LT3509_15 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 _{Overvoltage 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 (4mm × 3mm)}
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, LTM, Burst Mode, 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
3.3V and 5V Dual Output Step-Down Converter
6.5V TO 36V
(TRANSIENT TO 60V)
2.2μF
V_IN
BD
3.3V
700mA
6.8μH
0.1μF
31.6k
MBRM140
BOOST1 BOOST2
SW1
SW2
LT3509
DA1
DA2
FB1
FB2
0.1μF 10μH
MBRM140
53.6k
10μF
RUN/SS1 RUN/SS2
10.2k
1nF
SYNC
RT
1nF
GND
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
3509fc
1