LINER LTC3642IMS8E-TRPBF High effi ciency, high voltage 50ma synchronous step-down converter Datasheet

LTC3642
High Efficiency, High Voltage
50mA Synchronous
Step-Down Converter
DESCRIPTION
FEATURES
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Wide Input Voltage Range: 4.5V to 45V
Tolerant of 60V Input Transients
Internal High Side and Low Side Power Switches
No Compensation Required
50mA Output Current
Low Dropout Operation: 100% Duty Cycle
Low Quiescent Current: 12μA
0.8V Feedback Voltage Reference
Adjustable Peak Current Limit
Internal and External Soft-Start
Precise RUN Pin Threshold with Adjustable
Hysteresis
3.3V, 5V and Adjustable Output Versions
Only Three External Components Required for Fixed
Output Versions
Low Profile (0.75mm) 3mm × 3mm DFN and
Thermally-Enhanced MS8E Packages
APPLICATIONS
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The LTC®3642 is a high efficiency step-down DC/DC
converter with internal high side and synchronous power
switches that draws only 12μA typical DC supply current
at no load while maintaining output voltage regulation.
The LTC3642 can supply up to 50mA load current and
features a programmable peak current limit that provides
a simple method for optimizing efficiency in lower current
applications. The LTC3642’s combination of Burst Mode®
operation, integrated power switches, low quiescent current, and programmable peak current limit provides high
efficiency over a broad range of load currents.
With its wide 4.5V to 45V input range and internal
overvoltage monitor capable of protecting the part through
60V surges, the LTC3642 is a robust converter suited for
regulating a wide variety of power sources. Additionally,
the LTC3642 includes a precise run threshold and soft-start
feature to guarantee that the power system start-up is
well-controlled in any environment.
The LTC3642 is available in the thermally enhanced
3mm × 3mm DFN and MS8E packages.
4mA to 20mA Current Loops
Industrial Control Supplies
Distributed Power Systems
Portable Instruments
Battery-Operated Devices
Automotive Power Systems
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Efficiency and Power Loss vs Load Current
100
VIN = 10V
95
5V, 50mA Step-Down Converter
100
EFFICIENCY
VIN
SW
LTC3642-5
RUN
VOUT
SS
HYST
ISET
GND
VOUT
5V
10μF 50mA
EFFICIENCY (%)
150μH
85
80
10
POWER LOSS
75
1
POWER LOSS (mW)
90
VIN
5V TO 45V
1μF
70
3642 TA01a
65
0.1
1
10
LOAD CURRENT (mA)
0.1
100
3642 TA01b
3642f
1
LTC3642
ABSOLUTE MAXIMUM RATINGS (Note 1)
VIN Supply Voltage ..................................... –0.3V to 60V
SW Voltage (DC) ............................–0.3V to (VIN + 0.3V)
RUN Voltage .............................................. –0.3V to 60V
VFB/VOUT, HYST, ISET, SS Voltages ................ –0.3V to 6V
Operating Junction Temperature Range
(Note 2).................................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
MS8E ................................................................ 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
SW
VIN
ISET
SS
1
2
3
4
9
8
7
6
5
GND
HYST
VOUT/VFB
RUN
SW 1
8
GND
VIN 2
7
HYST
6
VOUT/VFB
5
RUN
ISET 3
9
SS 4
MS8E PACKAGE
8-LEAD PLASTIC MSOP
DD PACKAGE
8-LEAD (3mm s 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 40°C/W, θJC = 5°-10°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
TJMAX = 125°C, θJA = 43°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3642EMS8E#PBF
LTC3642EMS8E#TRPBF
LTDTH
8-Lead Plastic MSOP
–40°C to 125°C
LTC3642EMS8E-3.3#PBF
LTC3642EMS8E-3.3#TRPBF
LTDYN
8-Lead Plastic MSOP
–40°C to 125°C
LTC3642EMS8E-5#PBF
LTC3642EMS8E-5#TRPBF
LTDYQ
8-Lead Plastic MSOP
–40°C to 125°C
LTC3642IMS8E#PBF
LTC3642IMS8E#TRPBF
LTDTH
8-Lead Plastic MSOP
–40°C to 125°C
LTC3642IMS8E-3.3E#PBF
LTC3642IMS8E-3.3#TRPBF
LTDYN
8-Lead Plastic MSOP
–40°C to 125°C
LTC3642IMS8E-5#PBF
LTC3642IMS8E-5#TRPBF
LTDYQ
8-Lead Plastic MSOP
–40°C to 125°C
LTC3642EDD#PBF
LTC3642EDD#TRPBF
LDTJ
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
LTC3642EDD-3.3#PBF
LTC3642EDD-3.3#TRPBF
LDYM
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
LTC3642EDD-5#PBF
LTC3642EDD-5#TRPBF
LDYP
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
LTC3642IDD#PBF
LTC3642IDD#TRPBF
LDTJ
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
LTC3642IDD-3.3#PBF
LTC3642IDD-3.3#TRPBF
LDYM
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
LTC3642IDD-5#PBF
LTC3642IDD-5#TRPBF
LDYP
8-Lead (3mm × 3mm) Plastic DFN
–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/
3642f
2
LTC3642
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Supply (VIN)
VIN
Input Voltage Operating Range
4.5
UVLO
VIN Undervoltage Lockout
VIN Rising
VIN Falling
Hysteresis
OVLO
VIN Overvoltage Lockout
VIN Rising
VIN Falling
Hysteresis
IQ
DC Supply Current (Note 3)
Active Mode
Sleep Mode
Shutdown Mode
l
l
45
V
3.80
3.75
4.15
4.00
150
4.40
4.25
V
V
mV
47
45
50
48
2
52
50
V
V
V
125
12
3
220
22
6
μA
μA
μA
VRUN = 0V
l
l
LTC3642-3.3V, VOUT Rising
LTC3642-3.3V, VOUT Falling
l
l
3.277
3.257
3.310
3.290
3.343
3.323
V
V
LTC3642-5V, VOUT Rising
LTC3642-5V, VOUT Falling
l
l
4.965
4.935
5.015
4.985
5.065
5.035
V
V
VFB Rising
l
0.792
0.800
0.808
l
3.5
5
6.5
mV
-10
0
10
nA
Output Supply (VOUT/VFB)
VOUT
Output Voltage Trip Thresholds
VFB
Feedback Comparator Trip Voltage
VHYST
Feedback Comparator Hysteresis
IFB
Feedback Pin Current
Adjustable Output Version, VFB = 1V
ΔVLINEREG
Feedback Voltage Line Regulation
VIN = 4.5V to 45V
LTC3642-5, VIN = 6V to 45V
VRUN
Run Pin Threshold
RUN Rising
RUN Falling
Hysteresis
1.17
1.06
1.21
1.10
110
1.25
1.14
V
V
mV
IRUN
Run Pin Leakage Current
RUN = 1.3V
–10
0
10
nA
VHYSTL
Hysteresis Pin Voltage Low
RUN < 1V, IHYST = 1mA
0.07
0.1
V
IHYST
Hysteresis Pin Leakage Current
VHYST = 1.3V
–10
0
10
nA
ISS
Soft-Start Pin Pull-Up Current
VSS < 1.5V
4.5
5.5
6.5
tINTSS
Internal Soft-Start Time
SS Pin Floating
IPEAK
Peak Current Trip Threshold
ISET Floating
500k Resistor from ISET to GND
ISET Shorted to GND
0.001
V
%/V
Operation
RON
Power Switch On-Resistance
Top Switch
Bottom Switch
ISW = –25mA
ISW = 25mA
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 LTC3642E is guaranteed to meet specifications from 0°C
to 85°C with specifications over the –40°C to 125°C operating junction
temperature range assured by design, characterization and correlation
with statistical process controls. The LTC3642I is guaranteed to meet
specifications from –40°C to 125°C.
0.75
l
100
20
115
55
25
3.0
1.5
μA
ms
130
32
mA
mA
mA
Ω
Ω
TJ is calculated from the ambient temperature TA and power dissipation PD
according to the following formula:
TJ = TA + (PD • θJA°C/W)
Note 3: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
3642f
3
LTC3642
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current
Line Regulation
100
VIN = 15V
85
80
VIN = 45V
VIN = 24V
VIN = 36V
75
ILOAD = 25mA
FIGURE 10 CIRCUIT
5.03
0.10
0
–0.10
70
1
10
LOAD CURRENT (mA)
15
10
5
100
20 25 30 35
VIN VOLTAGE (V)
3642 G01
5.00
4.99
4.98
0.800
0.799
–10
5.6
VIN = 10V
5.4
5.2
5.0
4.8
4.6
4.4
–40
110
20
50
80
TEMPERATURE (°C)
–10
20
50
80
TEMPERATURE (°C)
3642 G04
VIN SUPPLY CURRENT (μA)
100
90
80
70
60
50
40
30
ISET OPEN
RISET = 500k
ISET = GND
20
50
80
TEMPERATURE (°C)
110
Quiescent Supply Current vs
Temperature
14
14
12
12
SLEEP
10
8
6
SHUTDOWN
4
50
3642 G06
Quiescent Supply Current vs
Input Voltage
VIN = 10V
110
110
130
V = 10V
120 IN
110
100
90
80
70
60
50
40
30
20
10
0
–40
–10
3642 G05
Peak Current Trip Threshold
vs RISET
120
30
40
20
LOAD CURRENT (mA)
Peak Current Trip Theshold vs
Temperature
VIN SUPPLY CURRENT (μA)
0.798
–40
10
0
3642 G03
PEAK CURRENT TRIP THRESHOLD (mA)
VIN = 10V
4.95
45
Feedback Comparator Hysteresis
vs Temperature
FEEDBACK COMPARATOR HYSTERESIS (mV)
0.801
40
3642 G02
Feedback Comparator Voltage vs
Temperature
FEEDBACK COMPARATOR TRIP VOLTAGE (V)
5.01
4.96
–0.30
60
0.1
PEAK CURRENT TRIP THRESHOLD (mA)
5.02
4.97
–0.20
65
VIN = 10V
FIGURE 10 CIRCUIT
ISET OPEN
5.04
0.20
$VOUT/VOUT (%)
EFFICIENCY (%)
90
VIN = 10V
Load Regulation
5.05
OUTPUT VOLTAGE (V)
FIGURE 10 CIRCUIT
95 ISET OPEN
VOUT = 5V
0.30
VIN = 10V
SLEEP
10
8
6
4
SHUTDOWN
2
2
20
0
10
0
200
400
600
800
RSET (kΩ)
1000
1200
3642 G07
5
15
25
35
VIN VOLTAGE (V)
45
3642 G08
0
–40
–10
20
50
80
TEMPERATURE (°C)
110
3642 G09
3642f
4
LTC3642
TYPICAL PERFORMANCE CHARACTERISTICS
Switch On-Resistance vs
Input Voltage
Switch On-Resistance vs
Temperature
5
4.5
Switch Leakage Current vs
Temperature
0.6
VIN = 10V
3.5
TOP
3.0
2.5
2.0
BOTTOM
1.5
1.0
SWITCH LEAKAGE CURRENT (μA)
SWITCH ON-RESISTANCE (Ω)
SWITCH ON-RESISTANCE (Ω)
4.0
4
TOP
3
BOTTOM
2
1
VIN = 45V
0.5
0.4
SW = 0V
0.3
0.2
SW = 45V
0.1
0.5
0
–40
0
10
30
20
VIN VOLTAGE (V)
50
40
–10
50
80
20
TEMPERATURE (°C)
EFFICIENCY (%)
ILOAD = 50mA
85
ILOAD = 10mA
80
ILOAD = 1mA
75
70
65
10
15
20
25
30
35
INPUT VOLTAGE (V)
40
45
1.20
1.25
RISING
1.20
1.15
FALLING
1.10
1.05
1.00
–40
–10
20
50
80
TEMPERATURE (°C)
1.10
1.05
1.00
0.95
0.90
–40
OUTPUT
VOLTAGE
50mV/DIV
SWITCH
VOLTAGE
5V/DIV
INDUCTOR
CURRENT
50mA/DIV
INDUCTOR
CURRENT
50mA/DIV
4632 G16
–10
20
50
80
TEMPERATURE (°C)
110
3642 G15
Operating Waveforms
OUTPUT
VOLTAGE
1V/DIV
VIN = 10V
500μs/DIV
CSS = 0.047μF
ISET OPEN
FIGURE 10 CIRCUIT
110
1.15
3642 G14
3642 G13
Soft-Start Waveforms
110
Internal Soft-Start Time vs
Temperature
1.30
RUN COMPARATOR THRESHOLD (V)
90
20
50
80
TEMPERATURE (°C)
3642 G12
Run Comparator Thresholds vs
Temperature
Efficiency vs Input Voltage
FIGURE 10 CIRCUIT
ISET OPEN
–10
3642 G11
3642 G10
95
0
–40
110
INTERNAL SOFT-START TIME (ms)
0
Load Step Transient Response
OUTPUT
VOLTAGE
25mV/DIV
LOAD
CURRENT
25mA/DIV
VIN = 10V
10μs/DIV
ISET OPEN
FIGURE 10 CIRCUIT
4632 G17
VIN = 10V
1ms/DIV
ISET OPEN
FIGURE 10 CIRCUIT
4632 G18
3642f
5
LTC3642
PIN FUNCTIONS
SW (Pin 1): Switch Node Connection to Inductor. This
pin connects to the drains of the internal power MOSFET
switches.
VIN (Pin 2): Main Supply Pin. A ceramic bypass capacitor
should be tied between this pin and GND (Pin 8).
VOUT/VFB (Pin 6): Output Voltage Feedback. For the fixed
output versions, connect this pin to the output supply. For
the adjustable version, an external resistive divider should
be used to divide the output voltage down for comparison
to the 0.8V reference.
ISET (Pin 3): Peak Current Set Input. A resistor from this
pin to ground sets the peak current trip threshold. Leave
floating for the maximum peak current (115mA). Short
this pin to ground for the minimum peak current (25mA).
A 1μA current is sourced out of this pin.
HYST (Pin 7): Run Hysteresis Open-Drain Logic Output.
This pin is pulled to ground when RUN (Pin 5) is below
1.2V. This pin can be used to adjust the RUN pin hysteresis.
See Applications Information.
SS (Pin 4): Soft-Start Control Input. A capacitor to ground
at this pin sets the ramp time to full current output during start-up. A 5μA current is sourced out of this pin. If
left floating, the ramp time defaults to an internal 0.75ms
soft-start.
Exposed Pad (Pin 9): Ground. Must be soldered to PCB
ground for optimal electrical and thermal performance.
GND (Pin 8): Chip Ground.
RUN (Pin 5): Run Control Input. A voltage on this pin
above 1.2V enables normal operation. Forcing this pin
below 0.7V shuts down the LTC3642, reducing quiescent
current to approximately 3μA.
3642f
6
LTC3642
BLOCK DIAGRAM
VIN
1μA
ISET
2
C2
3
–
PEAK CURRENT
COMPARATOR
+
RUN
LOGIC
AND
SHOOTTHROUGH
PREVENTION
+
5
1.2V
–
SW
L1
VOUT
1
C1
HYST
7
+
REVERSE CURRENT
COMPARATOR
FEEDBACK
COMPARATOR
GND
GND
8
9
–
VOLTAGE
REFERENCE
+
+
–
0.800V
5μA
SS
4
R1
VOUT/VFB
6
R2
PART
NUMBER
R1
R2
LTC3642
LTC3642-3.3
LTC3642-5
0
2.5M
4.2M
d
800k
800k
3642 BD
IMPLEMENT DIVIDER
EXTERNALLY FOR
ADJUSTABLE VERSION
3642f
7
LTC3642
OPERATION (Refer to Block Diagram)
The LTC3642 is a step-down DC/DC converter with internal
power switches that uses Burst Mode control, combining low quiescent current with high switching frequency,
which results in high efficiency across a wide range of
load currents. Burst Mode operation functions by using
short “burst” cycles to ramp the inductor current through
the internal power switches, followed by a sleep cycle
where the power switches are off and the load current is
supplied by the output capacitor. During the sleep cycle,
the LTC3642 draws only 12μA of supply current. At light
loads, the burst cycles are a small percentage of the total
cycle time which minimizes the average supply current,
greatly improving efficiency.
Main Control Loop
The feedback comparator monitors the voltage on the VFB
pin and compares it to an internal 800mV reference. If
this voltage is greater than the reference, the comparator
activates a sleep mode in which the power switches and
current comparators are disabled, reducing the VIN pin
supply current to only 12μA. As the load current discharges
the output capacitor, the voltage on the VFB pin decreases.
When this voltage falls 5mV below the 800mV reference,
the feedback comparator trips and enables burst cycles.
At the beginning of the burst cycle, the internal high side
power switch (P-channel MOSFET) is turned on and the
inductor current begins to ramp up. The inductor current
increases until either the current exceeds the peak current
comparator threshold or the voltage on the VFB pin exceeds
800mV, at which time the high side power switch is turned
off. The low side power switch (N-channel MOSFET) is
then turned on. The inductor current ramps down until
the reverse current comparator trips, signaling that the
current is close to zero. If the voltage on the VFB pin is
still less than the 800mV reference, the high side power
switch is turned on again and another cycle commences.
The average current during a burst cycle will normally be
greater than the average load current. For this architecture,
the maximum average output current is equal to half of
the peak current.
The hysteretic nature of this control architecture results
in a switching frequency that is a function of the input
voltage, output voltage and inductor value. This behavior
provides inherent short-circuit protection. If the output
is shorted to ground, the inductor current will decay very
slowly during a single switching cycle. Since the high side
switch turns on only when the inductor current is near
zero, the LTC3642 inherently switches at a lower frequency
during start-up or short-circuit conditions.
Start-Up and Shutdown
If the voltage on the RUN pin is less than 0.7V, the LTC3642
enters a shutdown mode in which all internal circuitry is
disabled, reducing the DC supply current to 3μA. When the
voltage on the RUN pin exceeds 1.21V, normal operation of
the main control loop is enabled. The RUN pin comparator
has 110mV of internal hysteresis, and therefore must fall
below 1.1V to disable the main control loop.
The HYST pin provides an added degree of flexibility for
the RUN pin operation. This open-drain output is pulled
to ground whenever the RUN comparator is not tripped,
signaling that the LTC3642 is not in normal operation. In
applications where the RUN pin is used to monitor the
VIN voltage through an external resistive divider, the HYST
pin can be used to increase the effective RUN comparator
hysteresis.
An internal 1ms soft-start function limits the ramp rate of
the output voltage on start-up to prevent excessive input
supply droop. If a longer ramp time and consequently less
supply droop is desired, a capacitor can be placed from the
SS pin to ground. The 5μA current that is sourced out of
this pin will create a smooth voltage ramp on the capacitor.
If this ramp rate is slower than the internal 1ms soft-start,
then the output voltage will be limited by the ramp rate
3642f
8
LTC3642
OPERATION (Refer to Block Diagram)
on the SS pin instead. The internal and external soft-start
functions are reset on start-up and after undervoltage or
overvoltage event on the input supply.
In order to ensure a smooth start-up transition in any
application, the internal soft-start also ramps the peak
inductor current from 25mA during its 1ms ramp time to
the set peak current threshold. The external ramp on the
SS pin does not limit the peak inductor current during
start-up; however, placing a capacitor from the ISET pin
to ground does provide this capability.
Peak Inductor Current Programming
The offset of the peak current comparator nominally
provides a peak inductor current of 115mA. This peak
inductor current can be adjusted by placing a resistor
from the ISET pin to ground. The 1μA current sourced out
of this pin through the resistor generates a voltage that is
translated into an offset in the peak current comparator,
which limits the peak inductor current.
3642f
9
LTC3642
APPLICATIONS INFORMATION
The basic LTC3642 application circuit is shown on the front
page of this data sheet. External component selection is
determined by the maximum load current requirement and
begins with the selection of the peak current programming
resistor, RISET. The inductor value L can then be determined,
followed by capacitors CIN and COUT.
Peak Current Resistor Selection
The peak current comparator has a maximum current limit
of 115mA nominally, which results in a maximum average current of 55mA. For applications that demand less
current, the peak current threshold can be reduced to as
little as 25mA. This lower peak current allows the use of
lower value, smaller components (input capacitor, output
capacitor and inductor), resulting in lower input supply
ripple and a smaller overall DC/DC converter.
The threshold can be easily programmed with an appropriately chosen resistor (RISET) between the ISET pin
and ground. The value of resistor for a particular peak
current can be computed by using Figure 1 or the following equation:
RISET = IPEAK • 9.09 • 106
where 25mA < IPEAK < 115mA.
The peak current is internally limited to be within the
range of 25mA to 115mA. Shorting the ISET pin to ground
programs the current limit to 25mA, and leaving it floating
sets the current limit to the maximum value of 115mA.
When selecting this resistor value, be aware that the
1100
1000
900
800
RISET (k)
700
600
500
400
300
200
100
0
10
15 20 25 30 35 40 45
MAXIMUM LOAD CURRENT (mA)
50
3642 F01
Figure 1. RISET Selection
maximum average output current for this architecture
is limited to half of the peak current. Therefore, be sure
to select a value that sets the peak current with enough
margin to provide adequate load current under all foreseeable operating conditions.
Inductor Selection
The inductor, input voltage, output voltage and peak current determine the switching frequency of the LTC3642.
For a given input voltage, output voltage and peak current,
the inductor value sets the switching frequency when the
output is in regulation. A good first choice for the inductor
value can be determined by the following equation:
⎛ V
⎞
L = ⎜ OUT ⎟
⎝ f • IPEAK ⎠
⎛ V ⎞
• ⎜ 1 – OUT ⎟
VIN ⎠
⎝
The variation in switching frequency with input voltage
and inductance is shown in the following two figures for
typical values of VOUT. For lower values of IPEAK, multiply
the frequency in Figure 2 and Figure 3 by 115mA/IPEAK.
An additional constraint on the inductor value is the
LTC3642’s 100ns minimum on-time of the high side switch.
Therefore, in order to keep the current in the inductor well
controlled, the inductor value must be chosen so that it is
larger than LMIN, which can be computed as follows:
L MIN =
VIN(MAX ) • tON(MIN)
IPEAK(MAX )
where VIN(MAX) is the maximum input supply voltage for
the application, tON(MIN) is 100ns, and IPEAK(MAX) is the
maximum allowed peak inductor current. Although the
above equation provides the minimum inductor value,
higher efficiency is generally achieved with a larger inductor
value, which produces a lower switching frequency. For a
given inductor type, however, as inductance is increased
DC resistance (DCR) also increases. Higher DCR translates into higher copper losses and lower current rating,
both of which place an upper limit on the inductance. The
recommended range of inductor values for small surface
mount inductors as a function of peak current is shown in
Figure 4. The values in this range are a good compromise
between the tradeoffs discussed above. For applications
3642f
10
LTC3642
APPLICATIONS INFORMATION
700
VOUT = 5V
ISET OPEN
SWITCHING FREQUENCY (kHz)
600
where board area is not a limiting factor, inductors with
larger cores can be used, which extends the recommended
range of Figure 4 to larger values.
L = 47μH
500
L = 68μH
400
L = 100μH
300
L = 150μH
200
L = 220μH
100
L = 470μH
Inductor Core Selection
0
10
5
15
20 25 30 35
VIN INPUT VOLTAGE (V)
40
45
3642 F02
Figure 2. Switching Frequency for VOUT = 5V
500
VOUT = 3.3V
ISET OPEN
SWITCHING FREQUENCY (kHz)
450
Ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can
concentrate on copper loss and preventing saturation.
Ferrite core material saturates “hard,” which means that
inductance collapses abruptly when the peak design current
is exceeded. This results in an abrupt increase in inductor
ripple current and consequently output voltage ripple. Do
not allow the core to saturate!
L = 47μH
400
350
L = 68μH
300
L = 100μH
250
200
L = 150μH
150
L = 220μH
100
L = 470μH
50
0
5
10
15 20 25 30 35
VIN INPUT VOLTAGE (V)
40
45
3642 F03
Figure 3. Switching Frequency for VOUT = 3.3V
10000
INDUCTOR VALUE (μH)
Once the value for L is known, the type of inductor must
be selected. High efficiency converters generally cannot
afford the core loss found in low cost powdered iron cores,
forcing the use of the more expensive ferrite cores. Actual
core loss is independent of core size for a fixed inductor
value but is very dependent of the inductance selected.
As the inductance increases, core losses decrease. Unfortunately, increased inductance requires more turns of
wire and therefore copper losses will increase.
Different core materials and shapes will change the
size/current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy materials are small and do not radiate energy but generally
cost more than powdered iron core inductors with similar
characteristics. The choice of which style inductor to use
mainly depends on the price vs size requirements and any
radiated field/EMI requirements. New designs for surface
mount inductors are available from Coiltronics, Coilcraft,
Toko, Sumida and Vishay.
CIN and COUT Selection
1000
100
10
100
The input capacitor, CIN, is needed to filter the trapezoidal
current at the source of the top high side MOSFET. To
prevent large ripple voltage, a low ESR input capacitor
sized for the maximum RMS current should be used.
Approximate RMS current is given by:
PEAK INDUCTOR CURRENT (mA)
3642 F04
Figure 4. Recommended Inductor Values for Maximum Efficiency
IRMS = IOUT(MAX ) •
VOUT
VIN
•
−1
VIN
VOUT
3642f
11
LTC3642
APPLICATIONS INFORMATION
This formula has a maximum at VIN = 2VOUT, where
IRMS = IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations
do not offer much relief. Note that ripple current ratings
from capacitor manufacturers are often based only on
2000 hours of life which makes it advisable to further
derate the capacitor, or choose a capacitor rated at a
higher temperature than required. Several capacitors may
also be paralleled to meet size or height requirements in
the design.
electrolytic capacitors have significantly higher ESR but
can be used in cost-sensitive applications provided that
consideration is given to ripple current ratings and longterm reliability. Ceramic capacitors have excellent low ESR
characteristics but can have high voltage coefficient and
audible piezoelectric effects. The high quality factor (Q)
of ceramic capacitors in series with trace inductance can
also lead to significant ringing.
The output capacitor, COUT, filters the inductor’s ripple
current and stores energy to satisfy the load current
when the LTC3642 is in sleep. The output voltage ripple
during a burst cycle is dominated by the output capacitor
equivalent series resistance (ESR) and can be estimated
by the following equation:
Higher value, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at the input and
output. When a ceramic capacitor is used at the input and
the power is supplied by a wall adapter through long wires,
a load step at the output can induce ringing at the input,
VIN. At best, this ringing can couple to the output and be
mistaken as loop instability. At worst, a sudden inrush
of current through the long wires can potentially cause a
voltage spike at VIN large enough to damage the part.
VOUT
< ΔVOUT ≤ IPEAK • ESR
160
where the lower limit of VOUT/160 is due to the 5mV
feedback comparator hysteresis.
The value of the output capacitor must be large enough
to accept the energy stored in the inductor without a large
change in output voltage. Setting this voltage step equal to
1% of the output voltage, the output capacitor must be:
COUT
⎛I
⎞
> 50 • L • ⎜ PEAK ⎟
⎝V ⎠
2
OUT
Typically, a capacitor that satisfies the ESR requirement is
adequate to filter the inductor ripple. To avoid overheating,
the output capacitor must also be sized to handle the ripple
current generated by the inductor. The worst-case ripple
current in the output capacitor is given by IRMS = IPEAK/2.
Multiple capacitors placed in parallel may be needed to
meet the ESR and RMS current handling requirements.
Dry tantalum, special polymer, aluminum electrolytic,
and ceramic capacitors are all available in surface mount
packages. Special polymer capacitors offer very low ESR
but have lower capacitance density than other types.
Tantalum capacitors have the highest capacitance density
but it is important only to use types that have been surge
tested for use in switching power supplies. Aluminum
Using Ceramic Input and Output Capacitors
For applications with inductive source impedance, such
as a long wire, a series RC network may be required in
parallel with CIN to dampen the ringing of the input supply.
Figure 5 shows this circuit and the typical values required
to dampen the ringing.
LTC3642
LIN
VIN
R=
LIN
CIN
4 • CIN
3642 F05
CIN
Figure 5. Series RC to Reduce VIN Ringing
Output Voltage Programming
For the adjustable version, the output voltage is set by
an external resistive divider according to the following
equation:
⎛ R1⎞
VOUT = 0.8 V • ⎜ 1+ ⎟
⎝ R2 ⎠
3642f
12
LTC3642
APPLICATIONS INFORMATION
The resistive divider allows the VFB pin to sense a fraction
of the output voltage as shown in Figure 6.
VIN
R1
RUN
VOUT
R2
R1
VFB
LTC3642
LTC3642
HYST
R3
3642 F08
R2
GND
Figure 8. Adjustable Undervoltage Lockout
Figure 6. Setting the Output Voltage
To minimize the no-load supply current, resistor values in
the megohm range should be used. The increase in supply
current due to the feedback resistors can be calculated
from:
⎛ V
⎞
ΔIVIN = ⎜ OUT ⎟
⎝ R1+ R2 ⎠
⎛V ⎞
• ⎜ OUT ⎟
⎝ VIN ⎠
The LTC3642 has a low power shutdown mode controlled
by the RUN pin. Pulling the RUN pin below 0.7V puts the
LTC3642 into a low quiescent current shutdown mode
(IQ ~ 3μA). When the RUN pin is greater than 1.2V, the
controller is enabled. Figure 7 shows examples of configurations for driving the RUN pin from logic.
VIN
LTC3642
RUN
⎛ R1⎞
Ri sin g VIN UVLO Threshold = 1.21V • ⎜ 1+ ⎟
⎝ R2 ⎠
⎛
R1 ⎞
Fallin g VIN UVLO Threshold = 1.10 V • ⎜ 1+
⎝ R2 + R3 ⎟⎠
Run Pin with Programmable Hysteresis
VSUPPLY
Specific values for these UVLO thresholds can be computed
from the following equations:
4.7M
LTC3642
RUN
3642 F07
Figure 7. RUN Pin Interface to Logic
The RUN pin can alternatively be configured as a precise
undervoltage lockout (UVLO) on the VIN supply with a
resistive divider from VIN to ground. The RUN pin comparator nominally provides 10% hysteresis when used in
this method; however, additional hysteresis may be added
with the use of the HYST pin. The HYST pin is an opendrain output that is pulled to ground whenever the RUN
comparator is not tripped. A simple resistive divider can
be used as shown in Figure 8 to meet specific VIN voltage
requirements.
The minimum value of these thresholds is limited to the
internal VIN UVLO thresholds that are shown in the Electrical Characteristics table. The current that flows through
this divider will directly add to the shutdown, sleep and
active current of the LTC3642, and care should be taken to
minimize the impact of this current on the overall efficiency
of the application circuit. Resistor values in the megohm
range may be required to keep the impact on quiescent
shutdown and sleep currents low. Be aware that the HYST
pin cannot be allowed to exceed its absolute maximum
rating of 6V. To keep the voltage on the HYST pin from
exceeding 6V, the following relation should be satisfied:
⎛
⎞
R3
< 6V
VIN(MAX ) • ⎜
⎝ R1+ R2 + R3 ⎟⎠
The RUN pin may also be directly tied to the VIN supply
for applications that do not require the programmable
undervoltage lockout feature. In this configuration, switching is enabled when VIN surpasses the internal undervoltage
lockout threshold.
Soft-Start
The internal 0.75ms soft-start is implemented by ramping
both the effective reference voltage from 0V to 0.8V and the
peak current limit set by the ISET pin (25mA to 115mA).
3642f
13
LTC3642
APPLICATIONS INFORMATION
To increase the duration of the reference voltage soft-start,
place a capacitor from the SS pin to ground. An internal
5μA pull-up current will charge this capacitor, resulting in
a soft-start ramp time given by:
tSS = CSS •
0.8 V
5μA
When the LTC3642 detects a fault condition (input supply
undervoltage or overvoltage) or when the RUN pin falls
below 1.1V, the SS pin is quickly pulled to ground and the
internal soft-start timer is reset. This ensures an orderly
restart when using an external soft-start capacitor.
The duration of the 1ms internal peak current soft-start
may be increased by placing a capacitor from the ISET pin
to ground. The peak current soft-start will ramp from 25mA
to the final peak current value determined by a resistor
from ISET to ground. A 1μA current is sourced out of the
ISET pin. With only a capacitor connected between ISET
and ground, the peak current ramps linearly from 25mA
to 115mA, and the peak current soft-start time can be
expressed as:
tSS(ISET) = CISET •
0.8 V
1μA
A linear ramp of peak current appears as a quadratic
waveform on the output voltage. For the case where the
peak current is reduced by placing a resistor from ISET
to ground, the peak current offset ramps as a decaying
exponential with a time constant of RISET • CISET. For this
case, the peak current soft-start time is approximately
3 • RISET • CISET.
Unlike the SS pin, the ISET pin does not get pulled to
ground during an abnormal event; however, if the ISET
pin is floating (programmed to 115mA peak current),
the SS and ISET pins may be tied together and connected
to a capacitor to ground. For this special case, both the
peak current and the reference voltage will soft-start on
power-up and after fault conditions. The ramp time for
this combination is CSS(ISET) • (0.8V/6μA).
Efficiency Considerations
The efficiency of a switching regulator is equal to the output
power divided by the input power times 100%. It is often
useful to analyze individual losses to determine what is
limiting the efficiency and which change would produce
the most improvement. Efficiency can be expressed as:
Efficiency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc. are the individual losses as a percentage of input power.
Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of
the losses: VIN operating current and I2R losses. The VIN
operating current dominates the efficiency loss at very
low load currents whereas the I2R loss dominates the
efficiency loss at medium to high load currents.
1. The VIN operating current comprises two components:
The DC supply current as given in the electrical characteristics and the internal MOSFET gate charge currents.
The gate charge current results from switching the gate
capacitance of the internal power MOSFET switches.
Each time the gate is switched from high to low to
high again, a packet of charge, dQ, moves from VIN to
ground. The resulting dQ/dt is the current out of VIN
that is typically larger than the DC bias current.
2. I2R losses are calculated from the resistances of the
internal switches, RSW, and external inductor RL. When
switching, the average output current flowing through
the inductor is “chopped” between the high side PMOS
switch and the low side NMOS switch. Thus, the series
resistance looking back into the switch pin is a function
of the top and bottom switch RDS(ON) values and the
duty cycle (DC = VOUT/VIN) as follows:
RSW = (RDS(ON)TOP)DC + (RDS(ON)BOT)(1 – DC)
The RDS(ON) for both the top and bottom MOSFETs can
be obtained from the Typical Performance Characteristics curves. Thus, to obtain the I2R losses, simply add
RSW to RL and multiply the result by the square of the
average output current:
I2R Loss = IO2(RSW + RL)
3642f
14
LTC3642
APPLICATIONS INFORMATION
Other losses, including CIN and COUT ESR dissipative
losses and inductor core losses, generally account for
less than 2% of the total power loss.
Thermal Considerations
The LTC3642 does not dissipate much heat due to its high
efficiency and low peak current level. Even in worst-case
conditions (high ambient temperature, maximum peak
current and high duty cycle), the junction temperature will
exceed ambient temperature by only a few degrees.
Design Example
As a design example, consider using the LTC3642 in an
application with the following specifications: VIN = 24V,
VOUT = 3.3V, IOUT = 50mA, f = 250kHz. Furthermore, assume for this example that switching should start when
VIN is greater than 12V and should stop when VIN is less
than 8V.
First, calculate the inductor value that gives the required
switching frequency:
⎛
⎞
3.3V
L=⎜
⎝ 250kHz • 115mA ⎟⎠
⎛ 3.3V ⎞
• ⎜ 1–
≅ 100μH
24V ⎟⎠
⎝
Next, verify that this value meets the LMIN requirement.
For this input voltage and peak current, the minimum
inductor value is:
24V • 100ns
L MIN =
≅ 22μH
115mA
Therefore, the minimum inductor requirement is satisfied,
and the 100μH inductor value may be used.
Next, CIN and COUT are selected. For this design, CIN should
be size for a current rating of at least:
COUT will be selected based on the ESR that is required
to satisfy the output voltage ripple requirement. For a 1%
output ripple, the value of the output capacitor ESR can
be calculated from:
ΔVOUT = 0.01 ≤ 115mA • ESR
A capacitor with a 90mΩ ESR satisfies this requirement.
A 10μF ceramic capacitor has significantly less ESR than
90mΩ.
The output voltage can now be programmed by choosing
the values of R1 and R2. Choose R2 = 240k and calculate
R1 as:
⎛V
⎞
R1 = ⎜ OUT – 1⎟ • R2 = 750k
⎝ 0.8 V ⎠
The undervoltage lockout requirement on VIN can be
satisfied with a resistive divider from VIN to the RUN and
HYST pins. Choose R1 = 2M and calculate R2 and R3 as
follows:
⎞
⎛
1.21V
R2 = ⎜
⎟ • R1 = 224k
⎝ VIN(RISING) – 1.21V ⎠
⎛
⎞
1.1V
R3 = ⎜
⎟ • R1 – R2 = 90.8k
⎝ VIN(FALLING) – 1.1V ⎠
Choose standard values for R2 = 226k and R3 = 91k. The
ISET pin should be left open in this example to select maximum peak current (115mA). Figure 9 shows a complete
schematic for this design example.
100μH
VIN
24V
VIN
1μF
2M
Due to the low peak current of the LTC3642, decoupling
the VIN supply with a 1μF capacitor is adequate for most
applications.
LTC3642
RUN
226k
3.3V
24V
IRMS = 50mA •
•
– 1 ≅ 18mA RMS
24V
3.3V
SW
91k
ISET
SS
750k
VFB
HYST
GND
240k
VOUT
3.3V
50mA
10μF
3642 F09
Figure 9. 24V to 3.3V, 50mA Regulator at 250kHz
3642f
15
LTC3642
APPLICATIONS INFORMATION
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3642. Check the following in your layout:
1. Large switched currents flow in the power switches
and input capacitor. The loop formed by these components should be as small as possible. A ground plane
is recommended to minimize ground impedance.
3. Keep the switching node, SW, away from all sensitive
small signal nodes. The rapid transitions on the switching
node can couple to high impedance nodes, in particular
VFB, and create increased output ripple.
4. Flood all unused area on all layers with copper. Flooding
with copper will reduce the temperature rise of power
components. You can connect the copper areas to any
DC net (VIN, VOUT, GND or any other DC rail in your
system).
2. Connect the (+) terminal of the input capacitor, CIN, as
close as possible to the VIN pin. This capacitor provides
the AC current into the internal power MOSFETs.
TYPICAL APPLICATIONS
Efficiency vs Load Current
VIN
CIN
4.7μF
SW
LTC3642
RUN
HYST
R1
4.2M
VFB
ISET
COUT
100μF
VIN = 10V
RSET = 750k
93
RSET = 500k
R2
800k
SS
CSS
47nF
GND
RSET
94
VOUT
5V
EFFICIENCY (%)
VIN
5V TO 45V
L1
220μH
3642 F10a
CIN: TDK C5750X7R2A475MT
COUT: AVX 1812D107MAT
L1: TDK SLF7045T-221MR33-PF
92
ISET OPEN
91
90
89
Figure 10. High Efficiency 5V Regulator
88
1
10
LOAD CURRENT (mA)
100
3642 F10b
3.3V, 50mA Regulator with Peak Current Soft-Start, Small Size
VIN
4.5V TO 24V
L1
47μH
VIN
CIN
1μF
SW
LTC3642
RUN
ISET
SS
CSS
0.1μF
VFB
HYST
GND
CIN: TDK C3216X7R1E105KT
COUT: AVX 08056D106KAT2A
L1: TAIYO YUDEN CBC2518T470K
R1
294k
COUT
10μF
VOUT
3.3V
50mA
Soft-Start Waveforms
OUTPUT VOLTAGE
1V/DIV
R2
93.1k
3642 TA02a
INDUCTOR CURRENT
20mA/DIV
2ms/DIV
3642 TA03b
3642f
16
LTC3642
TYPICAL APPLICATIONS
Positive-to-Negative Converter
L1
100μH
VIN
CIN
1μF
50
MAXIMUM OUTPUT CURRENT (mA)
VIN
4.5V TO 33V
Maximum Load Current vs Input Voltage
SW
LTC3642
RUN
ISET
R1
1M
COUT
10μF
VFB
SS
HYST
GND
R2
71.5k
VOUT
–12V
CIN: TDK C3225X7R1H105KT
COUT: MURATA GRM32DR71C106KA01
L1: TYCO/COEV DQ6530-101M
3642 TA04a
VOUT = –3V
45
VOUT = –5V
40
35
VOUT = –12V
30
25
20
15
10
5
10
15
20 25 30 35
VIN VOLTAGE (V)
40
45
3642 TA04b
Small Size, Limited Peak Current, 10mA Regulator
VIN
7V TO 45V
L1
470μH
VIN
CIN
1μF
R3
470k
SW
RUN
R4
100k
R5
33k
R1
470k
LTC3642
VFB
COUT
10μF
VOUT
5V
10mA
R2
88.7k
HYST
SS
ISET GND
3642 TA05a
CIN: TDK C3225X7R1H105KT
COUT: AVX 08056D106KAT2A
L1: MURATA LQH32CN471K23
High Efficiency 15V, 10mA Regulator
100
L1
4700μH
VIN
CIN
1μF
SW
LTC3642
RUN
ISET
SS
VFB
HYST
GND
R1
3M
R2
169k
3642 TA07a
COUT
4.7μF
VOUT
15V
10mA
95
VIN = 24V
90
EFFICIENCY (%)
VIN
15V TO 45V
Efficiency vs Load Current
VIN = 36V
85
80
VIN = 45V
75
70
CIN: AVX 18125C105KAT2A
COUT: TDK C3216X7R1E475KT
L1: COILCRAFT DS1608C-475
65
60
0.1
1
LOAD CURRENT (mA)
10
3642 TA07b
3642f
17
LTC3642
PACKAGE DESCRIPTION
DD Package
8-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698)
0.675 p0.05
3.5 p0.05
1.65 p0.05
2.15 p0.05 (2 SIDES)
PACKAGE
OUTLINE
0.25 p 0.05
0.50
BSC
2.38 p0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 p0.10
(4 SIDES)
R = 0.115
TYP
5
0.38 p 0.10
8
1.65 p 0.10
(2 SIDES)
PIN 1
TOP MARK
(NOTE 6)
(DD) DFN 1203
0.200 REF
0.75 p0.05
4
0.25 p 0.05
1
0.50 BSC
0.00 – 0.05
2.38 p0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON TOP AND BOTTOM OF PACKAGE
3642f
18
LTC3642
PACKAGE DESCRIPTION
MS8E Package
8-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1662 Rev D)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.06 ± 0.102
(.081 ± .004)
1
5.23
(.206)
MIN
1.83 ± 0.102
(.072 ± .004)
0.889 ± 0.127
(.035 ± .005)
2.794 ± 0.102
(.110 ± .004)
2.083 ± 0.102 3.20 – 3.45
(.082 ± .004) (.126 – .136)
8
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.65
(.0256)
BSC
0.42 ± 0.038
(.0165 ± .0015)
TYP
8
7 6 5
0.52
(.0205)
REF
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
DETAIL “A”
0° – 6° TYP
GAUGE PLANE
1
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
2 3
4
1.10
(.043)
MAX
0.86
(.034)
REF
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.65
(.0256)
BSC
0.1016 ± 0.0508
(.004 ± .002)
MSOP (MS8E) 0307 REV D
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
3642f
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
LTC3642
TYPICAL APPLICATION
5V, 50mA Regulator for Automotive Applications
VBATT
12V
L1
220μH
VIN
CIN
1μF
SW
LTC3642
RUN
ISET
SS
VFB
HYST
GND
R1
470k
COUT
10μF
VOUT
5V
50mA
R2
88.7k
3642 TA06a
CIN: TDK C3225X7R2A105M
COUT: KEMET C1210C106K4RAC
L1: COILTRONICS DRA73-221-R
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Converter
LT1934/LT1934-1 36V, 250mA (IOUT), Micropower Step-Down DC/DC Converter with
Burst Mode Operation
LT1936
36V, 1.4A (IOUT), 500kHz High Efficiency Step-Down DC/DC
Converter
LT1939
25V, 2A, 2.5MHz High Efficiency DC/DC Converter and LDO
Controller
LT1976/LT1977 60V, 1.2A (IOUT), 200kHz/500kHz, High Efficiency Step-Down DC/DC
Converter with Burst Mode Operation
LT3434/LT3435 60V, 2.4A (IOUT), 200kHz/500kHz, High Efficiency Step-Down DC/DC
Converter with Burst Mode Operation
LT3437
60V, 400mA (IOUT), Micropower Step-Down DC/DC Converter with
Burst Mode Operation
LT3470
40V, 250mA (IOUT), High Efficiency Step-Down DC/DC Converter
with Burst Mode Operation
LT3480
36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High
Efficiency Step-Down DC/DC Converter with Burst Mode Operation
LT3481
34V with Transient Protection to 36V, 2A (IOUT), 2.8MHz, High
Efficiency Step-Down DC/DC Converter with Burst Mode Operation
LT3493
36V, 1.4A (IOUT), 750kHz High Efficiency Step-Down DC/DC
Converter
LT3500
36V, 40VMAX, 2A, 2.5MHz High Efficiency DC/DC Converter and LDO
Controller
LT3505
36V with Transient Protection to 40V, 1.4A (IOUT), 3MHz, High
Efficiency Step-Down DC/DC Converter
LT3506/LT3506A 25V, Dual 1.6A (IOUT), 575kHz/1.1MHz High Efficiency Step-Down
DC/DC Converter
LT3508
36V with Transient Protection to 40V, Dual 1.4A (IOUT), 3MHz, High
Efficiency Step-Down DC/DC Converter
LT3684
34V with Transient Protection to 36V, 2A (IOUT), 2.8MHz, High
Efficiency Step-Down DC/DC Converter
LT3685
36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High
Efficiency Step-Down DC/DC Converter
ThinSOT is a trademark of Linear Technology Corporation.
COMMENTS
VIN: 3V to 18V, VOUT(MIN) = 1.2V, IQ = 10μA, ISD = 6μA, MSOP8
VIN: 5.5V to 60V, VOUT(MIN) = 1.2V, IQ = 2.5mA, ISD = 25μA,
TSSOP16/E
VIN: 3.2V to 34V, VOUT(MIN) = 1.25V, IQ = 12μA, ISD < 1μA,
ThinSOT™ Package
VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.9mA, ISD < 1μA, MS8E
VIN: 3.6V to 25V, VOUT(MIN) = 0.8V, IQ = 2.5mA, ISD < 10μA,
3mm × 3mm DFN10
VIN: 3.3V to 60V, VOUT(MIN) = 1.2V, IQ = 100μA, ISD < 1μA,
TSSOP16E
VIN: 3.3V to 60V, VOUT(MIN) = 1.2V, IQ = 100μA, ISD < 1μA,
TSSOP16E
VIN: 3.3V to 60V, VOUT(MIN) = 1.25V, IQ = 100μA, ISD < 1μA,
3mm × 3mm DFN10, TSSOP16E
VIN: 4V to 40V, VOUT(MIN) = 1.2V, IQ = 26μA, ISD < 1μA,
2mm × 3mm DFN8, ThinSOT
VIN: 3.6V to 38V, VOUT(MIN) = 0.78V, IQ = 70μA, ISD < 1μA,
3mm × 3mm DFN10, MSOP10E
VIN: 3.6V to 34V, VOUT(MIN) = 1.26V, IQ = 50μA, ISD < 1μA,
3mm × 3mm DFN10, MSOP10E
VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 1.9mA, ISD < 1μA,
2mm × 3mm DFN6
VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 2.5mA, ISD < 10μA,
3mm × 3mm DFN10
VIN: 3.6V to 34V, VOUT(MIN) = 0.78V, IQ = 2mA, ISD = 2μA,
3mm × 3mm DFN8, MSOP8E
VIN: 3.6V to 25V, VOUT(MIN) = 0.8V, IQ = 3.8mA, ISD = 30μA,
5mm × 4mm DFN16, TSSOP16E
VIN: 3.7V to 37V, VOUT(MIN) = 0.8V, IQ = 4.6mA, ISD = 1μA,
4mm × 4mm QFN24, TSSOP16E
VIN: 3.6V to 34V, VOUT(MIN) = 1.26V, IQ = 850μA, ISD < 1μA,
3mm × 3mm DFN10, MSOP10E
VIN: 3.6V to 38V, VOUT(MIN) = 0.78V, IQ = 70μA, ISD < 1μA,
3mm × 3mm DFN10, MSOP10E
3642f
20 Linear Technology Corporation
LT 1108 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
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