LT3645_15 Datasheet, PDF (1/24 Pages) Linear Technology – 36V 500mA Step-Down Regulator and 200mA LDO

LT3645
36V 500mA Step-Down
Regulator and 200mA LDO
FEATURES
n _{Wide Input Range:}
Operation from 3.6V to 36V
Overvoltage Lockout Protects Circuit Through
55V Transients on Input
n _{500mA Output Current Switching Regulator}
n _{High Switching Frequency: 750kHz}
n _{200mA Low Dropout Linear Regulator}
1.2V to 16V Input; 0.8V to 8V Output
310mV Dropout Voltage V_CC2 to OUT2
n _{Precision Programmable Undervoltage Lockout}
n _{Short-Circuit Robust}
n _{Internal Soft-Start}
n _{<2μA Shutdown Current}
n _{Small Thermally Enhanced 16-Lead (3mm × 3mm)}
QFN and 12-Lead MSE Packages
APPLICATIONS
n _{Automotive CMOS Image Sensors}
n _{Industrial/Automotive Micro-Controller Supply}
DESCRIPTION
The LT^®3645 is a dual output regulator combining a 500mA
buck regulator and a 200mA low dropout linear regula-
tor (LDO). The wide input voltage range of 3.6V to 36V
makes the LT3645 suitable for regulating power from a
wide variety of sources, including 24V industrial supplies
and automotive batteries. Its high operating frequency
allows the use of tiny, low cost inductors and capacitors,
resulting in a very small solution.
Cycle-by-cycle current limit and frequency foldback pro-
vide protection against shorted outputs. Soft-start and
frequency foldback eliminate input current surge during
start-up.
The linear regulator operates from the V_CC2 pin at voltages
down to 1.2V. It supplies 200mA of output current with a
typical dropout voltage of 310mV.
Other features of the LT3645 include a <2μA shutdown,
short circuit protection, soft-start and thermal shutdown.
The LT3645 is available in the thermally enhanced 16-lead
(3mm × 3mm) QFN package, or a 12-lead MSE package.
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
TYPICAL APPLICATION
3.3V/5V Step-Down Converter
6.2V TO 36V
ON OFF
BOOST
V_IN
SW
1μF
LT3645
DA
EN/UVLO
FB
0.1μF
15μH
52.3k
10μF
10k
5V
300mA
PGOOD
EN2
NPG
V_CC2
OUT2
FB2
GND
31.6k
2.2μF
10k
3645 TA01a
3.3V
200mA
Buck Regulator Efficiency
90
V_OUT = 5V
80
V_OUT = 3.3V
70
60
V_IN = 12V
50
0
100 200 300 400 500
LOAD CURRENT (mA)
3645 TA01b
3645f
1