datasheet for LT3504 by Linear Technology

datasheet for LT3504 by Linear Technology
LT3504
Quad 40V/1A Step-Down
Switching Regulator with
100% Duty Cycle Operation
DESCRIPTION
FEATURES
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Wide Input Range: 3.2V to 40V
Four 1A Outputs
100% Duty Cycle Operation
Resistor-Programmed Constant Frequency
Short-Circuit Robust
Wide SYNC Range: 250kHz 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
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. Cycleby-cycle peak current limit and catch diode current limit
sensing protect the part during overload conditions. Thermal 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.
APPLICATIONS
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Automotive Battery Regulation
Industrial Control Supplies
Wall Transformer Regulation
Distributed Supply 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.
TYPICAL APPLICATION
Quad Buck Regulator in 4 × 5 QFN
10µH
SW4
5V/1A
52.3k
DA4
FB4
SKY
LT3504
1µF
10k
10µH
VIN
5.4V to 20V
TRANSIENT TO 40V
1µF
10µF
LT3504 Start-Up and Shutdown
Waveform. VIN (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
6.8µH
SW5
SW3
EN/UVLO
VIN
VIN
VIN
VIN
RUN/SS1
RUN/SS2
RUN/SS3
RUN/SS4
DA3
FB3
3.3V/1A
31.6k
10µF
VIN 1V/DIV
5V CHANNEL BEGINS
100% DC OPERATION
3.3V CHANNEL BEGINS
100% DC OPERATION
10k
4.7µH
SW2
UVLO = ~2.9V
PARTS SHUTS
OFF
2.5V/1A
22.1k
DA2
FB2
22µF
CH4 1V/DIV
CH3 1V/DIV
CH2 1V/DIV
CH1 1V/DIV
10k
50nF
3.3µH
RT/SYNC
SW1
1µF
18.2k
DA1
FB1
GND
1.8V/1A
100ms/DIV
3504 TA01b
24.9k
22µF
20k
3504 TA01a
fSW = 1MHz
3504f
1
LT3504
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
PG
SW5
SKY
VIN
VIN
GND
TOP VIEW
EN/UVLO Pin.............................................................40V
EN/UVLO Pin Above VIN Pin........................................5V
VIN 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
22 FB2
SW2 2
21 FB3
DA3 3
20 FB1
SW3 4
19 FB4
29
GND
SW1 5
18 GND
17 RT/SYNC
DA1 6
SW4 7
16 EN/UVLO
DA4 8
15 RUN/SS3
RUN/SS2
RUN/SS1
RUN/SS4
VIN
VIN
GND
9 10 11 12 13 14
UFD PACKAGE
28-LEAD (4mm × 5mm) PLASTIC QFN
θJA = 43°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3504EUFD#PBF
LT3504EUFD#TRPBF
3504
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3504IUFD#PBF
LT3504IUFD#TRPBF
3504
28-Lead (4mm × 5mm) Plastic QFN
–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/
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V unless otherwise noted.
SYMBOL
CONDITIONS
EN/UVLO Threshold Voltage
Rising
l
MIN
TYP
MAX
1.2
1.44
1.6
EN/UVLO Threshold Voltage Hysteresis
EN/UVLO Threshold Current Hysteresis
VEN/UVLO = Measured Rising Threshold – 50mV
(Note 3)
Internal VIN Undervoltage Lockout
2.4
UNITS
V
110
mV
1.3
µA
2.9
3.2
V
0.01
2
µA
4
10
Quiescent Current (VIN) in Shutdown
VEN/UVLO = 0V
Quiescent Current (VIN)
VEN/UVLO = 1V (Note 4)
Quiescent Current (VIN)
VEN/UVLO = 1.5V, VRUN/SS(1,2,3,4) = Open,
VFB(1,2,3,4) = 0.9V, VSKY = 17V
2.7
mA
Quiescent Current (SKY)
VEN/UVLO = 1.5V, VRUN/SS(1,2,3,4) = Open,
VFB(1,2,3,4) = 0.9V, VSKY = 17V
4.4
mA
µA
3504f
2
LT3504
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V unless otherwise noted.
SYMBOL
CONDITIONS
RUN/SS Pin Source Current
VRUN/SS = 0V
RUN/SS Pin Threshold for Switching
VFB = 0V
MIN
l
FB Pin Current
VFB = Measured VFB (Note 5)
Reference Line Regulation
VIN = 5V to 40V
SKY Pin Current
ISW = 1A
VSKY – VIN
Switching Frequency
RT = 6.34k
RT = 18.2k
RT = 100k
Switching Phase
RT = 18.2k
SYNC Threshold Voltage
50
100
800
800
810
816
15
150
l
l
l
l
(Note 6)
Switch VCESAT (SW1,2,3,4)
ISW = 1A
mV
mV
nA
%/V
40
4.85
mA
V
1.8
0.85
200
2.1
1
250
2.4
1.15
300
MHz
MHz
kHz
150
180
210
Deg
1.6
V
2.2
MHz
2.1
A
0.25
Switch Current Limit (SW1,2,3,4)
mV
–0.015
27
UNITS
µA
790
784
0.9
SYNC Input Frequency
MAX
1.3
Feedback Voltage
SKY Voltage above VIN Voltage
TYP
1.45
1.75
400
Switch Leakage Current (SW1,2,3,4)
mV
0.1
2
µA
Catch Diode Current Limit (SW1,2,3,4)
FB = 0V
FB = 0.7V
0.92
1.15
1.15
1.45
1.33
1.67
A
A
Switch Current Limit (SW5)
(Note 6)
220
320
mA
Switch VCESAT (SW5)
ISW = 200mA
230
mV
Switch Leakage Current (SW5)
Boost Diode Current Limit (SW5)
0.1
VIN = 5V
350
65
2
450
PG Threshold Offset
VFB Rising
PG Hysteresis
VFB Rising – VFB Falling
35
PG Voltage Output Low
IPG = 250µA
180
300
mV
PG Pin Leakage
VPG = 2V
0.01
1
µA
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.
90
µA
mA
125
mV
mV
Note 3: Current flows into pin.
Note 4: Quiescent current (VIN) is measured at VEN/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.
3504f
3
LT3504
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency, f = 1MHz
80
Efficiency, f = 1MHz
90
VOUT = 1.8V
VOUT = 2.5V
50
40
30
VIN = 6V
VIN = 12V
VIN = 24V
VIN = 36V
10
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
70
70
60
60
50
40
30
VIN = 6V
VIN = 12V
VIN = 24V
VIN = 36V
20
10
0
1
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
Efficiency, f = 1MHz
0
PERCENT ERROR (%)
EFFICIENCY (%)
60
50
40
30
VIN = 6V
VIN = 12V
VIN = 24V
VIN = 36V
10
0
10
0
0
1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
VIN = 12V
–1.5
–2.0
–2.5
–3.0
–3.5
VOUT = 1.8V
VOUT = 2.5V
VOUT = 3.3V
VOUT = 5V
–4.0
–4.5
–5.0
1
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
Efficiency 5V/3.3V/2.5V/1.8V,
f = 1MHz
80
70
60
50
40
30
10
0
1
1.8
10
0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT EACH CHANNEL (A)
1.4
IEN/UVLO (µA)
RISING
1.45
1.40
FALLING
1.35
3504 G07
1.20
–50
25°C
1.0
0.8
150°C
0.4
1.25
1
–45°C
1.2
0.6
1.30
VIN = 6V
VIN = 12V
VIN = 24V
VIN = 36V
1
1.6
1.50
THRESHOLD (V)
OVERALL APPLICATION EFFICIENCY (%)
1.55
30
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT EACH CHANNEL (A)
EN/UVLO Pin Current
90
20
0
3504 G06
2.0
40
VIN = 6V
VIN = 12V
VIN = 24V
VIN = 36V
20
EN/UVLO Threshold
50
VOUT1,2,3,4 = 5V
90
1.60
80
1
3504 G03
100
70
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
LOAD CURRENT (A)
3504 G05
3504 G04
60
0
100
–1.0
70
VIN = 6V
VIN = 12V
VIN = 24V
VIN = 36V
Efficiency, f = 1MHz
–0.5
80
20
30
Load Regulation
VOUT = 5V
90
40
3504 G02
3504 G01
100
50
20
OVERALL APPLICATION EFFICIENCY (%)
20
VOUT = 3.3V
80
EFFICIENCY (%)
EFFICIENCY (%)
60
EFFICIENCY (%)
Efficiency, f = 1MHz
90
80
70
0
TA = 25°C, unless otherwise noted.
0.2
–25
25
50
0
75
TEMPERATURE (°C)
100
125
3504 G08
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
VEN/UVLO (V)
3504 G09
3504f
4
LT3504
TYPICAL PERFORMANCE CHARACTERISTICS
Input Voltage Undervoltage
Lockout
VIN Pin Current
10
900
3.4
9
800
8
700
2.8
FB VOLTAGE (mV)
3.0
IVIN (µA)
UVLO (V)
7
2.6
6
5
4
3
2.4
600
500
400
300
2
200
2.2
1
100
2.0
–50
0
–25
25
50
0
75
TEMPERATURE (°C)
100
125
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
VEN/UVLO (V)
1.20
–0.2
1.15
–0.4
FREQUENCY (MHz)
–1.0
–1.4
1.05
1.00
0.95
0.90
–1.6
–2.0
–50
–25
25
50
0
75
TEMPERATURE (°C)
100
0.80
–50 –25
125
0
200
2.0
1.9
1.9
CURRENT LIMIT (A)
1.8
260
240
1.7
1.6
1.5
1.4
1.3
1.2
220
125
3504 G16
400
600
800
SWITCH CURRENT (mA)
1.0
–50
1000
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.1
100
200
Switch Current Limit
2.0
SWITCH CURRENT LIMIT (A)
300
280
0
3504 G15
Switch and Diode Current Limit
320
25
50
0
75
TEMPERATURE (°C)
300
3504 G14
Switch Voltage Drop,
ISW = 500mA
–25
400
0
25 50 75 100 125 150
TEMPERATURE (°C)
3504 G13
200
–50
500
100
0.85
–1.8
1200
Switch Voltage Drop
1.10
–1.2
600
800 1000
400
RUN/SS VOLTAGE (mV)
600
SWITCH VOLTAGE DROP (mV)
0
–0.8
200
3504 G12
Switching Frequency
vs Temperature
Soft Start Current
–0.6
0
3504 G11
3504 G10
IRUN/SS (µA)
RUN/SS vs FB Voltage
3.6
3.2
SWITCH VOLTAGE DROP (mV)
TA = 25°C, unless otherwise noted.
–25
25
50
0
75
TEMPERATURE (°C)
100
125
3504 G17
1.0
0
20
40
60
DUTY CYCLE (%)
80
100
3504 G18
3504f
5
LT3504
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Beta
Minimum On-Time
70
120
65
110
0.5A
100
ON-TIME (ns)
BETA
60
55
50
90
80
70
1A
45
60
40
–50
–25
25
50
0
75
TEMPERATURE (°C)
100
50
–50
125
–25
25
50
0
75
TEMPERATURE (°C)
125
3504 G20
3504 G19
Feedback Voltage
Power Good Threshold
740
805
RISING
804
720
803
802
THRESHOLD (mV)
FEEDBACK VOLTAGE (mV)
100
801
800
799
798
700
680
FALLING
660
640
797
620
796
795
–50
–25
25
50
0
75
TEMPERATURE (°C)
100
125
600
–50
–25
25
50
0
75
TEMPERATURE (°C)
125
3504 G22
3504 G21
Operating Waveforms,
Discontinuous Mode
Operating Waveforms,
Continuous Mode
SW1
10V/DIV
SW1
10V/DIV
SW2
10V/DIV
SW2
10V/DIV
SW3
10V/DIV
SW3
10V/DIV
SW4
10V/DIV
SW4
10V/DIV
500ns/DIV
IOUT1,2,3,4 = 40mA
VOUT1,2,3,4 = 5V
100
3504 G23
500ns/DIV
3504 G24
IOUT1,2,3,4 = 0.5A
VOUT1,2,3,4 = 5V
3504f
6
LT3504
PIN FUNCTIONS
DA (Pins 1, 3, 6, 8): Return the Schottky catch diode
anode to the diode anode (DA) pin. An internal comparator senses the diode current and prevents switching when
the diode current is higher than the DA pin current limit.
SW (Pins 2, 4, 5, 7): The SW pins are the output of the
internal power switches. Connect each SW pin to an inductor and Schottky catch diode cathode.
VIN (Pins 9, 11, 26, 28): The VIN pins supply current to
the LT3504’s internal regulator and to the internal power
switches. The VIN pins should be tied together and locally
bypassed with a capacitor to ground, preferably to pins
10 and 27.
GND (Pins 10, 18, 27, Exposed Pad Pin 29): Tie the GND
pins to a local ground plane below the LT3504 and the
circuit components. The exposed pad must be soldered
to the PCB and electrically connected to ground. Use a
large ground plane and thermal vias to optimize thermal
performance.
RUN/SS (Pins 12, 13, 14, 15): The RUN/SS pins are used
to soft start each channel and to allow each channel to
track other outputs. Output tracking is implemented by
connecting a resistor divider to this pin from the tracked
output. For soft start, tie a capacitor from this pin to ground.
An internal 1.3µA soft-start current charges the capacitor
to create a voltage ramp at the pin. Each channel can be
individually shut down by pulling RUN/SS below 0.1V.
EN/UVLO (Pin 16): The EN/UVLO pin is used to start up
the internal regulator to power the reference and oscillator. It also starts up the internal boost regulator. Pull the
EN/UVLO pin below 1.44V to shut down the LT3504. The
LT3504 will draw less than 10µA of current from the VIN
pin when EN/UVLO is less than 1.44V. Pull EN/UVLO pin
below 0.7V to put the LT3504 in a state where the part
draws 0µA from the VIN pin. The threshold can function
as an accurate undervoltage lockout (UVLO), preventing
the regulator from operating until the input voltage has
reached the programmed level. Do not drive the EN/UVLO
pin more than 5V above VIN.
RT/SYNC (Pin 17): Set the switching frequency of the
LT3504 by tying an external resistor from this pin to
ground. Select the value of the programming resistor
(RT) according to Table 1 in the Applications Information
section. The RT/SYNC pin is also used to synchronize the
internal oscillator of the LT3504 to an external signal. The
synchronization (sync) signal is directly logical compatible
and can be driven by any signal with pulse width greater
than 50ns. The synchronization range is from 250kHz to
2.2MHz.
FB (Pins 19, 20, 21, 22): Each feedback pin is regulated
to 800mV. Connect the feedback resistor divider to this
pin. The output voltage is programmed according to the
following equation:

V
R1= R2 •  OUT − 1
 0.8V 
where R1 connects between OUT and FB, and R2 connects
between FB and GND. A good value for R2 is 10kΩ.
PG (Pin 23): The Power Good pin is the open collector
output of an internal comparator. PG remains low until
all FB pins are greater than 710mV. If not in use, this pin
can be left unconnected. The PG comparator is disabled
in shutdown.
SW5 (Pin 24): The SW5 pin is an open collector of an
internal boost regulator power switch. This power switch
generates the drive voltage 4.85V above the input voltage
(VIN), to drive the internal buck regulator power switches.
Connect an inductor from this pin to the VIN pin.
SKY (Pin 25): The SKY pin is the output of an integrated
power Schottky diode and is the source of drive voltage
to the internal buck regulator power switches. Connect a
1µF capacitor from this pin to the VIN pin. Do not drive this
pin with an external voltage source. Do not draw current
from this pin with an external component.
3504f
7
EN/UVLO
ON
1.44V
VIN
SW5
BOOST ERROR AMP
REF
BOOST SWITCH AND DRIVE
S
SKY
VIN
Q5
R NQ
4.85V
1.3µA
0.7V
Σ
0.4V
LOCK
D5
BOOST REGULATOR
1SHOT
STARTUP/SHUTDOWN
THERMAL SHUTDOWN
SLOPE
TO CH3
CLK1
CLK2
TO CH2, CH4
SKY
OSC
1SHOT
SLOPE
VIN
0
SYNC
DETECT
1
FREQUENCY
TO CURRENT
0.7V
2.2V
0.8V
1µA
S
Σ
Q1
R NQ
SW1
0.1V
+–
RAMP
OUT1
SWITCH AND DRIVE
SKYBAD
DA1
SKYBAD
ONE OF THE FOUR BUCK REGULATORS SHOWN
PGOOD
0.8V
PG
4.5V
VIN
SKY
SKYBAD
CURRENT LIMIT FOLDBACK
0.72V
FB1
RT/SYNC
RUN/SS1
FB1
GND
COMPARATORS FROM OTHER CHANNELS
POWER GOOD LOGIC
3504 BD
LT3504
BLOCK DIAGRAM
8
PRECISION UVLO
3504f
LT3504
OPERATION
A comparator starts the reference when the EN/UVLO pin
rises above the 1.44V rising threshold. Other comparators
prevent switching when the input voltage is below 2.9V or
the die temperature is above 175°C. When the EN/UVLO
is above 1.44V, the input voltage is above 3.2V, and the
temperature is below 175°C, the boost regulator begins
switching and charges the SKY capacitor to 5V above
VIN. When the SKY voltage is less than 4.5V above VIN,
the RUN/SS pins and VC nodes are actively pulled low to
prevent the buck regulators from switching.
The boost regulator (Channel 5) consists of an internal
0.4A power switch (Q5), an internal power Schottky diode
(D5), and the necessary logic and other control circuitry
to drive the switch. The switch current is monitored to
enforce cycle-by-cycle current limit. The diode current
is monitored to prevent inductor current runaway during
transient conditions. An error amplifier servos the SKY
voltage to 4.85V above VIN. A comparator detects when
the SKY voltage is 4.5V above VIN and allows the buck
regulators to begin switching.
The oscillator produces two antiphase clock signals running
at 50% duty cycle. Channels 1, 3 and 5 run antiphase to
Channels 2 and 4. The oscillator can be programmed by
connecting a single resistor from RT/SYNC to ground, or
by applying an external clock signal to RT/SYNC. A sync
detect circuit distinguishes between the type of input.
Tying a resistor to GND directly sets the bias current of
the oscillator. The sync signal is converted to a current to
set the bias current of the oscillator.
The oscillator enables an RS flip-flop, turning on the
internal 1.7A power switch Q1. 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 the VC node. A second
comparator enforces a catch diode current limit to prevent
inductor current runaway during transient conditions. An
error amplifier measures the output voltage through an
external resistor tied to the FB pin and servos the VC node.
If the error amplifier’s output increases, more current is
delivered to the output; if it decreases, less current is
delivered. A clamp on the VC pin provides switch current
limit. Each buck regulator switch driver operates by drawing
current from the SKY pin. Regulating the SKY pin to 4.85V
above the VIN pin voltage is necessary to fully saturate the
bipolar power switch for efficient operation.
Soft-start is implemented by generating a voltage ramp at
the RUN/SS pin. An internal 1.3µA current source pulls the
RUN/SS pin up to 2.1V. Connecting a capacitor from the
RUN/SS pin to ground programs the rate of the voltage
ramp on the RUN/SS pin. A voltage follower circuit with a
0.1V offset connected from the RUN/SS pin to the RAMP
node prevents switching until the voltage at the RUN/SS
pin increases above 0.1V. When the voltage at the RAMP
node is less than 0.9V, the error amplifier servos the FB
voltage to the RAMP node voltage. When the RAMP node
voltage increases above 0.9V, then the error amplifier servos the FB voltage to 0.8V. Additionally, a current amplifier
reduces the catch diode current limit when the FB voltage
is below 0.8V to limit the inductor current during startup.
Each individual buck regulator can be placed in shutdown
by pulling the respective RUN/SS pin below 0.1V. The EN/
UVLO pin can be pulled low (below a VBE) to place the
entire part in shutdown, disconnecting the outputs and
reducing the input current to less than 2µA.
3504f
9
LT3504
APPLICATIONS INFORMATION
FB Resistor Network
The output voltage is programmed with a resistor divider
connected from the output and the FB pin. Choose the 1%
resistor according to:

V
R1= R2 •  OUT − 1
 0.8V 
A good value for R2 is 10kΩ, R2 should not exceed 20kΩ
to avoid bias current error.
Input Voltage Range
The input voltage range for LT3504 applications depends
on the output voltage and on the absolute maximum rating of the VIN pin.
The minimum input voltage to regulate the output generally has to be at least 400mV greater than the greatest
programmed output voltage. The only exception is when
the largest programmed output voltage is less than 2.8V.
In this case the minimum input voltage is 3.2V.
The absolute maximum input voltage of the LT3504 is
40V and the part will regulate output voltages as long
as the input voltage remains less than or equal to 40V.
However for constant-frequency operation (no pulseskipping) the maximum input voltage is determined by
the minimum on-time of the LT3504 and the programmed
switching frequency. The minimum on-time is the shortest
period of time that it takes the switch to turn on and off.
Therefore the maximum input voltage to operate without
pulse skipping is:
VIN(PS) = [ (VOUT + VD)/(fSW • tON(MIN)) ] + VSW – VD
where:
• VIN(PS) is the maximum input voltage to operate in
constant frequency operation without skipping pulses.
• VOUT is the programmed output voltage
• VSW is the switch voltage drop, at IOUT = 1A, VSW =
0.4V
• VD is the catch diode forward voltage drop, for an appropriately sized diode, VD = 0.4V
• fSW is the programmed switching frequency
• tON(MIN) is the minimum on-time, worst-case over
temperature = 110ns (at T = 125°C)
At input voltages that exceed VIN(PS) the part will continue
to regulate the output voltage up to 40V. However the
part will skip pulses (see Figure 1) resulting in unwanted
harmonics, increased output voltage ripple, and increased
peak inductor current. Provided that the inductor does not
saturate and that the switch current remains below 2A,
operation above VIN(PS) is safe and will not damage the
part. For a more detailed discussion on minimum on-time
and pulse-skipping, refer to the Applications Information
section of the LT3505 data sheet.
IL
0.5A/DIV
IL
0.5A/DIV
VSW
10V/DIV
VSW
10V/DIV
2µs/DIV
3504 F01a
Figure 1a: The LT3504 Operating in Constant-Frequency
Operation (Below VIN(PS)), VIN = 26.5V, VOUT = 3.3V,
fSW = 2MHz, tON(MIN) = 74ns at T = 25°C
2µs/DIV
3504 F01b
Figure 1b.The LT3504 Operating in Pulse-Skipping Mode
(Above VIN(PS)), VIN = 27V, VOUT = 3.3V, fSW = 2MHz,
tON(MIN) = 74ns at T = 25°C
3504f
10
LT3504
APPLICATIONS INFORMATION
Frequency Selection
The maximum frequency that the LT3504 can be programmed to is 2.5MHz. The minimum frequency is 250kHz.
The switching frequency can be programmed in two ways.
The first method is by tying a 1% resistor (RT) from the
RT/SYNC pin to ground. Table 1 can be used to select the
value of RT. The second method is to synchronize (sync)
the internal oscillator to an external clock. The external
clock must have a minimum amplitude from 0V to 1.5V
and a minimum pulse-width of 50ns.
simply tie an RT resistor from the RT/SYNC pin to ground
(Figure 2). The sync signal should be capable of driving the
RT resistor. If the sync signal is in a low impedance state
or an unknown state when it is inactive, then the solution
is to tie the RT resistor from the RT/SYNC pin to ground
and then to drive the RT/SYNC pin with the sync signal
through a 1nF capacitor as shown in Figure 3.
LT3504
PORT
Table 1. RT/SYNC Pin Resistance to Program Oscillator
Frequency
FREQUENCY (MHz)
RT/SYNC PIN RESISTANCE (kΩ)
0.20
140
0.3
82.5
0.4
56.2
0.5
43.2
0.6
34.8
0.7
28.0
0.8
23.7
0.9
20.5
1.0
18.2
1.1
16.9
1.2
14.7
1.3
13.0
1.4
11.5
1.5
10.7
1.6
9.76
1.7
8.66
1.8
8.06
1.9
7.32
2.0
6.81
2.1
6.34
2.2
6.04
2.3
5.62
2.4
5.36
2.5
4.99
In certain applications, the LT3504 may be required to be
alive and switching for a period of time before it begins
to receive a sync signal. If the sync signal is in a high
impedance state when it is inactive then the solution is to
RT/SYNC
RT
GND
3504 F02
Figure 2. Driving the RT/SYNC Pin From
a Port That Is in a High Impedance State
When it Is Inactive
LT3504
1nF
PORT
RT/SYNC
RT
GND
3504 F03
Figure 3. Driving the RT/SYNC Pin from
a Port That Is in a Low Impedance State
When it Is Inactive
BOOST Regulator and SKY Pin Considerations
The on-chip boost regulator generates the SKY voltage
to be 4.85V above VIN. The SKY voltage is the source of
drive current for the buck regulators which is used to fully
saturate the power switch. The boost regulator requires
two external components: an inductor and a capacitor.
A good first choice for an inductor is given by:
L=
20.5µH
f
where f is in MHz.
Thus, for a 250kHz programmed switching frequency,
a good first choice for an inductor value is 82µH. For a
2.5MHz programmed switching frequency, a good first
3504f
11
LT3504
APPLICATIONS INFORMATION
choice for an inductor value is 8.2µH. These values will
ensure that each buck regulator will have sufficient drive
current to saturate the power switch in all applications
and under all operating conditions.
A user desiring a lower inductor current value can calculate
their optimum inductor size based on their output current requirements. Each buck regulator instantaneously
requires 20mA from the SKY pin per 1A of switch current.
The average current that each buck regulator draws from
the SKY pin is 20mA multiplied by the duty cycle. So if
all four buck regulators run at 100% duty cycle with each
channel supplying 1A of output current, then the SKY pin
should be able to source 80mA. However if each channel runs at 50% duty cycle then the SKY pin only has to
source 40mA. Alternatively if each channel runs at 100%
duty cycle but the output current requirement is 0.5A per
channel instead of 1A, then again the SKY pin only has to
source 40mA. To summarize, the SKY pin output current
requirement is calculated from the following equation:
 IOUT1 • VOUT1 + IOUT2 • VOUT2 + 


 IOUT3 • VOUT3 + IOUT4 • VOUT4 
=
50 • VIN
ISKY
where IOUTX is the desired output current from Channel
X, VOUTX is the programmed output voltage of Channel X,
and VIN is input voltage.
Once the SKY pin output current requirement is determined, the inductor value can be calculated based on
the maximum tolerable inductor current ripple from the
following equation:
L=
Soft-Start/Tracking
The RUN/SS pin can be used to soft-start the corresponding channel, reducing the maximum input current during
start-up. The RUN/SS pin is pulled up through a 1µA current
source to about 2.1V. A capacitor can be tied to the pin to
create a voltage ramp at this pin. The buck regulator will
not switch while the RUN/SS pin voltage is less than 0.1V.
As the RUN/SS pin voltage increases above 0.1V, the channel will begin switching and the FB pin voltage will track
the RUN/SS pin voltage (offset by 0.1V), until the RUN/SS
pin voltage is greater than 0.8V + 0.1V. At this point the
output voltage will be at 100% of it’s programmed value
and the FB pin voltage will cease to track the RUN/SS
pin voltage and remain at 0.8V (the RUN/SS pin will
continue ramping up to about 2.1V with no effect on the
output voltage). The ramp rate can be tailored so that the
peak start up current can be reduced to the current that
is required to regulate the output, with little overshoot.
Figure 4 shows the start-up waveforms with and without
a soft-start capacitor (CSS) on the RUN/SS pin.
IL
0.5A/DIV
VOUT
2V/DIV
100µs/DIV
3504 F04a
Figure 4a. Inductor Current Waveform During
Start-Up without a Soft-Start Capacitor
VIN • DC5
2 • fSW • 0.3 • (1− 0.25 • DC5) − ISKY 
where fSW is the programmed switching frequency and
DC5 is the boost regulator duty cycle, given by: DC5 =
5V/(VIN + 5V).
For a 1MHz application, with VIN = 12V, VOUT1 = 5V, VOUT2
= 3.3V, VOUT3 = 2.5V, VOUT4 = 1.8V, and all channels supplying 1A of output current, the required SKY pin current
is 47mA and the inductor value is 6µH.
IL
0.5A/DIV
VOUT
2V/DIV
100µs/DIV
3504 F04b
Figure 4b. Inductor Current Waveform During
Start-Up with a 1nF Soft-Start Capacitor (CSS)
3504f
12
LT3504
APPLICATIONS INFORMATION
Undervoltage Lockout
The LT3504 prevents switching when the input voltage
decreases below 3V. Alternatively, the EN/UVLO pin can be
used to program an undervoltage lockout at input voltages
exceeding 3V by tapping a resistor divider from VIN to EN/
UVLO as shown in Figure 5.
The rising threshold on the EN/UVLO pin is 1.44V. The
falling threshold on the EN/UVLO pin is 1.33V. When EN/
UVLO is rising and less than 1.44V then the EN/UVLO pin
sinks 1.3µA of current. This 1.3µA current can be used to
program additional hysteresis on the EN/UVLO pin. For the
circuit in Figure 5, R1 can be determined from:
R1=
(
0.11
V
1.33 IN,FALLING
1.3µA
VIN,HYSTERESIS −
)
where VIN,HYSTERESIS is the desired amount of hysteresis
on the input voltage and VIN,FALLING is the desired input
voltage threshold at which the part will shut down. Notice
that for a given falling threshold (VIN,FALLING), the amount
of hysteresis (VIN,HYSTERESIS) must be at least:
VIN, HYSTERESIS >
(
0.11
• VIN,FALLING
1.33
)
For a falling threshold of 10V, the minimum hysteresis
is 0.827V. For a falling threshold of 30V, the minimum
hysteresis is 2.48V.
R2 can be calculated once R1 is known:
R2 = R1•
1.33
VIN, FALLING − 1.33
The circuit shown in Figure 5 will start when the input
voltage rises above 11V and will shutdown when the input
voltage falls below 10V.
Inductor Selection and Maximum Output Current
A good first choice for the inductor value is:
L = 2 • (VOUT + VD)/fSW
where VD is the voltage drop of the catch diode (~0.4V),
L is in µH and fSW is in MHz. With this value there will
be no subharmonic oscillation for applications with 50%
or greater duty cycle. The inductor’s RMS current rating
must be greater than your maximum load current and
its saturation current should be about 30% higher. For
robust operation in fault conditions, the saturation current
should be above 2A. To keep efficiency high, the series
resistance (DCR) should be less than 0.1 . Table 2 lists
several vendors and types that are suitable.
Of course, such a simple design guide will not always
result in the optimum inductor for your application. A
larger value provides a higher maximum load current and
reduces output voltage ripple at the expense of slower
transient response. If your load is lower than 1A, 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. Low inductance may result in discontinuous mode operation, which is okay, but further reduces
maximum load current. For details on maximum output
current and discontinuous mode operation, see Linear
Technology Application Note 44.
SWITCHING
VIN
VIN
R1
133k
LT3504
EN/UVLO
R2
20.5k
GND
VIN, FALLING = 10V
VIN, RISING = 11V
NOT
SWITCHING
9
10
11
VIN (V)
12
3504 F05
Figure 5. Circuit to Prevent Switching When VIN < 10V, with 700mV of Hysteresis
3504f
13
LT3504
APPLICATIONS INFORMATION
Table 2. Inductor Vendors
VENDOR
URL
PART SERIES
INDUCTANCE (µH)
SIZE (mm)
Sumida
www.sumida.com
CDRH4D28
CDRH5D28
CDRH5D28
1.2 TO 4.7
2.5 TO 10
2.5 TO 33
4.5 × 4.5
5.5 × 5.5
8.3 × 8.3
Toko
www.toko.com
A916CY
D585LC
2 TO 12
1.1 TO 39
6.3 × 6.2
8.1 × 8
Würth Elektronik
www.we-online.com
WE-TPC(M)
WE-PD2(M)
WE-PD(S)
1 TO 10
2.2 TO 22
1 TO 27
4.8 × 4.8
5.2 × 5.8
7.3 × 7.3
Table 3. Capacitor Vendors
VENDOR
PHONE
URL
PART SERIES
COMMENTS
Panasonic
(714) 373-7366
www.panasonic.com
Ceramic, Polymer, Tantalum
EEF Series
Kemet
(864) 963-6300
www.kemet.com
Ceramic, Tantalum
T494, T495
Sanyo
(408) 749-9714
www.sanyovideo.com
Ceramic, Polymer, Tantalum
POSCAP
Murata
(404) 436-1300
AVX
Taiyo Yuden
(864) 963-6300
www.murata.com
Ceramic
www.avxcorp.com
Ceramic, Tantalum
www.taiyo-yuden.com
Ceramic
Catch Diode
Use a 1A Schottky diode. The diode must have a reverse
voltage rating equal to or greater than the maximum input
voltage. The ON Semiconductor MBRM140 is a good
choice; it is rated for 1A continuous forward current and
a maximum reverse voltage of 40V.
Input Capacitor
The input of the LT3504 circuit must be bypassed with a
X7R or X5R type ceramic capacitor. Y5V types have poor
performance over temperature and amplified voltage
and should not be used. There are four VIN pins. Each
VIN pin should be bypassed to the nearest ground pin.
However it is not necessary to use a dedicated capacitor for each VIN pin. Pins 9 and 11 may be tied together
on the board layout so that both pins can share a single
bypass capacitor. Since the channels running on Pins 9
and 11 are 180 degrees out-of-phase, it is not necessary
to double the capacitor value either. Similarly, Pins 26
and 28 may be tied together on the board layout to save
a bypass capacitor. For switching frequencies greater than
750kHz, a 1µF capacitor or higher value ceramic capacitor
should be used to bypass each group of two VIN pins. For
TPS Series
switching frequencies less than 750kHz, a 2.2µF or higher
value ceramic capacitor should be used to bypass each
group of two VIN pins. The ceramic bypass capacitors
should be located as close to the VIN pins as possible.
See the sample layout shown in the PCB Layout section.
All four VIN pins should be tied together on the board and
bypassing with a low performance electrolytic capacitor
is recommended especially if the input power source has
high impedance, or there is significant inductance due to
long wires or cables.
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 LT3504 and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
To accomplish this task, the input bypass capacitor must
be placed close to the LT3504 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 LT3504. A ceramic input capacitor
combined with trace or cable inductance forms a high
quality (underdamped) tank circuit. If the LT3504 circuit
is plugged into a live supply, the input voltage can ring to
3504f
14
LT3504
APPLICATIONS INFORMATION
twice its nominal value, possibly exceeding the LT3504’s
voltage rating. This situation can be easily avoided by adding an electrolytic capacitor in parallel with the ceramic
input capacitors. See Application Note 88.
Output Capacitor
The output capacitor has two essential functions. Along
with the inductor, it filters the square wave generated by
the LT3504 to produce the DC output. In this role it determines the output ripple so low impedance at the switching
frequency is important. The second function is to store
energy in order to satisfy transient loads and stabilize the
LT3504’s control loop.
Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance.
A good value is:
COUT = 33/(VOUT • fSW)
where COUT is in µF and fSW is in MHz. Use X5R or X7R
types and keep in mind that a ceramic capacitor biased
with VOUT will have less than its nominal capacitance. This
choice will provide low output ripple and good transient
response. Transient performance can be improved with a
high value capacitor, if the compensation network is also
adjusted to maintain the loop bandwidth.
A lower value of output capacitor can be used, but transient
performance will suffer.
High performance 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 0.1Ω
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 3 lists
several capacitor vendors.
Figure 6 shows the transient response of the LT3504 with
several output capacitor choices. The output is 3.3V. The
load current is stepped from 500mA to 1A and back to
500mA and the oscilloscope traces show the output voltage. The upper photo shows the recommended value. The
second photo shows the improved response (less voltage
drop) resulting from a larger output capacitor and a larger
phase lead capacitor. The last photo shows the response
to a high performance electrolytic capacitor. Transient performance is improved due to the large output capacitance.
Shorted and Reversed Input Protection
If the inductor is chosen so that it won’t saturate excessively, an LT3504 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
LT3504 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 LT3504’s
output. If the VIN pin is allowed to float and the EN/UVLO
pin is held high (either by a logic signal or because it is
tied to VIN), then the LT3504’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 EN/UVLO 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
LT3504 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.
3504f
15
LT3504
APPLICATIONS INFORMATION
VOUT
LT3504
IOUT
1A/DIV
31.6k
FB
10µF
10k
VOUT
20mV/DIV
20µs/DIV
3504 F06a
20µs/DIV
3504 F06b
20µs/DIV
3504 F06c
VOUT
LT3504
IOUT
1A/DIV
100pF
31.6k
10µF
×2
FB
10k
VOUT
20mV/DIV
VOUT
LT3504
IOUT
1A/DIV
31.6k
+
FB
22µF
10k
VOUT
20mV/DIV
Figure 6. Transient Load Response of the LT3504 with Different Output Capacitors as the
Load Current Is Stepped from 500mA to 1A. VIN = 12V, VOUT = 3.3V, L = 10µH, RT = 18.2k
VIN
EN/UVLO
VOUT
SW1
SKY
SW5
LT3504
D4
DA1
VIN
VIN
RUN/SS1
BACKUP
FB1
RT/SYNC
GND
3504 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 LT3504 Runs Only When the Input Is Present
3504f
16
LT3504
APPLICATIONS INFORMATION
PCB Layout
High Temperature Considerations
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.
The die temperature of the LT3504 must be lower than the
maximum rating of 125°C. This is generally not a concern
unless the ambient temperature is above 85°C. For higher
temperatures, extra care should be taken in the layout of
the circuit to ensure good heat sinking of the LT3504. The
maximum load current should be derated as the ambient
temperature approaches 125°C. Programming the LT3504
to a lower switching frequency will improve efficiency and
reduce the dependence of efficiency on input voltage. The
die temperature is calculated by multiplying the LT3504
power dissipation by the thermal resistance from junction to ambient. Power dissipation within the LT3504 can
be estimated by calculating the total power loss from an
efficiency measurement and subtracting the catch diode
losses. Thermal resistance depends on the layout of the
circuit board, but 43°C/W is typical for the MSE package.
Thermal shutdown will turn off the buck regulators and
the boost regulator when the die temperature exceeds
175°C, but this is not a warrant to allow operation at die
temperatures exceeding 125°C.
Note that large, switched currents flow in the LT3504’s VIN,
SW and DA pins, the catch diodes (D1, D2, D3, D4) and
the input capacitors (C5, C6). The loop formed by these
components should be as small as possible and tied to
system ground in only one place. These components,
along with the inductors (L1, L2, L3, L4, L5) and output
capacitors (C1, C2, C3, C4, C7), 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, and tie this
ground plane to system ground at one location (ideally
at the ground terminal of the output capacitors). Ground
pins (Pins 10, 27) are provided near the VIN pins so that
the VIN pins can be bypassed to these ground pins. The
SW nodes should be kept as small as possible and kept
far away from the RT/SYNC and FB nodes. Keep the RT/
SYNC node and FB nodes small so that the ground pin
and ground traces will shield them from the SW nodes. If
the user plans on using a SYNC signal to set the oscillator
frequency then the RT/SYNC node should be kept away
from the FB nodes. Include vias near the exposed pad of
the LT3504 to help transfer heat from the LT3504 to the
ground plane. Keep the SW5 pad/trace as far away from
the FB pads as possible.
Outputs Greater Than 9V
For outputs greater than 9V, add a 1k resistor in series with
a 1nF capacitor across the inductor to damp the discontinuous ringing of the SW node, preventing unintended
SW current. An application with a 15V output (back page)
shows the location of this damping network.
Other Linear Technology Publications
Application Notes 19, 35, 44 contain more detailed descriptions and design information for step-down regulators and
other switching regulators. Design Note 318 shows how
to generate a bipolar output supply using a step-down
regulator.
3504f
17
LT3504
APPLICATIONS INFORMATION
GND
+
C2
C8
C3
OUT2
L5
OUT3
SW5
L2
L3
VIN
C7
SKY
SW2
SW3
GND
C5
D2
GND
D3
PG
FB2
D1
R2
D4
GND
C6
VIN
R6
R1
R7
R4
R8
RT/SYNC
RUN/SS4
RUN/SS1
RUN/SS2
RUN/SS3
EN/UVLO
SW1
R5
R3
FB4
FB1
FB3
R9
SW4
L1
GND
GND
GND
L4
C4
OUT1
C1
GND
OUT4
GND
VIA TO LOCAL GROUND PLANE
OUTLINE OF LOCAL GROUND PLANE
3504 F08
VIA TO VIN
Figure 8
3504f
18
LT3504
PACKAGE DESCRIPTION
UFD Package
28-Lead Plastic QFN (4mm × 5mm)
(Reference LTC DWG # 05-08-1712 Rev B)
0.70 ±0.05
4.50 ± 0.05
3.10 ± 0.05
2.50 REF
2.65 ± 0.05
3.65 ± 0.05
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
3.50 REF
4.10 ± 0.05
5.50 ± 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ± 0.10
(2 SIDES)
0.75 ± 0.05
PIN 1 NOTCH
R = 0.20 OR 0.35
× 45° CHAMFER
2.50 REF
R = 0.115
TYP
R = 0.05
TYP
27
28
0.40 ± 0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
5.00 ± 0.10
(2 SIDES)
3.50 REF
3.65 ± 0.10
2.65 ± 0.10
(UFD28) QFN 0506 REV B
0.25 ± 0.05
0.200 REF
0.50 BSC
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X).
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
3504f
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.
19
LT3504
TYPICAL APPLICATION
40V Quad Output Application at 500kHz
4.7µH
SW4
1.2V/200mA
16.9k
DA4
FB4
SKY
LT3504
1µF
33.2k
15µH
VIN
15.4V to 40V
100µF
10µH
SW5
SW3
EN/UVLO
VIN
VIN
VIN
VIN
RUN/SS1
RUN/SS2
RUN/SS3
RUN/SS4
DA3
FB3
7V/200mA
39.2k
1nF
1.02k
10µF
4.99k
10µH
SW2
15V/200mA
45.3k
DA2
FB2
4.7µF
2.55k
50nF
4.7µH
RT/SYNC
SW1
2.2µF
43.2k
DA1
FB1
2.2µF
GND
3.3V/200mA
43.2k
22µF
13.7k
3504 TA02
RELATED PARTS
PART
DESCRIPTION
COMMENTS
LT3507/
LT3507A
36V 2.5MHz, Triple [2.4A + 1.5A + 1.5A (IOUT)] with LDO Controller
High Efficiency Step-Down DC/DC Converter
VIN(MIN) = 4V, VIN(MAX) = 36V, VOUT(MIN) = 0.8V, IQ = 7mA,
ISD = 1µA, 5mm x 7mm QFN-38 Package
LT8610
42V 2.2MHz, Synchronous, Low IQ = 2.5µA, Step-Down DC/DC
Converter
VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD = 1µA, MSOP-16E Package
LT3988
60V with Transient Protection to 80V, 2.5MHz, Dual 1A High
Efficiency Step-Down DC/DC Converter
VIN(MIN) = 4.0V, VIN(MAX) = 60V, VOUT(MIN) = 0.75V, IQ = 2mA,
ISD = 1µA, MSOP-16E Package
LT3509
36V with Transient Protection to 60V, Dual 0.70(IOUT), 2.2MHz,
High Efficiency Step-Down DC/DC Converter
VIN(MIN) = 3.6V, VIN(MAX) = 36V, VOUT(MIN) = 0.8V, IQ = 1.9mA,
ISD = 1µA, 3mm × 4mm DFN-14, MSOP-16E Packages
LT3500
36V, 40VMAX, 2A, 2.5MHz High Efficiency Step-Down DC/DC
Converter and LDO Controller
VIN(MIN) = 3.6V, VIN(MAX) = 36V, VOUT(MIN) = 0.8V, IQ = 2.5mA,
ISD <10µA, 3mm × 3mm DFN-10 Package
LT3508
36V with Transient Protection to 40V, Dual 1.4A (IOUT), 3MHz,
High Efficiency Step-Down DC/DC Converter
VIN(MIN) = 3.7V, VIN(MAX) = 37V, VOUT(MIN) = 0.8V, IQ = 4.6mA,
ISD = 1µA, 4mm × 4mm QFN-24, TSSOP-16E Packages
LT3980
58V with Transient Protection to 80V, 2A (IOUT), 2.4MHz, High
Efficiency Step-Down DC/DC Converter with Burst Mode® Operation
VIN(MIN) = 3.6V, VIN(MAX) = 58V, Transient to 80V, VOUT(MIN) = 0.8V,
IQ = 85µA, ISD <1µA, 3mm × 4mm DFN-16 and MSOP-16E Packages
LT3480
36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High
Efficiency Step-Down DC/DC Converter with Burst Mode Operation
VIN(MIN) = 3.6V, VIN(MAX) = 38V, VOUT(MIN) = 0.78V, IQ = 70µA,
ISD <1µA, 3mm × 3mm DFN-10, MSOP-10E Packages
LT3689
36V, 60V Transient Protection, 800mA, 2.2MHz High Efficiency
Micropower Step-Down DC/DC Converter with POR Reset and
Watchdog Timer
VIN(MIN) = 3.6V, VIN(MAX) = 36V, Transient to 60V, VOUT(MIN) = 0.8V,
IQ = 75µA, ISD <1µA. 3mm × 3mm QFN-16 Package
LT3970
40V, 350mA, 2MHz High Efficiency Micropower Step-Down
DC/DC Converter
VIN(MIN) = 4V, VIN(MAX) = 40V, Transient to 60V, VOUT(MIN) = 1.21V,
IQ = 2µA, ISD <1µA, 3mm × 2mm DFN-10 and MSOP-10 Packages
LT3682
36V, 60VMAX, 1A, 2.2MHz High Efficiency Micropower Step-Down
DC/DC Converter
VIN(MIN) = 3.6V, VIN(MAX) = 36V, VOUT(MIN) = 0.8V, IQ = 75µA,
ISD < 1µA, 3mm × 3mm DFN-12 Package
3504f
20 Linear Technology Corporation
LT 0712 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2012
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