Document
FEATURES
nn Ultralow Quiescent Current nn 2.5µA IQ at 12VIN to 3.3VOUT
nn Low Ripple Burst Mode® Operation nn Output Ripple < 10mVP-P
nn Wide Input Voltage Range: 4.2V to 42V Operating nn Adjustable Switching Frequency: 200kHz to 2.2MHz nn Integrated Boost and Catch Diodes nn 750mA Output Current nn Excellent Start-Up and Dropout Performance nn Fixed Output Voltages: 3.3V, 5V
nn 1.9µA IQ at 12VIN nn Accurate Programmable Undervoltage Lockout nn Low Shutdown Current: IQ = 0.75µA nn Internal Catch Diode Current Limit nn Power Good Flag nn Thermal Shutdown nn Small, Thermally Enhanced 10-Lead MSOP and
(3mm × 3mm) DFN Packages
APPLICATIONS
nn Automotive Battery Regulation nn Power for Portable Products nn Industrial Supplies nn Gate Drive Bias
LT3973/LT3973-3.3/LT3973-5 42V, 750mA Step-Down Regulator with 2.5µA Quiescent Current and Integrated Diodes
DESCRIPTION
The LT®3973 is an adjustable frequency monolithic buck switching regulator that accepts a wide input voltage range up to 42V, and consumes only 2.5µA of quiescent current. A high efficiency switch is included on the die along with the catch diode, boost diode, and the necessary oscillator, control and logic circuitry. Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping the output ripple below 10mV in a typical application. A minimum dropout voltage of 530mV is maintained when the input voltage drops below the programmed output voltage, such as during automotive cold crank. Current mode topology is used for fast transient response and good loop stability. A catch diode current limit provides protection against shorted outputs and overvoltage conditions, with thermal shutdown providing additional fault protection. An accurate programmable undervoltage lockout feature is available, producing a low shutdown current of 0.75µA. A power good flag signals when VOUT reaches 90% of the programmed output voltage. The LT3973 is available in small, thermally enhanced 10-lead MSOP and 3mm × 3mm DFN packages.
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
VIN 5.6V TO 42V
C1 4.7µF
5V Step-Down Converter
OFF ON 215k
VIN BOOST LT3973
EN/UVLO SW PG BD
OUT
RT FB GND
C3 0.47µF
L1 15µH
15pF
1M 316k
VOUT 5V 750mA C2 22µF
f = 600kHz
3973 TA01a
EFFICIENCY (%)
90 VIN = 12V 80
Efficiency
1000 100
70 10
60 1
50 0.1
40 0.01
0.1 1 10 100 LOAD CURRENT (mA)
0.01
3973 TA01b
For more information www.linear.com/LT3973
POWER LOSS (mW)
3973fb
1
LT3973/LT3973-3.3/LT3973-5
ABSOLUTE MAXIMUM RATINGS (Note 1)
VIN, EN/UVLO Voltage................................................42V BOOST Pin Voltage....................................................55V BOOST Pin Above SW Pin..........................................25V FB/VOUT, RT, PG Voltage..............................................6V BD Voltage.................................................................25V OUT Voltage...............................................................14V
Operating Junction Temperature Range (Note 2) LT3973E/LT3973E-X........................... –40°C to 125°C LT3973I/LT3973I-X............................. –40°C to 125°C LT3973H/LT3973H-X.......................... –40°C to 150°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) MSE Only........................................................... 300°C
PIN CONFIGURATION
TOP VIEW
*FB/VOUT OUT
EN/UVLO
VIN GND
1 2 3 4 5
10 RT
9 PG
11 GND
8 BD
7 BOOST
6 SW
DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN
θJA = 40°C/W, θJC = 5°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
* FB for LT3973, VOUT for LT3973-3.3, LT3973-5.
ORDER INFORMATION
LEAD FREE FINISH LT3973EDD#PBF LT3973IDD#PBF LT3973HDD#PBF LT3973EMSE#PBF LT3973IMSE#PBF LT3973HMSE#PBF LT3973EMSE-3.3#PBF LT3973IMSE-3.3#PBF LT3973HMSE-3.3#PBF LT3973EDD-3.3#PBF LT3973IDD-3.3#PBF LT3973HDD-3.3#PBF LT3973EMSE-5#PBF LT3973IMSE-5#PBF LT3973HMSE-5#PBF
TAPE AND REEL
PART MARKING*
LT3973EDD#TRPBF
LGCH
LT3973IDD#TRPBF
LGCH
LT3973HDD#TRPBF
LGCH
LT3973EMSE#TRPBF LTFYS
LT3973IMSE#TRPBF
LTFYS
LT3973HMSE#TRPBF LTFYS
LT3973EMSE-3.3#TRPBF LTGGB
LT3973IMSE-3.3#TRPBF LTGGB
LT3973HMSE-3.3#TRPBF LTGGB
LT3973EDD-3.3#TRPBF LGGC
LT3973IDD-3.3#TRPBF LGGC
LT3973HDD-3.3#TRPBF LGGC
LT3973EMSE-5#TRPBF LTGGD
LT3973IMSE-5#TRPBF LTGGD
LT3973HMSE-5#TRPBF LTGGD
*FB/VOUT 1 OUT 2
EN/UVLO 3 VIN 4
GND 5
TOP VIEW 11 GND
10 RT 9 PG 8 BD 7 BOOST 6 SW
MSE PACKAGE 10-LEAD PLASTIC MSOP θJA = 45°C/W, θJC = 10°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
PACKAGE DESCRIPTION 10-Lead (3mm × 3mm) Plastic DFN 10-Lead (3mm × 3mm) Plastic DFN 10-Lead (3mm × 3mm) Plastic DFN 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead (3mm × 3mm) Pla.