LT3509 Datasheet, PDF (1/24 Pages) Linear Technology – Dual 36V, 700mA Step-Down Regulator

LT3509
Dual 36V, 700mA
Step-Down Regulator
FEATURES
n _{Two 700mA Switching Regulators with Internal}
Power Switches
n _{Wide 3.6V to 36V Operating Range}
n _{Over-Voltage Lockout Protects Circuit Through 60V}
Supply Transients
n _{Short Circuit Robust}
n _{Low Dropout Voltage − 95% Maximum Duty Cycle}
n _{Adjustable 300kHz to 2.2MHz Switching Frequency}
Synchronizable Over the Full Range
n _{Uses Small Inductors and Ceramic Capacitors}
n _{Integrated Boost Diodes}
n _{Internal Compensation}
n _{Thermally Enhanced 14 Lead (4 mm × 3 mm)}
DFN and 16 Lead MSOP Packages
APPLICATIONS
n _{Automotive Electronics}
n _{Industrial Controls}
n _{Wall Transformer Regulation}
n _{Networking Devices}
n _{CPU, DSP, or FPGA Power}
DESCRIPTION
The LT^®3509 is a dual, current mode, step-down switching
regulator, with internal power switches each capable of
providing 700mA output current. This regulator provides a
compact and robust solution for multi-rail systems in harsh
environments. It incorporates several protection features
including overvoltage lockout and cycle by cycle current
limit. Thermal shutdown provides additional protection.
The loop compensation components and the boost diodes
are integrated on-chip. Switching frequency is set by a
single external resistor. External synchronization is also
possible. The high maximum switching frequency allows
the use of small inductors and ceramic capacitors for low
ripple. Constant frequency operation above the AM band
avoids interference with radio reception, making the LT3509
well suited for automotive applications. Each regulator
has an independent shutdown and soft-start control pin.
When both converters are powered down, the common
circuitry enters a low current shutdown state.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATION
6.5V TO 36V
(Transient
to 60V)
3.3V
700mA
10μF
3.3V and 5V Dual Output Step-Down Converter
2.2μF
6.8μH
0.1μF
31.6k
MBRM140
10.2k
1nF
V_IN
BOOST1
BD
BOOST2
SW1
SW2
LT3509
DA1
DA2
FB1
FB2
RUN/SS1 RUN/SS2
SYNC
R_T
GND
0.1μF 10μH
MBRM140
53.6k
1nF
60.4k
10.2k
5V
700mA
22μF
f_SW = 700kHz
3509 TA01a
Efficiency
90
85
V_OUT = 5V
80
V_OUT = 3.3V
75
70
65
60
55 ^VIN ^{= 12V}
f_SW = –700kHz
50
0.0 0.1 0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6 0.7
3509 TA01b
3509f
1