(4, 5)
VC
Q
C3
S
SW
Burst Mode
DETECT
DCATCH
L1
VOUT
6
C2
FB
R2
1
R1
3990 BD
3990p
7
LT3990
OPERATION
The LT3990 is a constant frequency, current mode stepdown 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
between the VIN and SW pins, turning the switch off when
this current reaches a level determined by the voltage at
VC (see Block Diagram). An error amplifier measures the
output voltage through an external resistor divider tied to
the FB pin and servos the VC node. If the error amplifier’s
output increases, more current is delivered to the output;
if it decreases, less current is delivered.
Another comparator monitors the current flowing through
the catch diode and reduces the operating frequency when
the current exceeds the 410mA 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.
An internal regulator provides power to the control circuitry. The bias regulator normally draws power from
the VIN pin, but if the BD pin is connected to an external
voltage higher than 3.2V, bias power will be drawn from
the external source (typically the regulated output voltage).
This improves efficiency.
If the EN pin is low, the LT3990 is shut down and draws
0.7μA from the input. When the EN pin exceeds 1V, the
switching regulator will become active.
The switch driver operates from either VIN or from the
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.
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 1.7μA.
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 VIN is above 4.2V.
3990p
8
LT3990
APPLICATIONS INFORMATION
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resistors according to:
⎛V
⎞
R1= R2 ⎜ OUT – 1⎟
⎝ 1.21 ⎠
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
that can be programmed to switch from 200kHz to 2.2MHz
by using a resistor tied from the RT pin to ground. A table
showing the necessary RT value for a desired switching
frequency is in Table 1.
Table 1. Switching Frequency vs RT Value
SWITCHING FREQUENCY (MHz)
RT VALUE (kΩ)
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
768
499
357
280
226
158
124
100
80.6
68.1
57.6
49.9
42.2
Operating Frequency Trade-Offs
Selection of the operating frequency is a trade-off between
efficiency, component size, minimum dropout voltage and
maximum input voltage. The advantage of high frequency
operation is that smaller inductor and capacitor values may
be used. The disadvantages are lower efficiency, lower
maximum input voltage, and higher dropout voltage. The
highest acceptable switching frequency (fSW(MAX)) for a
given application can be calculated as follows:
fSW(MAX ) =
VOUT + VD
tON(MIN) ( VIN – VSW + VD )
where VIN is the typical input voltage, VOUT is the output
voltage, VD is the integrated catch diode drop (~0.7V),
and VSW is the internal switch drop (~0.5V at max load).
This equation shows that slower switching frequency is
necessary to accommodate high VIN/VOUT ratio.
Lower frequency also allows a lower dropout voltage. The
input voltage range depends on the switching frequency
because the LT3990 switch has finite minimum on and off
times. The switch can turn on for a minimum of ~150ns and
turn off for a minimum of ~160ns (note that the minimum
on-time is a strong function of temperature). This means
that the minimum and maximum duty cycles are:
DCMIN = fSW • tON(MIN)
DCMAX = 1 – fSW • tON(MIN)
where fSW is the switching frequency, the tON(MIN) is the
minimum switch on-time (~150ns), and the tOFF(MIN) is
the minimum 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 adequate input voltage range (see next section) and keep
the inductor and capacitor values small.
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:
VIN(MIN) =
VOUT + VD
–V +V
1– fSW • tOFF(MIN) D SW
where VIN(MIN) is the minimum input voltage, VOUT is the
output voltage, VD is the catch diode drop (~0.7V), VSW
is the internal switch drop (~0.5V at max load), fSW is
the switching frequency (set by RT), and tOFF(MIN) is the
minimum switch off-time (160ns). Note that higher switching frequency will increase the minimum input voltage.
If a lower dropout voltage is desired, a lower switching
frequency should be used.
3990p
9
LT3990
APPLICATIONS INFORMATION
The highest allowed V IN during normal operation
(VIN(OP-MAX)) is limited by minimum duty cycle and can
be calculated by the following equation:
VIN(OP-MAX ) =
VOUT + VD
–V +V
fSW • tON(MIN) D SW
where tON(MIN) is the minimum switch on-time (~150ns).
However, the circuit will tolerate inputs up to the absolute
maximum ratings of the VIN and BOOST pins, regardless of
chosen switching frequency. During such transients where
VIN is higher than VIN(OP-MAX), the switching frequency will
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 VIN or VOUT and
decreases with higher inductance and faster switching
frequency. A good starting point for selecting the inductor value is:
L=3
VOUT + VD
fSW
Table 2. Inductor Vendors
where VD is the voltage drop of the catch diode (~0.7V),
L is in μH and fSW is in MHz. The inductor’s RMS current
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 500mA. 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.
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 application 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
the Typical Performance Characteristics section of this data
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 discontinuous mode operation, see Linear Technology Application
Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN
> 0.5), there is a minimum inductance required to avoid
subharmonic oscillations. See Application Note 19.
VENDOR
URL
Coilcraft
www.coilcraft.com
Input Capacitor
Sumida
www.sumida.com
Toko
www.tokoam.com
Würth Elektronik
www.we-online.com
Coiltronics
www.cooperet.com
Murata
www.murata.com
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
3990p
10
LT3990
APPLICATIONS INFORMATION
Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple
at the LT3990 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 1μF
capacitor is capable of this task, but only if it is placed
close to the LT3990 (see the PCB Layout section). A second
precaution regarding the ceramic input capacitor concerns
the maximum input voltage rating of the LT3990. A ceramic
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 voltage can ring to twice its nominal value, possibly exceeding
the LT3990’s voltage rating. This situation is easily avoided
(see the Hot Plugging Safely section).
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:
50
COUT =
VOUT • fSW
where fSW is in MHz and COUT is the recommended output
capacitance in μF. Use X5R or X7R types. This choice will
provide low output ripple and good transient response.
Transient performance can be improved with a higher value
capacitor if combined with a phase lead capacitor (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.
The second function is that the output capacitor, along
with the inductor, filters the square wave generated by the
LT3990 to produce the DC output. In this role it determines
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
WORST-CASE OUTPUT RIPPLE (mV)
the ripple current. Note that larger input capacitance is
required when a lower switching frequency is used (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.
FRONT PAGE APPLICATION
CLEAD = 47pF FOR COUT ≥ 47μF
16
14
12
10
8
6
4
VIN = 24V
2
VIN = 12V
0
0
20
60
40
COUT (μF)
80
100
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.
Table 3. Recommended Ceramic Capacitor Vendors
MANUFACTURER
WEBSITE
AVX
www.avxcorp.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
Vishay Siliconix
www.vishay.com
TDK
www.tdk.com
Ceramic Capacitors
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
when used with the LT3990 due to their piezoelectric nature.
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
3990p
11
LT3990
APPLICATIONS INFORMATION
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LT3990. As previously mentioned, a ceramic 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 voltage can ring to twice its nominal
value, possibly exceeding the LT3990’s rating. This situation
is easily avoided (see the Hot Plugging Safely section).
FRONT PAGE APPLICATION
600
500
400
300
200
100
0
0
50
100 150 200 250
LOAD CURRENT (mA)
300
350
3990 F03
Figure 3. Switching Frequency in Burst Mode Operation
Low Ripple Burst Mode Operation
To enhance efficiency at light loads, the LT3990 operates
in low ripple Burst Mode operation which keeps the output
capacitor charged to the proper voltage while minimizing
the input quiescent current. During Burst Mode operation, 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 capacitor. 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.
As the load current decreases towards a no load condition,
the percentage of time that the LT3990 operates in sleep
mode increases and the average input current is greatly
reduced resulting in high efficiency even at very low loads.
Note that during Burst Mode operation, the switching
frequency will be lower than the programmed switching
frequency. See Figure 3.
VSW
5V/DIV
IL
100mA/DIV
VOUT
5mV/DIV
2μs/DIV
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
ILOAD = 10mA
700
SWITCHING FREQUENCY (kHz)
operates at a lower current limit during Burst Mode operation, 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.
3990 G26
Figure 2. Burst Mode Operation
At higher output loads (above ~45mA for the front page
application) the LT3990 will be running at the frequency
programmed by the RT resistor, and will be operating in
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
Capacitor C3 and the internal boost Schottky diode (see the
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 arrange 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.
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
3990p
12
LT3990
APPLICATIONS INFORMATION
VOUT
5.0
FRONT PAGE APPLICATION
VOUT = 3.3V
BD
VIN
BOOST
4.5
C3
LT3990
INPUT VOLTAGE (V)
VIN
SW
GND
(4a) For VOUT ≥ 2.2V
VIN
TO RUN
3.5
3.0
2.5
BD
VIN
TO START
4.0
0
50
BOOST
C3
LT3990
SW
6.5
VOUT
100 150 200 250
LOAD CURRENT (mA)
300
350
300
350
FRONT PAGE APPLICATION
VOUT = 5V
GND
3990 F04
(4b) For VOUT < 2.2V; VIN < 27V
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 voltages, 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
worst-case situation where VIN is ramping very slowly.
For lower start-up voltage, the boost diode can be tied to
VIN; however, this restricts the input range to one-half of
the absolute maximum rating of the BOOST pin.
Enable Pin
The LT3990 is in shutdown when the EN pin is low and
active when the pin is high. The rising threshold of the EN
comparator is 1V, with a 30mV hysteresis. This threshold is
accurate when VIN is above 4.2V. If VIN is lower than 4.2V,
tie EN pin to GND to place the part in shutdown.
INPUT VOLTAGE (V)
6.0
TO START
5.5
TO RUN
5.0
4.5
4.0
0
50
100 150 200 250
LOAD CURRENT (mA)
3990 F05
Figure 5. The Minimum Input Voltage Depends on
Output Voltage, Load Current and Boost Circuit
Adding a resistor divider from VIN to EN programs the
LT3990 to regulate the output only when VIN is above a
desired voltage (see Figure 6). This threshold voltage,
VIN(EN), can be adjusted by setting the values R3 and R4
such that they satisfy the following equation:
VIN(EN) =
R3 + R4
• 1V
R4
where output regulation should not start until VIN is above
VIN(EN). Note that due to the comparator’s hysteresis,
regulation will not stop until the input falls slightly below
VIN(EN).
3990p
13
LT3990
APPLICATIONS INFORMATION
160
LT3990
VIN
R3
1V
EN
+
–
INPUT CURRENT (μA)
VIN
SHDN
R4
VIN(EN) = 6V
R3 = 5M
R4 = 1M
120
80
40
0
3990 F06
4
OUTPUT VOLTAGE (V)
Figure 6. Enable
Be aware that while VIN is below 4.2V, the input current
may rise up to several hundred μA and the part may begin
to switch while the internal circuitry starts up. Figure 7
shows the startup behavior of a typical application with
different programmed VIN(EN).
3
2
1
0
0
1
2
3
4
5
6
160
INPUT CURRENT (μA)
Shorted and Reversed Input Protection
8
VIN(EN) = 12V
R3 = 11M
R4 = 1M
120
80
40
0
4
OUTPUT VOLTAGE (V)
If the inductor is chosen so that it won’t saturate excessively, 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 applications or in battery backup systems where a battery
or some other supply is diode ORed with the LT3990’s
output. If the VIN pin is allowed to float and the EN pin
is held high (either by a logic signal or because it is tied
to VIN), then the LT3990’s internal circuitry will pull its
quiescent current through its SW pin. This is fine if the
system can tolerate a few μA in this state. If the EN pin is
grounded, the SW pin current will drop to 0.7μA. However,
if the VIN pin is grounded while the output is held high,
regardless of EN, parasitic diodes inside the LT3990 can
pull current from the output through the SW pin and the
VIN pin. Figure 8 shows a circuit that will run only when
the input voltage is present and that protects against a
shorted or reversed input.
7
INPUT VOLTAGE (V)
3
2
1
0
0
2
4
6
8
10
12
14
INPUT VOLTAGE (V)
3990 F07
Figure 7. VIN Start-Up of Front Page Application with VOUT = 3.3V,
No-Load Current, and VIN(EN) programmed as in Figure 6.
D4
MBRS140
VIN
BD
VIN
BOOST
LT3990
EN
SW
GND
FB
VOUT
+
BACKUP
3990 F08
Figure 8. 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
3990p
14
LT3990
APPLICATIONS INFORMATION
PCB Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Figure 9 shows
the recommended component placement with trace,
ground plane and via locations. Note that large, switched
currents flow in the LT3990’s VIN and SW pins, the internal
catch diode and the input capacitor. The loop formed by
these components should be as small as possible. These
components, along with the inductor and 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 of the DFN package 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.
GND
GND
1
10
EN
2
9
VIN
3
8
4
7
5
6
PG
VOUT
GND
VIAS TO LOCAL GROUND PLANE
VIAS TO VOUT
3990 F09
Figure 9. A Good PCB Layout Ensures Proper, Low EMI Operation
Hot Plugging Safely
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 capacitors 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
the VIN pin of the LT3990 can ring to twice the nominal
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
this overshoot. See Linear Technology Application Note 88
for a complete discussion.
High Temperature Considerations
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 of the
DFN package must be soldered to a ground plane. This
ground should be tied to large copper layers below with
thermal vias; these layers will spread the heat dissipated
by the LT3990. Placing additional vias can reduce thermal
resistance further. In the MSOP package, the copper lead
frame is fused to GND (Pin 5) so place thermal vias near
this pin. The maximum load current should be derated
as the ambient temperature approaches the maximum
junction rating.
Power dissipation within the LT3990 can be estimated by
calculating the total power loss from an efficiency measurement and subtracting inductor loss. The die temperature
is calculated by multiplying the LT3990 power dissipation
by the thermal resistance from junction to ambient.
Finally, be aware that at high ambient temperatures the
internal Schottky diode will have significant leakage current
(see Typical Performance Characteristics) increasing the
quiescent current of the LT3990 converter.
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.
3990p
15
LT3990
TYPICAL APPLICATIONS
3.3V Step-Down Converter
VIN
4.2V TO 60V
5V Step-Down Converter
VIN
6V TO 60V
C3
0.22μF
VIN
BOOST
OFF ON
EN
PG
BD
RT
226k
R1
1M
OFF ON
R2
576k
VOUT
5V
350mA
SW
BD
RT
R1
1M
FB
GND
226k
3990 TA02
f = 600kHz
EN
PG
L1
22μH
22pF
C1
2.2μF
C2
22μF
FB
GND
BOOST
LT3990
VOUT
3.3V
350mA
SW
22pF
C1
2.2μF
VIN
L1
22μH
LT3990
C3
0.22μF
R2
316k
C2
22μF
3990 TA03
f = 600kHz
2.5V Step-Down Converter
VIN
4.2V TO 60V
C3
0.47μF
VIN
BOOST
LT3990
OFF ON
EN
PG
SW
RT
FB
L1
15μH
BD
47pF
C1
2.2μF
VOUT
2.5V
350mA
GND
226k
R1
1M
R2
931k
C2
47μF
3990 TA04
f = 600kHz
1.8V Step-Down Converter
VIN
4.2V TO 27V
C3
0.22μF
VIN
BOOST
LT3990
OFF ON
C1
2.2μF
EN
BD
PG
f = 600kHz
VOUT
1.8V
350mA
SW
47pF
RT
226k
L1
10μH
R1
487k
FB
GND
R2
1M
C2
47μF
3990 TA05
3990p
16
LT3990
TYPICAL APPLICATIONS
12V Step-Down Converter
VIN
14V TO 60V
5V, 2MHz Step-Down Converter
VIN
8.5V TO 16V
TRANSIENTS
TO 60V
C3
0.1μF
VIN
BOOST
L1
33μH
LT3990
OFF ON
EN
PG
SW
RT
FB
R1
1M
22pF
C1
2.2μF
GND
226k
VIN
VOUT
12V
350mA
BD
BOOST
LT3990
OFF ON
EN
PG
L1
10μH
C1
1μF
BD
RT
49.9k
VOUT
5V
350mA
SW
22pF
C2
22μF
R2
113k
C3
0.1μF
R1
1M
C2
10μF
FB
GND
R2
316k
3990 TA06
f = 600kHz
f = 2MHz
3990 TA07
5V Step-Down Converter with Reduced Input Current During Start-Up
VIN
6V TO 60V
kΩ
+
0.22μF
VIN
5M
–
BOOST
LT3990
22μH
SW
1M
EN
PG
2.2μF
RT
FB
BD
22pF
226k
1M
22μF
GND
316k
3990 TA08a
f = 600kHz
Input Current During Start-Up
VOUT
5V
350mA
Start-Up from High Impedance Input Source
4.5
EN PROGRAMMED TO 6V
4.0
INPUT CURRENT (mA)
3.5
3.0
2.5
2.0
INPUT CURRENT
DROPOUT
CONDITIONS
VIN
5V/DIV
FRONT PAGE
APPLICATION
VOUT
2V/DIV
FRONT PAGE
APPLICATION
WITH EN
PROGRAMMED
TO 6V
1.5
1.0
0.5
5ms/DIV
FRONT PAGE APPLICATION
VOUT = 5V
1k INPUT SOURCE RESISTANCE
2.5mA LOAD
0
3990 TA08c
–0.5
0
2
6
8
4
INPUT VOLTAGE (V)
10
12
3990 TA08b
3990p
17
LT3990
PACKAGE DESCRIPTION
DDB Package
10-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1722 Rev Ø)
0.64 p0.05
(2 SIDES)
0.70 p0.05
2.55 p0.05
1.15 p0.05
PACKAGE
OUTLINE
0.25 p 0.05
0.50 BSC
2.39 p0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 p0.10
(2 SIDES)
R = 0.05
TYP
R = 0.115
TYP
6
0.40 p 0.10
10
2.00 p0.10
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0.75 p0.05
0 – 0.05
0.64 p 0.05
(2 SIDES)
5
0.25 p 0.05
PIN 1
R = 0.20 OR
0.25 s 45o
CHAMFER
1
(DDB10) DFN 0905 REV Ø
0.50 BSC
2.39 p0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
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
3990p
18
LT3990
PACKAGE DESCRIPTION
MS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661 Rev E)
0.889 p 0.127
(.035 p .005)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
3.00 p 0.102
(.118 p .004)
(NOTE 3)
0.50
0.305 p 0.038
(.0197)
(.0120 p .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
10 9 8 7 6
3.00 p 0.102
(.118 p .004)
(NOTE 4)
4.90 p 0.152
(.193 p .006)
DETAIL “A”
0.497 p 0.076
(.0196 p .003)
REF
0o – 6o TYP
GAUGE PLANE
1 2 3 4 5
0.53 p 0.152
(.021 p .006)
DETAIL “A”
0.86
(.034)
REF
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.1016 p 0.0508
(.004 p .002)
MSOP (MS) 0307 REV E
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
3990p
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LT3990
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT3689
36V, 60V Transient Protection, 800mA, 2.2MHz High Efficiency
Micropower Step-Down DC/DC Converter with POR Reset and
Watchdog Timer
VIN: 3.6V to 36V, Transient to 60V, VOUT(MIN) = 0.8V, IQ = 75μA,
ISD < 1μA, 3mm × 3mm QFN16
LT3682
36V, 60VMAX, 1A, 2.2MHz High Efficiency Micropower Step-Down
DC/DC Converter
VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 75μA, ISD < 1μA,
3mm × 3mm DFN12
LT3480
36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High
Efficiency Step-Down DC/DC Converter with Burst Mode® Operation
VIN: 3.6V to 38V, VOUT(MIN) = 0.78V, IQ = 70μA, ISD < 1μA,
3mm × 3mm DFN10, MSOP10E
LT3685
36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High
Efficiency Step-Down DC/DC Converter
VIN: 3.6V to 38V, VOUT(MIN) = 0.78V, IQ = 70μA, ISD < 1μA,
3mm × 3mm DFN10, MSOP10E
LT3481
34V with Transient Protection to 36V, 2A (IOUT), 2.8MHz, High
Efficiency Step-Down DC/DC Converter with Burst Mode Operation
VIN: 3.6V to 34V, VOUT(MIN) = 1.26V, IQ = 50μA, ISD < 1μA,
3mm × 3mm DFN10, MSOP10E
LT3684
34V with Transient Protection to 36V, 2A (IOUT), 2.8MHz,
High Efficiency Step-Down DC/DC Converter
VIN: 3.6V to 34V, VOUT(MIN) = 1.26V, IQ = 850μA, ISD < 1μA,
3mm × 3mm DFN10, MSOP10E
LT3508
36V with Transient Protection to 40V, Dual 1.4A (IOUT), 3MHz,
High Efficiency Step-Down DC/DC Converter
VIN: 3.7V to 37V, VOUT(MIN) = 0.8V, IQ = 4.6mA, ISD < 1μA,
4mm × 4mm QFN24, TSSOP16E
LT3505
36V with Transient Protection to 40V, 1.4A (IOUT), 3MHz,
High Efficiency Step-Down DC/DC Converter
VIN: 3.6V to 34V, VOUT(MIN) = 0.78V, IQ = 2mA, ISD < 2μA,
3mm × 3mm DFN8, MSOP8E
LT3500
36V, 40VMAX, 2A, 2.5MHz High Efficiency Step-Down DC/DC
Converter and LDO Controller
VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 2.5mA, ISD < 10μA,
3mm × 3mm DFN10
LT3507
36V 2.5MHz, Triple (2.4A + 1.5A + 1.5A (IOUT)) with LDO Controller
High Efficiency Step-Down DC/DC Converter
VIN: 4V to 36V, VOUT(MIN) = 0.8V, IQ = 7mA, ISD < 1μA,
5mm × 7mm QFN38
LT3437
60V, 400mA (IOUT), Micropower Step-Down DC/DC Converter with
Burst Mode Operation
VIN: 3.3V to 60V, VOUT(MIN) = 1.25V, IQ = 100μA, ISD < 1μA,
3mm × 3mm DFN10, TSSOP16E
LT1976/LT1977
60V, 1.2A (IOUT), 200/500kHz, High Efficiency Step-Down DC/DC
Converter with Burst Mode Operation
VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100μA, ISD < 1μA,
TSSOP16E
LT3434/LT3435
60V, 2.4A (IOUT), 200/500kHz, High Efficiency Step-Down DC/DC
Converter with Burst Mode Operation
VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100μA, ISD < 1μA,
TSSOP16E
LT1936
36V, 1.4A (IOUT) , 500kHz High Efficiency Step-Down DC/DC
Converter
VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.9mA, ISD < 1μA,
MS8E
LT3493
36V, 1.4A (IOUT), 750kHz High Efficiency Step-Down DC/DC
Converter
VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 1.9mA, ISD < 1μA,
2mm × 3mm DFN6
LT1766
60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down DC/DC
Converter
VIN: 5.5V to 60V, VOUT(MIN) = 1.20V, IQ = 2.5mA, ISD = 25μA,
TSSOP16E
LT3508
36V with Transient Protection to 40V, Dual 1.4A (IOUT), 3MHz,
High Efficiency Step-Down DC/DC Converter
VIN: 3.7V to 37V, VOUT(MIN) = 0.8V, IQ = 4.6mA, ISD < 1μA,
4mm × 4mm QFN24, TSSOP16E
LT3500
36V, 40VMAX, 2A, 2.5MHz High Efficiency Step-Down DC/DC
Converter and LDO Controller
VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 2.5mA, ISD < 10μA,
3mm × 3mm DFN10
LT3507
36V 2.5MHz, Triple (2.4A + 1.5A + 1.5A (IOUT)) with LDO Controller
High Efficiency Step-Down DC/DC Converter
VIN: 4V to 36V, VOUT(MIN) = 0.8V, IQ = 7mA, ISD < 1μA,
5mm × 7mm QFN38
Burst Mode is a registered trademark of Linear Technology Corporation.
3990p
20 Linear Technology Corporation
LT 0709 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
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