LTC3803-5
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
4.8V Undervoltage Lockout Threshold
Operating Junction Temperature from –40°C to
150°C
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
The LTC
®
3803-5 is a constant frequency current mode
flyback controller optimized for driving 4.5V and 6V-rated
N-channel MOSFETs in high input voltage applications.
The LTC3803-5 operates from inputs as low as 5V. Con-
stant 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 LTC3803-5 provides
±1.5%
output voltage accuracy
and consumes only 240µA of quiescent current. Ground-
referenced current sensing allows LTC3803-5-based con-
verters to accept input supplies beyond the LTC3803-5’s
absolute maximum V
CC
. For simplicity, the LTC3803-5
can be powered from a high V
IN
through a resistor, due to
its internal 8V shunt regulator. An internal undervoltage
lockout shuts down the IC when the input voltage falls
below 3.2V, guaranteeing at least 3.2V of gate drive to the
external MOSFET.
The LTC3803-5 is available in a low profile (1mm) 6-lead
SOT-23 (ThinSOT
TM
) package.
APPLICATIO S
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42V and 12V Automotive Power Supplies
Telecom Power Supplies
Auxiliary/Housekeeping Power Supplies
Power Over Ethernet
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
ThinSOT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
V
IN
6V TO 50V
PDZ9.1B
22k
Dual Output Wide Input Range Converter
VPH5-0155
1µF
100V
3x
MMBTA42
10nF
LTC3803-5
I
TH
/RUN NGATE
GND
8.06k
V
FB
V
CC
SENSE
0.1µF
57.6k
ALL CAPACITORS ARE X7R, TDK
38035 TA01
10MQ100N
13V/0.3A
20mA MIN
LOAD
90
85 V
IN
= 12V
EFFICIENCY (%)
22µF
10V
1µF
100V
1µF
100V
80
V
IN
= 24V
75
70
V
IN
= 48V
65
60
V
IN
= 12V
0
2
6
8
4
OUTPUT POWER (W)
10
7.5k
PHM25NQ10T
4.7k
B3100
0.012Ω
6.5V/1.2A
47µF
10V
U
Efficiency and Power Loss
vs Output Power
V
IN
= 8V
3.0
2.5
U
U
POWER LOSS (W)
38035f
2.0
1.5
1.0
0.5
0
12
38035 TA01b
1
LTC3803-5
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 (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 Junction Temperature Range (Note 2)
LTC3803E-5 ....................................... – 40°C to 85°C
LTC3803H-5 (Note 3) ....................... – 40°C to 150°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
*LTC3803-5 internal clamp circuit self regulates V
CC
voltage to 8V.
ORDER PART
NUMBER
LTC3803HS6-5
LTC3803ES6-5
S6 PART
MARKING
LTBMH
LTBPF
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
T
JMAX
= 150°C,
θ
JA
= 165°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
TURNON
V
TURNOFF
V
HYST
V
CLAMP1mA
V
CLAMP25mA
I
CC
PARAMETER
V
CC
Turn On Voltage
V
CC
Turn Off Voltage
V
CC
Hysteresis
V
CC
Shunt Regulator Voltage
V
CC
Shunt Regulator Voltage
Input DC Supply Current
Normal Operation
Undervoltage
Shutdown Threshold (at I
TH
/RUN)
Start-Up Current Source
Regulated Feedback Voltage
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
Peak Slope Compensation Output Current
Soft-Start Time
LTC3803E-5: The
●
indicates specifications which apply over the full –40°C
to 85°C operating junction temperature range, otherwise specifications are at T
J
= 25°C. V
CC
= 5V, unless otherwise noted. (Note 2)
CONDITIONS
●
●
V
ITHSHDN
I
ITHSTART
V
FB
g
m
∆V
O(LINE)
∆V
O(LOAD)
I
FB
f
OSC
DC
ON(MIN)
DC
ON(MAX)
t
RISE
t
FALL
V
IMAX
I
SLMAX
t
SFST
V
TURNON
– V
TURNOFF
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
V
ITH/RUN
= 0V
0°C
≤
T
J
≤
85°C (Note 5)
–40°C
≤
T
J
≤
85°C (Note 5)
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)
(Note 7)
●
●
●
MIN
4
3.3
0.05
6.2
6.3
TYP
4.8
4
0.8
8
8.1
240
40
0.28
0.34
0.800
0.800
333
0.1
3
3
10
200
6.5
80
40
40
100
5
0.7
MAX
5.7
4.9
9.9
10.3
350
90
0.45
0.8
0.812
0.816
500
UNITS
V
V
V
V
V
µA
µA
V
µA
V
V
µA/V
mV/V
mV/µA
mV/µA
nA
kHz
%
%
ns
ns
mV
µA
ms
●
●
●
●
0.12
0.07
0.788
0.780
200
170
70
50
230
8.5
90
●
90
115
2
U
W
U
U
W W
W
38035f
LTC3803-5
ELECTRICAL CHARACTERISTICS
SYMBOL
V
TURNON
V
TURNOFF
V
HYST
V
CLAMP1mA
V
CLAMP25mA
I
CC
PARAMETER
V
CC
Turn On Voltage
V
CC
Turn Off Voltage
V
CC
Hysteresis
V
CC
Shunt Regulator Voltage
V
CC
Shunt Regulator Voltage
Input DC Supply Current
Normal Operation
Undervoltage
Shutdown Threshold (at I
TH
/RUN)
Start-Up Current Source
Regulated Feedback Voltage
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
Peak Slope Compensation Output Current
Soft-Start Time
LTC3803H-5: The
●
indicates specifications which apply over the full –40°C
to 150°C operating junction temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 5V, unless otherwise noted.
(Notes 2, 3)
CONDITIONS
●
●
V
ITHSHDN
I
ITHSTART
V
FB
g
m
∆V
O(LINE)
∆V
O(LOAD)
I
FB
f
OSC
DC
ON(MIN)
DC
ON(MAX)
t
RISE
t
FALL
V
IMAX
I
SLMAX
t
SFST
V
TURNON
– V
TURNOFF
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
V
ITH/RUN
= 0V
0°C
≤
T
J
≤
85°C (Note 5)
–40°C
≤
T
J
≤
150°C (Note 5)
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)
(Note 7)
●
●
●
MIN
3.9
3.2
0.05
6.2
6.3
TYP
4.8
4
0.8
8
8.1
240
40
0.28
0.34
0.800
0.800
333
0.1
3
3
10
200
6.5
80
40
40
100
5
0.7
MAX
5.7
4.9
10.4
10.7
350
100
0.45
1
0.812
0.820
500
UNITS
V
V
V
V
V
µA
µA
V
µA
V
V
µA/V
mV/V
mV/µA
mV/µA
nA
kHz
%
%
ns
ns
mV
µA
ms
●
●
●
●
0.08
0.07
0.788
0.780
200
170
70
50
230
8.5
90
●
85
115
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3803H-5 is guaranteed to meet specifications from –40°C
to 150°C. The LTC3803E-5 is guaranteed to meet specifications from 0°C
to 85°C with specifications over the –40°C to 85°C temperature range
assured by design, characterization and correlation with statistical process
controls.
Junction temperature (T
J)
is calculated from the ambient temperature T
A
and the power dissipation P
D
in the LTC3803-5 using the formula:
T
J
= T
A
+ (P
D
• 230°C/W)
Note 3:
High junction temperatures degrade operating lifetimes. Operating
lifetime at junction temperatures greater than 125°C is derated to 1000
hours.
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 5:
The LTC3803-5 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
Applications Information section.
Note 7:
Guaranteed by design.
38035f
3
LTC3803-5
TYPICAL PERFOR A CE CHARACTERISTICS
Reference Voltage vs Temperature
812
808
V
CC
= 5V
V
FB
VOLTAGE (mV)
V
FB
VOLTAGE (mV)
804
800
796
792
788
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
38035 G01
804
800
796
792
788
4.0
4.5
5.0 5.5 6.0
6.5 7.0
V
CC
SUPPLY VOLTAGE (V)
7.5
V
FB
VOLTAGE (mV)
Oscillator Frequency
vs Temperature
220
OSCILLATOR FREQUENCY (kHz)
V
CC
= 5V
OSCILLATOR FREQUENCY (kHz)
215
210
205
200
195
190
185
180
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
38035 G04
210
205
200
195
190
185
180
4.0
4.5
6.5 7.0
5.0 5.5 6.0
V
CC
SUPPLY VOLTAGE (V)
7.5
OSCILLATOR FREQUENCY (kHz)
V
CC
Undervoltage Lockout
Thresholds vs Temperature
6.0
5.5
5.0
VOLTS
9.5
V
TURNON
SUPPLY CURRENT (µA)
4.5
4.0
V
TURNOFF
3.5
3.0
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
3803 G07
V
CC
(V)
4
U W
Reference Voltage
vs Supply Voltage
812
808
T
A
= 25°C
V
CC
≤
V
CLAMP1mA
812
808
804
800
796
792
788
Reference Voltage
vs V
CC
Shunt Regulator Current
T
A
= 25°C
0
5
10
15
I
CC
(mA)
20
25
38035 G03
38035 F02
Oscillator Frequency
vs Supply Voltage
220
215
T
A
= 25°C
220
215
210
205
200
195
190
185
180
Oscillator Frequency
vs V
CC
Shunt Regulator Current
T
A
= 25°C
0
5
15
10
I
CC
(mA)
20
25
38035 G06
38035 G05
V
CC
Shunt Regulator Voltage
vs Temperature
10.5
10.0
280
300
I
CC
Supply Current
vs Temperature
V
CC
= 5V
V
ITH/RUN
= 1.3V
9.0
8.5
I
CC
= 25mA
I
CC
= 1mA
260
240
8.0
7.5
7.0
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
38035 G08
220
200
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
38035 G08
38035f
LTC3803-5
TYPICAL PERFOR A CE CHARACTERISTICS
Start-Up I
CC
Supply Current
vs Temperature
70
V
CC
= V
TURNON
– 0.1V
SHUTDOWN THRESHOLD (mV)
60
50
40
30
20
10
0
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
38035 G10
400
350
300
250
200
150
100
50
0
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
3803 G11
I
TH
/RUN PIN CURRENT SOURCE (nA)
START-UP SUPPLY CURRENT (µA)
Peak Current Sense Voltage
vs Temperature
120
115
V
CC
= 5V
1.4
1.2
SENSE PIN VOLTAGE (mV)
SOFT-START TIME (ms)
110
105
100
95
90
85
80
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
38035 G13
U W
I
TH
/RUN Shutdown Threshold
vs Temperature
500
450
1000
I
TH
/RUN Start-Up Current Source
vs Temperature
V
CC
= V
TURNON
+ 0.1V
900 V
ITH/RUN
= 0V
800
700
600
500
400
300
200
100
0
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
38035 G12
Soft-Start Time vs Temperature
V
CC
= 5V
1.0
0.8
0.6
0.4
0.2
0
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
38035 G14
38035f
5
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