LT3505 Datasheet, PDF (1/24 Pages) Linear Technology – 1.2A, Step-Down Switching Regulator in 3mm × 3mm DFN

LT3505
1.2A, Step-Down
Switching Regulator in
3mm × 3mm DFN
FEATURES
! _{Wide Input Range: 3.6V to 36V Operating,}
40V Maximum
! _{Up to 1.2A Output Current}
! _{Resistor-Programmable Fixed-Frequency Operation}
from 200kHz to 3MHz
! _{Output Adjustable Down to 780mV}
! _{Short-Circuit Robust}
! _{Uses Tiny Capacitors and Inductors}
! _Soft-Start
! _{Low Shutdown Current: <2µA}
! _{Low VCESAT Switch: 350mV at 1A}
! _{Thermally Enhanced, Low Profile 3mm x 3mm}
DFN-8 and MSOP-8 Packages
APPLICATIONS
! _{Automotive Battery Regulation}
! _{Industrial Control Supplies}
! _{Wall Transformer Regulation}
! _{Distributed Supply Regulation}
! _{Battery-Powered Equipment}
DESCRIPTION
The LT^®3505 is a current mode PWM step-down DC/DC
converter with an internal 1.4A power switch. The wide
operating input range of 3.6V to 36V (40V maximum)
makes the LT3505 ideal for regulating power from a wide
variety of sources, including unregulated wall transform-
ers, 24V industrial supplies and automotive batteries. The
oscillator can be programmed for high frequency operation
allowing the use of tiny, low cost external components or
it can be programmed for lower frequency operation to
maximize efficiency.
Cycle-by-cycle current limit provides protection against
shorted outputs and soft-start eliminates input current
surge during start-up. The low current (<2µA) shutdown
mode provides output disconnect, enabling easy power
management in battery-powered systems.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
750kHz, 3.3V Step-Down Converter
V_IN
4.2V TO 36V
ON OFF
V_IN
BOOST
SHDN
SW
LT3505
FB
R_T
GND
V_C
0.1µF _10µH
36.5k
11.3k
22pF
V_OUT
3.3V
1.1A, V_IN > 5V
1.2A, V_IN > 8V
10µF
75.0k
1µF
69.8k
68pF
3505 TA01
Efficiency
90
85
80
75
70
65
60 _{VIN = 12V}
55
V_OUT = 3.3V
f_SW = 750kHz
L = 10 H
50
0 0.2 0.4 0.6 0.8 1.0 1.2
LOAD CURRENT (A)
3505fc
1