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PDF LTC3803 Data sheet ( Hoja de datos )
| Número de pieza | LTC3803 | |
| Descripción | Constant Frequency Current Mode Flyback DC/DC Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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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 VCC. A micropower hysteretic start-up
feature allows efficient operation at high input voltages.
For simplicity, the LTC3803 can also be powered from a
high VIN 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 (ThinSOTTM) package.
TYPICAL APPLICATIO
5V Output Nonisolated Telecom Housekeeping Power Supply
Efficiency vs Load Current
10µF
10V
X5R
56k
0.0022µF
VIN
36V TO 72V
10k
UPS840
T1
4.7µF •
100V
X5R
•
300µF*
6.3V
X5R
VOUT
5V
2A MAX
VCC
ITH/RUN NGATE
LTC3803
GND SENSE
VFB
FDC2512
68mΩ
20k 105k
3803 TA01
T1: COOPER CTX02-15242
*THREE 100µF UNITS IN PARALLEL
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
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.
1
1 page  
LTC3803
PI FU CTIO S
ITH/RUN (Pin 1): This pin performs two functions. It
serves as the error amplifier compensation point as well as
wwwt.hdaetarsuhne/est4huu.ctdomown control input. Nominal voltage range is
0.7V to 1.9V. Forcing this pin below 0.28V causes the
LTC3803 to shut down. In shutdown mode, the NGATE pin
is held low.
GND (Pin 2): Ground Pin.
VFB (Pin 3): Receives the feedback voltage from an exter-
nal resistive divider across the output.
SENSE (Pin 4): This pin performs two functions. It moni-
tors switch current by reading the voltage across an
external current sense resistor to ground. It also injects a
current ramp that develops slope compensation voltage
across an optional external programming resistor.
VCC (Pin 5): Supply Pin. Must be closely decoupled to GND
(Pin 2).
NGATE (Pin 6): Gate Drive for the External N-Channel
MOSFET. This pin swings from 0V to VCC.
BLOCK DIAGRA
5
VCC
800mV
REFERENCE
VCC
SHUNT
REGULATOR
0.3µA 0.28V
SHUTDOWN
+ COMPARATOR
–
VCC < VTURNON UNDERVOLTAGE
LOCKOUT
VFB
3
GND
2
SOFT-
START
CLAMP
ERROR
+ AMPLIFIER
–
1.2V
ITH/RUN
1
CURRENT
– COMPARATOR
R
+Q
S
20mV
200kHz
OSCILLATOR
SHUTDOWN
SWITCHING
LOGIC AND
BLANKING
CIRCUIT
VCC
GATE
DRIVER NGATE
6
SLOPE
COMP
CURRENT
RAMP
SENSE
4
3803 BD
3803i
5
5 Page 
PACKAGE DESCRIPTIO
www.datasheet4u.com
0.62
MAX
0.95
REF
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
1.22 REF
2.90 BSC
(NOTE 4)
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC 1.50 – 1.75
(NOTE 4)
PIN ONE ID
LTC3803
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.20 BSC
DATUM ‘A’
0.95 BSC
0.80 – 0.90
1.00 MAX
0.30 – 0.50 REF
0.09 – 0.20
NOTE:
(NOTE 3)
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
1.90 BSC
0.30 – 0.45
6 PLCS (NOTE 3)
0.01 – 0.10
S6 TSOT-23 0302
3803i
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC3803.PDF ] | |
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