LINER LT3695IMSEPBF

LT3695
1A Fault Tolerant Micropower
Step-Down Regulator
FEATURES
DESCRIPTION
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The LT®3695 is an adjustable frequency (250kHz to 2.2MHz)
monolithic buck switching regulator that accepts input voltages up to 36V and can safely sustain transient voltages
up to 60V. The device includes a high efficiency switch, a
boost diode, and the necessary oscillator, control and logic
circuitry. Current mode topology is used for fast transient
response and good loop stability. A SYNC pin allows the
user to synchronize the part to an external clock, and to
choose between low ripple Burst Mode operation and
standard PWM operation.
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Wide Input Range:
Operation from 3.6V to 36V
Overvoltage Lockout Protects Circuits Through
60V Transients
FMEA Fault Tolerant:
Output Stays at or Below Regulation Voltage
During Adjacent Pin Short or When a Pin Is Left
Floating
1A Output Current
Low Ripple (< 15mVP-P) Burst Mode® Operation
IQ = 75μA for 12VIN to 3.3VOUT with No Load
Adjustable Switching Frequency: 250kHz to 2.2MHz
Short-Circuit Protected
Synchronizable Between 300kHz and 2.2MHz
Output Voltage: 0.8V to 20V
Power Good Flag
Small Thermally Enhanced 16-Pin MSOP Package
The LT3695 tolerates adjacent pin shorts or an open pin
without raising the output voltage above its programmed
value.
Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping output ripple
below 15mV in a typical application. Shutdown reduces
input supply current to less than 1μA while a resistor and
capacitor on the RUN/SS pin provide a controlled output
voltage ramp (soft-start). Protection circuitry senses the
current in the power switch and external Schottky catch
diode to protect the LT3695 against short-circuit conditions. Frequency foldback and thermal shutdown provide
additional protection.
APPLICATIONS
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Automotive Battery Regulation
Automotive Entertainment Systems
Distributed Supply Regulation
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.
The LT3695 is available in a thermally enhanced 16-Pin
MSOP package.
TYPICAL APPLICATION
Efficiency
5V Step-Down Converter
2.2μF
ON OFF
VIN
RUN/SS
VOUT
5V
0.9A, VIN > 6.9V
1A, VIN > 12V
BD
BOOST
0.22μF
SW
VC
RT
16.2k
40.2k
470pF 100k
10μH
LT3695
PG
DA
SYNC
GND
FB
PGND
f = 800kHz
VOUT = 5V
90
EFFICIENCY (%)
VIN
6.9V TO 36V
TRANSIENT TO 60V
100
VOUT = 3.3V
80
70
536k
60
102k
VIN = 12V
L = 10µH
f = 800kHz
10μF
3695 TA01a
50
0
0.2
0.4
0.6
LOAD CURRENT (A)
0.8
1
3695 TA01b
3695f
1
LT3695
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Notes 1, 2)
TOP VIEW
VIN, RUN/SS Voltage (Note 3) ...................................60V
BOOST Pin Voltage ...................................................50V
BOOST Pin Above SW Pin.........................................30V
BD Voltage ................................................................30V
RT , VC Voltage ............................................................5V
RT Pin Current .........................................................1mA
SYNC Voltage ............................................................20V
FB Voltage ...................................................................5V
PG Voltage ................................................................30V
Operating Junction Temperature Range (Notes 4, 5)
LT3695E ............................................. –40°C to 125°C
LT3695I .............................................. –40°C to 125°C
LT3695H ............................................ –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
PGND
DA
NC
SW
RUN/SS
RT
SYNC
VIN
1
2
3
4
5
6
7
8
17
16
15
14
13
12
11
10
9
BOOST
BD
GND
PG
NC
FB
NC
VC
MSE PACKAGE
16-LEAD PLASTIC MSOP
θJA = 40°C/W WITH EXPOSED PAD SOLDERED
θJA = 110°C/W WITHOUT EXPOSED PAD SOLDERED
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3695EMSE#PBF
LT3695EMSE#TRPBF
3695
16-Lead Plastic MSOP
–40°C to 125°C
LT3695IMSE#PBF
LT3695IMSE#TRPBF
3695
16-Lead Plastic MSOP
–40°C to 125°C
LT3695HMSE#PBF
LT3695HMSE#TRPBF
3695
16-Lead Plastic MSOP
–40°C to 150°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/
3695f
2
LT3695
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, unless otherwise noted. (Note 4)
PARAMETER
Minimum Operating Voltage (Note 6)
CONDITIONS
VBD = 3.3V
VBD < 3V
MIN
l
l
l
VIN Overvoltage Lockout
Quiescent Current from VIN
VRUN/SS = 0.2V
VRUN/SS = 10V, VBD = 3.3V, Not Switching
VRUN/SS = 10V, VBD = 0V, Not Switching
l
Quiescent Current from BD Pin
VRUN/SS = 0.2V
VRUN/SS = 10V, VBD = 3.3V, Not Switching
VRUN/SS = 10V, VBD = 0V, Not Switching
l
l
36
FB Pin Bias Current
FB Pin Voltage = 800mV
Reference Voltage Line Regulation
3.6V < VIN < 36V
Error Amp gm
IVC = ±1.5μA
MAX
3.4
3.4
3.6
4.3
UNITS
V
V
38
39.9
V
0.01
35
90
0.5
60
160
μA
μA
μA
35
0.01
55
0
0.5
100
–5
μA
μA
μA
2.8
3
792
785
800
800
808
815
mV
mV
–5
–40
nA
0.001
0.005
%/V
Minimum BD Pin Voltage
Feedback Voltage
TYP
l
V
430
μS
1300
V/V
VC Source Current
50
μA
VC Sink Current
50
μA
1.25
A/V
Error Amp Voltage Gain
VC Pin to Switch Current Gain
VC Switching Threshold
0.4
VC Clamp Voltage
0.8
2
Switching Frequency
RRT = 8.06k
RRT = 29.4k
RRT = 158k
Minimum Switch Off-Time
E- and I-Grades
H-Grade
Switch Current Limit (Note 7)
SYNC = 0V
SYNC = 3.3V or Clocked
Switch VCESAT
ISW = 1A
DA Pin Current to Stop OSC
Switch Leakage Current
0.6
1.98
0.9
225
l
l
1.45
1.18
VSW = 0V, VIN = 36V
2.2
1.0
250
2.42
1.1
275
MHz
MHz
kHz
130
130
210
250
ns
ns
1.7
1.4
2
1.66
A
A
350
1.25
V
V
mV
1.6
1.95
A
0.01
1
μA
3695f
3
LT3695
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, unless otherwise noted. (Note 4)
PARAMETER
CONDITIONS
Boost Schottky Diode Voltage Drop
Boost Schottky Diode Reverse Leakage
MIN
TYP
MAX
UNITS
IBSD = 50mA
720
900
mV
VSW = 10V, VBD = 0V
0.1
1
μA
l
Minimum Boost Voltage (Note 8)
BOOST Pin Current
ISW = 0.5A
RUN/SS Pin Current
VRUN/SS = 2.5V
VRUN/SS = 10V
l
RUN/SS Input Voltage High
1.7
2.3
V
10.5
17.5
mA
4.5
12
7.5
20
μA
μA
2.5
V
RUN/SS Input Voltage Low
PG Leakage Current
VPG = 5V
0.1
PG Sink Current
VPG = 0.4V
PG Threshold as % of VFB
Measured at FB Pin (Pin Voltage Rising)
PG Threshold Hysteresis
Measured at FB Pin
l
100
1000
88
90
V
1
μA
μA
92
12
SYNC Threshold Voltage
300
SYNC Input Frequency
0.3
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 the device
reliability and lifetime.
Note 2: Positive currents flow into pins, negative currents flow out of pins.
Minimum and maximum values refer to absolute values.
Note 3: Absolute maximum voltage at VIN and RUN/SS pins is 60V for
nonrepetitive 1 second transients, and 36V for continuous operation.
Note 4: The LT3695E 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
LT3695I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3695H is guaranteed over the full –40°C to
150°C operating junction temperature range.
0.2
550
%
mV
800
mV
2.2
MHz
Note 5: This IC includes overtemperature protection that is intended to
protect the devices during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
when overtemperature protection is active. Continuous operation above
the specified maximum operating junction temperature may impair device
reliability.
Note 6: This is the voltage necessary to keep the internal bias circuitry in
regulation.
Note 7: Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycles.
Note 8: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.
3695f
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LT3695
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Efficiency (VOUT = 3.3V, SYNC = 0V)
Efficiency (VOUT = 5V, SYNC = 0V)
L = 10μH
f = 800kHz
L = 10μH
80 f = 800kHz
VIN = 12V
EFFICIENCY (%)
60
50
VIN = 24V
40
50
VIN = 24V
40
30
20
20
1
10
100
LOAD CURRENT (mA)
1000
VIN = 34V
60
30
10
0.1
VIN = 12V
70
VIN = 34V
1
10
100
LOAD CURRENT (mA)
SUPPLY CURRENT (μA)
SUPPLY CURRENT (μA)
100
80
60
40
20
10
10
0.1
1000
15 20 25 30
INPUT VOLTAGE (V)
35
40
1
0.001
1000
10
100
LOAD CURRENT (mA)
3695 G03
No-Load Supply Current
120
5
0.01
40
3695 G02
VOUT = 3.3V
0
60
50
20
10
0.1
No-Load Supply Current
0
0.1
30
3695 G01
140
70
Maximum Load Current
1300
CATCH DIODE: DIODES, INC. B140
1200 V = 12V
IN
1100 VOUT = 3.3V
1000
900
800
700
600
INCREASED SUPPLY CURRENT
500
DUE TO CATCH DIODE LEAKAGE
400 AT HIGH TEMPERATURE
300
200
100
0
25 50 75 100 125 150
–50 –25 0
TEMPERATURE (°C)
1.75
TYPICAL
1.50
1.25
1.00
0.75
MINIMUM
0.50
SYNC = 0V
SYNC = 3.3V
0.25
0
5
10
VOUT = 3.3V
L = 10μH
f = 800kHz
15
20 25 30
INPUT VOLTAGE (V)
3695 G05
3695 G04
Maximum Load Current
35
40
3695 G06
Maximum Load Current
Maximum Load Current
1.75
1.50
1.50
POWER LOSS(W)
EFFICIENCY (%)
70
1
VIN = 12V
90 VOUT = 3.3V
L = 10μH
80 f = 800kHz
LOAD CURRENT (A)
80
Efficiency (VOUT = 3.3V, SYNC = 0V)
100
90
EFFICIENCY (%)
90
TYPICAL
TYPICAL
0.75
MINIMUM
0.50
SYNC = 0V
SYNC = 5V
0.25
5
10
15
20
25
30
INPUT VOLTAGE (V)
1.00
0.75
MINIMUM
0.50
VOUT = 5V
L = 10μH
f = 800kHz
SYNC = 0V
SYNC = 5V
0.25
35
40
3682 G07
LOAD CURRENT (A)
1.00
TYPICAL
1.50
1.25
LOAD CURRENT (A)
LOAD CURRENT (A)
1.25
8
10
12
14
16
INPUT VOLTAGE (V)
VOUT = 5V
L = 4.7μH
f = 2MHz
18
1.25
1.00
0.75
MINIMUM
0.50
20
3695 G08
0.25
SYNC = 0V
SYNC = 3.3V
0
5
10
VOUT = 1.8V
L = 10μH
f = 500kHz
15 20 25 30
INPUT VOLTAGE (V)
35
40
3695 G09
3695f
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LT3695
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Switch Current Limit
(SYNC Pin Grounded)
Switch Current Limit
1.9
1.9
1.7
1.7
Switch Voltage Drop
400
1.5
1.3
SYNC > 0.8V
OR CLOCKED
1.1
0.9
0.7
0.5
1.5
VOLTAGE DROP (mV)
SYNC < 0.3V
SWITCH CURRENT LIMIT (A)
SWITCH CURRENT LIMIT (A)
DC = 10%
DC = 90%
1.3
1.1
0.9
0
40
60
DUTY CYCLE (%)
20
80
100
0.5
–50 –25
100
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
BOOST Pin Current
0.25
0.50
0.75
1.00
SWITCH CURRENT (A)
1.25
3695 G28
Feedback Voltage
Switching Frequency
810
1.20
RT = 29.4k
1.15
25
20
15
10
800
1.10
FREQUENCY (MHz)
FEEDBACK VOLTAGE (mV)
30
BOOST PIN CURRENT (mA)
0
3695 G11
35
790
1.05
1.00
0.95
0.90
780
5
0.85
0
0.25
0.50
0.75
1.00
SWITCH CURRENT (A)
770
–50 –25
1.25
0
0.80
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
Frequency Foldback
RRT = 29.4k
600
400
200
Soft-Start
2.0
IOUT = 1A
SYNC < 0.3V
1.8
100
SWITCH CURRENT LIMIT (A)
MINIMUM SWITCH ON TIME (ns)
800
25 50 75 100 125 150
TEMPERATURE (°C)
3695 G15
Minimum Switch On Time
120
1200
1000
0
3695 G14
3695 G13
FREQUENCY (kHz)
200
0.7
3695 G10
0
300
80
60
40
20
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0 100 200 300 400 500 600 700 800 900
FB PIN VOLTAGE (mV)
3695 G16
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3695 G17
0
0
0.5
1.0 1.5
2.0 2.5
3.0
RUN/SS PIN VOLTAGE (V)
3.5
3695 G20
3695f
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LT3695
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Boost Diode Forward Voltage
RUN/SS Pin Current
12
1.4
10
1.2
Error Amplifier Output Current
60
6
4
2
40
VC PIN CURRENT (μA)
BOOST DIODE VF (V)
8
1.0
0.8
0.6
0.4
10 15 20 25 30
RUN/SS PIN VOLTAGE (V)
35
0.25
0.5
0.75
BOOST DIODE CURRENT (A)
0
40
3695 G21
Minimum Input Voltage
VOUT = 3.3V
L = 10μH
4.5 f = 800kHz
–30
1
–100
0
100
FB PIN ERROR VOLTAGE (mV)
200
3659 G23
VOUT = 5V
L = 10μH
f = 800kHz
INPUT VOLTAGE (V)
6.0
4.0
3.5
3.0
5.5
5.0
4.5
2.5
4
1
10
100
LOAD CURRENT (mA)
1000
1
10
100
LOAD CURRENT (mA)
Maximum VIN for Full Frequency
Maximum VIN for Full Frequency
40
40
35
35
TA = 25˚C
TA = 25˚C
30
1000
3695 G27
3695 G26
30
TA = 85˚C
25
20
TA = 85˚C
25
20
15
15
VOUT = 3.3V
L = 10μH
f = 800kHz
SYNC = 3.3V
10
5
–20
Minimum Input Voltage
6.5
5.0
2.0
0
–10
3695 G21
VIN (V)
5
INPUT VOLTAGE (V)
0
20
10
–60
–200
0
0
30
–40
–50
0.2
VIN (V)
RUN/SS PIN CURRENT (μA)
50
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT(A)
VOUT = 5V
L = 10μH
f = 800kHz
SYNC = 5V
10
5
1
3695 G29
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT(A)
1
3695 G30
3695f
7
LT3695
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Maximum VIN for Full Frequency
Switching Waveforms,
60V Input Voltage Transient
VC Voltages
2.5
40
VSW
10V/DIV
TA = 25˚C
35
2.0
CURRENT LIMIT CLAMP
VC VOLTAGE (V)
30
VIN (V)
TA = 85˚C
25
20
1.5
VIN
20V/DIV
1.0
VOUT
5V/DIV
VOUT = 5V
L = 4.7μH
f = 2MHz
SYNC = 5V
10
5
5ms/DIV
SWITCHING THRESHOLD
15
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT(A)
0.5
1
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3695 G32
3695 G31
VSW
5V/DIV
VSW
5V/DIV
IL
0.2A/DIV
IL
0.2A/DIV
VOUT
20mV/DIV
VOUT
20mV/DIV
5μs/DIV
Switching Waveforms,
Full Frequency Continuous
Operation
Switching Waveforms,
Transition from Burst Mode
Operation to Full Frequency
Switching Waveforms,
Burst Mode Operation
VIN = 12V, FRONT PAGE APPLICATION
ILOAD = 5mA
3695 G34
3695 G33
VIN = 12V, FRONT PAGE APPLICATION
ILOAD = 500mA
VSW
5V/DIV
IL
0.5A/DIV
VOUT
20mV/DIV
1μs/DIV
VIN = 12V, FRONT PAGE APPLICATION
ILOAD = 55mA
3695 G35
1μs/DIV
3695 G36
VIN = 12V, FRONT PAGE APPLICATION
ILOAD = 500mA
3695f
8
LT3695
PIN FUNCTIONS
PGND (Pin 1): This is the power ground used by the catch
diode (D1 in the Block Diagram) when its anode is connected to the DA pin.
VIN (Pin 8): The VIN pin supplies current to the internal
regulator and to the internal power switch. This pin must
be locally bypassed.
DA (Pin 2): Connect the anode of the catch diode (D1)
to this pin. Internal circuitry senses the current through
the catch diode providing frequency foldback in extreme
situations.
VC (Pin 9): The VC pin is the output of the internal error
amplifier. The voltage on this pin controls the peak switch
current. Tie an RC network from this pin to ground to
compensate the control loop.
NC (Pins 3, 10, 12): No Connects. These pins are not
connected to internal circuitry and must be left floating
to ensure fault tolerance.
FB (Pin 11): The LT3695 regulates the FB pin to 0.8V. Connect the feedback resistor divider tap to this pin.
SW (Pin 4): The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.
RUN/SS (Pin 5): The RUN/SS pin is used to put the LT3695
in shutdown mode. Tie to ground to shut down the LT3695.
Tie to 2.5V or more for normal operation. RUN/SS also
provides a soft-start function; see the Applications Information section for more information.
RT (Pin 6): Oscillator Resistor Input. Connect a resistor
from this pin to ground to set the switching frequency.
SYNC (Pin 7): This is the external clock synchronization
input. Ground this pin with a 100k resistor for low ripple
Burst Mode operation at low output loads. Tie to 0.8V or
more for pulse-skipping mode operation. Tie to a clock
source for synchronization. Clock edges should have rise
and fall times faster than 1μs. Note that the maximum
load current depends on which mode is chosen. See the
Applications Information section for more information.
PG (Pin 13): The PG pin is the open-collector output of
an internal comparator. PG remains low until the FB pin
is within 10% of the final regulation voltage. PG output is
valid when VIN is above the minimum input voltage and
RUN/SS is high.
GND (Pin 14): The GND pin is the ground of all the internal
circuitry. Tie directly to the local GND plane.
BD (Pin 15): This pin connects to the anode of the boost
Schottky diode and also supplies current to the LT3695’s
internal regulator.
BOOST (Pin 16): This pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar
NPN power switch. Connect a capacitor (typically 0.22μF)
between BOOST and SW.
Exposed Pad (Pin 17): PGND. This is the power ground
used by the catch diode (D1) when its anode is connected
to the DA pin. The Exposed Pad may be soldered to the
PCB in order to lower the thermal resistance.
3695f
9
LT3695
BLOCK DIAGRAM
VIN
8
VIN
–
+
C1
OVLO
INTERNAL 0.8V REF
THERMAL
SHUTDOWN
SLOPE COMP
R
6
OUT
RT
OSCILLATOR
250kHz-2.2MHz
OUTB
RT
7
5
13
SYNC
RUN/SS
SYNC
PG
ERROR AMP
BOOST
SW
DISABLE
DA
+
–
VC
C3
L1
4
VOUT
C2
D1
2
9
CC
PGND
PGND
11
R2
16
VC CLAMP
FB
14
15
Q
+
–
0.720V
GND
S
Burst Mode
DETECT
SOFT-START
+
–
BD
17
RC
CF
1
R1
3695 BD
3695f
10
LT3695
OPERATION
The LT3695 is a constant frequency, current mode stepdown regulator. An oscillator, with frequency set by RT ,
enables 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. An error amplifier measures the output
voltage through an external resistor divider tied to the FB
pin and servos the VC pin. If the error amplifier’s output
increases, more current is delivered to the output; if it
decreases, less current is delivered. An active clamp on the
VC pin provides current limit. The VC pin is also clamped to
the voltage on the RUN/SS pin; soft-start is implemented
by generating a voltage ramp at the RUN/SS pin using an
external resistor and capacitor.
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 3V, bias power will be drawn from the external
source. This improves efficiency. The RUN/SS pin is used
to place the LT3695 in shutdown, disconnecting the output
and reducing the input current to less than 1μA.
The switch driver operates from either the input or from
the BOOST pin. An external capacitor and the internal boost
diode are 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 LT3695 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 75μA in a typical application.
The oscillator reduces the LT3695’s operating frequency
when the voltage at the FB pin is low. This frequency foldback helps to control the output current during start-up
and overload conditions.
Internal circuitry monitors the current flowing through the
catch diode via the DA pin and delays the generation of
new switch pulses if this current is too high (above 1.6A
nominal). This mechanism also protects the part during
short-circuit and overload conditions by keeping the current through the inductor under control.
The LT3695 contains a power good comparator which trips
when the FB pin is at 90% of its regulated value. The PG
output is an open-collector 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 LT3695 is
enabled and VIN is above the minimum input voltage.
The LT3695 has an overvoltage protection feature which
disables switching action when VIN goes above 38V (typical) during transients. The LT3695 can then safely sustain
transient input voltages up to 60V.
3695f
11
LT3695
APPLICATIONS INFORMATION
FB Resistor Network
Operating Frequency Trade-Offs
The output voltage of the LT3695 is programmed with a
resistor divider between the output and the FB pin. Choose
the resistor values according to:
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:
⎛V
⎞
R1= R2 ⎜ OUT − 1⎟
⎝ 0.8 V ⎠
Reference designators refer to the Block Diagram of the
LT3695. 1% resistors are recommended to maintain output
voltage accuracy.
fSW(MAX ) =
VOUT + VD
tON(MIN)( VIN − VSW + VD )
Setting the Switching Frequency
The LT3695 uses a constant frequency PWM architecture
that can be programmed to switch from 250kHz 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)
0.25
158
where VIN is the typical input voltage, VOUT is the output
voltage, VD is the catch diode drop (~0.5V) and VSW is the
internal switch drop (~0.5V at max load). This equation
shows that lower switching frequency is necessary to
safely accommodate high VIN/VOUT ratio. Also, as shown
in the Input Voltage Range section, lower frequency allows
a lower dropout voltage. Input voltage range depends on
the switching frequency because the LT3695 switch has
finite minimum on and off times. An internal timer forces
the switch to be off for at least tOFF(MIN) per cycle; this timer
has a maximum value of 210ns (250ns for TJ > 125°C). On
the other hand, delays associated with turning off the power
switch dictate the minimum on-time, tON(MIN), before the
switch can be turned off; tON(MIN) has a maximum value
of 150ns over temperature. The minimum and maximum
duty cycles that can be achieved taking minimum on and
off times into account are:
0.3
127
0.4
90.9
0.5
71.5
0.6
57.6
0.7
47.5
0.8
40.2
0.9
34
1.0
29.4
1.2
22.6
DCMIN = fSWtON(MIN)
1.4
18.2
1.6
14.7
DCMAX = 1 – fSWtOFF(MIN)
1.8
12.1
2.0
9.76
2.2
8.06
where fSW is the switching frequency, tON(MIN) is the
minimum switch on time (150ns), and tOFF(MIN) is the
minimum switch off time (210ns, 250ns for TJ > 125°C).
These equations show that the duty cycle range increases
when the switching frequency is decreased.
3695f
12
LT3695
APPLICATIONS INFORMATION
A good choice of switching frequency should allow an
adequate input voltage range (see Input Voltage Range section) and keep the inductor and capacitor values small.
Input Voltage Range
The minimum input voltage is determined by either the
LT3695’s minimum operating voltage of ~3.6V (VBD > 3V)
or by its maximum duty cycle (see equation in Operating
Frequency Trade-Offs 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, and tOFF(MIN)
is the minimum switch off time. Note that a higher switching frequency will increase the minimum input voltage.
If a lower dropout voltage is desired, a lower switching
frequency should be used.
switching frequency will reduce the maximum operating
input voltage. Conversely, a lower switching frequency
will be necessary to achieve optimum operation at high
input voltages.
Special attention must be paid when the output is in startup, short-circuit or other overload conditions. During these
events, the inductor peak current might easily reach and
even exceed the maximum current limit of the LT3695,
especially in those cases where the switch already operates
at minimum on-time. The circuitry monitoring the current
through the catch diode via the DA pin prevents the switch
from turning on again if the inductor valley current is above
1.6A nominal. In these cases, the inductor peak current is
therefore the maximum current limit of the LT3695 plus
the additional current overshoot during the turn off delay
due to minimum on time:
IL(PEAK ) = 2A +
VIN(MAX ) − VOUT(OL )
L
• tON(MIN)
The maximum input voltage for LT3695 applications
depends on switching frequency, the Absolute Maximum
Ratings of the VIN and BOOST pins and the operating mode.
The LT3695 can operate from continuous input voltages
up to 36V. Input voltage transients of up to 60V are also
safely withstood. However, note that while VIN > VOVLO
(overvoltage lockout, 38V typical), the LT3695 will stop
switching, allowing the output to fall out of regulation.
where IL(PEAK) is the peak inductor current, VIN(MAX) is
the maximum expected input voltage, L is the inductor
value, tON(MIN) is the minimum on time and VOUT(OL) is the
output voltage under the overload condition. The part is
robust enough to survive prolonged operation under these
conditions as long as the peak inductor current does not
exceed 3.5A. Inductor current saturation and excessive
junction temperature may further limit performance.
For a given application where the switching frequency
and the output voltage are already fixed, the maximum
input voltage that guarantees optimum output voltage
ripple for that application can be found by applying the
following expression:
Input voltage transients of up to VOVLO are acceptable
regardless of the switching frequency. In this case, the
LT3695 may enter pulse-skipping operation where some
switching pulses are skipped to maintain output regulation.
In this mode the output voltage ripple and inductor current
ripple will be higher than in normal operation.
VIN(MAX ) =
VOUT + VD
−V +V
fSW tON(MIN) D SW
where VIN(MAX) is the maximum operating input voltage,
VOUT is the output voltage, VD is the catch diode drop
(~0.5V), VSW is the internal switch drop (~0.5V at max load),
fSW is the switching frequency (set by RT) and tON(MIN) is
the minimum switch on time (~150ns). Note that a higher
Input voltage transients above VOVLO and up to 60V can
be tolerated. However, since the part will stop switching
during these transients, the output will fall out of regulation
and the output capacitor may eventually be completely
discharged. This case must be treated then as a start-up
condition as soon as VIN returns to values below VOVLO
and the part starts switching again.
3695f
13
LT3695
APPLICATIONS INFORMATION
Inductor Selection and Maximum Output Current
A good first choice for the inductor value is:
L = ( VOUT + VD) •
1.8
fSW
where fSW is the switching frequency in MHz, VOUT is the
output voltage, VD is the catch diode drop (~0.5V) and L
is the inductor value in μH.
The inductor’s RMS current rating must be greater than the
maximum load current and its saturation current should be
about 30% higher. 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.
For robust operation in fault conditions (start-up or shortcircuit) and high input voltage (>30V), the saturation
current should be chosen high enough to ensure that the
inductor peak current does not exceed 3.5A. For example,
an application running from an input voltage of 36V
using a 10μH inductor with a saturation current of 2.5A
will tolerate the mentioned fault conditions.
The optimum inductor for a given application may differ
from the one indicated by this simple design guide. A larger
value inductor provides a higher maximum load current
and reduces the output voltage ripple. If your load is lower
than the maximum load current, then you can relax the
value of the inductor and operate with higher ripple current. This allows you to use a physically smaller inductor,
or one with a lower DCR resulting in higher efficiency.
Be aware that if the inductance differs from the simple
rule above, then the maximum load current will depend
on input voltage. In addition, low inductance may result
in discontinuous mode operation, which further reduces
maximum load current. For details of maximum output
current and discontinuous mode operation, see Linear
Technology’s Application Note 44. Finally, for duty cycles
greater than 50% (VOUT/VIN > 0.5), a minimum inductance
is required to avoid sub-harmonic oscillations:
L MIN = ( VOUT + VD) •
1.2
fSW
The current in the inductor is a triangle wave with an average value equal to the load current. The peak inductor
and switch current is:
ΔIL
2
where IL(PEAK) is the peak inductor current, IOUT(MAX) is
the maximum output load current and ΔIL is the inductor ripple current. The LT3695 limits its switch current in
order to protect itself and the system from overload faults.
Therefore, the maximum output current that the LT3695 will
deliver depends on the switch current limit, the inductor
value and the input and output voltages.
I SW(PEAK ) = IL(PEAK ) = IOUT(MAX ) +
When the switch is off, the potential across the inductor
is the output voltage plus the catch diode drop. This gives
the peak-to-peak ripple current in the inductor:
ΔIL =
(1− DC) •( VOUT + VD)
L • fSW
where fSW is the switching frequency of the LT3695, DC
is the duty cycle and L is the value of the inductor.
To maintain output regulation, the inductor peak current
must be less than the LT3695’s switch current limit, ILIM.
If the SYNC pin is grounded, ILIM is at least 1.45A at low
duty cycles and decreases to 1.1A at DC = 90%. If the
SYNC pin is tied to 0.8V or more or if it is tied to a clock
source for synchronization, ILIM is at least 1.18A at low
duty cycles and decreases to 0.85A at DC = 90%. The
maximum output current is also a function of the chosen
inductor value and can be approximated by the following
expressions depending on the SYNC pin configuration:
For the SYNC pin grounded:
IOUT(MAX ) = ILIM −
ΔIL
ΔI
= 1.45A •(1− 0.24 • DC) − L
2
2
For the SYNC pin tied to 0.8V or more, or tied to a clock
source for synchronization:
IOUT(MAX ) = ILIM −
ΔIL
ΔI
= 1.18 A •(1− 0.29 • DC) − L
2
2
3695f
14
LT3695
APPLICATIONS INFORMATION
Choosing an inductor value so that the ripple current is
small will allow a maximum output current near the switch
current limit.
Table 2. Inductor Vendors
VENDOR
URL
Murata
www.murata.com
TDk
www.componenttdk.com
Toko
www.toko.com
Coilcraft
Sumida
PART SERIES
TYPE
switching current into a tight local loop, minimizing EMI.
A 2.2μF capacitor is capable of this task, but only if it is
placed close to the LT3695 (see the PCB Layout section
for more information). A second precaution regarding
the ceramic input capacitor concerns the maximum input
voltage rating of the LT3695. A ceramic input capacitor
combined with trace or cable inductance forms a high-Q
(underdamped) tank circuit. If the LT3695 circuit is plugged
into a live supply, the input voltage can ring to twice its
nominal value, possibly exceeding the LT3695’s voltage
rating. For details see Application Note 88.
LQH55D
Open
SLF7045
SLF10145
Shielded
Shielded
D62CB
D63CB
D73C
D75F
Shielded
Shielded
Shielded
Open
www.coilcraft.com
MSS7341
MSS1038
Shielded
Shielded
Output Capacitor and Output Ripple
www.sumida.com
CR54
CDRH74
CDRH6D38
CR75
Open
Shielded
Shielded
Open
The output capacitor has two essential functions. Along
with the inductor, it filters the square wave generated by the
LT3695 to produce the DC output. In this role it determines
the output ripple, and low impedance at the switching
frequency is important. The second function is to store
energy in order to satisfy transient loads and stabilize the
LT3695’s control loop. Ceramic capacitors have very low
equivalent series resistance (ESR) and provide the best
ripple performance. A good starting value is:
One approach to choosing the inductor is to start with the
simple rule given above, look at the available inductors,
and choose one to meet cost or space goals. Then use
these equations to check that the LT3695 will be able to
deliver the required output current. Note again that these
equations assume that the inductor current is continuous. Discontinuous operation occurs when IOUT is less
than ΔIL/2.
Input Capacitor
Bypass the input of the LT3695 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 2.2μF to 10μF ceramic capacitor is adequate to
bypass the LT3695 and will easily handle the ripple current.
Note that larger input capacitance is required when a lower
switching frequency is used. 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 lower performance
electrolytic capacitor.
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 LT3695 and to force this very high frequency
COUT =
50
f
VOUT SW
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 the compensation network is also
adjusted to maintain the loop bandwidth. A lower value
of output capacitor can be used to save space and cost
but transient performance will suffer. See the Frequency
Compensation section to choose an appropriate compensation network.
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. High performance tantalum or
electrolytic capacitors can be used for the output capacitor.
3695f
15
LT3695
APPLICATIONS INFORMATION
Table 3. Capacitor Vendors
VENDOR
PHONE
URL
PART SERIES
COMMANDS
Panasonic
(714) 373-7366
www.panasonic.com
Ceramic, Polymer, Tantalum
EEF Series
Kemet
(864) 963-6300
www.kemet.com
Ceramic, Tantalum
T494, T495
Sanyo
(408) 749-9714
www.sanyovideo.com
Ceramic, Polymer, Tantalum
POSCAP
Murata
(408) 436-1300
AVX
Taiyo Yuden
(864) 963-6300
www.murata.com
Ceramic
www.avxcorp.com
Ceramic, Tantalum
www.taiyo-yuden.com
Ceramic
Low ESR is important, so choose one that is intended for
use in switching regulators. The ESR should be specified
by the supplier, and should be 0.05Ω or less. Such a
capacitor will be larger than a ceramic capacitor and will
have a larger capacitance, because the capacitor must be
large to achieve low ESR. Table 3 lists several capacitor
vendors.
Table 4. Schottky Diodes
Diode Selection
Diodes Inc.
The catch diode (D1 from Block Diagram) conducts current only during switch off time. Average forward current
in normal operation can be calculated from:
ID(AVG) = IOUT • (1 – DC)
where DC is the duty cycle. The only reason to consider a
diode with larger current rating than necessary for nominal
operation is for the case of shorted or overloaded output
conditions. For the worst case of shorted output the diode
average current will then increase to a value that depends
on the following internal parameters: switch current limit,
catch diode (DA pin) current threshold and minimum
on-time. The worst case (taking maximum values for the
above mentioned parameters) is given by the following
expression:
1 V
ID( AVG)MAX = 2A + • IN • 150ns
2 L
Peak reverse voltage is equal to the regulator input voltage
if it is below the overvoltage protection threshold. This
feature keeps the switch off for VIN > VOVLO (39.9V maximum). For inputs up to the maximum operating voltage
of 36V, use a diode with a reverse voltage rating greater
PART NUMBER
TPS Series
VR (V)
IAVE (A)
VF at 1A (mV)
MBR0520L
20
0.5
MBR0540
40
0.5
620
MBRM120E
20
1
530
MBRM140
40
1
550
30
0.5
B0540W
40
0.5
620
B120
20
1
500
B130
30
1
500
B140
40
1
500
B220
20
2
B230
30
2
B140HB
40
1
DFLS240L
40
2
DFLS140
40
1.1
B240
40
2
VF at 2A (mV)
On-Semiconducor
B0530W
595
500
500
530
500
510
500
Central Semiconductor
CMSH1-40M
40
1
500
CMSH1-40ML
40
1
400
CMSH2-40M
40
2
550
CMSH2-40L
40
2
400
CMSH2-40
40
2
500
than the input voltage. If transients at the input of up to
60V are expected, use a diode with a reverse voltage rating of 40V. Table 4 lists several Schottky diodes and their
manufacturers. If operating at high ambient temperatures,
consider using a Schottky with low reverse leakage.
3695f
16
LT3695
APPLICATIONS INFORMATION
Audible Noise
Ceramic capacitors are small, robust and have very
low ESR. However, ceramic capacitors can sometimes
cause problems when used with the LT3695 due to their
piezoelectric nature. When in Burst Mode operation, the
LT3695’s switching frequency depends on the load current,
and at very light loads the LT3695 can excite the ceramic
capacitor at audio frequencies, generating audible noise.
Since the LT3695 operates at a lower current limit during
Burst Mode operation, the noise is typically very quiet. If
this is unacceptable, use a high performance tantalum or
electrolytic capacitor at the output.
Frequency Compensation
The LT3695 uses current mode control to regulate the
output. This simplifies loop compensation. In particular, the
LT3695 does not require the ESR of the output capacitor
for stability, so you are free to use ceramic capacitors to
achieve low output ripple and small circuit size. Frequency
compensation is provided by the components tied to the
VC pin, as shown in Figure 1. Generally a capacitor (CC)
and a resistor (RC) in series to ground are used. In addition, there may be a lower value capacitor in parallel.
This capacitor (CF) is used to filter noise at the switching
frequency, and is required only if a phase-lead capacitor
(CPL) is used or if the output capacitor has high ESR.
LT3695
CURRENT MODE
POWER STAGE
gm = 1.25S
SW
OUTPUT
R1
CPL
FB
–
gm = 430µS
ESR
C1
+
0.8V
+
CF
RC
VOUT
100mV/DIV
C1
3M
VC
Loop compensation determines the stability and transient
performance. Optimizing the design of the compensation
network depends on the application and type of output
capacitor. A practical approach is to start with one of the
circuits in this data sheet that is similar to your application and tune the compensation network to optimize the
performance. Stability should then be checked across all
operating conditions, including load current, input voltage
and temperature. The LT1375 data sheet contains a more
thorough discussion of loop compensation and describes
how to test the stability using a transient load. Figure 1
shows an equivalent circuit for the LT3695 control loop.
The error amplifier is a transconductance amplifier with
finite output impedance. The power section, consisting of
the modulator, power switch and inductor, is modeled as
a transconductance amplifier generating an output current proportional to the voltage at the VC pin. Note that
the output capacitor integrates this current, and that the
capacitor on the VC pin (CC) integrates the error amplifier output current, resulting in two poles in the loop. In
most cases a zero is required and comes from either the
output capacitor ESR or from a resistor RC in series with
CC. This simple model works well as long as the value
of the inductor is not too high and the loop crossover
frequency is much lower than the switching frequency.
A phase lead capacitor (CPL) across the feedback divider
may improve the transient response. Figure 2 shows the
transient response when the load current is stepped from
300mA to 650mA and back to 300mA.
GND
R2
CERAMIC
POLYMER
OR
TANTALUM
OR
ELECTROLITIC
ILOAD
0.5A/DIV
20μs/DIV
CC
3695 F01
3695 F02
Figure 2. Transient Load Response of the LT3695. A 3.3VOUT
Typical Application with VIN = 12V as the Load Current is
Stepped from 300mA to 650mA
Figure 1. Model for Loop Response
3695f
17
LT3695
APPLICATIONS INFORMATION
Low Ripple Burst Mode Operation
The LT3695 is capable of operating in either low ripple
Burst Mode operation or pulse-skipping mode which are
selected using the SYNC pin. See the Synchronization
section for more information.
To enhance efficiency at light loads, the LT3695 can be
operated 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 LT3695 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 LT3695 delivers power to the
output with single, low current pulses, the output ripple
is kept below 15mV for a typical application. In addition,
VIN and BD quiescent currents are reduced to typically
35μA and 55μA respectively during the sleep time. As the
load current decreases towards a no-load condition, the
percentage of time that the LT3695 operates in sleep mode
increases and the average input current is greatly reduced
resulting in high efficiency even at very low loads. (See
Figure 3). At higher output loads (above about 70mA for
the front page application) the LT3695 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 operation is seamless,
and will not disturb the output voltage.
If low quiescent current is not required, tie SYNC high to
select pulse-skipping mode. The benefit of this mode is
that the LT3695 will enter full frequency standard PWM
operation at a lower output load current than when in
Burst Mode operation. With the SYNC pin tied low, the
front page application circuit will switch at full frequency
VSW
5V/DIV
IL
0.2A/DIV
VOUT
20mV/DIV
5μs/DIV
3695 F03
VIN = 12V, FRONT PAGE APPLICATION
ILOAD = 5mA
Figure 3. Switching Waveforms, Burst Mode Operation
at output loads higher than about 100mA. With the SYNC
pin tied high, the front page application circuit will switch
at full frequency at output loads higher than about 30mA.
The maximum load current that the LT3695 can supply is
reduced when SYNC is high.
BOOST 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 three ways to
arrange the boost circuit for the LT3695. The BOOST pin
must be more than 2.3V above the SW pin for best efficiency. For outputs of between 3V and 8V, the standard
circuit (Figure 4a) is best. For outputs between 2.8V and
3V, use a 1μF boost capacitor. A 2.5V output presents a
special case because it is marginally adequate to support
the boosted drive stage while using the internal boost
diode. For reliable BOOST pin operation with 2.5V outputs
use a good external Schottky diode (such as the ON Semi
MBR0540), and a 1μF boost capacitor (see Figure 4b).
For lower output voltages the boost diode can be tied to
the input (Figure 4c), or to another supply greater than
2.8V. Keep in mind that a minimum input voltage of 4.3V
is required if the voltage at the BD pin is smaller than 3V.
Tying BD to VIN reduces the maximum input voltage to
25V. The circuit in Figure 4a is more efficient because the
BOOST pin current and BD pin quiescent current come
from a lower voltage source. You must also be sure that
the maximum voltage ratings of the BOOST and BD pins
are not exceeded.
As mentioned, a minimum of 2.5V across the BOOST
capacitor is required for proper operation of the internal
BOOST circuitry to provide the base current for the power
NPN switch. For BD pin voltages higher than 3V, the excess
voltage across the BOOST capacitor does not bring an
increase in performance but dissipates additional power in
the internal BOOST circuitry instead. The BOOST circuitry
tolerates reasonable amounts of power, however excessive
power dissipation on this circuitry may impair reliability. For
reliable operation, use no more than 8V on the BD pin for
the circuit in Figure 4a. For higher output voltages, make
sure that there is no more than 8V at the BD pin either by
connecting it to another available supply higher than 3V or
3695f
18
LT3695
APPLICATIONS INFORMATION
VOUT
VIN
BD
BOOST
VIN
C3
LT3695 SW
D1
DA
GND
PGND
3695 F04a
(4a) For VOUT > 2.8V, VIN(MIN) = 4.3V if VOUT < 3V
VOUT
VIN
D2
BD
BOOST
VIN
C3
LT3695 SW
D1
DA
GND
PGND
3695 F04b
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. At light
loads, the inductor current becomes discontinuous and
the effective duty cycle can be very high. This reduces the
minimum input voltage to approximately 300mV above
VOUT . At higher load currents, the inductor current is
continuous and the duty cycle is limited by the maximum
duty cycle of the LT3695, requiring a higher input voltage
to maintain regulation.
(4b) For 2.5V < VOUT < 2.8V, VIN(MIN) = 4.3V
6.0
5.5
5.0
BD
BOOST
VIN
C3
VOUT
LT3695 SW
D1
DA
GND
PGND
INPUT VOLTAGE (V)
VIN
TO START
(WORST CASE)
4.5
4.0
3.5
TO RUN
3.0
VOUT = 3.3V
TA = 25˚C
L = 10μH
f = 800kHz
2.5
3695 F04c
2.0
(4c) For VOUT < 2.5V, VIN(MAX) = 25V
Figure 4. Three Circuits for Generating
the Boost Voltage
10
100
LOAD CURRENT (mA)
1
1000
8.0
7.5
The minimum operating voltage of the LT3695 application is limited by the minimum input voltage and by the
maximum duty cycle as outlined previously. For proper
start-up, the minimum input voltage is also limited by the
boost circuit. If the input voltage is ramped slowly, or the
LT3695 is turned on with its RUN/SS pin when the output
is already in regulation, then the boost capacitor may not
be fully charged. Because 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
7.0
INPUT VOLTAGE (V)
by using a Zener diode between VOUT and BD to maintain
the BD pin voltage between 3V and 8V.
TO START
(WORST CASE)
6.5
6.0
5.5
5.0 TO RUN
4.5
4.0
3.5
VOUT = 5V
TA = 25˚C
L = 10μH
f = 800kHz
3.0
2.5
2.0
1
10
100
LOAD CURRENT(mA)
1000
3695 F05
Figure 5. The Minimum Input Voltage depends on
Output Voltage, Load Current and Boost Circuit
3695f
19
LT3695
APPLICATIONS INFORMATION
Soft-Start
The RUN/SS pin can be used to soft-start the LT3695,
reducing the maximum input current during start-up. The
RUN/SS pin is driven through an external RC network to
create a voltage ramp at this pin. Figure 6 shows the startup and shutdown waveforms with the soft-start circuit.
By choosing a large RC time constant, the peak start-up
current can be reduced to the current that is required
to regulate the output, with no overshoot. Choose the
value of the resistor so that it can supply 7.5μA when the
RUN/SS pin reaches 2.5V. For fault tolerant applications,
see the discussion of the RUN/SS resistor in the Fault
Tolerance section.
VRUN
5V/DIV
RUN
15k
RUN/SS
0.22μF
GND
The LT3695 may be synchronized over a 300kHz to 2.2MHz
range. The RT resistor should be chosen to set the LT3695
switching frequency 20% below the lowest synchronization
input. For example, if the synchronization signal is 360kHz,
the RT should be chosen for 300kHz. To assure reliable and
safe operation the LT3695 will only synchronize when the
output voltage is near regulation as indicated by the PG
flag. It is therefore necessary to choose a large enough
inductor value to supply the required output current at the
frequency set by the RT resistor. See the Inductor Selection
section for more information. It is also important to note
that slope compensation is set by the RT value; to avoid
subharmonic oscillations, calculate the minimum inductor
value using the frequency determined by RT .
Shorted and Reversed Input Protection
VRUN/SS
5V/DIV
VOUT
5V/DIV
IL
1A/DIV
5ms/DIV
3695 F05
Figure 6. To Soft-Start the LT3695, Add a
Resistor and Capacitor to the RUN/SS Pin
Synchronization
If the inductor is chosen so that it won’t saturate excessively, the LT3695 will tolerate a shorted output. When
operating in short-circuit condition, the LT3695 will reduce
its frequency until the valley current is at a typical value of
1.6A (see Figure 7). There is another situation to consider
in systems where the output will be held high when the
input to the LT3695 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
To select low ripple Burst Mode operation, tie the SYNC
pin below 0.3V (this can be ground or a logic output).
Synchronizing the oscillator of the LT3695 to an external
frequency can be done by connecting a square wave (with
20% to 80% duty cycle) to the SYNC pin. The square wave
amplitude should have valleys that are below 0.3V and
peaks that are above 0.8V (up to 6V).
The LT3695 will not enter Burst Mode operation at low
output loads while synchronized to an external clock, but
instead will skip pulses to maintain regulation.
The maximum load current that the part can supply is
reduced when a clock signal is applied to SYNC.
VSW
20V/DIV
0V
IL
500mA/DIV
0A
2μs/DIV
3695 F07
Figure 7. The LT3695 Reduces its Frequency to
Protect Against Shorted Output with 36V Input
3695f
20
LT3695
APPLICATIONS INFORMATION
LT3695’s output. If the VIN pin is allowed to float and the
RUN/SS pin is held high (either by a logic signal or because
it is tied to VIN), then the LT3695’s internal circuitry will
pull its quiescent current through its SW pin. This is fine
if your system can tolerate a few mA in this state. If you
ground the RUN/SS pin, the SW pin current will drop to
essentially zero. However, if the VIN pin is grounded while
the output is held high, then parasitic diodes inside the
LT3695 can pull large currents 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.
GND
VOUT
C2
L
C3
D1
R2
RT
R1
RC
D4
MBRS140
VIN
C1
BD
VIN
VIN
BOOST
CC
GND
LT3695
RUN/SS
SW
VC
GND PGND
DA
FB
VOUT
BACKUP
3695 F09
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 Regulator Runs Only when the Input
is Present
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 LT3695’s VIN, SW and PGND pins, the catch
diode and the input capacitor (CIN). The loop formed by
these components should be as small as possible. These
3695 F09
Figure 9. A Good PCB Layout Ensures Proper,
Low EMI Operation
components, along with the inductor and output capacitor
(COUT), should be placed on the same side of the circuit
board, and their connections should be made on that layer.
All connections to GND should be made at a common
star ground point or directly to a local, unbroken ground
plane below these components. The SW and BOOST nodes
should be laid out carefully to avoid interference. Finally,
keep the FB, RT and VC nodes small so that the ground
traces will shield them from the SW and BOOST nodes.
To keep thermal resistance low, extend the ground plane
as much as possible and add thermal vias under and near
the LT3695 to any additional ground planes within the
circuit board and on the bottom side. Keep in mind that
the thermal design must keep the junctions of the IC below
the specified absolute maximum temperature.
3695f
21
LT3695
APPLICATIONS INFORMATION
High Temperature Considerations
The PCB must provide heat sinking to keep the LT3695
cool. The Exposed Pad on the bottom of the package
may be soldered to a copper area which should be tied
to large copper layers below with thermal vias; these layers will spread the heat dissipated by the LT3695. Place
additional vias to reduce thermal resistance further. With
these steps, the thermal resistance from die (or junction)
to ambient can be reduced to θJA = 40°C/W or less. With
100 LFPM airflow, this resistance can fall by another 25%.
Further increases in airflow will lead to lower thermal
resistance. Because of the large output current capability
of the LT3695, it is possible to dissipate enough heat to
raise the junction temperature beyond the absolute maximum. When operating at high ambient temperatures, the
maximum load current should be derated as the ambient
temperature approaches these maximums. If the junction
temperature reaches the thermal shutdown threshold, the
part will stop switching to prevent internal damage due
to overheating.
Power dissipation within the LT3695 can be estimated
by calculating the total power loss from an efficiency
measurement. The die temperature rise is calculated by
multiplying the power dissipation of the LT3695 by the
thermal resistance from junction to ambient. Die temperature rise was measured on a 2-layer, 10cm × 10cm circuit
board in still air at a load current of 1A (fSW = 800kHz).
For a 12V input to 5V output the die temperature elevation
above ambient was 22°C with the exposed pad soldered
and 44°C without the exposed pad soldered.
Fault Tolerance
The LT3695 is designed to tolerate single fault conditions.
Shorting two adjacent pins together or leaving one single
pin floating does not raise VOUT or cause damage to the
LT3695. However, the application circuit must meet the
requirements discussed in this section in order to achieve
this tolerance level.
Tables 5 and 6 show the effects that result from shorting
adjacent pins or from a floating pin, respectively.
Table 5: Effects of Pin Shorts
PINS
EFFECT
PGND-DA
No effect if VIN < VIN(MAX). See Input Voltage Range section for description of VIN(MAX).
SW-RUN/SS
The result of this short depends on the load resistance and on R3 (Figure 10). See the following discussion.
RUN/SS-RT
No effect or VOUT will fall below regulation voltage if IR3 (Figure 10) < 1mA.
RT -SYNC
No effect or VOUT will fall below regulation voltage if the current into the RT pin is less than 1mA.
SYNC-VIN
No effect if VIN does not exceed the absolute maximum voltage of SYNC (20V).
PG-GND
No effect.
GND-BD
VOUT may fall below regulation voltage, power dissipation of the power switch will be increased. Note that this short also grounds the
voltage source supplying BD. Make sure it is safe to short the supply for BD to ground. For this reason BD should not be connected to
VIN, but it is safe to connect it to VOUT .
BD-BOOST
If diode D2 (see Figure 10) is used, no effect or VOUT may fall below regulation voltage. Otherwise the device may be damaged.
3695f
22
LT3695
APPLICATIONS INFORMATION
Table 6: Effects of Floating Pins
PIN
EFFECT
PGND
No effect if the Exposed Pad is soldered.
Otherwise: VOUT may fall below regulation voltage. Make sure that VIN < VIN(MAX) (see Input Voltage Range section for details) and
provide a bypass resistor at the DA pin. See the following discussion.
DA
VOUT may fall below regulation voltage. Make sure that VIN < VIN(MAX) (see Input Voltage Range section for details) and provide a bypass
resistor. See the following discussion.
SW
VOUT will fall below regulation voltage.
RUN/SS
VOUT will fall below regulation voltage.
RT
VOUT will fall below regulation voltage.
SYNC
VOUT may fall below regulation voltage. A floating SYNC pin configures the LT3695 for pulse-skipping mode. However, a floating SYNC
pin is sensitive to noise which can degrade device performance.
VIN
VOUT will fall below regulation voltage.
VC
VOUT may fall below regulation voltage. Disconnecting the VC pin alters the loop compensation and potentially degrades device
performance. The output voltage ripple will increase if the part becomes unstable.
FB
VOUT will fall below regulation voltage.
PG
No effect.
GND
Output maintains regulation, but potential degradation of device performance.
BD
VOUT may fall below regulation voltage. If BD is not connected, the boost capacitor cannot be charged and thus the power switch cannot
saturate properly, which increases its power dissipation.
BOOST
VOUT may fall below regulation voltage. If BOOST is not connected, the boost capacitor cannot be charged and thus the power switch
cannot saturate properly, which increases its power dissipation.
For the best fault tolerance to inadvertent adjacent pin
shorts, the RUN/SS pin must not be directly connected to
either ground or VIN. If there was a short between RUN/SS
and SW then connecting RUN/SS to VIN would tie SW to VIN
and would thus raise VOUT . Likewise, grounding RUN/SS
would tie SW to ground and would damage the power
switch if this is done when the power switch is on. A short
between RT and a RUN/SS pin that is connected to VIN
would violate the absolute maximum ratings of the RT pin.
Therefore, the current supplying the RUN/SS pin must be
limited, for example, with resistor R3 in Figure 10. In case
of a short between RUN/SS and SW this resistor charges
C2 through the inductor L1 if the current it supplies from
VIN
R3
D2
VIN
BD
RUN/SS BOOST
C3
VOUT
D1
RT
CSS
220nF
L1
LT3695 SW
RSS
47Ω
RT
DA
R1
RLOAD
FB
R2
C2
3695 F10
Figure 10. The Dashed Lines Show where a Connection Would
Occur if There Were an Inadvertent Short from RUN/SS to an
Adjacent Pin or from BOOST to BD. In These Cases, R3 Protects
Circuitry Tied to the RT or SW Pins, and D2 Shields BOOST from
VOUT. If CSS is Used for Soft Start, RSS Isolates it from SW
3695f
23
LT3695
APPLICATIONS INFORMATION
VIN is not completely drawn by RLOAD, R1 + R2, and the BD
pin (if connected to VOUT). Since this causes VOUT to rise,
the LT3695 stops switching. The resistive divider formed
by R3, RLOAD, and R1 + R2 must be adjusted for VOUT not
to exceed its nominal value at the required maximum input
voltage VIN(MAX). R3 must supply sufficient current into
RUN/SS at the required minimum input voltage VIN(MIN)
for normal non-fault situations. Based on the maximum
RUN/SS current of 7.5μA at VRUN/SS = 2.5V this gives
R3 ≤
VIN(MIN) – 2.5V
VIN(MAX) VIN(MIN)
(V)
(V)
VOUT
(V)
R3
(kΩ)
R1
(kΩ)
R2
(kΩ)
IR1+R2
(μA)
16
3.8
1.8
169
11.5
9.09
87
VIN(MAX ) – VOUT
36
3.8
1.8
169
4.75
3.74
212
R3
16
4.5
2.5
261
93.1
43.2
18
36
4.5
2.5
261
16.9
7.87
101
16
5
3.3
365
432
137
6
36
5
3.3
365
43.2
13.7
58
16
7
5
274
536
102
8
36
7
5
590
221
42.2
19
16
10
8
200
562
61.9
13
36
10
8
475
280
30.9
26
27
14
12
301
511
36.5
22
36
14
12
442
511
36.5
22
This current must be drawn by RLOAD, R1 + R2, and the
BD pin, if connected to VOUT:
IR3 ≤
If RUN/SS is controlled by an external circuitry, the current
this circuitry can supply must be limited. This can be done
as discussed above. In addition, it may be necessary to
protect this external circuitry from the voltage at SW, for
example by using a diode.
Table 7. Example Values for R1, R2 and R3 for Common
Combinations of VIN and VOUT . IR1+R2 is the Current Drawn by
R1 + R2 in Normal Operation
7.5µA
The current through R3 is maximal at VIN(MAX) with RUN/SS
shorted to SW:
IR3 =
Table 7 shows example values for common applications.
RSS must be included as the switch node would otherwise
have to charge CSS if the SW pin and the RUN/SS pin are
shorted, which may damage the power switch.
VOUT
+I
RLOAD || (R1+ R2) BD
Without load (RLOAD = ∞) and assuming the minimum
current of 35μA into the BD pin, this leads to
VOUT
R1+ R2 ≤
VIN(MAX ) – VOUT
R3
– 35µA
as upper limit for the feedback resistors. For VOUT < 2.5V
assume no current drawn by the BD pin, which gives
R1+ R2 ≤
VOUT • R3
VIN(MAX ) – VOUT
The BOOST pin must not be shorted to a low impedance
node like VOUT that clamps its voltage. For best fault tolerance, supply current into the BD pin through the Schottky
diode D2 as shown in Figure 10. Note that this diode must
be able to handle the maximum output current in case there
is a short between the BD pin and the GND pin.
A short between RUN/SS and SW may also increase the
output ripple. To suppress this, connect the soft-start
3695f
24
LT3695
APPLICATIONS INFORMATION
network consisting of RSS and CSS to RUN/SS as shown
in Figure 10. CSS should not be smaller than 0.22μF.
The SYNC pin must not be directly connected to either
ground or VIN. A short between RT and a SYNC pin that
is connected to VIN could violate the absolute maximum
ratings of the RT pin. A short between the SYNC pin and
the VIN pin could damage an external driver circuit which
may be connected to SYNC or would short VIN to ground
if SYNC is grounded.
The recommended connection for SYNC is shown in Figure 11. If SYNC is to be driven by an external circuitry, RS
may be used to isolate this circuitry from VIN. CS must be
used in this case to provide a low impedance path for the
synchronization signal. If SYNC is pulled low, RS prevents
VIN from being shorted to ground in case of an inadvertent
short between SYNC and VIN. If SYNC is pulled high to VIN,
then RS protects the RT pin during an inadvertent short
between SYNC and RT.
If the DA pin or the PGND pin are inadvertently left floating, the current path of the catch diode is interrupted
unless a bypass resistor is connected from DA to ground.
Use a 360mΩ (5% tolerance) resistor rated for a power
dissipation of
P = I2LOAD(MAX) • 0.36 • (1 – DCMIN)
where ILOAD(MAX) is the maximum load current and DCMIN
is the minimum duty cycle. For example, this would require
a power rating of at least 219mW for an output current of
800mA and a minimum duty cycle of 5%. Make sure not
to exceed VIN(MAX) (see Input Voltage Range section for
details) during start-up or overload conditions.
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 318
shows how to generate a bipolar output supply using a
buck regulator.
VIN
RS
100k
VIN
SYNC
SYNC
CS
100pF
LT3695
RT
RT
3695 F11
Figure 11. The Dashed Lines Show Where a Connection Would Occur
if There Were an Inadvertent Short from SYNC to an Adjacent Pin. In
This Case, RS Protects Circuitry Connecting to SYNC
3695f
25
LT3695
TYPICAL APPLICATIONS
Fully Tolerant 3.3V Step-Down Converter with Soft-Start
VIN
5V TO 28.5V
TRANSIENT TO 36V
324k
VIN
RUN/SS
D2
B140
BD
BOOST
0.22μF
VC
SW
47Ω
0.22μF
14k
40.2k
D1
B140
LT3695
RT
2.2μF
PG
DA
SYNC
FB
470pF 100k
L
10μH
VOUT
3.3V
0.9A, VIN > 5V
1A, VIN > 6.5V
GND
56.2k
0.36Ω
PGND
17.8k
10μF
3695 TA02
f = 800kHz
1.8V Step-Down Converter
VIN
3.6V TO 25V
4.7μF
ON OFF
VIN
RUN/SS
BD
BOOST
VC
RT
17.4k
71.5k
330pF 100k
L1
0.22μF 6.8μH
SW
D1
B140
LT3695
PG
DA
SYNC
GND
FB
PGND
VOUT
1.8V
1A
127k
102k
22μF
3695 TA03
f = 500kHz
5V, 2MHz Step-Down Converter
VOUT
5V
0.9A
VIN
10V TO 16.5V
TRANSIENT TO 36V
2.2μF
ON OFF
VIN
RUN/SS
BD
BOOST
VC
RT
13.3k
9.76k
680pF 100k
L
0.22μF 4.7μH
SW
D1
B140
LT3695
PG
DA
SYNC
GND
FB
PGND
f = 2MHz
536k
102k
10μF
3695 TA04
3695f
26
LT3695
PACKAGE DESCRIPTION
MSE Package
16-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1667 Rev A)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 p 0.102
(.112 p .004)
5.23
(.206)
MIN
2.845 p 0.102
(.112 p .004)
0.889 p 0.127
(.035 p .005)
8
1
1.651 p 0.102
(.065 p .004)
1.651 p 0.102 3.20 – 3.45
(.065 p .004) (.126 – .136)
0.305 p 0.038
(.0120 p .0015)
TYP
16
0.50
(.0197)
BSC
4.039 p 0.102
(.159 p .004)
(NOTE 3)
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
0.35
REF
0.12 REF
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
9
NO MEASUREMENT PURPOSE
0.280 p 0.076
(.011 p .003)
REF
16151413121110 9
DETAIL “A”
0o – 6o TYP
3.00 p 0.102
(.118 p .004)
(NOTE 4)
4.90 p 0.152
(.193 p .006)
GAUGE PLANE
0.53 p 0.152
(.021 p .006)
1234567 8
DETAIL “A”
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
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
0.86
(.034)
REF
0.1016 p 0.0508
(.004 p .002)
MSOP (MSE16) 0608 REV A
3695f
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.
27
LT3695
TYPICAL APPLICATION
5V Step-Down Converter
VIN
6.9V TO 36V
TRANSIENT TO 60V
2.2μF
ON OFF
VIN
RUN/SS
VOUT
5V
0.9A, VIN > 6.9V
1A, VIN > 12V
BD
BOOST
0.22μF
VC
RT
16.2k
40.2k
470pF 100k
10μH
SW
D1
B140
LT3695
PG
DA
SYNC
GND
FB
PGND
f = 800kHz
536k
102k
10μF
3695 TA05
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LT3970
40V, 350mA, 2MHz High Efficiency MicroPower Step-Down DC/DC
Converter
VIN: 4V to 40V Transient to 60V, VOUT(MAX) = 1.21V, IQ = 2μA,
ISD < 1μA, 3mm × 2mm DFN-10, MSOP-10 Packages
LT3689
36V, 60V Transient Protection, 800mA, 2.2MHz High Efficiency MicroPower VIN: 3.6V to 36V Transient to 60V, VOUT(MAX) = 0.8V,
IQ = 75μA, ISD < 1μA, 3mm × 3mm QFN-16 Package
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LT3685
36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High Efficiency
Step-Down DC/DC Converter
VIN: 3.6V to 38V, VOUT(MAX) = 0.78V, IQ = 70μA, ISD < 1μA,
3mm × 3mm DFN-10, MSOP-10E Packages
LT3684
34V with Transient Protection to 36V, 2A (IOUT), 2.8MHz, High Efficiency
Step-Down DC/DC Converter
VIN: 3.6V to 34V, VOUT(MAX) = 1.26V, IQ = 850μA, ISD < 1μA,
3mm × 3mm DFN-10, MSOP-10E Packages
LT3682
36V, 60VMAX, 1A, 2.2MHz High Efficiency Micropower Step-Down DC/DC
Converter
VIN: 3.6V to 36V, VOUT(MAX) = 0.8V, IQ = 75μA, ISD < 1μA,
3mm × 3mm DFN-12 Package
LT3508
36V with Transient Protection to 40V, Dual 1.4A (IOUT), 3MHz, High
Efficiency Step-Down DC/DC Converter
VIN: 3.7V to 36V, VOUT(MAX) = 0.8V, IQ = 4.6mA, ISD = 1μA,
4mm × 4mm QFN-24, TSSOP-16E Packages
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(MAX) = 0.8V, IQ = 7mA, ISD = 1μA,
5mm × 7mm QFN-38 Package
LT3505
36V with Transient Protection to 40V, 1.4A (IOUT), 3MHz, High Efficiency
Step-Down DC/DC Converter
VIN: 3.6V to 34V, VOUT(MAX) = 0.78V, IQ = 2mA, ISD = 2μA,
3mm × 3mm DFN-8, MSOP-8E Packages
LT3500
36V, 40VMAX, 2A, 2.5MHz High Efficiency Step-Down DC/DC Converter and VIN: 3.6V to 36V, VOUT(MAX) = 0.8V, IQ = 2.5mA, ISD < 10μA,
LDO Controller
3mm × 3mm DFN-10 Package
LT3493
36V, 1.4A (IOUT), 750kHz High Efficiency Step-Down DC/DC Converter
VIN: 3.6V to 36V, VOUT(MAX) = 0.8V, IQ = 1.9mA, ISD < 1μA,
2mm × 3mm DFN-6 Package
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(MAX) = 1.26V, IQ = 50μA, ISD < 1μA,
3mm × 3mm DFN-10, MSOP-10E Packages
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(MAX) = 0.78V, IQ = 70μA, ISD < 1μA,
3mm × 3mm DFN-10, MSOP-10E Packages
LT3437
60V, 400mA (IOUT), MicroPower Step-Down DC/DC Converter with Burst
Mode Operation
VIN: 3.3V to 60V, VOUT(MAX) = 1.25V, IQ = 100μA, ISD < 1μA,
3mm × 3mm DFN-10, TSSOP-16E Package
LT3434/LT3435 60V, 2.4A (IOUT), 200kHz/500kHz, High Efficiency Step-Down DC/DC
Converter with Burst Mode Operation
VIN: 3.3V to 60V, VOUT(MAX) = 1.2V, IQ = 100μA, ISD < 1μA,
TSSOP-16E Package
LT1976/LT1977 60V, 1.2A (IOUT), 200kHz/500kHz, High Efficiency Step-Down DC/DC
Converter with Burst Mode Operation
VIN: 3.3V to 60V, VOUT(MAX) = 1.2V, IQ = 100μA, ISD < 1μA,
TSSOP-16E Package
LT1936
36V, 1.4A (IOUT), 500kHz High Efficiency Step-Down DC/DC Converter
VIN: 3.6V to 36V, VOUT(MAX) = 1.2V, IQ = 1.9mA, ISD < 1μA,
MS8E Package
LT1766
60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter
VIN: 5.5V to 60V, VOUT(MAX) = 1.2V, IQ = 2.5mA, ISD = 25μA,
TSSOP-16/E Package
3695f
28 Linear Technology Corporation
LT 0709 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
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www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2009