Datasheet

LTC3803
1
3803fc
TYPICAL APPLICATION
DESCRIPTION
Constant Frequency
Current Mode Flyback
DC/DC Controller in ThinSOT
The LTC
®
3803 is a constant frequency current mode fl yback
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 V
CC
. A micropower hysteretic start-up feature
allows effi cient operation at high input voltages. For sim-
plicity, the LTC3803 can also be powered from a high V
IN
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 suffi cient
gate drive to the external MOSFET.
The LTC3803 is available in a low profi le (1mm) 6-lead
SOT-23 (ThinSOT™) package.
5V Output Nonisolated Telecom Housekeeping Power Supply
FEATURES
APPLICATIONS
n
V
IN
and V
OUT
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 Profi le (1mm) SOT-23 Package
n
Telecom Power Supplies
n
42V and 12V Automotive Power Supplies
n
Auxiliary/Housekeeping Power Supplies
n
Power Over Ethernet
Effi ciency vs Load Current
V
CC
I
TH
/RUN
LTC3803
GND
NGATE
SENSE
V
FB
UPS840
300µF*
6.3V
X5R
4.7µF
100V
X5R
10µF
10V
X5R
V
OUT
5V
2A MAX
3803 TA01
68mΩ
20k
10k
56k
0.0022µF
105k
FDC2512
T1: COOPER CTX02-15242
*THREE 100µF UNITS IN PARALLEL
T1
•
•
V
IN
36V TO 72V
I
OUT
(A)
0.1
EFFICIENCY (%)
50
60
70
10
3803 TA02
40
30
0
1
20
10
90
80
V
IN
= 36V
V
IN
= 72V
V
IN
= 60V
V
IN
= 48V
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
and ThinSOT and No R
SENSE
are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.