Document
FEATURES
n Wide Input Range: 4V to 36V n One 2.7A and Two 1.8A Output Switching
Regulators with Internal Power Switches n Low Dropout Linear Regulator with External
Transistor n Antiphase Switching Reduces Ripple n Independent Run, Tracking/Soft-Start, and Power
Good Indicators Ease Supply Sequencing n Uses Small Inductors and Ceramic Capacitors n Adjustable, 250kHz to 2.5MHz Switching Frequency,
Synchronizable Over the Full Range n User Programmable Overvoltage and Undervoltage
Lockouts n Thermally Enhanced, 38-Lead TSSOP and
5mm × 7mm QFN Packages
APPLICATIONS
n Automotive n Industrial Supplies n Distributed Power Regulation n DSP Power
LT3507A
Triple Monolithic Step-Down Regulator with LDO
DESCRIPTION
The LT®3507A 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 2.7A output and two 1.8A outputs. All three converters are synchronized to a single oscillator. The 2.7A 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 regulation, 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 capacitors, results in low, predictable output ripple. Frequency foldback and thermal shutdown provide protection against fault conditions. The LT3507A provides higher output current than available with the LT3507.
L, LT, LTC, LTM, Linear Technology and the Linear logo 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
VIN 6V TO 36V
VOUT1 1.8V 2.7A
VOUT3 5V
1.8A
22µF 4.7µH
VIN1 VIN2 VIN3
BOOST1
BOOST2
0.22µF
SW1
18.7k
100µF 15k
25.5k
VOUT2 15µH
680pF
FB1 VC1
LT3507A
0.22µF BOOST3
SW3
53.6k
22µF 10.2k
25.5k 680pF
FB3 VC3
SW2
FB2 VC2 BIAS DRIVE
RT/SYNC 107k GND
FB4
0.22µF 10µH 34.8k
680pF 25.5k 11k
24.3k 11.5k
VOUT2 3.3V 33µF 1.5A
2.2µF
VOUT4 2.5V 0.3A
fSW = 450kHz
3507A TA01a
Start-Up Waveforms—Coincident Tracking
1V/DIV
VOUT3
VOUT2 VOUT4 VOUT1
1ms/DIV
3507 TA01b
3507af
1
LT3507A
ABSOLUTE MAXIMUM RATINGS (Note 1)
VIN Pins....................................................... –0.3V to 36V BOOST Pins...............................................................55V BOOST Above SW......................................................25V PGOOD Pins...............................................................36V BIAS Pin.....................................................................16V TRK/SS, VC, FB, RT/SYNC Pins....................................6V RUN, OVLO, UVLO Pins............................................ VIN1
DRIVE Pin....................................................................5V Operating Junction Temperature Range (Notes 2, 5) LT3507AE, LT3507AI.......................... –40°C to 125°C LT3507AH........................................... –40°C to 150°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) TSSOP Only....................................................... 300°C
PIN CONFIGURATION
TOP VIEW
SW1 SW1 VIN3 VIN3 SW3 SW3 BOOST3
BOOST1 1
VIN1 VIN1 VINSW OVLO
2 3 4 5
UVLO 6
VC1 7 TRK/SS1 8
FB1 9
PGOOD1 10
PGOOD2 11
PGOOD3 12
38 37 36 35 34 33 32 39 GND
13 14 15 16 17 18 19
31 VIN2 30 VIN2 29 SW2 28 SW2 27 BOOST2 26 TRK/SS4 25 FB4 24 DRIVE 23 VC2 22 FB2 21 TRK/SS2 20 FB3
RT/SYNC RUN1 RUN2 RUN3 BIAS
TRK/SS3 VC3
UHF PACKAGE 38-LEAD (5mm × 7mm) PLASTIC QFN
θJA = 34°C/W EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
VIN3 1 SW1 2
SW1 3
BOOST1 4
VIN1 VIN1 VINSW OVLO
5 6 7 8
UVLO 9
VC1 10 TRK/SS1 11
FB1 12
PGOOD1 13
PGOOD2 14
PGOOD3 15
RT/SYNC 16
RUN1 17
RUN2 18
RUN3 19
TOP VIEW 39 GND
38 SW3 37 BOOST3 36 VIN2 35 VIN2 34 NC 33 SW2 32 BOOST2 31 TRK/SS4 30 FB4 29 DRIVE 28 VC2 27 NC 26 FB2 25 TRK/SS2 24 FB3 23 VC3 22 TRK/SS3 21 BIAS 20 GND
FE PACKAGE 38-LEAD PLASTIC TSSOP
θJA = 24°C/W EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3507AEUHF#PBF LT3507AIUHF#PBF LT3507AHUHF#PBF LT3507AEFE#PBF
LT3507AEUHF#TRPBF LT3507AIUHF#TRPBF LT3507AHUHF#TRPBF LT3507AEFE#TRPBF
3507A 3507A 3507A LT3507AFE
38-Lead (5mm × 7mm) Plastic QFN 38-Lead (5mm × 7mm) Plastic QFN 38-Lead (5mm × 7mm) Plastic QFN 38-Lead Plastic TSSOP
–40°C to 125°C –40°C to 125°C –40°C to 150°C –40°C to 125°C
LT3507AIFE#PBF
LT3507AIFE#TRPBF
LT3507AFE
38-Lead Plastic TSSO.