LTC3803
Constant Frequency
Current Mode Flyback
DC/DC Controller in ThinSOT
FEATURES
n VIN and VOUT Limited Only by External Components
n Adjustable Slope Compensation
n Internal Soft-Start
n Constant Frequency 200kHz Operation
n ±1.5% Reference Accuracy
n Current Mode Operation for Excellent Line and Load
Transient Response
n No Minimum Load Requirement
n Low Quiescent Current: 240μA
n Low Profile (1mm) SOT-23 Package
APPLICATIONS
n Telecom Power Supplies
n 42V and 12V Automotive Power Supplies
n Auxiliary/Housekeeping Power Supplies
n Power Over Ethernet
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
and ThinSOT and No RSENSE are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
DESCRIPTION
The LTC®3803 is a constant frequency current mode flyback
controller optimized for driving N-channel MOSFETs in high
input voltage applications. Constant frequency operation
is maintained down to very light loads, resulting in less
low frequency noise generation over a wide range of load
currents. Slope compensation can be programmed with
an external resistor.
The LTC3803 provides ±1.5% output voltage accuracy and
consumes only 240μA of quiescent current. Ground-refer-
enced current sensing allows LTC3803-based converters
to accept input supplies beyond the LTC3803’s absolute
maximum VCC. A micropower hysteretic start-up feature
allows efficient operation at high input voltages. For sim-
plicity, the LTC3803 can also be powered from a high VIN
through a resistor, due to its internal shunt regulator. An
internal undervoltage lockout shuts down the LTC3803
when the input voltage is too low to provide sufficient
gate drive to the external MOSFET.
The LTC3803 is available in a low profile (1mm) 6-lead
SOT-23 (ThinSOT™) package.
TYPICAL APPLICATION
5V Output Nonisolated Telecom Housekeeping Power Supply
10μF
10V
X5R
56k
0.0022μF
VIN
36V TO 72V
10k
UPS840
T1
4.7μF •
100V
X5R
•
VCC
ITH/RUN NGATE
LTC3803
GND SENSE
VFB
FDC2512
68mΩ
300μF*
6.3V
X5R
VOUT
5V
2A MAX
20k 105k
3803 TA01
T1: COOPER CTX02-15242
*THREE 100μF UNITS IN PARALLEL
Efficiency vs Load Current
90
80 VIN = 36V
70
VIN = 48V
60
VIN = 60V
50
40
VIN = 72V
30
20
10
0
0.1
1
IOUT (A)
10
3803 TA02
3803fc
1
