FEATURES
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LT3507
Triple Monolithic Step-Down
Regulator with LDO
DESCRIPTION
The LT
®
3507 is a triple, current mode, DC/DC converter
with internal power switches and a low dropout regulator.
The switching converters are step-down converters capable
of generating one 2.4A output and two 1.5A outputs. All
three converters are synchronized to a single oscillator.
The 2.4A output runs with opposite phase to the other two
converters, reducing input ripple current. Each regulator
has independent shutdown and soft-start circuits, and
generates a power good signal when its output is in regu-
lation, easing power supply sequencing and interfacing
with microcontrollers and DSPs.
The switching frequency is set with a single resistor yielding
a range of 250kHz to 2.5MHz. The high switching frequency
allows the use of small inductors and capacitors resulting
in a very small triple output supply. The constant switching
frequency, combined with low impedance ceramic capaci-
tors, results in low, predictable output ripple. With its wide
input voltage range of 4V to 36V, the LT3507 regulates a
broad array of power sources including 5V logic rails,
unregulated wall transformers, lead acid batteries and
distributed power supplies.
Wide Input Range: 4V to 36V
One 2.4A and Two 1.5A Output Switching
Regulators with Internal Power Switches
Low Dropout Linear Regulator with External
Transistor
Antiphase Switching Reduces Ripple
Independent Run, Tracking/Soft-Start, and Power
Good Indicators Ease Supply Sequencing
Uses Small Inductors and Ceramic Capacitors
Adjustable, 250kHz to 2.5MHz Switching Frequency,
Synchronizable Over the Full Range
User Programmable Overvoltage and Undervoltage
Lockouts
Thermally Enhanced, 38-Lead 5mm
×
7mm QFN
Package
DSL and Cable Modems
Distributed Power Regulation
DSP Power
Automotive
APPLICATIONS
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L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
5V, 3.3V, 2.5V and 1.8V Step-Down Regulator
V
IN
6V TO 36V
22μF
V
IN1
BOOST1
V
OUT1
1.8V
2.4A
4.7μH
0.22μF
SW1
18.7k
100μF
15k
18.7k
680pF
V
C1
0.22μF BOOST3
SW3
53.6k
22μF
10.2k
24.3k
680pF
V
C3
R
T
/SYNC
DRIVE
24.3k
FB4
GND
11.5k
2.2μF
107k
V
OUT4
2.5V
0.2A
FB3
BIAS
LT3507
FB2
1000pF
V
C2
11.5k
16.2k
35.7k
10μH
FB1
SW2
V
OUT2
3.3V
1.3A
22μF
0.22μF
V
IN2
V
IN3
BOOST2
Start-Up Waveforms—Coincident Tracking
V
OUT3
V
OUT2
V
OUT4
V
OUT1
1V/DIV
V
OUT2
V
OUT3
5V
1.5A
15μH
1ms/DIV
3507 TA01b
f
SW
= 450kHz
3507 TA01a
3507f
1
LT3507
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
BOOST3
31 V
IN2
30 V
IN2
29 SW2
28 SW2
27 BOOST2
39
26 TRK/SS4
25 FB4
24 DRIVE
23 V
C2
22 FB2
21 TRK/SS2
20 FB3
13 14 15 16 17 18 19
R
T
/SYNC
RUN1
RUN2
RUN3
BIAS
TRK/SS3
V
C3
TOP VIEW
SW1
SW1
SW3
SW3
V
IN3
V
IN3
V
IN
Pins...................................................... –0.3V to 36V
BOOST Pins ..............................................................55V
BOOST Above SW .....................................................25V
PGOOD Pins..............................................................36V
BIAS Pin....................................................................16V
TRK/SS, V
C
, FB, R
T
/SYNC Pins ...................................6V
RUN, OVLO, UVLO Pins ........................................... V
IN1
DRIVE Pin ...................................................................5V
Operating Junction Temperature Range (Notes 2, 5)
LT3507E, LT3507I .............................. –40°C to 125°C
LT3507H ............................................ –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
38 37 36 35 34 33 32
BOOST1 1
V
IN1
2
V
IN1
3
V
INSW
4
OVLO 5
UVLO 6
V
C1
7
TRK/SS1 8
FB1 9
PGOOD1 10
PGOOD2 11
PGOOD3 12
UHF PACKAGE
38-LEAD (5mm
×
7mm) PLASTIC QFN
θ
JA
= 34°C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3507EUHF#PBF
LT3507IUHF#PBF
LT3507HUHF#PBF
TAPE AND REEL
LT3507EUHF#TRPBF
LT3507IUHF#TRPBF
LT3507HUHF#TRPBF
PART MARKING*
3507
3507
3507
PACKAGE DESCRIPTION
38-Lead (5mm
×
7mm) Plastic QFN
38-Lead (5mm
×
7mm) Plastic QFN
38-Lead (5mm
×
7mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
*For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN1
, V
IN2
, V
IN3
= 12V, V
BOOST1
, V
BOOST2
, V
BOOST3
= 17V, unless
otherwise noted. (Note 2)
PARAMETER
Minimum Operating Voltage
Input Quiescent Current
Bias Quiescent Current
Shutdown Current
Reference Voltage Line Regulation
CONDITIONS
Internal UVLO on V
IN1
Not Switching, V
BIAS
= 3.3V
Not Switching, V
BIAS
= 3.3V
V
RUN1,2,3
= 0V
5V < V
IN1
< 36V
0.01
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ELECTRICAL CHARACTERISTICS
MIN
TYP
3.8
2
5
MAX
4
3.5
7.5
1
UNITS
V
mA
mA
μA
%/V
3507f
2
LT3507
ELECTRICAL CHARACTERISTICS
PARAMETER
V
C
Source Current
V
C
Sink Current
V
C
Clamp Voltage
Switching Frequency
Switching Phase
Foldback Frequency
Frequency Shift Threshold on FB
RUN Threshold
PGOOD Output Voltage Low
PGOOD Pin Leakage
PGOOD Threshold Offset
Feedback Pin Voltage
Feedback Pin Bias Current
Error Amplifier Transconductance
Error Amplifier Voltage Gain
V
C
Switching Threshold
Switch Leakage Current
Minimum Boost Voltage Above Switch (Note 4)
Converter 1
V
C1
to Switch Current Gain
Switch 1 Current Limit (Note 3)
Switch 1 V
CESAT
BOOST1 Operating Current
Converter 2
V
C2
to Switch Current Gain
Switch 2 Current Limit (Note 3)
Switch 2 V
CESAT
BOOST2 Operating Current
Converter 3
V
C3
to Switch Current Gain
Switch 3 Current Limit (Note 3)
Switch 3 V
CESAT
BOOST3 Operating Current
LDO Regulator
Feedback Pin Voltage
Feedback Pin Bias Current
Error Amplifier Voltage Gain
Line Regulation
V
IN
from 5V to 36V
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN1
, V
IN2
, V
IN3
= 12V, V
BOOST1
, V
BOOST2
, V
BOOST3
= 17V, unless
otherwise noted. (Note 2)
CONDITIONS
V
C
= 0.6V
V
C
= 0.6V
R
T
= 40.2k
SW1 to SW2,3, R
T
= 40.2k
V
FB
= 0V, R
T
= 40.2k
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MIN
TYP
100
100
1.7
MAX
UNITS
μA
μA
V
0.9
180
120
0.4
1
1.1
MHz
Deg
kHz
V
1.5
0.4
400
105
812
–500
V
V
nA
mV
mV
nA
μS
V/V
V
I
PGOOD
= 200μA
V
PGOOD
= 2V
V
FB
Rising
l
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0.2
10
58
788
80
800
–50
330
500
0.9
0.01
1.8
5
10
2.5
μA
V
A/V
Duty Cycle = 15%
I
SW1
= 2A
I
SW1
= 2A
l
3
4.3
400
40
3.6
6
600
60
A
mV
mA
A/V
Duty Cycle = 15%
I
SW2
= 1.5A
I
SW2
= 1.5A
l
2
2.9
350
40
3.6
4
500
60
A
mV
mA
A/V
Duty Cycle = 15%
I
SW3
= 1.5A
I
SW3
= 1.5A
l
2
2.9
350
40
4
500
60
812
–500
A
mV
mA
mV
nA
V/V
%/V
3507f
788
800
–150
1100
0.05
3
LT3507
ELECTRICAL CHARACTERISTICS
PARAMETER
Load Regulation
DRIVE Output Current Limit
Dropout Voltage, V
IN1
to DRIVE
Dropout Voltage, BIAS to DRIVE
Over/Undervoltage Lockout
Undervoltage Lockout Threshold
Overvoltage Lockout Threhold
Undervoltage Lockout Hysteresis Current
Overvoltage Lockout Hysteresis Current
Input Bias Current (OVLO and UVLO)
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 LT3507E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT3507I is guaranteed to meet performance specifications from –40°C
to 125°C junction temperature. The LT3507H is guaranteed over the full
–40°C to 150°C operating junction temperature range. High junction
temperatures degrade operating lifetimes. Operating lifetime is derated at
junction temperatures greater than 125°C.
V(UVLO) < 1.2V
V(OVLO) > 1.2V
1.15
1.15
7
–7
1.20
1.20
10
–10
–100
1.25
1.25
13
–13
–200
V
V
μA
μA
nA
I
DRIVE
= 10mA
I
DRIVE
= 10mA
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN1
, V
IN2
, V
IN3
= 12V, V
BOOST1
, V
BOOST2
, V
BOOST3
= 17V, unless
otherwise noted (Note 2)
CONDITIONS
I
DRIVE
from 0.1mA to 10mA
l
MIN
10
TYP
0.005
15
1.7
0.5
MAX
22.5
2.0
0.8
UNITS
%/mA
mA
V
V
Note 3:
Current limit is guaranteed by design and/or correlation to static
test. Slope compensation reduces current limit at higher duty cycles.
Note 4:
This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
Note 5:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions.
Junction temperature will exceed the maximum operating range when
overtemperature protection is active. Continuous operation above the
specified maximum operating junction temperature may impair device
reliability.
3507f
4
LT3507
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current,
Channel 1, V
OUT
= 1.8V
90
T
A
= 25°C
f
SW
= 450kHz
V
IN
= 6V
EFFICIENCY (%)
V
IN
= 12V
70
V
IN
= 36V
60
100
90
80
70
60
50
40
0
0.5
1
1.5
I
OUT
(A)
2
2.5
3507 G01
Efficiency vs Load Current,
Channels 2 and 3, V
OUT
= 3.3V
T
A
= 25°C
f
SW
= 450kHz
V
IN
= 6V
V
IN
= 12V
V
IN
= 36V
V
SW
(V)
0.6
0.5
0.4
0.3
0.2
0.1
0
Switch V
CESAT
vs Switch Current,
Channels 1, 2 and 3
T
A
= 25°C
80
EFFICIENCY (%)
CHANNELS 2 & 3
CHANNEL 1
50
40
0
0.3
0.9
0.6
I
OUT
(A)
1.2
1.5
3507 G02
0
0.5
1
1.5
I
SW
(A)
2
2.5
3
3507 G03
BOOST Pin Current vs Switch
Current, Channels 1, 2 and 3
100
90
80
70
I
BOOST
(mA)
V
FB
(mV)
60
50
40
30
20
10
0
0
0.5
1
1.5
I
SW
(A)
2
2.5
3
3507 G04
V
FB
vs Temperature
805
804
803
2.5
Frequency vs R
T
T
A
= 25°C
T
A
= 25°C
CHANNELS 2 & 3
801
800
799
798
797
796
795
–50 –30 –10 30 50 70 90 110 130 150
TEMPERATURE (°C)
3507 G05
CHANNEL 1
FREQUENCY (MHz)
0.25
10
R
T
(kΩ)
3507 G06
802
100
Frequency vs Temperature
0.5
1200
1000
FRERQUENCY (kHz)
800
Frequency vs V
FB
(Foldback)
R
T
= 40.2k
T
A
= 25°C
1.30
I
TRK/SS
vs Temperature
FREQUENCY DEVIATION (%)
0.0
1.28
–0.5
I
TRK/SS
(μA)
0
0.2
0.4
0.6
V
FB
(V)
0.8
1
3507 G08
1.26
600
400
200
0
–1.0
1.24
–1.5
1.22
–2.0
–50 –30 –10 30 50 70 90 110 130 150
TEMPERATURE (°C)
3507 G07
1.20
–50 –30 –10 30 50 70 90 110 130 150
TEMPERATURE (°C)
3507 G09
3507f
5
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