LINER LT3684 36v, 2a, 2.8mhz step-down switching regulator Datasheet

LT3684
36V, 2A, 2.8MHz Step-Down
Switching Regulator
FEATURES
DESCRIPTION
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The LT®3684 is an adjustable frequency (300kHz to 2.8MHz)
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
(soft-start). A power good flag signals when VOUT reaches
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.
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Wide Input Range: 3.6V to 34V Operating,
36V Maximum
2A Maximum Output Current
Adjustable Switching Frequency: 300kHz to 2.8MHz
Low Shutdown Current: IQ < 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
APPLICATIONS
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Automotive Battery Regulation
Power for Portable Products
Distributed Supply Regulation
Industrial Supplies
Wall Transformer Regulation
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
3.3V Step-Down Converter
Efficiency
VIN
4.5V TO
34V
VIN
BD
RUN/SS
BOOST
0.47µF
16.2k
4.7µH
SW
VC
4.7µF
LT3684
RT
330pF
BIAS
PG
324k
60.4k
GND
90
80
EFFICIENCY (%)
OFF ON
VOUT
3.3V
2A
70
60
50
FB
200k
22µF
3684 TA01
VIN = 12V
VOUT = 3.3V
L = 4.7µH
f = 800kHz
40
30
0
0.5
1
1.5
LOAD CURRENT (A)
2
3684 TA01b
3684f
1
LT3684
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, RUN/SS Voltage .................................................36V
BOOST Pin Voltage ...................................................56V
BOOST Pin Above SW Pin.........................................30V
FB, RT, VC Voltage .......................................................5V
BIAS, PG, BD Voltage ................................................30V
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range (Note 2)
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)
(MSE Only) ....................................................... 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
TOP VIEW
BD
1
10 RT
BOOST
2
9 VC
SW
3
VIN
4
7 BIAS
RUN/SS
5
6 PG
11
BD
BOOST
SW
VIN
RUN/SS
8 FB
1
2
3
4
5
10
9
8
7
6
11
RT
VC
FB
BIAS
PG
MSE PACKAGE
10-LEAD PLASTIC MSOP
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 45°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
TJMAX = 125°C, θJA = 45°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
DD PART MARKING*
ORDER PART NUMBER
MSE PART MARKING*
LT3684EDD
LT3684IDD
LCVT
LCVT
LT3684EMSE
LT3684IMSE
LTCVS
LTCVS
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 ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUNS/SS = 10V, VBOOST = 15V, VBIAS = 3.3V unless otherwise
noted. (Note 2)
PARAMETER
CONDITIONS
TYP
MAX
3
3.6
V
0.01
0.5
µA
0.4
0.8
mA
VBIAS = 0, Not Switching
1.2
2.0
mA
VRUN/SS = 0.2V
0.01
0.5
µA
0.85
1.5
mA
0
0.1
mA
●
Minimum Input Voltage
Quiescent Current from VIN
VRUN/SS = 0.2V
VBIAS = 3V, Not Switching
Quiescent Current from BIAS
MIN
VBIAS = 3V, Not Switching
VBIAS = 0, Not Switching
●
●
UNITS
3684f
2
LT3684
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUNS/SS = 10V VBOOST = 15V, VBIAS = 3.3V unless otherwise
noted. (Note 2)
PARAMETER
CONDITIONS
MIN
Minimum Bias Voltage
Feedback Voltage
●
●
FB Pin Bias Current (Note 3)
FB Voltage Line Regulation
1.25
1.24
4V < VIN < 34V
TYP
MAX
2.7
3
V
1.265
1.265
1.28
1.29
V
V
30
100
nA
0.002
0.02
%/V
Error Amp gm
330
Error Amp Gain
1000
UNITS
µMho
VC Source Current
75
µA
VC Sink Current
100
µA
VC Pin to Switch Current Gain
3.5
A/V
VC Clamp Voltage
Switching Frequency
2
RT = 8.66k
RT = 29.4k
RT = 187k
2.7
1.25
250
●
Minimum Switch Off-Time
Switch Current Limit
Duty Cycle = 5%
Switch VCESAT
ISW = 2A
Boost Schottky Reverse Leakage
VSW = 10V, VBIAS = 0V
3.1
Minimum Boost Voltage (Note 4)
ISW = 1A
RUN/SS Pin Current
VRUN/SS = 2.5V
3.3
1.55
350
MHz
MHz
kHz
100
150
nS
3.6
4.0
360
●
BOOST Pin Current
RUN/SS Input Voltage High
2
1.6
2.1
V
18
30
mA
5
10
µA
2.5
VFB Rising
PG Leakage
VPG = 5V
PG Sink Current
VPG = 0.4V
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 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.
100
V
100
mV
10
mV
0.1
●
µA
V
0.2
PG Hysteresis
A
mV
0.02
RUN/SS Input Voltage Low
PG Threshold Offset from Feedback Voltage
V
3.0
1.4
300
300
1
µA
µA
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.
3684f
3
LT3684
TYPICAL PERFORMANCE CHARACTERISTICS
90
80
70
VIN = 24V
80
VIN = 12V
75
70
65
0
55
50
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOAD CURRENT (A)
Maximum Load Current
0
LOAD CURRENT (A)
2.0
VOUT = 3.3V
TA = 25°C
L = 4.7µH
f = 800kHz
10
25
20
15
INPUT VOLTAGE (V)
3.0
2.5
MINIMUM
2.0
VOUT = 5V
TA = 25°C
L = 4.7µH
f = 800kHz
1.5
1.0
5
10
25
20
15
INPUT VOLTAGE (V)
3684 G04
1.0
0
1.5
1.0
0
25
50
75
TEMPERATURE (°C)
100
125
3684 G07
100
80
500
400
300
200
100
0.5
80
Boost Pin Current
BOOST PIN CURRENT (mA)
VOLTAGE DROP (mV)
DUTY CYCLE = 90 %
60
40
DUTY CYCLE (%)
90
600
2.0
20
3684 G06
700
–25
2.0
30
DUTY CYCLE = 10 %
3.0
0
–50
2.5
Switch Voltage Drop
Switch Current Limit
2.5
3.0
3684 G05
4.5
4.0
3.5
1.5
1.0
30
3
Switch Current Limit
TYPICAL
MINIMUM
1
2
2.5
1.5
SWITCHING FREQUENCY (MHz)
4.0
3.5
3.0
0.5
3684 G03
SWITCH CURRENT LIMIT (A)
3.5
LOAD CURRENT (A)
0
Maximum Load Current
TYPICAL
VOUT = 3.3V
L = 10µH
LOAD = 1A
50
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOAD CURRENT (A)
4.0
5
65
3684 G02
4.0
1.5
70
55
L: NEC PLC-0745-4R7
f = 800kHz
3684 G01
2.5
VIN = 24V
75
60
60
L: NEC PLC-0745-4R7
f = 800kHz
VIN = 12V
85
80
EFFICIENCY (%)
EFFICIENCY (%)
VIN = 7V
EFFICIENCY (%)
VIN = 12V
60
SWITCH CURRENT LIMIT (A)
90
85
VIN = 24V
50
Efficiency
Efficiency (VOUT = 3.3V)
Efficiency (VOUT = 5.0V)
100
90
(TA = 25°C unless otherwise noted)
70
60
50
40
30
20
10
0
0
0
500
1000 1500 2000 2500 3000 3500
SWITCH CURRENT (mA)
3684 G08
0
500 1000 1500 2000 2500 3000 3500
SWITCH CURRENT (mA)
3684 G09
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LT3684
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency
1.20
1.285
1.15
1.280
1.10
1.275
1.270
1.265
0.95
1.255
0.85
0
25
50
75
TEMPERATURE (°C)
100
0.80
–50
125
RT = 45.3k
1.00
0.90
–25
RT = 45.3k
1.05
1.260
1.250
–50
Frequency Foldback
1200
400
200
0
25
50
75
TEMPERATURE (°C)
100
0
125
120
3.5
80
60
40
20
RUN/SS Pin Current
3.0
2.5
2.0
1.5
1.0
25
0
50
75
TEMPERATURE (˚C)
100
125
8
6
4
0
0
–25
10
2
0.5
0
–50
0
0.5
1
2
2.5
1.5
RUN/SS PIN VOLTAGE (V)
3684 G13
3
0
3.5
Boost Diode
1.4
80
Minimum Input Voltage
4.0
0.4
INPUT VOLTAGE (V)
VC PIN CURRENT (µA)
0.6
40
20
0
–20
–40
0.2
3.5
3.0
2.5
–60
0
1.0
0.5
1.5
BOOST DIODE CURRENT (A)
2.0
3684 G16
–80
1.065
35
4.5
60
0.8
20
30
15
25
10
RUN/SS PIN VOLTAGE (V)
3684 G15
Error Amp Output Current
100
1.0
5
3684 G14
1.6
1.2
400 600 800 1000 1200 1400
FB PIN VOLTAGE (mV)
12
RUN/SS PIN CURRENT (µA)
4.0
100
200
3684 G12
Soft-Start
140
SWITCH CURRENT LIMIT (A)
MINIMUM SWITCH ON-TIME (ns)
600
3684 G11
Minimum Switch On-Time
BOOST DIODE Vf (V)
800
0
–25
3684 G10
0
1000
SWITCHING FREQUENCY (kHz)
1.290
FREQUENCY (MHz)
FEEDBACK VOLTAGE (V)
Feedback Voltage
(TA = 25°C unless otherwise noted)
1 .265
1.165
1.365
FB PIN VOLTAGE (V)
1.465
3684 G17
2.0
0.001
VOUT = 3.3V
TA = 25°C
L = 4.7µH
f = 800kHz
0.1
0.01
1
LOAD CURRENT (A)
10
3684 G18
3684f
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LT3684
TYPICAL PERFORMANCE CHARACTERISTICS
6.0
2.00
5.5
5.0
VOUT = 5V
TA = 25°C
L = 4.7µH
f = 800kHz
4.0
0.001
0.1
0.01
1
LOAD CURRENT (A)
1.200
THRESHOLD VOLTAGE (V)
2.50
4.5
Power Good Threshold
VC Voltages
6.5
THRESHOLD VOLTAGE (V)
INPUT VOLTAGE (V)
Minimum Input Voltage
(TA = 25°C unless otherwise noted)
CURRENT LIMIT CLAMP
1.50
1.00
SWITCHING THRESHOLD
0.50
10
PG RISING
1.180
1.160
1.140
1.120
0
–50
–25
0
50
25
75
TEMPERATURE (°C)
100
125
1.100
–50
–25
0
50
25
75
TEMPERATURE (°C)
3684 G20
3684 G19
Switching Waveforms
(Discontinuous Operation)
100
125
3684 G21
Switching Waveforms
(Continuous Operation)
IL
0.5A/DIV
IL
0.5A/DIV
VSW
5V/DIV
VRUN/SS
5V/DIV
VOUT
10mV/DIV
VOUT
10mV/DIV
VIN = 12V, FRONT PAGE APPLICATION
ILOAD = 140mA
1µs/DIV
VIN = 12V, FRONT PAGE APPLICATION
ILOAD = 1A
3684 G22
1µs/DIV
3684 G23
3684f
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LT3684
PIN FUNCTIONS
BD (Pin 1): This pin connects to the anode of the boost
Schottky diode.
BOOST (Pin 2): This pin is used to provide a drive
voltage, higher than the input voltage, to the internal bipolar
NPN power switch.
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.
VIN (Pin 4): The VIN pin supplies current to the LT3684’s
internal regulator and to the internal power switch. This
pin must be locally bypassed.
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
the shutdown feature is not used, tie this pin to the VIN
pin. RUN/SS also provides a soft-start function; see the
Applications Information section.
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
valid when VIN is above 3.5V and RUN/SS is high.
BIAS (Pin 7): The BIAS pin supplies the current to the
LT3684’s internal regulator. Tie this pin to the lowest
available voltage source above 3V (typically VOUT). This
architecture increases efficiency especially when the input
voltage is much higher than the output.
FB (Pin 8): The LT3684 regulates the FB pin to 1.265V.
Connect the feedback resistor divider tap to this pin.
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.
RT (Pin 10): Oscillator Resistor Input. Connecting a resistor
to ground from this pin sets the switching frequency.
Exposed Pad (Pin 11): Ground. The Exposed Pad must
be soldered to PCB.
3684f
7
LT3684
BLOCK DIAGRAM
VIN
4
VIN
C1
7
5
10
BIAS
–
+
INTERNAL 1.265V REF
RUN/SS
Σ
SLOPE COMP
BD
SWITCH
LATCH
BOOST
2
C3
R
RT
OSCILLATOR
300kHz–2.8MHz
RT
Q
S
SW
SOFT-START
6
1
L1
VOUT
3
VC CLAMP
C2
D1
PG
ERROR AMP
+
–
+
–
1.12V
FB
GND
11
VC
9
CC
RC
CF
8
R2
R1
3684 BD
3684f
8
LT3684
OPERATION
The LT3684 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 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).
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.
The oscillator reduces the LT3684’s operating frequency
when the voltage at the FB pin is low. This frequency
foldback helps to control the output current during startup
and overload.
The LT3684 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 LT3684 is
enabled and VIN is above 3.6V.
3684f
9
LT3684
APPLICATIONS INFORMATION
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resistors according to:
⎞
⎛V
R1= R2 ⎜ OUT – 1⎟
⎝ 1.265 ⎠
Reference designators refer to the Block Diagram.
Setting the Switching Frequency
The LT3684 uses a constant frequency PWM architecture
that can be programmed to switch from 300kHz to 2.8MHz
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 Figure 1.
SWITCHING FREQUENCY (MHz)
RT VALUE (kΩ)
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
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
Figure 1. Switching Frequency vs RT Value
Operating Frequency Tradeoffs
Selection of the operating frequency is a tradeoff between
efficiency, component size, minimum dropout voltage, and
maximum input voltage. The advantage of high frequency
operation is that smaller inductor and capacitor values may
be used. The disadvantages are lower efficiency, lower
maximum input voltage, and higher dropout voltage. The
highest acceptable switching frequency (fSW(MAX)) for a
given application can be calculated as follows:
fSW(MAX ) =
VD + VOUT
tON(MIN) ( VD + VIN – VSW )
where VIN is the typical input voltage, VOUT is the output
voltage, is the catch diode drop (~0.5V), VSW is the internal
switch drop (~0.5V at max load). This equation shows
that slower switching frequency is necessary to safely
accommodate high VIN/VOUT ratio. Also, as shown in
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:
DCMIN = fSW tON(MIN)
DCMAX = 1– fSW tOFF(MIN)
where fSW is the switching frequency, the tON(MIN) is the
minimum switch on time (~150ns), and the tOFF(MIN) is
the minimum switch off time (~150ns). These equations
show that duty cycle range increases when switching
frequency is decreased.
A good choice of switching frequency should allow adequate input voltage range (see next section) and keep
the inductor and capacitor values small.
Input Voltage Range
The maximum input voltage for LT3684 applications depends on switching frequency, the Absolute Maximum Ratings on VIN and BOOST pins, and on operating mode.
If the output is in start-up or short-circuit operating modes,
then VIN must be below 34V and below the result of the
following equation:
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 switching frequency will depress the maximum
operating input voltage. Conversely, a lower switching
3684f
10
LT3684
APPLICATIONS INFORMATION
frequency will be necessary to achieve safe operation at
high input voltages.
If the output is in regulation and no short-circuit or start-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 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.
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:
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 (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.
Inductor Selection
For a given input and output voltage, the inductor value
and switching frequency will determine the ripple current.
The ripple current ΔIL increases with higher VIN or VOUT
and decreases with higher inductance and faster switching frequency. A reasonable starting point for selecting
the ripple current is:
ΔIL = 0.4(IOUT(MAX))
where IOUT(MAX) is the maximum output load current. To
guarantee sufficient output current, peak inductor current
must be lower than the LT3684’s switch current limit (ILIM).
The peak inductor current is:
IL(PEAK) = IOUT(MAX) + 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 LT3684’s switch current limit (ILIM) is
at least 3.5A at low duty cycles and decreases linearly to
2.5A at DC = 0.8. The maximum output current is a function of the inductor ripple current:
IOUT(MAX) = ILIM – ΔIL/2
Be sure to pick an inductor ripple current that provides
sufficient maximum output current (IOUT(MAX)).
The largest inductor ripple current occurs at the highest
VIN. To guarantee that the ripple current stays below the
specified maximum, the inductor value should be chosen
according to the following equation:
⎛V +V ⎞⎛ V +V ⎞
L = ⎜ OUT D ⎟ ⎜ 1– OUT D ⎟
VIN(MAX ) ⎟⎠
⎝ f∆IL ⎠ ⎜⎝
where VD is the voltage drop of the catch diode (~0.4V),
VIN(MAX) is the maximum input voltage, VOUT is the output
voltage, fSW is the switching frequency (set by RT), and L
is in the inductor value.
The inductor’s RMS current rating must be greater than the
maximum load current and its saturation current should be
about 30% higher. For robust operation in fault conditions
(start-up or short circuit) and high input voltage (>30V),
the saturation current should be above 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.
Table 1. Inductor Vendors
VENDOR
URL
Murata
www.murata.com
LQH55D
Open
TDK
www.componenttdk.com
SLF7045
SLF10145
Shielded
Shielded
Toko
www.toko.com
D62CB
Shielded
D63CB
Shielded
D75C
Shielded
Sumida
www.sumida.com
PART SERIES
TYPE
D75F
Open
CR54
Open
CDRH74
Shielded
CDRH6D38
Shielded
CR75
Open
3684f
11
LT3684
APPLICATIONS INFORMATION
Of course, such a simple design guide will not always result 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 operation, see Linear Technology Application Note 44. Finally,
for duty cycles greater than 50% (VOUT/VIN > 0.5), there
is a minimum inductance required to avoid subharmonic
oscillations. See AN19.
Input Capacitor
Bypass the input of the LT3684 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 4.7µF to 10µF ceramic capacitor is adequate to
bypass the LT3684 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 low 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 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
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 capacitor can be used for local bypassing of the LT3684 input.
However, the lower input capacitance will result in increased 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.
Output Capacitor and Output Ripple
The output capacitor has two essential functions. Along
with the inductor, it filters the square wave generated by the
LT3684 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
LT3684’s control loop. Ceramic capacitors have very low
equivalent series resistance (ESR) and provide the best
ripple performance. A good starting value is:
COUT =
100
VOUT fSW
where fSW is in MHz, and COUT is the recommended
output capacitance in µF. Use X5R or X7R types. This
choice will provide low output ripple and good transient
response. Transient performance can be improved with
a higher value capacitor if 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.
3684f
12
LT3684
APPLICATIONS INFORMATION
Table 2. Capacitor Vendors
VENDOR
PHONE
URL
Panasonic
(714) 373-7366
www.panasonic.com
PART SERIES
COMMANDS
Ceramic,
Polymer,
EEF Series
Tantalum
Kemet
(864) 963-6300
www.kemet.com
Sanyo
(408) 749-9714
www.sanyovideo.com
Ceramic,
Tantalum
T494, T495
Ceramic,
Polymer,
POSCAP
Tantalum
Murata
(408) 436-1300
AVX
www.murata.com
Ceramic
www.avxcorp.com
Ceramic,
Tantalum
Taiyo Yuden
(864) 963-6300
www.taiyo-yuden.com
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.
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.
TPS Series
Ceramic
Table 3. Diode Vendors
PART NUMBER
VR
(V)
IAVE
(A)
VF AT 1A
(mV)
VF AT 2A
(mV)
On Semicnductor
MBRM120E
MBRM140
20
40
1
1
530
550
595
Diodes Inc.
B120
B130
B220
B230
DFLS240L
20
30
20
30
40
1
1
2
2
2
500
500
International Rectifier
10BQ030
20BQ030
30
30
1
2
420
500
500
500
470
470
Catch Diode
Frequency Compensation
The catch diode conducts current only during switch off
time. Average forward current in normal operation can
be calculated from:
The LT3684 uses current mode control to regulate the
output. This simplifies loop compensation. In particular, 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
VC pin, as shown in Figure 2. Generally a capacitor (CC)
and a resistor (RC) in series to ground are used. In addition, there may be lower value capacitor in parallel. This
capacitor (CF) is not part of the loop compensation but
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.
ID(AVG) = IOUT (VIN – VOUT)/VIN
where IOUT is the output load current. The only reason to
consider a diode with a larger current rating than necessary
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.
3684f
13
LT3684
APPLICATIONS INFORMATION
VOUT = 12V, FRONT PAGE APPLICATION
LT3684
CURRENT MODE
POWER STAGE
gm = 3.5mho
SW
ERROR
AMPLIFIER
OUTPUT
R1
IL
1A/DIV
CPL
FB
–
gm =
330µmho
ESR
1.265V
C1
+
+
3M
C1
VC
CF
RC
POLYMER
OR
TANTALUM
GND
VOUT
100mV/DIV
CERAMIC
10µs/DIV
3684 F03
R2
Figure 3. Transient Load Response of the LT3684 Front Page
Application as the Load Current is Stepped from 500mA to
1500mA. VOUT = 3.3V
CC
3684 F02
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 application 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 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 3 shows the
transient response when the load current is stepped from
500mA to 1500mA and back to 500mA.
BOOST and BIAS 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 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
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. 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.
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
3684f
14
LT3684
APPLICATIONS INFORMATION
6.0
VOUT
TO START
BD
5.5
VIN
LT3684
GND
4.7µF
INPUT VOLTAGE (V)
BOOST
VIN
C3
SW
5.0
4.5
4.0
TO RUN
3.5
3.0
(4a) For VOUT > 2.8V
2.5
2.0
0.001
VOUT
D2
BD
BOOST
VIN
VIN
LT3684
VOUT = 3.3V
TA = 25°C
L = 4.7µH
f = 800kHz
0.1
0.01
1
LOAD CURRENT (A)
10
8.0
TO START
C3
7.0
SW
INPUT VOLTAGE (V)
GND
4.7µF
(4b) For 2.5V < VOUT < 2.8V
VOUT
BD
VIN
LT3684
5.0
TO RUN
4.0
3.0
2.0
0.001
BOOST
VIN
6.0
C3
VOUT = 5V
TA = 25°C
L = 4.7µH
f = 800kHz
0.1
0.01
1
LOAD CURRENT (A)
10
3684 F05
4.7µF
GND
SW
Figure 5. The Minimum Input Voltage Depends on
Output Voltage, Load Current and Boost Circuit
3684 FO4
(4c) For VOUT < 2.5V
Figure 4. Three Circuits For Generating The Boost Voltage
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
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.
This occurs, for example, if RUN/SS is asserted after VIN
is applied. 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 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 startup 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
of the resistor so that it can supply 20µA when the RUN/SS
pin reaches 2.3V.
IL
1A/DIV
RUN
15k
VRUN/SS
2V/DIV
RUN/SS
GND
0.22µF
VOUT
2V/DIV
2ms/DIV
3481 F06
Figure 6. To Soft-Start the LT3684, Add a Resisitor
and Capacitor to the RUN/SS Pin
Shorted and Reversed Input Protection
If the inductor is chosen so that it won’t saturate excessively, 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 applications or in battery backup systems where a battery
or some other supply is diode OR-ed with the LT3684’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 LT3684’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
VIN
VIN
BOOST
LT3684
RUN/SS
VOUT
SW
VC
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
LT3684 can pull large currents from the output through
the SW pin and the VIN pin. Figure 7 shows a circuit that
will run only when the input voltage is present and that
protects against a shorted or reversed input.
PCB Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Figure 8 shows
the recommended component placement with trace,
ground plane and via locations. Note that large, switched
currents flow in the LT3684’s VIN and SW pins, the catch
diode (D1) and the input capacitor (C1). The loop formed
by these components should be as small as possible. These
components, along with the inductor and output capacitor,
should be placed on the same side of the circuit board,
and their connections should be made on that layer. Place
a local, unbroken ground plane below these components.
The SW and BOOST nodes should be as small as possible.
Finally, keep the FB and VC nodes small so that the ground
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.
3684f
16
LT3684
APPLICATIONS INFORMATION
L1
C2
VOUT
RRT
CC
RC
R2
R1
D1
C1
RPG
GND
3684 F08
VIAS TO LOCAL GROUND PLANE
VIAS TO RUN/SS
VIAS TO VOUT
VIAS TO PG
VIAS TO VIN
OUTLINE OF LOCAL
GROUND PLANE
Figure 8. A Good PCB Layout Ensures Proper, Low EMI Operation
Hot Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LT3684 circuits. However, these capacitors 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
voltage at the VIN pin of the LT3684 can ring to twice the
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
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.
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 layers will spread the heat dissipated by the LT3684. Place
additional vias can reduce thermal resistance further. With
these steps, the thermal resistance from die (or junction)
to ambient can be reduced to θJA = 35°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 LT3684, it is possible to dissipate enough heat to raise
the junction temperature beyond the absolute maximum of
125°C. When operating at high ambient temperatures, the
3684f
17
LT3684
APPLICATIONS INFORMATION
CLOSING SWITCH
SIMULATES HOT PLUG
IIN
VIN
DANGER
VIN
20V/DIV
RINGING VIN MAY EXCEED
ABSOLUTE MAXIMUM RATING
LT3684
+
4.7µF
LOW
IMPEDANCE
ENERGIZED
24V SUPPLY
IIN
10A/DIV
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
20µs/DIV
(9a)
0.7Ω
LT3684
VIN
20V/DIV
+
0.1µF
4.7µF
IIN
10A/DIV
(9b)
LT3684
+
22µF
35V
AI.EI.
20µs/DIV
VIN
20V/DIV
+
4.7µF
IIN
10A/DIV
(9c)
20µs/DIV
3684 F09
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
temperature approaches 125°C.
Power dissipation within the LT3684 can be estimated by
calculating the total power loss from an efficiency measurement 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.
Other Linear Technology Publications
Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 100
shows how to generate a bipolar output supply using a
buck regulator.
3684f
18
LT3684
TYPICAL APPLICATIONS
5V Step-Down Converter
VOUT
5V
2A
VIN
6.3V TO 34V
BD
VIN
RUN/SS
ON OFF
BOOST
0.47µF
VC
4.7µF
SW
LT3684
D
RT
20k
L
6.8µH
BIAS
PG
590k
60.4k
FB
GND
330pF
22µF
200k
f = 800kHz
3684 TA02
D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB6R8M
3.3V Step-Down Converter
VOUT
3.3V
2A
VIN
4.4V TO 34V
BD
VIN
RUN/SS
ON OFF
BOOST
0.47µF
VC
4.7µF
LT3684
SW
D
RT
16.2k
L
4.7µH
BIAS
PG
324k
60.4k
330pF
f = 800kHz
GND
FB
22µF
200k
3684 TA03
D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB4R7M
3684f
19
LT3684
TYPICAL APPLICATIONS
2.5V Step-Down Converter
VOUT
2.5V
2A
VIN
4V TO 34V
BD
VIN
RUN/SS
ON OFF
D2
BOOST
L
4.7mH
1mF
VC
4.7mF
LT3684
SW
D1
RT
22.1k
BIAS
PG
196k
84.5k
GND
FB
220pF
47mF
200k
f = 600kHz
3684 TA04
D1: DIODES INC. DFLS240L
D2: MBR0540
L: TAIYO YUDEN NP06DZB4R7M
5V, 2MHz Step-Down Converter
VIN
8.6V TO 22V
TRANSIENT TO 36V
VOUT
5V
2A
BD
VIN
RUN/SS
ON OFF
BOOST
0.47mF
VC
2.2mF
LT3684
SW
D
RT
20k
L
2.2mH
BIAS
PG
590k
16.9k
330pF
f = 2MHz
GND
FB
10mF
200k
3684 TA05
D: DIODES INC. DFLS240L
L: SUMIDA CDRH4D22/HP-2R2
3684f
20
LT3684
TYPICAL APPLICATIONS
12V Step-Down Converter
VOUT
12V
2A
VIN
15V TO 34V
BD
VIN
RUN/SS
ON OFF
BOOST
L
10µH
0.47µF
VC
10µF
SW
LT3684
D
RT
30k
BIAS
PG
845k
60.4k
FB
GND
330pF
22µF
100k
f = 800kHz
3684 TA06
D: DIODES INC. DFLS240L
L: NEC/TOKIN PLC-0755-100
1.8V Step-Down Converter
VOUT
1.8V
2A
VIN
3.5V TO 27V
BD
VIN
RUN/SS
ON OFF
BOOST
L
3.3µH
0.47µF
VC
4.7µF
LT3684
SW
D
RT
15.4k
BIAS
PG
84.5k
105k
330pF
f = 500kHz
GND
FB
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
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
PACKAGE
OUTLINE
0.25 ± 0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 ±0.10
(4 SIDES)
R = 0.115
TYP
6
0.38 ± 0.10
10
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD) DFN 1103
5
0.200 REF
1
0.75 ±0.05
0.00 – 0.05
0.25 ± 0.05
0.50 BSC
2.38 ±0.10
(2 SIDES)
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
2.794 ± 0.102
(.110 ± .004)
5.23
(.206)
MIN
0.889 ± 0.127
(.035 ± .005)
1
2.06 ± 0.102
(.081 ± .004)
1.83 ± 0.102
(.072 ± .004)
2.083 ± 0.102 3.20 – 3.45
(.082 ± .004) (.126 – .136)
10
0.50
0.305 ± 0.038
(.0197)
(.0120 ± .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
0.254
(.010)
DETAIL “A”
0° – 6° TYP
1 2 3 4 5
GAUGE PLANE
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
0.18
(.007)
0.497 ± 0.076
(.0196 ± .003)
REF
10 9 8 7 6
SEATING
PLANE
1.10
(.043)
MAX
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
NOTE:
BSC
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
0.127 ± 0.076
(.005 ± .003)
MSOP (MSE) 0603
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 representation 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
VOUT
1.265V
2A
VIN
3.6V TO 27V
BD
VIN
RUN/SS
ON OFF
BOOST
0.47mF
VC
4.7mF
LT3648
SW
D
RT
13k
BIAS
PG
105k
L
3.3mH
GND
FB
47mF
330pF
f = 500kHz
3648 TA08
D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB3R3M
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1933
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LT1936
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DC/DC Converter
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LT3493
36V, 1.2A (IOUT), 750kHz High Efficiency Step-Down
DC/DC Converter
VIN: 3.6V to 40V, VOUT(MIN) = 0.8V, IQ = 1.9mA, ISD < 1µA, DFN Package
LT1976/LT1977
60V, 1.2A (IOUT), 200kHz/500kHz, High Efficiency StepDown DC/DC Converter with Burst Mode Operation
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Package
LT1767
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LT1940
Dual 25V, 1.4A (IOUT), 1.1MHz, High Efficiency Step-Down VIN: 3.6V to 25V, VOUT(MIN) = 1.20V, IQ = 3.8mA, ISD < 30µA, TSSOP16E
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Package
LT1766
60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down
DC/DC Converter
VIN: 5.5V to 60V, VOUT(MIN) = 1.20V, IQ = 2.5mA, ISD < 25µA, TSSOP16E
Package
LT3434/LT3435
60V, 2.4A (IOUT), 200/500kHz, High Efficiency Step-Down
DC/DC Converter with Burst Mode Operation
VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100µA, ISD < 1µA, TSSOP16E
Package
LT3481
36V, 2A (IOUT), Micropower 2.8MHz, High Efficiency
Step-Down DC/DC Converter
VIN: 3.6V to 36V, VOUT(MIN) = 1.265V, IQ = 5µA, ISD < 1µA, 3mm × 3mm
DFN and MS10E Packages
3684f
24 Linear Technology Corporation
LT 0207 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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© LINEAR TECHNOLOGY CORPORATION 2007