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 LTC3803-3 provides ±1.5% output voltage accuracy
and consumes only 240μA of quiescent current. Ground-
referenced current sensing allows LTC3803-3-based con-
verters to accept input supplies beyond the LTC3803-3’s
absolute maximum V
CC
. A micropower hysteretic start-up
feature allows efficient operation at high input voltages. For
simplicity, the LTC3803-3 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 LTC3803-3
when the input voltage is too low to provide sufficient gate
drive to the external MOSFET.
The LTC3803-3 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
–55°C to 150°C Operating Temperature Range
Constant Frequency 300kHz 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 Powered Devices
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.
TYPICAL APPLICATION
5V Output Nonisolated Telecom Housekeeping Power Supply
V
IN
36V TO 72V
T1
10k
1μF
10V
X5R
82k
470pF
1μF
100V
X5R
100
UPS840
V
OUT
5V
2A MAX
EFFICIENCY (%)
95
90
85
80
75
70
65
60
55
50
250
38033 TA01
Efficiency vs Load Current
V
OUT
= 5V
•
•
FDC2512
300μF*
6.3V
X5R
V
CC
I
TH
/RUN NGATE
LTC3803-3
GND
V
FB
20k
105k
T1: COOPER CTX02-15242
*THREE 100μF UNITS IN PARALLEL
SENSE
68mΩ
4.7k
150pF
200V
220Ω
V
IN
= 36V
V
IN
= 48V
V
IN
= 60V
V
IN
= 72V
500
750 1000 1250 1500 1750 2000
LOAD CURRENT (mA)
38033 TA02
38033fd
1
LTC3803-3
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
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 VCC
V
FB
, I
TH
/RUN Voltages............................... –0.3V to 3.5V
SENSE Voltage ............................................ –0.3V to 1V
NGATE Peak Output Current (<10μs) ......................... 1A
Operating Junction Temperature Range (Notes 2, 3)
LTC3803E-3, LTC3803I-3 ................... –40°C to 125°C
LTC3803H-3 ....................................... –40°C to 150°C
LTC3803MP-3 .................................... –55°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
*LTC3803-3 internal clamp circuit self regulates V
CC
voltage to 9.5V.
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
T
JMAX
= 150°C,
θ
JA
= 192°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3803ES6-3#PBF
LTC3803IS6-3#PBF
LTC3803HS6-3#PBF
LTC3803MPS6-3#PBF
LEAD BASED FINISH
LTC3803MPS6-3
TAPE AND REEL
LTC3803ES6-3#TRPBF
LTC3803IS6-3#TRPBF
LTC3803HS6-3#TRPBF
LTC3803MPS6-3#TRPBF
TAPE AND REEL
LTC3803MPS6-3#TR
PART MARKING*
LTCJS
LTCJT
LTCJT
LTCJT
PART MARKING
LTCJT
PACKAGE DESCRIPTION
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
PACKAGE DESCRIPTION
6-Lead Plastic TSOT-23
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–55°C to 150°C
TEMPERATURE RANGE
–55°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.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
ELECTRICAL CHARACTERISTICS
SYMBOL
V
TURNON
PARAMETER
V
CC
Turn On Voltage
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 8V, unless otherwise noted. (Notes 2, 3)
CONDITIONS
LTC3803E-3, LTC3803I-3
LTC3803H-3
LTC3803MP-3
LTC3803E-3
LTC3803I-3
LTC3803H-3
LTC3803MP-3
I
CC
= 1mA, V
ITH/RUN
= 0V
LTC3803E-3, LTC3803I-3
LTC3803H-3
LTC3803MP-3
l
l
l
l
l
l
l
l
l
l
l
MIN
7.6
7.5
7.5
4.6
4.4
4
4
1
8.3
8.3
8
TYP
8.7
8.7
8.7
5.7
5.7
5.7
5.7
3
9.4
9.4
9.4
MAX
9.2
9.25
9.4
7
7
7
7.2
UNITS
V
V
V
V
V
V
V
V
V
TURNOFF
V
CC
Turn Off Voltage
V
HYST
V
CLAMP1mA
V
CC
Hysteresis (V
TURNON
– V
TURN0FF
)
V
CC
Shunt Regulator Voltage
10.3
10.5
10.5
V
V
V
38033fd
2
LTC3803-3
ELECTRICAL CHARACTERISTICS
SYMBOL
V
CLAMP25mA
PARAMETER
V
CC
Shunt Regulator Voltage
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 8V, unless otherwise noted. (Notes 2, 3)
CONDITIONS
I
CC
= 25mA, V
ITH/RUN
= 0V
LTC3803E-3, LTC3803I-3
LTC3803H-3
LTC3803MP-3
LTC3803E-3, LTC3803I-3,
LTC3803H-3
LTC3803MP-3
(Note 4)
V
ITH/RUN
= 1.3V
V
CC
= V
TURNON
– 100mV
V
CC
> V
TURNON
, V
ITH/RUN
Falling
LTC3803E-3
LTC3803I-3, LTC3803H-3
LTC3803MP-3
V
ITH/RUN
= 0V
(Note 5)
0°C ≤ T
J
≤ 85°C
LTC3803E-3: –40°C ≤ T
J
≤ 85°C
LTC3803I-3: –40°C ≤ T
J
≤ 125°C
LTC3803H-3: –40°C ≤ T
J
≤ 150°C
LTC3803MP-3: –55°C ≤ T
J
≤ 150°C
R
SL
= 0 (Note 6)
LTC3803E-3
LTC3803I-3, LTC3803H-3
LTC3803MP-3
I
TH/RUN
Pin Load = ±5μA (Note 5)
(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 (Note 7)
70
270
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
MIN
8.4
8.4
8.1
0.05
0.03
TYP
9.5
9.5
9.5
0.6
0.6
240
40
MAX
10.5
10.7
10.7
UNITS
V
V
V
V
V
V
MARGIN
V
CLAMP1mA
– V
TURNON
Margin
I
CC
Input DC Supply Current
Normal Operation
Start-Up
Shutdown Threshold (at I
TH
/RUN)
350
90
0.45
0.45
0.45
0.4
0.812
0.812
0.820
0.820
0.820
115
115
120
500
50
330
9.6
90
μA
μA
V
V
V
μA
V
V
V
V
V
mV
mV
mV
μA/V
mV/V
nA
kHz
%
%
ns
ns
μA
ms
V
ITHSHDN
0.15
0.10
0.09
0.2
0.788
0.780
0.780
0.780
0.780
90
85
85
200
0.28
0.28
0.28
0.3
0.800
0.800
0.800
0.800
0.800
100
100
100
333
0.05
10
300
8
80
40
40
5
1.4
I
ITHSTART
V
FB
Start-Up Current Source
Regulated Feedback Voltage
V
IMAX
Peak Current Sense Voltage
g
m
ΔV
O(LINE)
I
FB
f
OSC
DC
ON(MIN)
DC
ON(MAX)
t
RISE
t
FALL
I
SLMAX
t
SFST
Error Amplifier Transconductance
Output Voltage Line 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
Soft-Start Time
Peak Slope Compensation Output Current (Note 7)
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 LTC3803-3 is tested under pulsed load conditions such
that T
J
≈ T
A
. The LTC3803E-3 is guaranteed to meet specifications
from 0°C to 85°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3803I-3 is guaranteed over the –40°C to 125°C operating junction
temperature range, the LTC3803H-3 is guaranteed over the –40°C to
150°C operating junction temperature range and the LTC3803MP-3 is
tested and guaranteed over the full –55°C to 150°C operating junction
temperature range. High junction temperatures degrade operating
lifetimes; operating lifetime is derated for junction temperatures greater
than 125°C. Note that the maximum ambient temperature consistent with
these specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal impedance and
other environmental factors.
Note 3:
Junction temperature 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 LTC3803-3 is tested in a feedback loop that servos V
FB
to the
output of the error amplifier while maintaining 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
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