FeaTures
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LT3504
Quad 40V/1A Step-Down
Switching Regulator with
100% Duty Cycle Operation
DescripTion
The
LT
®
3504
consists of four 1A output current buck
regulators. The LT3504 has a wide operating input range
of 3.2V to 40V. An on-chip boost regulator allows each
channel to operate up to 100% duty cycle and eliminates
the need for four external charge pump circuits. The LT3504
is designed to minimize external component count and
results in a simple and small application circuit.
The LT3504 operates robustly in fault conditions. Cycle-
by-cycle peak current limit and catch diode current limit
sensing protect the part during overload conditions. Ther-
mal shutdown protects the power switches at elevated
temperatures. Soft-start helps keep the peak inductor
current under control during startup.
The LT3504 also features output voltage tracking and
sequencing, programmable frequency, programmable
undervoltage lockout, and a power good pin to indicate
when all outputs are in regulation.
L,
LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
Wide Input Range: 3.2V to 40V
Four 1A Outputs
100% Duty Cycle Operation
Resistor-Programmed Constant Frequency
Short-Circuit Robust
Wide SYNC Range: 350kHz to 2.2MHz
Anti-Phase Switching Reduces Ripple
800mV FB Voltage
Independent Run/Soft-Start Pins
Shutdown with UVLO
Internal Compensation
Thermal Shutdown
Tiny 28-Lead (4mm × 5mm) Thermally Enhanced
QFN Package
applicaTions
n
n
n
n
Automotive Battery Regulation
Industrial Control Supplies
Wall Transformer Regulation
Distributed Supply Regulation
Typical applicaTion
Quad Buck Regulator in 4 × 5 QFN
10µH
SW4
DA4
FB4
LT3504
10µH
SW5
EN/UVLO
V
IN
V
IN
V
IN
V
IN
RUN/SS1
RUN/SS2
RUN/SS3
RUN/SS4
50nF
RT/SYNC
1µF
18.2k
GND
SW1
DA1
FB1
24.9k
20k
3504 TA01a
5V/1A
52.3k
10k
6.8µH
10µF
SKY
1µF
V
IN
5.4V to 20V
TRANSIENT TO 40V
LT3504 Start-Up and Shutdown
Waveform. V
IN
(Top Trace) Is Ramped
from 0V Up to 8V and Then Back Down
to 0V. The Other Four Traces Are the
Output Voltages of All Four Channels
V
IN
1V/DIV
SW3
DA3
FB3
31.6k
10k
4.7µH
SW2
DA2
FB2
3.3µH
22.1k
10k
22µF
10µF
3.3V/1A
5V CHANNEL BEGINS
100% DC OPERATION
3.3V CHANNEL BEGINS
100% DC OPERATION
UVLO = ~2.9V
PARTS SHUTS
OFF
CH4 1V/DIV
CH3 1V/DIV
CH2 1V/DIV
CH1 1V/DIV
2.5V/1A
1µF
1.8V/1A
100ms/DIV
3504 TA01b
22µF
f
SW
= 1MHz
3504fa
For more information
www.linear.com/LT3504
1
LT3504
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
SW5
RUN/SS1
GND
SKY
V
IN
V
IN
PG
22 FB2
21 FB3
20 FB1
29
GND
19 FB4
18 GND
17 RT/SYNC
16 EN/UVLO
15 RUN/SS3
9 10 11 12 13 14
GND
RUN/SS4
RUN/SS2
V
IN
V
IN
EN/UVLO Pin.............................................................40V
EN/UVLO Pin Above V
IN
Pin........................................5V
V
IN
Pin ......................................................................40V
SKY Pin.....................................................................46V
SW5 Pin ....................................................................47V
RUN/SS Pins ...............................................................6V
FB Pins........................................................................6V
RT/SYNC Pin ...............................................................6V
PG Pin .......................................................................25V
Operating Junction Temperature Range (Notes 2, 8)
LT3504EUFD .......................................... –40°C to 125°C
LT3504IUFD ........................................... –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
28 27 26 25 24 23
DA2 1
SW2 2
DA3 3
SW3 4
SW1 5
DA1 6
SW4 7
DA4 8
UFD PACKAGE
28-LEAD (4mm
×
5mm) PLASTIC QFN
θ
JA
= 43°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LT3504EUFD#PBF
LT3504IUFD#PBF
TAPE AND REEL
LT3504EUFD#TRPBF
LT3504IUFD#TRPBF
PART MARKING
3504
3504
PACKAGE DESCRIPTION
28-Lead (4mm
×
5mm) Plastic QFN
28-Lead (4mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V unless otherwise noted.
SYMBOL
EN/UVLO Threshold Voltage
EN/UVLO Threshold Voltage Hysteresis
EN/UVLO Threshold Current Hysteresis
Internal V
IN
Undervoltage Lockout
Quiescent Current (V
IN
) in Shutdown
Quiescent Current (V
IN
)
Quiescent Current (V
IN
)
Quiescent Current (SKY)
V
EN/UVLO
= 0V
V
EN/UVLO
= 1V (Note 4)
V
EN/UVLO
= 1.5V, V
RUN/SS(1,2,3,4)
= Open,
V
FB(1,2,3,4)
= 0.9V, V
SKY
= 17V
V
EN/UVLO
= 1.5V, V
RUN/SS(1,2,3,4)
= Open,
V
FB(1,2,3,4)
= 0.9V, V
SKY
= 17V
V
EN/UVLO
= Measured Rising Threshold – 50mV
(Note 3)
2.4
CONDITIONS
Rising
l
elecTrical characTerisTics
MIN
1.2
TYP
1.44
110
1.3
2.9
0.01
4
2.7
4.4
MAX
1.6
UNITS
V
mV
µA
3.2
2
10
V
µA
µA
mA
mA
3504fa
2
For more information
www.linear.com/LT3504
LT3504
elecTrical characTerisTics
SYMBOL
RUN/SS Pin Source Current
RUN/SS Pin Threshold for Switching
Feedback Voltage
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V unless otherwise noted.
CONDITIONS
V
RUN/SS
= 0V
V
FB
= 0V
50
790
784
MIN
TYP
1.3
100
800
800
15
–0.015
27
4.85
l
l
l
MAX
UNITS
µA
mV
810
816
150
40
2.4
1.15
300
210
2.2
mV
mV
nA
%/V
mA
V
MHz
MHz
kHz
Deg
V
MHz
A
mV
µA
A
A
mA
mV
FB Pin Current
Reference Line Regulation
SKY Pin Current
SKY Voltage above V
IN
Voltage
Switching Frequency
V
FB
= Measured V
FB
(Note 5)
V
IN
= 5V to 40V
I
SW
= 1A
V
SKY
– V
IN
R
T
= 6.34k
R
T
= 18.2k
R
T
= 100k
R
T
= 18.2k
l
1.8
0.85
200
150
0.35
2.1
1
250
180
1.25
Switching Phase
SYNC Threshold Voltage
SYNC Input Frequency
Switch Current Limit (SW1,2,3,4)
Switch V
CESAT
(SW1,2,3,4)
Switch Leakage Current (SW1,2,3,4)
Catch Diode Current Limit (SW1,2,3,4)
Switch Current Limit (SW5)
Switch V
CESAT
(SW5)
Switch Leakage Current (SW5)
Boost Diode Current Limit (SW5)
PG Threshold Offset
PG Hysteresis
PG Voltage Output Low
PG Pin Leakage
(Note 6)
I
SW
= 1A
FB = 0V
FB = 0.7V
(Note 6)
I
SW
= 200mA
V
IN
= 5V
V
FB
Rising
V
FB
Rising – V
FB
Falling
I
PG
= 250µA
V
PG
= 2V
1.45
1.75
400
0.1
2.1
2
1.33
1.67
0.75
1.0
220
1.15
1.45
320
230
0.1
2
125
300
1
µA
mA
mV
mV
mV
µA
350
65
450
90
35
180
0.01
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 LT3504EUF 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
LT3504IUF is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 3:
Current flows into pin.
Note 4:
Quiescent current (V
IN
) is measured at V
EN/UVLO
= 1V
Note 5:
Current flows out of pin.
Note 6:
Current limit is guaranteed by design and/or correlation to static
test. Slope compensation reduces current limit at higher duty cycles.
Note 7:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
3504fa
For more information
www.linear.com/LT3504
3
LT3504
Typical perForMance characTerisTics
Efficiency, f = 1MHz
80
70
60
EFFICIENCY (%)
EFFICIENCY (%)
50
40
30
20
10
0
0
V
IN
= 6V
V
IN
= 12V
V
IN
= 24V
V
IN
= 36V
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
1
V
OUT
= 1.8V
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0
V
IN
= 6V
V
IN
= 12V
V
IN
= 24V
V
IN
= 36V
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
1
T
A
= 25°C, unless otherwise noted.
Efficiency, f = 1MHz
V
OUT
= 2.5V
90
80
70
60
50
40
30
20
10
0
Efficiency, f = 1MHz
V
OUT
= 3.3V
V
IN
= 6V
V
IN
= 12V
V
IN
= 24V
V
IN
= 36V
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
1
3504 G01
3504 G02
3504 G03
Efficiency, f = 1MHz
100
90
80
PERCENT ERROR (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0
V
IN
= 6V
V
IN
= 12V
V
IN
= 24V
V
IN
= 36V
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
1
V
OUT
= 5V
0
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
–3.5
–4.0
–4.5
–5.0
Load Regulation
OVERALL APPLICATION EFFICIENCY (%)
V
IN
= 12V
100
90
80
70
60
50
40
30
20
10
0
Efficiency, f = 1MHz
V
OUT1,2,3,4
= 5V
V
OUT
= 1.8V
V
OUT
= 2.5V
V
OUT
= 3.3V
V
OUT
= 5V
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
1
V
IN
= 6V
V
IN
= 12V
V
IN
= 24V
V
IN
= 36V
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT EACH CHANNEL (A)
1
3504 G04
3504 G05
3504 G06
Efficiency 5V/3.3V/2.5V/1.8V,
f = 1MHz
100
OVERALL APPLICATION EFFICIENCY (%)
90
80
THRESHOLD (V)
70
60
50
40
30
20
10
0
0
V
IN
= 6V
V
IN
= 12V
V
IN
= 24V
V
IN
= 36V
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT EACH CHANNEL (A)
1
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.25
EN/UVLO Threshold
2.0
1.8
1.6
I
EN/UVLO
(µA)
RISING
1.4
1.2
1.0
0.8
0.6
0.4
0.2
–25
25
50
0
75
TEMPERATURE (°C)
100
125
0
EN/UVLO Pin Current
–45°C
25°C
FALLING
150°C
1.20
–50
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
V
EN/UVLO
(V)
3504 G09
3504 G07
3504 G08
4
3504fa
For more information
www.linear.com/LT3504
LT3504
Typical perForMance characTerisTics
Input Voltage Undervoltage
Lockout
3.6
3.4
3.2
UVLO (V)
I
VIN
(µA)
3.0
2.8
2.6
2.4
2.2
2.0
–50
–25
25
50
0
75
TEMPERATURE (°C)
100
125
10
INPUT QUIESCENT CURRENT (mA)
9
8
7
6
5
4
3
2
1
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
V
EN/UVLO
(V)
3504 G11
T
A
= 25°C, unless otherwise noted.
Input Quiescent Current
vs Input Voltage
40
35
30
25
20
15
10
5
0
0
5
10
ALL SS = 2V
ALL SS = 0V
15 20 25 30 35
INPUT VOLTAGE (V)
40
45
V
IN
Pin Current
3504 G10
3504 G12
RUN/SS vs FB Voltage
900
800
700
FB VOLTAGE (mV)
I
RUN/SS
(µA)
600
500
400
300
200
100
0
0
200
600
800 1000
400
RUN/SS VOLTAGE (mV)
1200
0
–0.2
–0.4
Soft Start Current
1.20
1.15
1.10
FREQUENCY (MHz)
1.05
1.00
0.95
0.90
0.85
–25
25
50
0
75
TEMPERATURE (°C)
100
125
Switching Frequency
vs Temperature
–0.6
–0.8
–1.0
–1.2
–1.4
–1.6
–1.8
–2.0
–50
0.80
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3504 G15
3504 G13
3504 G14
Switch Voltage Drop
600
SWITCH VOLTAGE DROP (mV)
SWITCH VOLTAGE DROP (mV)
500
400
300
200
100
0
320
300
280
260
240
220
Switch Voltage Drop,
I
SW
= 500mA
2.0
1.9
1.8
CURRENT LIMIT (A)
1.7
1.6
1.5
1.4
1.3
1.2
1.1
Switch and Diode Current Limit
0
200
400
600
800
SWITCH CURRENT (mA)
1000
3504 G16
200
–50
–25
25
50
0
75
TEMPERATURE (°C)
100
125
1.0
–50
–25
25
50
0
75
TEMPERATURE (°C)
100
125
3504 G17
3504 G18
3504fa
For more information
www.linear.com/LT3504
5
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