LT3973/LT3973-3.3/LT3973-5
1
3973fb
For more information www.linear.com/LT3973
TYPICAL APPLICATION
DESCRIPTION
42V, 750mA Step-Down
Regulator with 2.5µA
Quiescent Current and
Integrated Diodes
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 keep
-
ing 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 volt
-
age, 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 V
OUT
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 , LT C , 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.
5V Step-Down Converter
FEATURES
APPLICATIONS
n
Ultralow Quiescent Current
n
2.5µA I
Q
at 12V
IN
to 3.3V
OUT
n
Low Ripple Burst Mode
®
Operation
n
Output Ripple < 10mV
P-P
n
Wide Input Voltage Range: 4.2V to 42V Operating
n
Adjustable Switching Frequency: 200kHz to 2.2MHz
n
Integrated Boost and Catch Diodes
n
750mA Output Current
n
Excellent Start-Up and Dropout Performance
n
Fixed Output Voltages: 3.3V, 5V
n
1.9µA I
Q
at 12V
IN
n
Accurate Programmable Undervoltage Lockout
n
Low Shutdown Current: I
Q
= 0.75µA
n
Internal Catch Diode Current Limit
n
Power Good Flag
n
Thermal Shutdown
n
Small, Thermally Enhanced 10-Lead MSOP and
(3mm × 3mm) DFN Packages
n
Automotive Battery Regulation
n
Power for Portable Products
n
Industrial Supplies
n
Gate Drive Bias
V
IN
BOOST
LT3973
SWEN/UVLO
PG
RT
C3
0.47µF
15pF
C2
22µF
C1
4.7µF
V
IN
5.6V TO 42V
V
OUT
5V
750mA
1M
316k
215k
f = 600kHz
L1
15µH
BD
OUT
FB
GND
OFF ON
3973 TA01a
Efficiency
LOAD CURRENT (mA)
0.01
40
EFFICIENCY (%)
POWER LOSS (mW)
80
70
60
50
90
1000.1 1
3973 TA01b
10
0.01
10
100
1
0.1
1000
V
IN
= 12V