back 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-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 efficient 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 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™) package.
V
IN
and V
OUT
Limited Only by External Components
Adjustable Slope Compensation
Internal Soft-Start
Constant Frequency 200kHz Operation
±1.5% Reference Accuracy
Current Mode Operation for Excellent Line and Load
Transient Response
No Minimum Load Requirement
Low Quiescent Current: 240μA
Low Profile (1mm) SOT-23 Package
APPLICATIONS
n
n
n
n
Telecom Power Supplies
42V and 12V Automotive Power Supplies
Auxiliary/Housekeeping Power Supplies
Power Over Ethernet
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation. ThinSOT is
a trademark of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
TYPICAL APPLICATION
5V Output Nonisolated Telecom Housekeeping Power Supply
V
IN
36V TO 72V
T1
10k
10μF
10V
X5R
56k
0.0022μF
4.7μF
100V
X5R
90
UPS840
V
OUT
5V
2A MAX
EFFICIENCY (%)
80
70
60
50
40
30
20
68mΩ
105k
3803 TA01
Efficiency vs Load Current
V
IN
= 36V
V
IN
= 48V
V
IN
= 60V
V
IN
= 72V
•
•
FDC2512
300μF*
6.3V
X5R
V
CC
I
TH
/RUN NGATE
LTC3803
GND
V
FB
20k
SENSE
10
0
0.1
1
I
OUT
(A)
3803 TA02
10
T1: COOPER CTX02-15242
*THREE 100μF UNITS IN PARALLEL
3803fb
1
LTC3803
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
I
TH
/RUN 1
GND 2
V
FB
3
6 NGATE
5 V
CC
4 SENSE
V
CC
to GND
Low Impedance Source ........................... –0.3V to 8V
Current Fed ........................................25mA into V
CC
*
NGATE Voltage ............................................–0.3V to V
CC
V
FB
, I
TH
/RUN Voltages............................... –0.3V to 3.5V
SENSE Voltage ............................................. –0.3V to 1V
NGATE Peak Output Current (<10μs) ......................... 1A
Operating Temperature Range (Note 2)
LTC3803E.............................................– 40°C to 85°C
LTC3803I............................................– 40°C to 125°C
LTC3803H ..........................................– 40°C to 150°C
Junction Temperature (Note 3) ............................. 150°C
Storage Temperature Range...................–65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
*LTC3803 internal clamp circuit self regulates V
CC
voltage to 9.5V.
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
T
JMAX
= 150°C,
θ
JA
= 230°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3803ES6#PBF
LTC3803IS6#PBF
LTC3803HS6#PBF
LEAD BASED FINISH
LTC3803ES6
LTC3803IS6
LTC3803HS6
TAPE AND REEL
LTC3803ES6#TRPBF
LTC3803IS6#TRPBF
LTC3803HS6#TRPBF
TAPE AND REEL
LTC3803ES6#TR
LTC3803IS6#TR
LTC3803HS6#TR
PART MARKING*
LTACV
LTBNC
LTBNC
PART MARKING*
LTACV
LTBNC
LTBNC
PACKAGE DESCRIPTION
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
PACKAGE DESCRIPTION
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 150°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 8V, unless otherwise noted. (Note 2)
SYMBOL
V
TURNON
V
TURNOFF
V
HYST
V
CLAMP1mA
PARAMETER
V
CC
Turn On Voltage
V
CC
Turn Off Voltage
V
CC
Hysteresis
V
CC
Shunt Regulator Voltage
CONDITIONS
LTC3803E
LTC3803H, LTC3803I
LTC3803E
LTC3803H, LTC3803I
V
TURNON
– V
TURNOFF
I
CC
= 1mA, V
ITH/RUN
= 0V
LTC3803E
LTC3803H, LTC3803I
I
CC
= 25mA, V
ITH/RUN
= 0V
LTC3803E
LTC3803H, LTC3803I
l
l
l
l
l
l
l
l
l
ELECTRICAL CHARACTERISTICS
MIN
7.8
7.7
4.6
4
1.5
8.3
8.3
8.4
8.4
TYP
8.7
8.7
5.7
5.7
3.0
9.4
9.4
9.5
9.5
MAX
9.2
9.25
6.8
6.8
UNITS
V
V
V
V
V
10.3
10.5
10.5
10.7
V
V
V
V
3803fb
V
CLAMP25mA
V
CC
Shunt Regulator Voltage
2
LTC3803
ELECTRICAL CHARACTERISTICS
SYMBOL
V
MARGIN
I
CC
I
CC(UV)
PARAMETER
V
CLAMP1mA
– V
TURNON
Margin
Input DC Supply Current in Normal
Operation
Input DC Supply Current in Undervoltage
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 8V, unless otherwise noted. (Note 2)
CONDITIONS
LTC3803E
LTC3803H, LTC3803I
(Note 4)
V
ITH/RUN
= 1.3V
V
CC
= V
TURNON
– 100mV
LTC3803E
LTC3803H, LTC3803I
V
CC
= V
TURNON
+ 100mV
LTC3803E
LTC3803H, LTC3803I
V
ITH/RUN
= 0V
(Note 5)
LTC3803E:
0°C ≤ T
J
≤ 85°C
–40°C ≤ T
J
≤ 85°C
LTC3803I:
0°C ≤ T
J
≤ 85°C
–40°C ≤ T
J
≤ 125°C
LTC3803H:
0°C ≤ T
J
≤ 85°C
–40°C ≤ T
J
≤ 150°C
I
TH/RUN
Pin Load = ±5μA (Note 5)
V
TURNOFF
< V
CC
< V
CLAMP
(Note 5)
I
TH
/RUN Sinking 5μA (Note 5)
I
TH
/RUN Sourcing 5μA (Note 5)
(Note 5)
V
ITH/RUN
= 1.3V
V
ITH/RUN
= 1.3V, V
FB
= 0.8V
V
ITH/RUN
= 1.3V, V
FB
= 0.8V
C
LOAD
= 3000pF
C
LOAD
= 3000pF
R
SL
= 0 (Note 6)
LTC3803E
LTC3803H, LTC3803I
(Note 7)
l
l
l
l
l
l
l
l
MIN
0.05
0.03
TYP
0.6
0.6
240
40
40
MAX
UNITS
V
V
350
90
110
0.45
0.46
0.4
μA
μA
μA
V
V
μA
V
ITHSHDN
Shutdown Threshold (at I
TH
/RUN)
0.15
0.09
0.2
0.28
0.28
0.3
I
ITHSTART
V
FB
Start-Up Current Source
Regulated Feedback Voltage
l
l
l
0.788
0.780
0.788
0.780
0.788
0.780
200
0.800
0.800
0.800
0.800
0.800
0.800
333
0.05
3
3
10
0.812
0.816
0.812
0.820
0.812
0.820
500
V
V
V
V
V
V
μA/V
mV/V
mV/μA
mV/μA
g
m
ΔV
O(LINE)
ΔV
O(LOAD)
I
FB
f
OSC
DC
ON(MIN)
DC
ON(MAX)
t
RISE
t
FALL
V
IMAX
Error Amplifier Transconductance
Output Voltage Line Regulation
Output Voltage Load Regulation
V
FB
Input Current
Oscillator Frequency
Minimum Switch On Duty Cycle
Maximum Switch On Duty Cycle
Gate Drive Rise Time
Gate Drive Fall Time
Peak Current Sense Voltage
50
240
8
90
nA
kHz
%
%
ns
ns
180
70
200
6
80
40
40
90
90
100
100
5
1.4
115
120
mV
mV
μA
ms
I
SLMAX
t
SFST
Peak Slope Compensation Output Current
Soft-Start Time
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3803E is guaranteed to meet specifications from 0°C to
85°C. Specifications over the – 40°C to 85°C operating temperature range
are assured by design, characterization and correlation with statistical
process controls. The LTC3803I is guaranteed to meet performance
specifications over the –40°C to 125°C operating temperature range. The
LTC3803H is guaranteed to meet performance specifications over the
–40°C to 150°C operating temperature range.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
• 230°C/W).
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 5:
The LTC3803 is tested in a feedback loop that servos V
FB
to the
output of the error amplifier while maintaing I
TH
/RUN at the midpoint of
the current limit range.
Note 6:
Peak current sense voltage is reduced dependent on duty cycle
and an optional external resistor in series with the SENSE pin (R
SL
). For
details, refer to the programmable slope compensation feature in the
PCB设计
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