LTCVS [Linear]
36V, 2A, 2.8MHz Step-Down Switching Regulator; 36V ，2A ， 2.8MHz降压型开关稳压器
| 型号： | LTCVS |
| 厂家： | 
Linear |
| 描述： | 36V, 2A, 2.8MHz Step-Down Switching Regulator |
| 文件： | 总24页 (文件大小：327K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3684
36V, 2A, 2.8MHz Step-Down
Switching Regulator
FEATURES
DESCRIPTION
TheLT®3684isanadjustablefrequency(300kHzto2.8MHz)
monolithic buck switching regulator that accepts input
voltages up to 34V (36V maximum). A high efficiency
0.18Ω switch is included on the die along with a boost
Schottky diode and the necessary oscillator, control and
logic circuitry. Current mode topology is used for fast
transient response and good loop stability. The LT3684’s
high operating frequency allows the use of small, low cost
inductors and ceramic capacitors resulting in low output
ripple while keeping total solution size to a minimum.
The low current shutdown mode reduces input supply
current to less than 1µA while a resistor and capacitor on
the RUN/SS pin provide a controlled output voltage ramp
■
Wide Input Range: 3.6V to 34V Operating,
36V Maximum
■
2A Maximum Output Current
■
Adjustable Switching Frequency: 300kHz to 2.8MHz
Low Shutdown Current: I < 1µA
Integrated Boost Diode
Power Good Flag
Saturating Switch Design: 0.18Ω On-Resistance
1.265V Feedback Reference Voltage
Output Voltage: 1.265V to 20V
Soft-Start Capability
Small 10-Pin Thermally Enhanced MSOP and
(3mm × 3mm) DFN Packages
■
Q
■
■
■
■
■
■
■
(soft-start). A power good flag signals when V
reaches
OUT
APPLICATIONS
90% of the programmed output voltage. The LT3684 is
available in 10-Pin MSOP and 3mm × 3mm DFN packages
with Exposed Pads for low thermal resistance.
■
Automotive Battery Regulation
■
Power for Portable Products
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
■
Distributed Supply Regulation
■
Industrial Supplies
■
Wall Transformer Regulation
TYPICAL APPLICATION
3.3V Step-Down Converter
Efficiency
V
IN
V
3.3V
2A
90
80
OUT
4.5V TO
34V
V
BD
IN
RUN/SS
BOOST
OFF ON
16.2k
0.47µF
4.7µH
70
60
V
SW
C
4.7µF
LT3684
GND
RT
PG
330pF
BIAS
FB
50
40
30
324k
60.4k
V
V
= 12V
IN
OUT
= 3.3V
200k
22µF
L = 4.7µH
f = 800kHz
3684 TA01
0
0.5
1
1.5
2
LOAD CURRENT (A)
3684 TA01b
3684f
1
LT3684
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Operating Temperature Range (Note 2)
V , RUN/SS Voltage.................................................36V
IN
LT3684E............................................... –40°C to 85°C
LT3684I ............................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
BOOST Pin Voltage ...................................................56V
BOOST Pin Above SW Pin.........................................30V
FB, RT, V Voltage.......................................................5V
C
BIAS, PG, BD Voltage................................................30V
(MSE Only) ....................................................... 300°C
Maximum Junction Temperature .......................... 125°C
PACKAGE/ORDER INFORMATION
TOP VIEW
TOP VIEW
BD
BOOST
SW
1
2
3
4
5
10 RT
BD
BOOST
SW
1
2
3
4
5
10 RT
9
8
7
6
V
C
9
8
7
6
V
C
11
FB
11
FB
V
BIAS
PG
IN
V
BIAS
PG
IN
RUN/SS
RUN/SS
MSE PACKAGE
10-LEAD PLASTIC MSOP
DD PACKAGE
T
= 125°C, θ = 45°C/W, θ = 10°C/W
JA JC
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
JMAX
10-LEAD (3mm × 3mm) PLASTIC DFN
= 125°C, θ = 45°C/W, θ = 10°C/W
JA JC
T
JMAX
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
DD PART MARKING*
LCVT
LCVT
ORDER PART NUMBER
LT3684EMSE
LT3684IMSE
MSE PART MARKING*
LTCVS
LTCVS
LT3684EDD
LT3684IDD
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
ELECTRICAL CHARACTERISTICS The
noted. (Note 2)
●
denotes the specifications which apply over the full operating
= 10V, V = 15V, V = 3.3V unless otherwise
temperature range, otherwise specifications are at T = 25°C. V = 10V, V
A
IN
RUNS/SS
BOOST
BIAS
PARAMETER
CONDITIONS
MIN
TYP
3
MAX
3.6
0.5
0.8
2.0
0.5
1.5
0.1
UNITS
V
●
●
Minimum Input Voltage
Quiescent Current from V
V
V
V
V
V
V
= 0.2V
0.01
0.4
1.2
0.01
0.85
0
µA
IN
RUN/SS
= 3V, Not Switching
= 0, Not Switching
mA
mA
µA
BIAS
BIAS
Quiescent Current from BIAS
= 0.2V
RUN/SS
●
= 3V, Not Switching
= 0, Not Switching
mA
mA
BIAS
BIAS
3684f
2
LT3684
ELECTRICAL CHARACTERISTICS
noted. (Note 2)
The
●
denotes the specifications which apply over the full operating
= 10V V = 15V, V = 3.3V unless otherwise
temperature range, otherwise specifications are at T = 25°C. V = 10V, V
A
IN
RUNS/SS
BOOST
BIAS
MIN
PARAMETER
CONDITIONS
TYP
MAX
UNITS
Minimum Bias Voltage
Feedback Voltage
2.7
3
V
1.25
1.24
1.265
1.265
1.28
1.29
V
V
●
●
FB Pin Bias Current (Note 3)
FB Voltage Line Regulation
30
0.002
330
1000
75
100
nA
%/V
4V < V < 34V
0.02
IN
Error Amp g
µMho
m
Error Amp Gain
V Source Current
µA
µA
A/V
V
C
V Sink Current
C
100
3.5
V Pin to Switch Current Gain
C
V Clamp Voltage
C
2
Switching Frequency
R = 8.66k
2.7
1.25
250
3.0
1.4
300
3.3
1.55
350
MHz
MHz
kHz
T
R = 29.4k
T
R = 187k
T
●
●
Minimum Switch Off-Time
Switch Current Limit
100
3.6
360
0.02
1.6
18
150
4.0
nS
A
Duty Cycle = 5%
3.1
Switch V
I
= 2A
SW
mV
µA
V
CESAT
Boost Schottky Reverse Leakage
Minimum Boost Voltage (Note 4)
BOOST Pin Current
V
SW
= 10V, V
= 0V
BIAS
2
2.1
30
10
I
SW
= 1A
mA
µA
V
RUN/SS Pin Current
V
= 2.5V
5
RUN/SS
RUN/SS Input Voltage High
RUN/SS Input Voltage Low
PG Threshold Offset from Feedback Voltage
PG Hysteresis
2.5
0.2
1
V
V
FB
Rising
100
10
mV
mV
µA
µA
PG Leakage
V
V
= 5V
0.1
300
PG
●
PG Sink Current
= 0.4V
100
PG
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 3: Bias current measured in regulation. Bias current flows into the FB
pin.
Note 4: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.
Note 2: The LT3684E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT3684I specifications are
guaranteed over the –40°C to 125°C temperature range.
3684f
3
LT3684
TYPICAL PERFORMANCE CHARACTERISTICS (T = 25°C unless otherwise noted)
A
Efficiency (V
= 3.3V)
Efficiency
Efficiency (V
= 5.0V)
OUT
OUT
100
90
90
85
80
75
70
65
60
55
50
90
V
= 7V
IN
V
= 12V
IN
85
80
V
V
= 12V
= 24V
IN
IN
V
= 24V
V
= 12V
V
= 24V
IN
IN
IN
75
70
65
60
55
80
70
60
50
V
= 3.3V
OUT
L: NEC PLC-0745-4R7
f = 800kHz
L: NEC PLC-0745-4R7
f = 800kHz
L = 10µH
LOAD = 1A
50
0.5
1
2
2.5
3
0
1.5
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOAD CURRENT (A)
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
SWITCHING FREQUENCY (MHz)
LOAD CURRENT (A)
3684 G03
3684 G01
3684 G02
Maximum Load Current
Maximum Load Current
Switch Current Limit
4.0
3.5
3.0
4.0
3.5
3.0
4.0
3.5
3.0
TYPICAL
TYPICAL
2.5
2.0
2.5
2.0
2.5
2.0
MINIMUM
MINIMUM
V
T
= 3.3V
V
T
= 5V
OUT
A
OUT
A
= 25°C
= 25°C
1.5
1.0
1.5
1.0
1.5
1.0
L = 4.7µH
L = 4.7µH
f = 800kHz
f = 800kHz
20
60
40
DUTY CYCLE (%)
80
100
10
20
INPUT VOLTAGE (V)
25
30
0
5
15
10
20
INPUT VOLTAGE (V)
25
30
5
15
3684 G06
3684 G04
3684 G05
Switch Current Limit
Switch Voltage Drop
Boost Pin Current
4.5
4.0
3.0
2.5
2.0
1.5
1.0
0.5
0
90
80
70
60
50
40
30
20
10
700
600
DUTY CYCLE = 10 %
500
400
300
200
100
DUTY CYCLE = 90 %
0
0
–50 –25
0
25
50
75 100 125
2000
3000 3500
0
500 1000 1500
2500
0
500 1000 1500
3500
2000 2500 3000
TEMPERATURE (°C)
SWITCH CURRENT (mA)
SWITCH CURRENT (mA)
3684 G07
3684 G08
3684 G09
3684f
4
LT3684
TYPICAL PERFORMANCE CHARACTERISTICS (T = 25°C unless otherwise noted)
A
Feedback Voltage
Switching Frequency
Frequency Foldback
1.290
1.285
1.280
1.275
1.270
1.265
1.260
1.255
1.250
1200
1000
800
1.20
1.15
1.10
1.05
1.00
0.95
0.90
0.85
0.80
R
= 45.3k
R
= 45.3k
T
T
600
400
200
0
–50 –25
0
25
50
75 100 125
800
1200 1400
1000
–50 –25
0
25
50
75 100 125
0
200 400 600
TEMPERATURE (°C)
TEMPERATURE (°C)
FB PIN VOLTAGE (mV)
3684 G10
3684 G11
3684 G12
Minimum Switch On-Time
Soft-Start
RUN/SS Pin Current
12
10
8
140
120
4.0
3.5
3.0
100
2.5
2.0
1.5
1.0
0.5
80
60
40
20
6
4
2
0
0
0
20
RUN/SS PIN VOLTAGE (V)
30
35
0
5
10
15
25
0.5
1
2
2.5
3
3.5
–50 –25
0
25
50
75 100 125
0
1.5
TEMPERATURE (˚C)
RUN/SS PIN VOLTAGE (V)
3684 G15
3684 G13
3684 G14
Boost Diode
Error Amp Output Current
Minimum Input Voltage
100
80
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
4.5
4.0
3.5
3.0
60
40
20
0
–20
–40
–60
V
A
= 3.3V
OUT
2.5
2.0
T
= 25°C
L = 4.7µH
f = 800kHz
–80
1.065
1.0
BOOST DIODE CURRENT (A)
0
0.5
1.5
2.0
0.001
0.01
0.1
LOAD CURRENT (A)
1
1.165
1 .265
1.365
1.465
10
FB PIN VOLTAGE (V)
3684 G16
3684 G17
3684 G18
3684f
5
LT3684
TYPICAL PERFORMANCE CHARACTERISTICS (T = 25°C unless otherwise noted)
A
Minimum Input Voltage
Power Good Threshold
V Voltages
C
2.50
1.200
6.5
6.0
5.5
5.0
PG RISING
2.00
1.50
1.180
1.160
CURRENT LIMIT CLAMP
1.00
0.50
0
1.140
1.120
1.100
SWITCHING THRESHOLD
V
A
= 5V
OUT
4.5
4.0
T
= 25°C
L = 4.7µH
f = 800kHz
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
0.001
0.01
0.1
LOAD CURRENT (A)
1
10
TEMPERATURE (°C)
TEMPERATURE (°C)
3684 G20
3684 G21
3684 G19
Switching Waveforms
(Discontinuous Operation)
Switching Waveforms
(Continuous Operation)
I
L
0.5A/DIV
I
L
0.5A/DIV
V
V
SW
RUN/SS
5V/DIV
5V/DIV
V
OUT
V
OUT
10mV/DIV
10mV/DIV
V
I
= 12V, FRONT PAGE APPLICATION
LOAD
IN
= 140mA
3684 G23
3684 G22
1µs/DIV
1µs/DIV
3684f
6
LT3684
PIN FUNCTIONS
BD (Pin 1): This pin connects to the anode of the boost
PG (Pin 6): 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
Schottky diode.
BOOST (Pin 2): This pin is used to provide a drive
voltage,higherthantheinputvoltage,totheinternalbipolar
NPN power switch.
valid when V is above 3.5V and RUN/SS is high.
IN
BIAS (Pin 7): The BIAS pin supplies the current to the
LT3684’s internal regulator. Tie this pin to the lowest
SW (Pin 3): The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.
available voltage source above 3V (typically V ). This
OUT
architectureincreasesefficiencyespeciallywhentheinput
voltage is much higher than the output.
V (Pin 4): The V pin supplies current to the LT3684’s
IN
IN
FB (Pin 8): The LT3684 regulates the FB pin to 1.265V.
Connect the feedback resistor divider tap to this pin.
internal regulator and to the internal power switch. This
pin must be locally bypassed.
V (Pin 9): The V pin is the output of the internal error
C
C
RUN/SS (Pin 5): The RUN/SS pin is used to put the
LT3684 in shutdown mode. Tie to ground to shut down
the LT3684. Tie to 2.3V or more for normal operation. If
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.
the shutdown feature is not used, tie this pin to the V
IN
pin. RUN/SS also provides a soft-start function; see the
RT (Pin10):OscillatorResistorInput.Connectingaresistor
to ground from this pin sets the switching frequency.
Applications Information section.
Exposed Pad (Pin 11): Ground. The Exposed Pad must
be soldered to PCB.
3684f
7
LT3684
BLOCK DIAGRAM
V
IN
V
4
7
IN
C1
BIAS
–
+
INTERNAL 1.265V REF
BD
1
2
RUN/SS
RT
5
SLOPE COMP
Σ
SWITCH
LATCH
BOOST
C3
R
OSCILLATOR
300kHz–2.8MHz
Q
10
S
L1
R
SW
T
V
OUT
3
9
SOFT-START
V
CLAMP
C2
C
D1
PG
6
ERROR AMP
+
–
+
–
1.12V
V
C
C
C
C
F
R
C
GND
11
FB
8
R2
R1
3684 BD
3684f
8
LT3684
OPERATION
The LT3684 is a constant frequency, current mode step-
down 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
This improves efficiency. The RUN/SS pin is used to place
the LT3684 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 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.
flowing between the V and SW pins, turning the switch
IN
off when this current reaches a level determined by the
voltage at V . An error amplifier measures the output
C
voltage through an external resistor divider tied to the FB
pin and servos the V pin. If the error amplifier’s output
C
increases, more current is delivered to the output; if it
The oscillator reduces the LT3684’s operating frequency
when the voltage at the FB pin is low. This frequency
foldbackhelpstocontroltheoutputcurrentduringstartup
and overload.
decreases,lesscurrentisdelivered.Anactiveclamponthe
V pinprovidescurrentlimit. TheV pinisalsoclampedto
C
C
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.
TheLT3684containsapowergoodcomparatorwhichtrips
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 LT3684 is
An internal regulator provides power to the control cir-
cuitry. The bias regulator normally draws power from the
V
IN
pin, but if the BIAS pin is connected to an external
voltage higher than 3V bias power will be drawn from the
external source (typically the regulated output voltage).
enabled and V is above 3.6V.
IN
3684f
9
LT3684
APPLICATIONS INFORMATION
FB Resistor Network
where V is the typical input voltage, V
is the output
IN
OUT
SW
voltage,isthecatchdiodedrop(~0.5V),V istheinternal
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis-
tors according to:
switch drop (~0.5V at max load). This equation shows
that slower switching frequency is necessary to safely
accommodate high V /V
ratio. Also, as shown in
IN OUT
V
⎛
⎞
⎠
the next section, lower frequency allows a lower dropout
voltage. The reason input voltage range depends on the
switching frequency is because the LT3684 switch has
finite minimum on and off times. The switch can turn on
for a minimum of ~150ns and turn off for a minimum of
~150ns. This means that the minimum and maximum
duty cycles are:
OUT
R1=R2
–1
⎜
⎝
⎟
1.265
Reference designators refer to the Block Diagram.
Setting the Switching Frequency
The LT3684 uses a constant frequency PWM architecture
thatcanbeprogrammedtoswitchfrom300kHzto2.8MHz
by using a resistor tied from the RT pin to ground. A table
DCMIN = fSWtON MIN
(
)
DCMAX =1– fSWtOFF MIN
showing the necessary R value for a desired switching
T
(
)
frequency is in Figure 1.
where f is the switching frequency, the t
is the
ON(MIN)
SW
SWITCHING FREQUENCY (MHz)
R VALUE (kΩ)
T
minimum switch on time (~150ns), and the t
is
OFF(MIN)
0.2
0.3
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
267
187
the minimum switch off time (~150ns). These equations
show that duty cycle range increases when switching
frequency is decreased.
133
84.5
60.4
45.3
36.5
29.4
23.7
20.5
16.9
14.3
12.1
10.2
8.66
A good choice of switching frequency should allow ad-
equate input voltage range (see next section) and keep
the inductor and capacitor values small.
Input Voltage Range
The maximum input voltage for LT3684 applications de-
pendsonswitchingfrequency,theAbsoluteMaximumRat-
ings on V and BOOST pins, and on operating mode.
IN
Figure 1. Switching Frequency vs R Value
T
Iftheoutputisinstart-uporshort-circuitoperatingmodes,
Operating Frequency Tradeoffs
then V must be below 34V and below the result of the
IN
following equation:
Selection of the operating frequency is a tradeoff between
efficiency,componentsize,minimumdropoutvoltage,and
maximum input voltage. The advantage of high frequency
operationisthatsmallerinductorandcapacitorvaluesmay
be used. The disadvantages are lower efficiency, lower
maximum input voltage, and higher dropout voltage. The
VOUT + VD
V
=
) – VD + VSW
IN MAX
(
)
fSWtON MIN
(
where V
OUT
is the maximum operating input voltage,
IN(MAX)
V
is the output voltage, V is the catch diode drop
D
highest acceptable switching frequency (f
given application can be calculated as follows:
) for a
SW(MAX)
(~0.5V), V is the internal switch drop (~0.5V at max
SW
load), f is the switching frequency (set by R ), and
SW
ON(MIN)
T
VD + VOUT
t
istheminimumswitchontime(~150ns).Notethat
fSW MAX
=
(
)
a higher switching frequency will depress the maximum
operating input voltage. Conversely, a lower switching
tON MIN V + V – V
(
)
D
IN
SW
(
)
3684f
10
LT3684
APPLICATIONS INFORMATION
frequency will be necessary to achieve safe operation at
high input voltages.
at least 3.5A at low duty cycles and decreases linearly to
2.5A at DC = 0.8. The maximum output current is a func-
tion of the inductor ripple current:
Iftheoutputisinregulationandnoshort-circuitorstart-up
events are expected, then input voltage transients of up to
36V are acceptable regardless of the switching frequency.
In this mode, the LT3684 may enter pulse skipping opera-
tion 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.
I
= I – ΔI /2
LIM L
OUT(MAX)
Be sure to pick an inductor ripple current that provides
sufficient maximum output current (I ).
OUT(MAX)
The largest inductor ripple current occurs at the highest
V . To guarantee that the ripple current stays below the
IN
specified maximum, the inductor value should be chosen
according to the following equation:
The minimum input voltage is determined by either the
LT3684’s minimum operating voltage of ~3.6V or by its
maximum duty cycle (see equation in previous section).
The minimum input voltage due to duty cycle is:
⎛
⎜
⎞
⎟
⎛
⎞
VOUT + VD
f∆IL
VOUT + VD
L =
1–
⎜
⎟
⎜
⎝
⎟
⎠
V
⎝
⎠
IN MAX
(
)
VOUT + VD
where V is the voltage drop of the catch diode (~0.4V),
D
V
=
) – VD + VSW
IN MIN
(
)
1– fSWtOFF MIN
V
is the maximum input voltage, V
is the output
IN(MAX)
OUT
(
voltage, f is the switching frequency (set by R ), and L
SW
T
whereV
istheminimuminputvoltage,andt
OFF(MIN)
IN(MIN)
is in the inductor value.
is the minimum switch off time (150ns). Note that higher
switching frequency will increase the minimum input
voltage. If a lower dropout voltage is desired, a lower
switching frequency should be used.
Theinductor’sRMScurrentratingmustbegreaterthanthe
maximumloadcurrentanditssaturationcurrentshouldbe
about 30% higher. For robust operation in fault conditions
(start-up or short circuit) and high input voltage (>30V),
the saturation current should be above 3.5A. 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 1 lists several vendors
and suitable types.
Inductor Selection
For a given input and output voltage, the inductor value
and switching frequency will determine the ripple current.
The ripple current ΔI increases with higher V or V
L
IN
OUT
and decreases with higher inductance and faster switch-
ing frequency. A reasonable starting point for selecting
the ripple current is:
Table 1. Inductor Vendors
VENDOR
Murata
TDK
URL
PART SERIES
TYPE
www.murata.com
LQH55D
Open
ΔI = 0.4(I
)
L
OUT(MAX)
www.componenttdk.com SLF7045
SLF10145
Shielded
Shielded
where I
is the maximum output load current. To
OUT(MAX)
Toko
www.toko.com
D62CB
D63CB
D75C
Shielded
Shielded
Shielded
Open
guarantee sufficient output current, peak inductor current
mustbelowerthantheLT3684’sswitchcurrentlimit(I ).
LIM
The peak inductor current is:
D75F
I
= I
+ ΔI /2
OUT(MAX) L
L(PEAK)
Sumida
www.sumida.com
CR54
Open
CDRH74
CDRH6D38
CR75
Shielded
Shielded
Open
where I
is the peak inductor current, I
is
OUT(MAX)
L(PEAK)
the maximum output load current, and ΔI is the inductor
L
ripple current. The LT3684’s switch current limit (I ) is
LIM
3684f
11
LT3684
APPLICATIONS INFORMATION
Of course, such a simple design guide will not always re-
sult in the optimum inductor for your application. A larger
value inductor provides a slightly higher maximum load
current and will reduce the output voltage ripple. If your
load is lower than 2A, then you can decrease 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. There are
several graphs in the Typical Performance Characteristics
section of this data sheet that show the maximum load
current as a function of input voltage and inductor value
for several popular output voltages. Low inductance may
result in discontinuous mode operation, which is okay
but further reduces maximum load current. For details of
maximum output current and discontinuous mode opera-
tion, see Linear Technology Application Note 44. Finally,
ceramic input capacitor concerns the maximum input
voltage rating of the LT3684. A ceramic input capacitor
combined with trace or cable inductance forms a high
quality (under damped) tank circuit. If the LT3684 circuit
is plugged into a live supply, the input voltage can ring to
twice its nominal value, possibly exceeding the LT3684’s
voltage rating. This situation is easily avoided (see the Hot
Plugging Safety section).
For space sensitive applications, a 2.2µF ceramic capaci-
tor can be used for local bypassing of the LT3684 input.
However, the lower input capacitance will result in in-
creased input current ripple and input voltage ripple, and
may couple noise into other circuitry. Also, the increased
voltage ripple will raise the minimum operating voltage
of the LT3684 to ~3.7V.
for duty cycles greater than 50% (V /V > 0.5), there
OUT IN
Output Capacitor and Output Ripple
is a minimum inductance required to avoid subharmonic
The output capacitor has two essential functions. Along
withtheinductor,itfiltersthesquarewavegeneratedbythe
LT3684toproducetheDCoutput. Inthisroleitdetermines
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
LT3684’s control loop. Ceramic capacitors have very low
equivalent series resistance (ESR) and provide the best
ripple performance. A good starting value is:
oscillations. See AN19.
Input Capacitor
BypasstheinputoftheLT3684circuitwithaceramiccapaci-
tor of X7R or X5R type. Y5V types have poor performance
over temperature and applied voltage, and should not be
used. A 4.7µF to 10µF ceramic capacitor is adequate to
bypasstheLT3684andwilleasilyhandletheripplecurrent.
Notethatlargerinputcapacitanceisrequiredwhenalower
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 low performance
electrolytic capacitor.
100
COUT
=
VOUT SW
f
where f
is in MHz, and C is the recommended
OUT
SW
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 Fre-
quency Compensation section to choose an appropriate
compensation network.
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage
ripple at the LT3684 and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
A 4.7µF capacitor is capable of this task, but only if it is
placed close to the LT3684 and the catch diode (see the
PCB Layout section). A second precaution regarding the
3684f
12
LT3684
APPLICATIONS INFORMATION
Table 2. Capacitor Vendors
VENDOR
PHONE
URL
PART SERIES
Ceramic,
Polymer,
Tantalum
Ceramic,
Tantalum
Ceramic,
Polymer,
Tantalum
Ceramic
COMMANDS
Panasonic
(714) 373-7366
www.panasonic.com
EEF Series
Kemet
Sanyo
(864) 963-6300
(408) 749-9714
www.kemet.com
T494, T495
POSCAP
www.sanyovideo.com
Murata
AVX
(408) 436-1300
(864) 963-6300
www.murata.com
www.avxcorp.com
Ceramic,
Tantalum
Ceramic
TPS Series
Taiyo Yuden
www.taiyo-yuden.com
Table 3. Diode Vendors
PART NUMBER
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
electrolyticcapacitorscanbeusedfortheoutputcapacitor.
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 2 lists several capacitor
vendors.
V
I
V AT 1A
V AT 2A
R
AVE
F
F
(V)
(A)
(mV)
(mV)
On Semicnductor
MBRM120E
MBRM140
20
40
1
1
530
550
595
Diodes Inc.
B120
20
30
20
30
40
1
1
2
2
2
500
500
B130
B220
500
500
500
B230
DFLS240L
International Rectifier
10BQ030
20BQ030
30
30
1
2
420
470
470
Frequency Compensation
Catch Diode
The LT3684 uses current mode control to regulate the
output.Thissimplifiesloopcompensation.Inparticular,the
LT3684 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
The catch diode conducts current only during switch off
time. Average forward current in normal operation can
be calculated from:
I
= I
(V – V )/V
OUT IN OUT IN
D(AVG)
where I
is the output load current. The only reason to
OUT
V pin, as shown in Figure 2. Generally a capacitor (C )
C
C
consideradiodewithalargercurrentratingthannecessary
for nominal operation is for the worst-case condition of
shorted output. The diode current will then increase to the
typical peak switch current. Peak reverse voltage is equal
to the regulator input voltage. Use a diode with a reverse
voltage rating greater than the input voltage. Table 3 lists
several Schottky diodes and their manufacturers.
and a resistor (R ) in series to ground are used. In addi-
C
tion, there may be lower value capacitor in parallel. This
capacitor (C ) is not part of the loop compensation but
F
is used to filter noise at the switching frequency, and is
required only if a phase-lead capacitor is used or if the
output capacitor has high ESR.
3684f
13
LT3684
APPLICATIONS INFORMATION
V
= 12V, FRONT PAGE APPLICATION
OUT
LT3684
CURRENT MODE
POWER STAGE
m
SW
OUTPUT
ERROR
AMPLIFIER
g
= 3.5mho
I
L
C
PL
R1
1A/DIV
FB
–
g
=
m
330µmho
ESR
+
1.265V
C1
+
V
3M
OUT
100mV/DIV
C1
POLYMER
OR
TANTALUM
CERAMIC
V
GND
C
10µs/DIV
3684 F03
R
C
R2
C
F
Figure 3. Transient Load Response of the LT3684 Front Page
Application as the Load Current is Stepped from 500mA to
C
C
1500mA. V
= 3.3V
OUT
3684 F02
may improve the transient response. Figure 3 shows the
transient response when the load current is stepped from
500mA to 1500mA and back to 500mA.
Figure 2. Model for Loop Response
Loop compensation determines the stability and transient
performance. Designing the compensation network is a
bit complicated and the best values depend on the ap-
plication and in particular the 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 2
shows an equivalent circuit for the LT3684 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 cur-
BOOST and BIAS Pin Considerations
Capacitor C3 and the internal boost Schottky diode (see
the Block Diagram) are used to generate a boost volt-
age that is higher than the input voltage. In most cases
a 0.22µF capacitor will work well. Figure 2 shows three
ways to arrange the boost circuit. The BOOST pin must be
more than 2.3V above the SW pin for best efficiency. For
outputs of 3V and above, 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
whileusingtheinternalboostdiode.ForreliableBOOSTpin
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. The circuit in Figure 4a
is more efficient because the BOOST pin current and BIAS
pin quiescent current comes from a lower voltage source.
You must also be sure that the maximum voltage ratings
of the BOOST and BIAS pins are not exceeded.
rent proportional to the voltage at the V pin. Note that
C
the output capacitor integrates this current, and that the
capacitor on the V pin (C ) integrates the error ampli-
C
C
fier 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 R in series with
C
C . This simple model works well as long as the value
C
The minimum operating voltage of an LT3684 application
is limited by the minimum input voltage (3.6V) and by the
maximum duty cycle as outlined in a previous section. For
of the inductor is not too high and the loop crossover
frequency is much lower than the switching frequency.
A phase lead capacitor (C ) across the feedback divider
PL
3684f
14
LT3684
APPLICATIONS INFORMATION
6.0
5.5
5.0
4.5
4.0
3.5
3.0
V
OUT
TO START
BD
BOOST
V
V
IN
IN
LT3684
GND
C3
SW
4.7µF
TO RUN
V
A
= 3.3V
OUT
T
= 25°C
(4a) For V
> 2.8V
OUT
2.5
2.0
L = 4.7µH
f = 800kHz
0.1
0.01
LOAD CURRENT (A)
0.001
1
10
V
OUT
D2
BD
BOOST
8.0
7.0
6.0
5.0
4.0
3.0
2.0
TO START
V
V
IN
LT3684
IN
C3
SW
GND
4.7µF
TO RUN
(4b) For 2.5V < V
< 2.8V
OUT
V
T
= 5V
OUT
A
V
OUT
= 25°C
L = 4.7µH
f = 800kHz
BD
BOOST
V
0.1
LOAD CURRENT (A)
0.001
0.01
1
10
V
IN
LT3684
IN
C3
3684 F05
SW
GND
4.7µF
Figure 5. The Minimum Input Voltage Depends on
Output Voltage, Load Current and Boost Circuit
3684 FO4
voltage. In many cases the discharged output capacitor
will present a load to the switcher and the minimum input
to start will be the same as the minimum input to run.
(4c) For V
< 2.5V
OUT
Figure 4. Three Circuits For Generating The Boost Voltage
This occurs, for example, if RUN/SS is asserted after V
IN
is applied. The plots show the worst-case situation where
proper start-up, the minimum input voltage is also limited
by the boost circuit. If the input voltage is ramped slowly,
or the LT3684 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 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
V is ramping very slowly. For lower start-up voltage, the
IN
boost diode can be tied to V ; however, this restricts the
IN
input range to one-half of the absolute maximum rating
of the BOOST pin.
At light loads, the inductor current becomes discontinu-
ous and the effective duty cycle can be very high. This
reduces the minimum input voltage to approximately
300mV above V . At higher load currents, the inductor
OUT
current is continuous and the duty cycle is limited by the
maximum duty cycle of the LT3684, requiring a higher
input voltage to maintain regulation.
3684f
15
LT3684
APPLICATIONS INFORMATION
Soft-Start
D4
MBRS140
The RUN/SS pin can be used to soft-start the LT3684,
reducing the maximum input current during start-up.
The RUN/SS pin is driven through an external RC filter to
create a voltage ramp at this pin. Figure 7 shows the start-
up and shut-down 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
oftheresistorsothatitcansupply20µAwhentheRUN/SS
pin reaches 2.3V.
V
V
BOOST
SW
IN
IN
LT3684
V
RUN/SS
OUT
V
C
GND FB
BACKUP
3684 F07
Figure 7. Diode D4 Prevents a Shorted Input from
Discharging a Backup Battery Tied to the Output. It Also
Protects the Circuit from a Reversed Input. The LT3684
Runs Only When the Input is Present
I
L
LT3684 can pull large currents from the output through
1A/DIV
RUN
15k
the SW pin and the V pin. Figure 7 shows a circuit that
IN
will run only when the input voltage is present and that
protects against a shorted or reversed input.
V
RUN/SS
GND
RUN/SS
2V/DIV
0.22µF
V
OUT
2V/DIV
PCB Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Figure 8 shows
the recommended component placement with trace,
ground plane and via locations. Note that large, switched
3481 F06
2ms/DIV
Figure 6. To Soft-Start the LT3684, Add a Resisitor
and Capacitor to the RUN/SS Pin
currents flow in the LT3684’s V and SW pins, the catch
IN
Shorted and Reversed Input Protection
diode (D1) and the input capacitor (C1). The loop formed
bythesecomponentsshouldbeassmallaspossible.These
components,alongwiththeinductorandoutputcapacitor,
should be placed on the same side of the circuit board,
and their connections should be made on that layer. Place
a local, unbroken ground plane below these components.
The SW and BOOST nodes should be as small as possible.
If the inductor is chosen so that it won’t saturate exces-
sively, an LT3684 buck regulator will tolerate a shorted
output. There is another situation to consider in systems
where the output will be held high when the input to the
LT3684 is absent. This may occur in battery charging ap-
plications or in battery backup systems where a battery
or some other supply is diode OR-ed with the LT3684’s
Finally, keep the FB and V nodes small so that the ground
C
traces will shield them from the SW and BOOST nodes.
The Exposed Pad on the bottom of the package must be
soldered to ground so that the pad acts as a heat sink. To
keep thermal resistance low, extend the ground plane as
much as possible, and add thermal vias under and near
the LT3684 to additional ground planes within the circuit
board and on the bottom side.
output. If the V pin is allowed to float and the RUN/SS
IN
pin is held high (either by a logic signal or because it is
tied to V ), then the LT3684’s internal circuitry will pull
IN
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 V pin is grounded while
the output is held high, then parasitic diodes inside the
IN
3684f
16
LT3684
APPLICATIONS INFORMATION
L1
C2
V
OUT
C
C
R
RT
R
C
R2
R1
C1
D1
R
GND
PG
3684 F08
VIAS TO V
VIAS TO LOCAL GROUND PLANE
VIAS TO V
VIAS TO RUN/SS
VIAS TO PG
IN
OUTLINE OF LOCAL
GROUND PLANE
OUT
Figure 8. A Good PCB Layout Ensures Proper, Low EMI Operation
Hot Plugging Safely
input to eliminate the voltage overshoot (it also reduces
the peak input current). A 0.1µF capacitor improves high
frequency filtering. For high input voltages its impact on
efficiency is minor, reducing efficiency by 1.5 percent for
a 5V output at full load operating from 24V.
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypasscapacitorofLT3684circuits.However,thesecapaci-
tors can cause problems if the LT3684 is plugged into a
live supply (see Linear Technology Application Note 88 for
a complete discussion). The low loss ceramic capacitor,
combined with stray inductance in series with the power
source, forms an under damped tank circuit, and the
High Temperature Considerations
The PCB must provide heat sinking to keep the LT3684
cool. The Exposed Pad on the bottom of the package must
be soldered to a ground plane. This ground should be tied
to large copper layers below with thermal vias; these lay-
ers will spread the heat dissipated by the LT3684. Place
additionalviascanreducethermalresistancefurther. With
these steps, the thermal resistance from die (or junction)
voltage at the V pin of the LT3684 can ring to twice the
IN
nominal input voltage, possibly exceeding the LT3684’s
rating and damaging the part. If the input supply is poorly
controlled or the user will be plugging the LT3684 into an
energized supply, the input network should be designed
to prevent this overshoot. Figure 9 shows the waveforms
that result when an LT3684 circuit is connected to a 24V
supply through six feet of 24-gauge twisted pair. The
first plot is the response with a 4.7µF ceramic capacitor
at the input. The input voltage rings as high as 50V and
the input current peaks at 26A. A good solution is shown
in Figure 9b. A 0.7Ω resistor is added in series with the
to ambient can be reduced to θ = 35°C/W or less. With
JA
100 LFPM airflow, this resistance can fall by another 25%.
Further increases in airflow will lead to lower thermal re-
sistance. Because of the large output current capability of
the LT3684, it is possible to dissipate enough heat to raise
thejunctiontemperaturebeyondtheabsolutemaximumof
125°C. When operating at high ambient temperatures, the
3684f
17
LT3684
APPLICATIONS INFORMATION
CLOSING SWITCH
DANGER
SIMULATES HOT PLUG
V
IN
I
IN
20V/DIV
V
IN
RINGING V MAY EXCEED
LT3684
4.7µF
IN
ABSOLUTE MAXIMUM RATING
+
I
IN
LOW
STRAY
10A/DIV
IMPEDANCE
ENERGIZED
24V SUPPLY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
20µs/DIV
(9a)
0.7Ω
V
IN
20V/DIV
LT3684
4.7µF
+
0.1µF
I
IN
10A/DIV
20µs/DIV
(9b)
V
IN
20V/DIV
LT3684
4.7µF
+
+
22µF
35V
AI.EI.
I
IN
10A/DIV
3684 F09
20µs/DIV
(9c)
Figure 9. A Well Chosen Input Network Prevents Input Voltage Overshoot and
Ensures Reliable Operation when the LT3684 is Connected to a Live Supply
maximum load current should be derated as the ambient
Other Linear Technology Publications
temperature approaches 125°C.
Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 100
shows how to generate a bipolar output supply using a
buck regulator.
Power dissipation within the LT3684 can be estimated by
calculatingthetotalpowerlossfromanefficiencymeasure-
ment and subtracting the catch diode loss and inductor
loss. The die temperature is calculated by multiplying the
LT3684 power dissipation by the thermal resistance from
junction to ambient.
3684f
18
LT3684
TYPICAL APPLICATIONS
5V Step-Down Converter
V
5V
2A
OUT
V
IN
6.3V TO 34V
V
IN
BD
RUN/SS
BOOST
ON OFF
L
0.47µF
6.8µH
V
SW
C
LT3684
GND
4.7µF
D
RT
PG
20k
BIAS
FB
590k
60.4k
f = 800kHz
330pF
22µF
200k
3684 TA02
D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB6R8M
3.3V Step-Down Converter
V
OUT
V
IN
3.3V
4.4V TO 34V
2A
V
IN
BD
RUN/SS
BOOST
ON OFF
L
0.47µF
4.7µH
V
SW
C
LT3684
GND
4.7µF
D
RT
PG
16.2k
BIAS
FB
324k
60.4k
f = 800kHz
330pF
22µF
200k
3684 TA03
D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB4R7M
3684f
19
LT3684
TYPICAL APPLICATIONS
2.5V Step-Down Converter
V
2.5V
2A
OUT
V
IN
4V TO 34V
V
IN
BD
D2
RUN/SS
BOOST
ON OFF
L
1 F
4.7 H
V
SW
C
4.7 F
LT3684
GND
D1
RT
PG
22.1k
BIAS
FB
196k
84.5k
f = 600kHz
220pF
47 F
200k
3684 TA04
D1: DIODES INC. DFLS240L
D2: MBR0540
L: TAIYO YUDEN NP06DZB4R7M
5V, 2MHz Step-Down Converter
V
V
5V
2A
IN
OUT
8.6V TO 22V
TRANSIENT TO 36V
V
IN
BD
RUN/SS
BOOST
ON OFF
L
0.47 F
2.2 H
V
SW
C
LT3684
GND
2.2 F
D
RT
PG
20k
BIAS
FB
590k
16.9k
f = 2MHz
330pF
10 F
200k
3684 TA05
D: DIODES INC. DFLS240L
L: SUMIDA CDRH4D22/HP-2R2
3684f
20
LT3684
TYPICAL APPLICATIONS
12V Step-Down Converter
V
12V
2A
OUT
V
IN
15V TO 34V
V
IN
BD
RUN/SS
BOOST
ON OFF
L
0.47µF
10µH
V
SW
C
LT3684
GND
10µF
D
RT
PG
30k
BIAS
FB
845k
60.4k
f = 800kHz
330pF
22µF
100k
3684 TA06
D: DIODES INC. DFLS240L
L: NEC/TOKIN PLC-0755-100
1.8V Step-Down Converter
V
1.8V
2A
OUT
V
IN
3.5V TO 27V
V
IN
BD
RUN/SS
BOOST
ON OFF
L
0.47µF
3.3µH
V
SW
C
LT3684
GND
4.7µF
D
RT
PG
15.4k
BIAS
FB
84.5k
105k
f = 500kHz
330pF
47µF
200k
3684 TA07
D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB3R3M
3684f
21
LT3684
PACKAGE DESCRIPTION
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
0.675 0.05
3.50 0.05
2.15 0.05 (2 SIDES)
1.65 0.05
PACKAGE
OUTLINE
0.25 0.05
0.50
BSC
2.38 0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
0.38 0.10
TYP
6
10
3.00 0.10
(4 SIDES)
1.65 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD) DFN 1103
5
1
0.25 0.05
0.50 BSC
0.75 0.05
0.200 REF
2.38 0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
3684f
22
LT3684
PACKAGE DESCRIPTION
MSE Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1664)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.06 0.102
(.081 .004)
2.794 0.102
(.110 .004)
0.889 0.127
(.035 .005)
1
1.83 0.102
(.072 .004)
5.23
(.206)
MIN
2.083 0.102 3.20 – 3.45
(.082 .004) (.126 – .136)
10
0.50
(.0197)
BSC
0.305 0.038
(.0120 .0015)
TYP
3.00 0.102
(.118 .004)
(NOTE 3)
0.497 0.076
(.0196 .003)
REF
10 9
8
7 6
RECOMMENDED SOLDER PAD LAYOUT
3.00 0.102
(.118 .004)
(NOTE 4)
4.90 0.152
(.193 .006)
DETAIL “A”
0.254
(.010)
0° – 6° TYP
1
2
3
4 5
GAUGE PLANE
0.53 0.152
(.021 .006)
0.86
(.034)
REF
1.10
(.043)
MAX
DETAIL “A”
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.127 0.076
(.005 .003)
MSOP (MSE) 0603
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
3684f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
23
LT3684
TYPICAL APPLICATION
1.265V Step-Down Converter
V
OUT
V
IN
1.265V
2A
3.6V TO 27V
V
IN
BD
RUN/SS
BOOST
ON OFF
L
0.47 F
3.3 H
V
SW
C
LT3648
GND
4.7 F
D
RT
PG
13k
BIAS
FB
105k
f = 500kHz
330pF
47 F
3648 TA08
D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB3R3M
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LT1933
LT3437
LT1936
LT3493
500mA (I ), 500kHz Step-Down Switching Regulator in V : 3.6V to 36V, V
= 12V, I = 1.6mA, I < 1µA, ThinSOTTM
Q SD
OUT
IN
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
SOT-23
Package
60V, 400mA (I ), MicroPower Step-Down DC/DC
V : 3.3V to 80V, V
IN
= 1.25V, I = 100µA, I < 1µA, DFN Package
Q SD
OUT
Converter with Burst Mode Operation
36V, 1.4A (I ), 500kHz High Efficiency Step-Down
V : 3.6V to 36V, V
IN
= 1.2V, I = 1.9mA, I < 1µA, MS8E Package
Q SD
OUT
DC/DC Converter
36V, 1.2A (I ), 750kHz High Efficiency Step-Down
V : 3.6V to 40V, V
IN
= 0.8V, I = 1.9mA, I < 1µA, DFN Package
Q SD
OUT
DC/DC Converter
LT1976/LT1977 60V, 1.2A (I ), 200kHz/500kHz, High Efficiency Step-
V : 3.3V to 60V, V
= 1.20V, I = 100µA, I < 1µA, TSSOP16E
Q SD
OUT
IN
Down DC/DC Converter with Burst Mode Operation
Package
LT1767
LT1940
LT1766
25V, 1.2A (I ), 1.1MHz, High Efficiency Step-Down
V : 3V to 25V, V
= 1.20V, I = 1mA, I < 6µA, MS8E Package
OUT(MIN) Q SD
OUT
IN
DC/DC Converter
Dual 25V, 1.4A (I ), 1.1MHz, High Efficiency Step-Down V : 3.6V to 25V, V
= 1.20V, I = 3.8mA, I < 30µA, TSSOP16E
Q SD
OUT
IN
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
DC/DC Converter
Package
60V, 1.2A (I ), 200kHz, High Efficiency Step-Down
V : 5.5V to 60V, V
= 1.20V, I = 2.5mA, I < 25µA, TSSOP16E
Q SD
OUT
IN
DC/DC Converter
Package
LT3434/LT3435 60V, 2.4A (I ), 200/500kHz, High Efficiency Step-Down V : 3.3V to 60V, V
= 1.20V, I = 100µA, I < 1µA, TSSOP16E
Q SD
OUT
IN
DC/DC Converter with Burst Mode Operation
Package
LT3481
36V, 2A (I ), Micropower 2.8MHz, High Efficiency
V : 3.6V to 36V, V
= 1.265V, I = 5µA, I < 1µA, 3mm × 3mm
Q SD
OUT
IN
Step-Down DC/DC Converter
DFN and MS10E Packages
3684f
LT 0207 • PRINTED IN USA
24 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
相关型号：
©2020 ICPDF网 联系我们和版权申明