LT3845
High Voltage Synchronous
Current Mode Step-Down
Controller with Adjustable
Operating Frequency
FEATURES
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
■
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
directly from V .
IN
■
Reverse Inductor Current Inhibit for Discontinuous
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.
Operation Improves Efficiency with Light Loads
■
Programmable Soft-Start
■
120μA No Load Quiescent Current
■
10μA Shutdown Supply Current
■
1% Regulation Accuracy
■
Additional features include adjustable fixed operating
frequency that can be synchronized to an external clock
for noise sensitive applications, gate drivers capable of
drivinglargeN-channelMOSFETs,aprecisionundervoltage
lockout, 10μA shutdown current, short-circuit protection
and a programmable soft-start.
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
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.
■
12V and 42V Automotive and Heavy Equipment
■
48V Telecom Power Supplies
■
Avionics and Industrial Control Systems
Distributed Power Converters
■
TYPICAL APPLICATION
Efficiency and Power Loss vs
Load Current
High Voltage Step-Down Regulator 48V to 12V at 75W
V
IN
20V TO 55V
100
95
90
85
80
75
70
65
7
6
5
4
3
2
1
0
V
IN
= 48V
0.1μF
2.2μF
100V
1M
V
BOOST
TG
IN
47μF
63V
Si7370DP
SHDN
V
0.01Ω
LT3845
OUT
1500pF
C
SW
12V
82.5k
SS
BAS521
15μH
B160
75W
BURST_EN
V
CC
33μF
×3
Si7370DP
V
V
BG
FB
C
20k
PGND
LOSS
100pF
16.2k
+
SYNC
SENSE
2200pF
–
1μF
f
SENSE
SET
SGND
49.9k
0.1
10
1N4148
1
143k
LOAD CURENT (A)
3845 TA01a
3845 TA01b
3845fd
1