LT3845_1 Datasheet, PDF (1/26 Pages) Linear Technology – High Voltage Synchronous Current Mode Step-Down Controller with Adjustable Operating Frequency

FEATURES
■ _{High Voltage Operation: Up to 60V}
■ _{Synchronizable Up to 600kHz}
■ _{Adjustable Constant Frequency: 100kHz to 500kHz}
■ _{Output Voltages Up to 36V}
■ _{Adaptive Nonoverlap Circuitry Prevents Switch}
Shoot-Through
■ _{Reverse Inductor Current Inhibit for Discontinuous}
Operation Improves Efficiency with Light Loads
■ _{Programmable Soft-Start}
■ _{120μA No Load Quiescent Current}
■ _{10μA Shutdown Supply Current}
■ _{1% Regulation Accuracy}
■ _{Standard Gate N-Channel Power MOSFETs}
■ _{Current Limit Unaffected by Duty Cycle}
■ _{Reverse Overcurrent Protection}
■ _{16-Lead Thermally Enhanced TSSOP Package,}
16-Pin PDIP
APPLICATIONS
■ _{12V and 42V Automotive and Heavy Equipment}
■ _{48V Telecom Power Supplies}
■ _{Avionics and Industrial Control Systems}
■ _{Distributed Power Converters}
LT3845
High Voltage Synchronous
Current Mode Step-Down
Controller with Adjustable
Operating Frequency
DESCRIPTION
The LT^®3845 is a high voltage, synchronous, current
mode controller used for medium to high power, high
efficiency supplies. It offers a wide 4V to 60V input range
(7.5V minimum start-up voltage). An onboard regulator
simplifies the biasing requirements by providing IC power
directly from V_IN.
Burst Mode^® operation maintains high efficiency at light
loads by reducing IC quiescent current to 120μA. Light
load efficiency is also improved with the reverse inductor
current inhibit function which supports discontinuous
operation.
Additional features include adjustable fixed operating
frequency that can be synchronized to an external clock
for noise sensitive applications, gate drivers capable of
driving large N-channel MOSFETs, a precision undervoltage
lockout, 10μA shutdown current, short-circuit protection
and a programmable soft-start.
The LT3845 is available in a 16-lead thermally enhanced
TSSOP package and 16-pin through hole N package.
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.. Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258.
TYPICAL APPLICATION
High Voltage Step-Down Regulator 48V to 12V at 75W
V_IN
20V TO 55V
2.2μF
100V
47μF
63V
82.5k
1M
1500pF
V_IN
BOOST
SHDN
TG
LT3845
C_SS
SW
BURST_EN
V_CC
16.2k
143k
20k
2200pF
100pF
49.9k
V_FB
V_C
SYNC
f_SET
BG
PGND
SENSE⁺
SENSE^–
SGND
0.1μF
BAS521
Si7370DP
Si7370DP
15μH
B160
0.01Ω
V_OUT
12V
75W
33μF
×3
1μF
1N4148
3845 TA01a
Efficiency and Power Loss vs
Load Current
100
7
V_IN = 48V
95
6
90
5
85
4
80
3
75
2
LOSS
70
1
65
0.1
1
LOAD CURENT (A)
0
10
3845 TA01b
3845fd
1