LTC3803-3
Constant Frequency
Current Mode Flyback
DC/DC Controller in ThinSOT
FEATURES
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DESCRIPTIO
V
IN
and V
OUT
Limited Only by External Components
Adjustable Slope Compensation
Internal Soft-Start
–40°C to 125°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
The LTC
®
3803-3 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 LTC3803-3 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 9.4V shunt
regulator. An internal undervoltage lockout shuts down
the LTC3803-3 when the input voltage falls below 4.4V,
guaranteeing at least 4.4V of gate drive to the external
MOSFET.
The LTC3803-3 is available in a low profile (1mm) 6-lead
SOT-23 (ThinSOT
TM
) package.
APPLICATIO S
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Telecom Power Supplies
42V and 12V Automotive Power Supplies
Auxiliary/Housekeeping Power Supplies
Power Over Ethernet Powered Devices
, 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 APPLICATIO
V
IN
36V TO 72V
5V Output Nonisolated Telecom Housekeeping Power Supply
UPS840
T1
10k
1μF
10V
X5R
82k
470pF
1μF
100V
X5R
100
V
OUT
5V
2A MAX
EFFICIENCY (%)
95
90
85
80
75
70
65
60
55
•
•
FDC2512
300μF*
6.3V
X5R
V
CC
I
TH
/RUN NGATE
LTC3803-3
GND
V
FB
20k
105k
38033 TA01
4.7k
68mΩ
SENSE
150pF
200V
220Ω
50
250
T1: COOPER CTX02-15242
*THREE 100μF UNITS IN PARALLEL
U
Efficiency vs Load Current
V
OUT
= 5V
V
IN
= 36V
V
IN
= 48V
V
IN
= 60V
V
IN
= 72V
500
750 1000 1250 1500 1750 2000
LOAD CURRENT (mA)
38033 TA02
U
U
38033fa
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 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-3 ....................................... – 40°C to 85°C
LTC3803I-3 ...................................... – 40°C to 125°C
Junction Temperature (Note 3) ............................ 125°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
= 125°C,
θ
JA
= 230°C/W
ORDER PART NUMBER
LTC3803ES6-3
LTC3803IS6-3
S6 PART MARKING
LTCJS
LTCJT
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
TURNON
V
TURNOFF
V
HYST
V
CLAMP1mA
V
CLAMP25mA
V
MARGIN
I
CC
PARAMETER
V
CC
Turn On Voltage
V
CC
Turn Off Voltage
V
CC
Hysteresis (V
TURNON
– V
TURN0FF
)
V
CC
Shunt Regulator Voltage
V
CC
Shunt Regulator Voltage
V
CLAMP1mA
– V
TURNON
Margin
Input DC Supply Current
Normal Operation
Start-Up
Shutdown Threshold (at I
TH
/RUN)
The
●
indicates 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
●
MIN
7.6
4.6
4.4
1
8.3
8.4
0.05
●
●
●
●
●
●
TYP
8.7
5.7
5.7
3
9.4
9.5
0.6
240
40
MAX
9.2
7
7
10.3
10.5
UNITS
V
V
V
V
V
V
V
LTC3803E-3
LTC3803I-3
I
CC
= 1mA, V
ITH/RUN
= 0V
I
CC
= 25mA, V
ITH/RUN
= 0V
(Note 4)
V
ITH/RUN
= 1.3V
V
CC
= V
TURNON
– 100mV
V
CC
= V
TURNON
– 100mV
LTC3803E-3
LTC3803I-3
V
ITH/RUN
= 0V
0°C
≤
T
A
≤
85°C
LTC3803E-3: –40°C
≤
T
A
≤
85°C
LTC3803I-3: –40°C
≤
T
A
≤
125°C
R
SL
= 0 (Note 6)
LTC3803E-3
LTC3803I-3
I
TH/RUN
Pin Load =
±5μA
(Note 5)
V
TURNOFF
< V
CC
< V
CLAMP
(Note 5)
(Note 5)
V
ITH/RUN
= 1.3V
350
90
0.45
0.45
0.4
0.812
0.812
0.820
115
115
500
50
330
V
ITHSHDN
●
●
0.15
0.10
0.2
0.788
0.780
0.780
90
85
200
0.28
0.28
0.3
0.800
0.800
0.800
100
100
333
0.05
10
I
ITHSTART
V
FB
Start-Up Current Source
Regulated Feedback Voltage (Note 5)
●
●
●
●
V
IMAX
Peak Current Sense Voltage
g
m
ΔV
O(LINE)
I
FB
f
OSC
Error Amplifier Transconductance
Output Voltage Line Regulation
V
FB
Input Current
Oscillator Frequency
270
300
38033fa
2
U
W
U
U
W W
W
μA
μA
V
V
μA
V
V
V
V
V
μA/V
mV/V
nA
kHz
LTC3803-3
ELECTRICAL CHARACTERISTICS
SYMBOL
DC
ON(MIN)
DC
ON(MAX)
t
RISE
t
FALL
I
SLMAX
t
SFST
PARAMETER
Minimum Switch On Duty Cycle
Maximum Switch On Duty Cycle
Gate Drive Rise Time
Gate Drive Fall Time
Peak Slope Compensation Output Current
Soft-Start Time
The
●
indicates 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
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)
(Note 7)
70
MIN
TYP
8
80
40
40
5
1.4
MAX
9.6
90
UNITS
%
%
ns
ns
μA
ms
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-3 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-3 is guaranteed to meet performance
specifications over the –40°C to 125°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 LTC3803-3 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
Applications Information section.
Note 7:
Guaranteed by design.
38033fa
3
LTC3803-3
TYPICAL PERFOR A CE CHARACTERISTICS
Reference Voltage vs Temperature
812
808
801.0
V
CC
= 8V
V
FB
VOLTAGE (mV)
V
FB
VOLTAGE (mV)
804
800
796
792
788
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
38033 G01
V
FB
VOLTAGE (mV)
6
6.5
8
7.5
8.5
V
CC
SUPPLY VOLTAGE (V)
7
9
9.5
Oscillator Frequency
vs Temperature
330
V
CC
= 8V
OSCILLATOR FREQUENCY (kHz)
330
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY (kHz)
320
310
300
290
280
270
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
38033 G04
V
CC
Undervoltage Lockout
Thresholds vs Temperature
10.0
9.5
V
CC
UNDERVOLTAGE LOCKOUT (V)
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
V
TURNON
9.7
V
CC
(V)
9.6
9.5
9.4
9.3
I
CC
= 25mA
SUPPLY CURRENT (μA)
V
TURNOFF
4.5
–50 –30 –10 10 30 50 80 90 110 130
TEMPERATURE (°C)
38033 G07
4
U W
T
A
= 25°C unless otherwise noted.
Reference Voltage
vs V
CC
Shunt Regulator Current
804
803
802
801
800
799
798
797
796
0
5
10
15
I
CC
(mA)
20
25
38033 G03
Reference Voltage
vs Supply Voltage
800.8
800.6
800.4
800.2
800.0
799.8
799.6
799.4
799.2
799.0
V
CC
≤
V
CLAMP1mA
38033 F02
Oscillator Frequency
vs Supply Voltage
330
320
310
300
290
280
270
6
6.5
8.5
7
7.5
8
V
CC
SUPPLY VOLTAGE (V)
9
Oscillator Frequency
vs V
CC
Shunt Regulator Current
320
310
300
290
280
270
0
5
10
15
20
I
CC
(mA)
25
30
35
38033 G05
38033 G06
V
CC
Shunt Regulator Voltage
vs Temperature
10.0
9.9
9.8
300
275
250
225
200
175
350
325
I
CC
Supply Current
vs Temperature
V
CC
= 8V
V
ITH/RUN
= 1.3V
I
CC
= 1mA
9.2
9.1
9.0
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
38033 G08
150
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
38033 G09
38033fa
LTC3803-3
TYPICAL PERFOR A CE CHARACTERISTICS
Start-Up I
CC
Supply Current
vs Temperature
70
V
CC
= V
TURNON
– 0.1V
SHUTDOWN THRESHOLD (mV)
START-UP SUPPLY CURRENT (μA)
60
50
40
30
20
10
0
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
38033 G10
I
TH
/RUN PIN CURRENT SOURCE (nA)
Peak Current Sense Voltage
vs Temperature
120
115
V
CC
= 8V
SENSE PIN VOLTAGE (mV)
SOFT-START TIME (ms)
110
105
100
95
90
85
80
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
38033 G13
U W
T
A
= 25°C unless otherwise noted.
I
TH
/RUN Start-Up Current Source
vs Temperature
700
600
500
400
300
200
100
0
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
38033 G12
I
TH
/RUN Shutdown Threshold
vs Temperature
450
400
350
300
250
200
150
100
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
38033 G11
V
CC
= V
TURNON
+ 0.1V
V
ITH/RUN
= 0V
Soft-Start Time vs Temperature
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
38033 G14
38033fa
5
FPGA/CPLD
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