LTC3803 Datasheet, PDF (1/12 Pages) Linear Technology – Constant Frequency Current Mode Flyback DC/DC Controller in ThinSOT

FEATURES
s _{VIN and VOUT Limited Only by External Components}
s _{Adjustable Slope Compensation}
s _{Internal Soft-Start}
s _{Constant Frequency 200kHz Operation}
s _{±1.5% Reference Accuracy}
s _{Current Mode Operation for Excellent Line and Load}
Transient Response
s _{No Minimum Load Requirement}
s _{Low Quiescent Current: 240µA}
s _{Low Profile (1mm) SOT-23 Package}
U
APPLICATIO S
s _{Telecom Power Supplies}
s _{42V and 12V Automotive Power Supplies}
s _{Auxiliary/Housekeeping Power Supplies}
s _{Power Over Ethernet}
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
Final Electrical Specifications
LTC3803
Constant Frequency
Current Mode Flyback
DC/DC Controller in ThinSOT
DESCRIPTION
August 2003
The LTC^®3803 is a constant frequency current mode
flyback controller optimized for driving 6V-rated 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-
referenced current sensing allows LTC3803-based con-
verters to accept input supplies beyond the LTC3803’s
absolute maximum V_CC. A micropower hysteretic start-up
feature allows efficient operation at high input voltages.
For simplicity, the LTC3803 can also be powered from a
high V_IN through a resistor, due to its internal 9.4V shunt
regulator. An internal undervoltage lockout shuts down
the LTC3803 when the input voltage falls below 4.6V,
guaranteeing at least 4.6V of gate drive to the external
MOSFET.
The LTC3803 is available in a low profile (1mm) 6-lead
SOT-23 (ThinSOT^TM) package.
TYPICAL APPLICATIO
5V Output Nonisolated Telecom Housekeeping Power Supply
Efficiency vs Load Current
10µF
10V
X5R
56k
0.0022µF
V_IN
36V TO 72V
10k
UPS840
T1
4.7µF ^•
100V
X5R
•
300µF*
6.3V
X5R
V_OUT
5V
2A MAX
V_CC
I_TH/RUN NGATE
LTC3803
GND SENSE
V_FB
FDC2512
68mΩ
20k 105k
3803 TA01
T1: COOPER CTX02-15242
*THREE 100µF UNITS IN PARALLEL
90
80 ^VIN ^{= 36V}
70
V_IN = 48V
60
V_IN = 60V
50
40
V_IN = 72V
30
20
10
0
0.1
1
I_OUT (A)
10
3803 TA02
3803i
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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