LT3489
2MHz Boost DC/DC
Converter with 2.5A Switch
and Soft-Start
DESCRIPTIO
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FEATURES
■
■
■
■
■
■
■
■
■
The LT®3489 is a fixed frequency step-up DC/DC converter
containing an internal 2.5A, 40V switch. The LT3489 is
ideal for large TFT-LCD panel power supplies. The LT3489
switches at 2MHz, allowing the use of tiny, low profile
inductors and low value ceramic capacitors. Loop compensation can be either internal or external, giving the
user flexibility in setting loop compensation and allowing optimized transient response with low ESR ceramic
output capacitors. Soft-start is controlled with an external
capacitor, which determines the input current ramp rate
during start-up.
2.5A, 0.12Ω, 40V Internal Switch
2MHz Switching Frequency
Integrated Soft-Start Function
VIN Range: 2.6V to 16V
Adjustable Output from VIN to 40V
Low VCESAT Switch: 110mV at 1A (Typical)
8V at 610mA from a 3.3V Input
Internal or External Loop Compensation
Small 8-Lead MS8E
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APPLICATIO S
■
■
■
■
The 8-lead MS8E package and high switching frequency ensure a low profile overall solution less than 1.1mm high.
TFT-LCD Bias Supplies
GPS Receivers
DSL Modems
Local Power Supply
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
Low Profile, Triple Output TFT Supply (8V, –8V, 23V)
Efficiency
90
VON
23V
10mA
85
0.1µF
2.2µH
VIN
3.3V
VIN
OFF ON
+
SW
LT3489
FB
COMP
VC
20µF
2µF
GND
5.23k
100nF
75
70
65
60
28.7k
SHDN
SS
4.7µF
AVDD
8V
610mA
EFFICIENCY (%)
80
0.1µF
0.1µF
55 V LOAD = 10mA
ON
VOFF LOAD = 20mA
50
100 200 300 400 500 600
0
AVDD LOAD CURRENT (mA)
700
3489 TA01b
37.4k
220pF
0.1µF
2µF
3489 TA01
VOFF
–8V
20mA
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LT3489
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
VIN Voltage ................................................................16V
SW Voltage ................................................ –0.4V to 40V
FB, VC, COMP, SS Voltages .........................................6V
SHDN Voltage ...........................................................16V
Current Into FB Pin ................................................±1mA
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range (Note 2) ... –40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
TOP VIEW
VC
FB
SHDN
GND
8
7
6
5
1
2
3
4
SS
COMP
VIN
SW
MS8E PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 40°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 9) IS GND (MUST BE SOLDERED TO PCB)
ORDER PART NUMBER
MS8E PART MARKING
LT3489EMS8E
LTBYF
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.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, VSHDN = VIN unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
MIN
Minimum Operating Voltage
TYP
MAX
2.4
2.6
V
16
V
1.235
1.26
1.26
V
V
100
250
nA
Maximum Operating Voltage
Feedback Voltage
●
FB Pin Bias Current
VFB = 1.25V (Note 3)
Error Amp Transconductance
ΔI = 10μA
1.22
1.21
●
100
Error Amp Voltage Gain
UNITS
μmhos
80
V/V
Quiescent Current
VSHDN = 2.5V, Not Switching
2
4
mA
Quiescent Current in Shutdown
VSHDN = 0V, VIN = 3V
0
1
μA
Reference Line Regulation
2.6V ≤ VIN ≤ 16V
0.01
0.05
%
2
2.2
MHz
●
Switching Frequency
Maximum Switch Duty Cycle
1.8
●
85
90
●
2.5
3.5
Switch Current Limit
(Note 4)
Switch VCESAT
ISW = 2A
0.23
Switch Leakage Current
VSW = 5V
0.01
SHDN Pin Current
VSHDN = 5V
VSHDN = 1.4V
VSHDN = 0V
100
20
2
SHDN Pin Threshold
Soft-Start Charging Current
VSS = 0.5V
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 LT3489E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the 40°C to 85°C operating
%
5
A
V
1
μA
μA
μA
μA
0.3
1.5
2
V
5
10
20
μA
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Current flows out of the FB pin.
Note 4: Current limit guaranteed by design and/or correlation to static test.
Current limit is independent of duty cycle and is guaranteed by design.
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LT3489
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TYPICAL PERFOR A CE CHARACTERISTICS
Feedback Pin Voltage
Oscillator Frequency
1.27
1.25
1.24
1.23
1.22
3.5
2.2
3.0
CURRENT LIMIT (A)
OSCILLATOR FREQUENCY (MHz)
FEEDBACK VOLTAGE (V)
Current Limit
4.0
2.4
1.26
2.0
1.8
2.5
2.0
1.5
1.0
0.5
1.21
–50 –25
50
25
75
0
TEMPERATURE (˚C)
100
1.6
–50
125
–25
75
0
25
50
TEMPERATURE (°C)
Switch VCE(SAT) Voltage
500
3.5
QUIESCENT CURRENT (mA)
4.0
400
300
200
–50°C
25°C
125°C
0
1
0.5
1.0
1.5
2.0
SWITCH CURRENT (A)
125
0
–50
2.5
3489 G04
–25
0
50
25
TEMPERATURE (°C)
75
100
3489 03
Switching Waveform for
the Cover Page Circuit
Quiescent Current
600
100
100
3489 G02
3489 G01
VCE(SAT) (mV)
TA = 25°C unless otherwise noted.
VOUT
100mV/DIV
AC COUPLED
3.0
VSW
10V/DIV
2.5
IL
1A/DIV
2.0
1.5
1.0
–50 –25
50
25
75
0
TEMPERATURE (˚C)
100
125
VIN = 3.3V
200ns/DIV
AVDD = 8V
ILOAD, AVDD = 400mA
VON = 23V, 10mA
VOFF = –8V, 20mA
3489 G06
3489 G05
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LT3489
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PI FU CTIO S
VC (Pin 1): Error Amplifier Output Pin. Tie external compensation network to this pin, or use the internal compensation
network by shorting the VC pin to the COMP pin.
VIN (Pin 6): Input Supply Pin. Must be locally bypassed.
COMP (Pin 7): Internal Compensation Pin. Provides an
internal compensation network. Tie directly to the VC pin
for internal compensation. Tie to GND if not in use.
FB (Pin 2): Feedback Pin. Reference voltage is 1.235V.
Connect resistive divider tap here. Minimize the trace area at
FB. Set VOUT according to VOUT = 1.235 • (1 + R1/R2).
SS (Pin 8): Soft-Start Pin. Place a soft-start capacitor here.
Upon start-up, 10μA of current charges the capacitor to
1.8V. Use a larger capacitor for slower start-up. Leave
floating if not in use.
SHDN (Pin 3): Shutdown Pin. Tie to 2V or more to enable
device. Ground to shut down. Do not float this pin.
GND (Pin 4): Ground. Tie directly to local ground plane.
Exposed Pad (Pin 9): Ground. Must be soldered to
PCB.
SW (Pin 5): Switch Pin. This is the collector of the internal
NPN power switch. Minimize the metal trace area connected
to this pin to minimize EMI.
W
BLOCK DIAGRA
VC
COMP
1
7
100k
125pF
SW
5
–
COMPARATOR
DRIVER
+
A2
R
Q
Q1
S
VIN
6
1.235V
REFERENCE
+
+
–
SS 8
VOUT
+
A1
Σ
–
RAMP
GENERATOR
R1 (EXTERNAL)
FB
R2 (EXTERNAL)
SHUTDOWN
0.01Ω
2MHz
OSCILLATOR
3
2
SHDN
FB
4
9
GND
GND
3489 F01
Figure 1. Block Diagram
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LT3489
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OPERATIO
The LT3489 uses a constant frequency, current mode control scheme to provide excellent line and load regulation.
Please refer to Figure 1 for the following description of the
part’s operation. At the start of the oscillator cycle, the SR
latch is set, turning on the power switch, Q1. The switch
current flows through the internal current sense resistor
generating a voltage. This voltage is added to a stabilizing
ramp and the resulting sum is fed into the positive terminal
of the PWM comparator, A2. When this voltage exceeds
the level at the negative input of A2, the SR latch is reset,
turning off the power switch. The level at the negative
input of A2 (VC pin) is set by the error amplifier (gm) and
is simply an amplified version of the difference between
the feedback voltage and the reference voltage of 1.235V.
In this manner, the error amplifier sets the correct peak
current level to keep the output in regulation.
A soft-start function is provided to enable a clean start-up
for the LT3489. When the part is brought out of shutdown, 10µA of current is sourced out of the SS pin. By
connecting an external capacitor to the SS pin, the rate
of voltage rise on the pin can be set. Typical values for
the soft-start capacitor range from 10nF to 200nF. The SS
pin indirectly limits the rate of rise on the VC pin, which
in turn limits the peak switch current. Current limit is
not shown in Figure 1. The switch current is constantly
monitored and not allowed to exceed the nominal value
of 2.5A. If the switch current reaches 2.5A, the SR latch
is reset regardless of the output of comparator A2. This
current limit helps protect the power switch as well as the
external components connected to the LT3489.
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LT3489
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APPLICATIO S I FOR ATIO
Inductor Selection
Capacitor Selection
Several inductors that work well with the LT3489 are listed
in Table 1. This table is not exclusive; there are many other
manufacturers and inductors that can be used. Consult
each manufacturer for more detailed information and for
their entire selection of related parts, as many different
sizes and shapes are available. Ferrite core inductors
should be used to obtain the best efficiency, as core
losses at 2MHz are much lower for ferrite cores than for
the cheaper powdered-iron ones. Choose an inductor that
can handle at least 2.5A without saturating, and ensure
that the inductor has a low DCR (copper wire resistance)
to minimize I2R power losses. A 2.2μH to 5μH inductor
will be the best choice for most LT3489 designs. Note
that in some applications, the current handling requirements of the inductor can be lower, such as in the SEPIC
topology where each inductor only carries one-half of the
total switch current. The inductors shown in Table 1 were
chosen for small size. For better efficiency, use similar
valued inductors with a larger volume.
Low ESR (equivalent series resistance) capacitors should
be used at the output to minimize the output ripple voltage.
Multilayer ceramic capacitors are an excellent choice, as
they have an extremely low ESR and are available in very
small packages. X5R or X7R dielectrics are preferred, as
these materials retain the capacitance over wide voltage
and temperature ranges. A 4.7µF to 20µF output capacitor
is sufficient for most applications, but systems with very
low output currents may need only a 1µF or 2.2µF output
capacitor. Solid tantalum or OS-CON capacitors can be
used, but they will occupy more board area than a ceramic
and will have a higher ESR. Always use a capacitor with a
sufficient voltage rating.
Ceramic capacitors also make a good choice for the input
decoupling capacitor, which should be placed as close as
possible to the LT3489. A 2.2μF to 4.7μF input capacitor
is sufficient for most applications. Table 2 shows a list
of several ceramic capacitor manufacturers. Consult the
manufacturers for detailed information on their entire
selection of ceramic parts.
Table 1. Recommended Inductors
PART
SIZE
L × W × H (mm)
L (μH)
TYPICAL DCR (mΩ)
SD25-2R2
SD25-3R3
SD25-4R7
2.2
3.3
4.7
31
38
47
5.45 × 5.45 × 2.7
A916CY-2R7M
A916CY-3R3M
A916CY-4R7M
2.7
3.3
4.7
18.3
21.4
26.3
6 × 6 × 3.5
LQH55DN2R2M03
LQH55DN3R3M03
LQH55DN4R7M03
2.2
3.3
4.7
29
36
41
5.7 × 5 × 4.7
VENDOR
CooperBussmann
(888) 414-2645
www.cooperet.com
Toko
www.toko.com
Murata
(770) 436-1300
www.murata.com
Table 2. Ceramic Capacitor Manufacturers
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
AVX
(843) 448-9411
www.avxcorp.com
Murata
(770) 436-1300
www.murata.com
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LT3489
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APPLICATIO S I FOR ATIO
Diode Selection
Setting Output Voltage
Schottky diodes, with their low forward voltage drop and
fast switching speed, are ideal for LT3489 applications.
Table 3 lists several Schottky diodes that work well with the
LT3489. The diode’s average current rating must exceed
the average output current. The diode’s maximum reverse
voltage must exceed the output voltage. The diode conducts
current only when the power switch is turned off (typically
less than 50% duty cycle), so a 3A diode is sufficient for
most designs. The companies below also offer Schottky
diodes with high voltage and current ratings.
To set the output voltage, select the values of R1 and R2
(see Figure 1) according to the following equation:
Table 3. Suggested Diodes
MANUFACTURER MAXIMUM
PART NUMBER
CURRENT (A)
MAXIMUM
REVERSE
VOLTAGE (V)
MANUFACTURER
UPS340
UPS315
3
3
40
15
Microsemi
www.microsemi.com
B220
B230
B240
B320
B330
B340
SBM340
2
2
2
3
3
3
3
20
30
40
20
30
40
40
Diodes, Inc
www.diodes.com
⎛ V
⎞
R1= R2 • ⎜ OUT − 1⎟
⎝ 1.235V ⎠
A good range for R2 is from 5k to 30k.
Board Layout
The high speed operation of the LT3489 demands careful attention to board layout. For high-current switching
regulators like the LT3489, the board layout must have
good thermal performance. Vias located underneath the
part should be connected to an internal ground plane to
improve heat transfer from the LT3489 to the PCB board.
You will not get advertised performance with careless layout. Thermal and noise consideration must be taken into
account. Figure 2 shows the recommended component
placement for a boost converter.
GROUND PLANE
CSS
C1
CC
Frequency Compensation
To compensate the feedback loop of the LT3489, a series
resistor-capacitor network should be connected from the
COMP pin to GND. For most applications, a capacitor in
the range of 220pF to 680pF will suffice. A good starting
value for the compensation capacitor, CC, is 470pF. The
compensation resistor, RC, is usually in the range of 20k
to 100k. A thorough analysis of the switching regulator
control loop is not within the scope of this data sheet and
will not be presented here, but values of 20k and 680pF
will be a good choice for many designs.
+
VIN
RC
1
8
R1
2
R2
SHUTDOWN
7
LT3489
3
6
4
5
L1
MULTIPLE
VIAs
GND
C2
VOUT
3489 F02
Figure 2. Recommended Component Placement for Boost Converter.
Note Direct High Current Paths Using Wide PC Traces. Minimize
Trace Area at Pin 1 (VC) and Pin 2 (FB). Use Multiple Vias to Tie
Pin 4 Copper to Ground Plane. Use Vias at One Location Only to
Avoid Introducing Switching Currents Into the Ground Plane
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LT3489
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TYPICAL APPLICATIO S
8V Output Boost Converter
L1
2.2µH
VIN
3.3V TO 5V
OFF ON
3
8
+
C1
4.7µF
7
6
VIN
D1
5
SW
R1
28.7k
SHDN
SS
LT3489
COMP
VC
1
RC
35.7k
CC
330pF
CSS
100nF
FB
VOUT
650mA, VIN = 3.3V
1.1A, VIN = 5V
2
C2
20µF
GND
4
R2
5.23k
C1: AVX 08056D475KAT
C2: 2 × 10µF, TAIYO YUDEN LMK3168BJ106ML
D1: DIODES INC. DFLS220L
L1: COOPER BUSSMANN SD25-2R2
*EXPOSED PAD MUST ALSO BE GROUNDED
3489 TA02
Efficiency
Transient Response
90
VOUT
100mV/DIV
AC COUPLED
85
EFFICIENCY (%)
80
IL1
1A/DIV
75
70
400mA
65
IOUT
200mA
60
55
50
VIN = 3.3V
VIN = 5V
VIN = 3.3V
50µs/DIV
3489 G10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
LOAD CURRENT (A)
3489 TA09
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LT3489
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TYPICAL APPLICATIO S
12V Output Boost Converter
L1
3.3µH
VIN
3.3V TO 5V
OFF ON
C1
4.7µF
3
1
RC
16.5k
6
VIN
CSS
100nF
5
SW
LT3489
FB
VC
8
2
COMP GND
7
VOUT
12V
625mA, VIN = 5V
410mA, VIN = 3.3V
R1
84.5k
SHDN
SS
CC
680pF
D1
4
C2
10µF
R2
9.76k
C1: Taiyo Yuden JMK212BJ475MG, 4.7µF, 6.3V
C2: Taiyo Yuden GMK316BJ106ML, 10µF, 35V
D1: Diodes, Inc. DFLS220
L1: Toko A916CY-3R3M (Type D63CB)
3489 TA03
Efficiency
Transient Response
90
VOUT
500mV/DIV
AC COUPLED
85
EFFICIENCY (%)
80
75
IL1
1A/DIV
70
65
60
300mA
IOUT
100mA
55
50
VIN = 3.3V
VIN = 5V
45
40
0
0.1
0.2 0.3 0.4
0.5
LOAD CURRENT (A)
0.6
VIN = 3.3V
50µs/DIV
3489 TA06
0.7
3489 TA05
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LT3489
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TYPICAL APPLICATIO
D2
C6
0.1µF
C5
0.1µF
L1
2.2µH
VIN
3.3V
OFF ON
3
8
+
C1
4.7µF
7
6
VIN
LT3489
FB
C7
0.1µF
AVDD
8V
610mA
R2
28.7k
2
C2
20µF
GND*
1
CSS
100nF
VON
23V
10mA
10mA
5
SW
COMP
VC
D5
D1
SHDN
SS
D4
D3
4
C4
2µF
R3
5.23k
37.4k
220pF
C1 TO C8: X5R OR X7R
C1: AVX 08056D475KAT
C2: 2 × 10µF, TAIYO YUDEN LMK316BJ106ML
C3: 2 × 10µF, 10V
C4: 2 × 1µF, AVX08053D105KAT
C5, C6, C7: 0.1µF, 10V
C8: 0.1µF, 16V
D1: DIODES INC. DFLS220L
D2 TO D7: ZETEX BAT54S OR EQUIVALENT
L1: COOPER BUSSMANN SD25-2R2
* EXPOSED PAD MUST ALSO BE GROUNDED
Effciency
C8
0.1µF
D7
C3
2µF
D6
3489 TA04
Transient Response
VOFF
–8V
20mA
Start-Up Waveforms
90
AVDD
100mV/DIV
AC COUPLED
85
AVDD
5V/DIV
VON
20V/DIV
EFFICIENCY (%)
80
75
IL1
1A/DIV
VOFF
5V/DIV
70
65
400mA
ILOAD
200mA
60
55 V LOAD = 10mA
ON
VOFF LOAD = 20mA
50
100 200 300 400 500 600
0
AVDD LOAD CURRENT (mA)
IIN
0.5A/DIV
5µs/DIV
3489 TA07
5ms/DIV
3489 TA08
700
3489 TA01b
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LT3489
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PACKAGE DESCRIPTIO
MS8E Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1662)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.06 ± 0.102
(.081 ± .004)
1
5.23
(.206)
MIN
1.83 ± 0.102
(.072 ± .004)
0.889 ± 0.127
(.035 ± .005)
2.794 ± 0.102
(.110 ± .004)
2.083 ± 0.102 3.20 – 3.45
(.082 ± .004) (.126 – .136)
8
0.42 ± 0.038
(.0165 ± .0015)
TYP
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.65
(.0256)
BSC
8
7 6 5
0.52
(.0205)
REF
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
DETAIL “A”
0° – 6° TYP
GAUGE PLANE
1
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
2 3
4
1.10
(.043)
MAX
0.86
(.034)
REF
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.65
(.0256)
BSC
0.127 ± 0.076
(.005 ± .003)
MSOP (MS8E) 0603
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
3489f
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.
11
LT3489
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1613
550mA (ISW), 1.4MHz, High Efficiency Step-Up
DC/DC Converter
VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD =
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