LTC3805-5
Adjustable Frequency
Current Mode Flyback/
Boost/SEPIC DC/DC Controller
FEATURES
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DESCRIPTION
The LTC
®
3805-5 is a current mode DC/DC controller de-
signed to drive an N-channel MOSFET in flyback, boost
and SEPIC converter applications. Operating frequency
and slope compensation can be programmed by external
resistors. Programmable overcurrent sensing protects
the converter from overload and short-circuit conditions.
Soft-start can be programmed using an external capacitor
and the soft-start capacitor also programs an automatic
restart feature.
The LTC3805-5 provides ±1.5% output voltage accuracy
and consumes only 360μA of quiescent current during
normal operation and only 40μA during micropower start-
up. Using a 9.5V internal shunt regulator, the LTC3805-5
can be powered from a high V
IN
through a resistor or it
can be powered directly from a low impedance DC voltage
from 4.7V to 8.8V.
The LTC3805-5 is available in the 10-lead MSOP package
and the 3mm
×
3mm DFN package.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
V
IN
and V
OUT
Limited Only by External Components
4.5V Undervoltage Lockout Threshold
Adjustable Slope Compensation
Adjustable Overcurrent Protection With Automatic
Restart
Adjustable Operating Frequency (70kHz to 700kHz)
With One External Resistor
Synchronizable to an External Clock
±1.5% Reference Accuracy
Only 100mV Current Sense Voltage Drop
RUN Pin With Precision Threshold and Adjustable
Hysteresis
Programmable Soft-Start With One External Capacitor
Low Quiescent Current: 360μA
Small 10-Lead MSOP and 3mm
×
3mm DFN
APPLICATIONS
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Automotive Power Supplies
Telecom Power Supplies
Isolated Electronic Equipment
Auxiliary/Housekeeping Power Supplies
Power over Ethernet
TYPICAL APPLICATION
Efficiency and Power Loss vs Load Current
5V to 12V/1A Boost Converter
4.3μH
V
IN
5V
22μF
×2
RUN
I
TH
20k
470pF
0.1μF
118k
SSFLT
FS
SYNC
GND
UPS840
V
OUT
12V
1A
EFFICIENCY (%)
100
2.5
95
V
CC
GATE
LTC3805-5
OC
I
SENSE
FB
3k
191k
1.33k
100μF
5V EFFICIENCY
8.5V EFFICIENCY
2.0
POWER LOSS (W)
90
8.5V LOSS
85
5V LOSS
1.5
1
80
8mΩ
13.7k
38055 TA01
0.5
75
0.01
1
0.1
LOAD CURRENT (A)
10
38055TA01b
0
38055fb
1
LTC3805-5
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
CC
to GND
Low Impedance Source ........................ –0.3V to 8.8V
Current Fed ........................................25mA into V
CC
*
SYNC ........................................................... –0.3V to 6V
SSFLT ........................................................... –0.3V to 5V
FB, I
TH
, FS ................................................. –0.3V to 3.5V
RUN ........................................................... –0.3V to 18V
OC, I
SENSE
.................................................... –0.3V to 1V
Operating Junction Temperature Range (Notes 2, 3)
E-Grade ................................................–40°C to 85°C
I-Grade............................................... –40°C to 125°C
H-Grade ............................................. –40°C to 150°C
Junction Temperature ........................................... 125°C
Storage Temperature Range...................–65°C to 125°C
Lead Temperature (Soldering, 10 sec)
LTC3805EMSE-5 Only ....................................... 300°C
*LTC3805-5 internal clamp circuit regulates V
CC
voltage to 9.5V
PIN CONFIGURATION
TOP VIEW
SSFLT
I
TH
FB
RUN
FS
1
2
3
4
5
11
10 GATE
9 V
CC
8 OC
7 I
SENSE
6 SYNC
TOP VIEW
SSFLT
I
TH
FB
RUN
FS
1
2
3
4
5
10
9
8
7
6
GATE
V
CC
OC
I
SENSE
SYNC
11
DD PACKAGE
10-LEAD (3mm 3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 45°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE CONNECTED TO GND
MSE PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 45°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE CONNECTED TO GND
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
LTC3805EMSE-5#TRMPBF LTC3805EMSE-5#TRPBF
LTDGX
10-Lead Plastic MSOP
LTC3805IMSE-5#TRMPBF LTC3805IMSE-5#TRPBF
LTDGX
10-Lead Plastic MSOP
LTC3805HMSE-5#TRMPBF LTC3805HMSE-5#TRPBF
LTDGX
10-Lead Plastic MSOP
LTC3805EDD-5#TRMPBF
LTC3805EDD-5#TRPBF
LDHB
10-Lead (3mm
×
3mm) Plastic DFN
LTC3805IDD-5#TRMPBF
LTC3805IDD-5#TRPBF
LDHB
10-Lead (3mm
×
3mm) Plastic DFN
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on 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/
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 150°C
–40°C to 85°C
–40°C to 125°C
ELECTRICAL CHARACTERISTICS
SYMBOL
V
TURNON
V
TURNOFF
V
HYST
V
CLAMP1mA
V
CLAMP25mA
PARAMETER
V
CC
Turn-On Voltage
V
CC
Turn-Off Voltage
V
CC
Hysteresis
V
CC
Shunt Regulator Voltage
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
= 5V, unless otherwise noted (Note 2).
CONDITIONS
V
CC
Rising
V
CC
Falling
I
CC
= 1mA, V
RUN
= 0
I
CC
= 25mA, V
RUN
= 0
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MIN
4.3
3.75
8.8
8.9
TYP
4.5
3.95
0.55
9.25
9.5
MAX
4.7
4.15
9.65
9.9
UNITS
V
V
V
V
V
38055fb
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LTC3805-5
ELECTRICAL CHARACTERISTICS
SYMBOL
I
CC
PARAMETER
Input DC Supply Current
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C, V
CC
= 5V, unless otherwise noted (Note 2).
CONDITIONS
Normal Operation (f
OSC
= 200kHz)
(Note 4)
V
RUN
< V
RUNON
or V
CC
< V
TURNON
– 100mV
(Micropower Start-Up)
V
CC
= V
TURNON
+ 100mV
V
CC
= V
TURNON
+ 100mV
0°C ≤ T
A
≤ 85°C (E-Grade) (Note 5)
–40°C ≤ T
A
≤ 85°C (E-Grade) (Note 5)
–40°C ≤ T
A
≤ 125°C (I-Grade) (Note 5)
–40°C ≤ T
A
≤ 150°C (H-Grade) (Note 5)
V
ITH
= 1.3V (Note 5)
I
TH
Pin Load = ±5μA (Note 5)
V
TURNOFF
< V
CC
< V
CLAMP1mA
(Note 5)
I
TH
Sinking 5μA (Note 5)
I
TH
Sourcing 5μA (Note 5)
R
FS
= 350k
R
FS
= 36k
f
OSC
= 200kHz
f
OSC
= 200kHz
70kHz < f
OSC
< 700kHz,
70kHz < f
SYNC
< 700kHz
MIN
TYP
360
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MAX
UNITS
μA
40
1.122
1.092
4
0.788
0.780
0.780
0.770
1.207
1.170
5
0.800
0.800
0.800
0.800
20
333
0.05
3
3
70
700
6
80
90
1.292
1.248
5.8
0.812
0.812
0.812
0.820
μA
V
V
μA
V
V
V
V
nA
μA/V
mV/V
mV/μA
mV/μA
kHz
kHz
%
%
%
V
μA
μA
ms
ms
ns
ns
mV
μA
mV
μA
V
RUNON
V
RUNOFF
I
RUN(HYST)
V
FB
RUN Turn-On Voltage
RUN Turn-Off Voltage
RUN Hysteresis Current
Regulated Feedback Voltage
I
FB
g
m
ΔV
O(LINE)
ΔV
O(LOAD)
f
OSC
DC
ON(MIN)
DC
ON(MAX)
f
SYNC
V
SYNC
I
SS
I
FTO
t
SS(INT)
t
FTO(INT)
t
RISE
t
FALL
V
I(MAX)
I
SL(MAX)
V
OCT
I
OC
V
FB
Input Current
Error Amplifier Transconductance
Output Voltage Line Regulation
Output Voltage Load Regulation
Oscillator Frequency
Minimum Switch-On Duty Cycle
Maximum Switch-On Duty Cycle
As a Function of f
OSC
Minimum SYNC Amplitude
Soft-Start Current
Fault Timeout Current
Internal Soft-Start Time
Internal Fault Timeout
Gate Drive Rise Time
Gate Drive Fall Time
Peak Current Sense Voltage
Peak Slope Compensation Output Current
Overcurrent Threshold
Overcurrent Threshold Adjust Current
70
67
9
95
133
2.9
No External Capacitor on SSFLT
No External Capacitor on SSFLT
C
LOAD
= 3000pF
C
LOAD
= 3000pF
R
SL
= 0 (Note 6)
(Note 7)
R
OC
= 0 (Note 8)
l
l
85
85
–6
2
1.8
4.5
30
30
100
10
100
10
115
115
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 LTC3805E-5 is guaranteed to meet specifications from
0°C to 85°C. Specifications over the –40°C to 85°C operating junction
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3805I-5 is guaranteed over the
–40°C to 125°C operating junction temperature range and the LTC3805H-5
is guaranteed over the full –40°C to 150°C operating junction temperature
range. High junction temperatures degrade operating lifetimes. Operating
lifetime is derated at junction temperatures greater than 125°C.
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
• 45°C/W)
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 5:
The LTC3805-5 is tested in a feedback loop that servos V
FB
to the
output of the error amplifier while maintaining I
TH
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. For
details, refer to Programmable Slope Compensation in the Applications
Information section.
Note 7:
Guaranteed by design.
Note 8:
Overcurrent threshold voltage is reduced dependent on an
optional external resistor in series with the OC pin. For details, refer to
Programmable Overcurrent in the Applications Information section.
38055fb
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LTC3805-5
TYPICAL PERFORMANCE CHARACTERISTICS
Reference Voltage
vs Temperature
812
808
V
FB
VOLTAGE (mV)
804
V
FB
(V)
800
796
792
788
–50 –25
0.800300
0.800200
0.800100
0.800000
0.799900
0.799800
100
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G01
Reference Voltage
vs Supply Voltage
800
700
600
f
OSC
(kHz)
4
5
6
7
V
CC
(V)
38055 G02
Oscillator Frequency vs R
FS
500
400
300
200
0.799700
8
9
10
0
0
100
200
R
FS
(kΩ)
300
400
38055 G03
Oscillator Frequency
vs Supply Voltage
203
OSCILLATOR FREQUENCY (kHz)
202
201
f
OSC
(kHz)
200
199
198
197
196
4
5
6
V
CC
(V)
38055 G04
Oscillator Frequency
vs Temperature
202
1.205
1.200
201
R
FS
= 124kΩ
200
RUN VOLTAGE (V)
1.195
1.190
1.185
1.180
1.175
198
–50 –25
RUN Undervoltage Lockout
Thresholds vs Temperature
V
RUN(ON)
R
FS
= 124kΩ
199
V
RUN(OFF)
7
8
9
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G05
1.170
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G06
RUN Hysteresis Current
vs Temperature
5.20
V
CC
UNDERVOLTAGE LOCKOUT (V)
5.0
V
CC
Undervoltage Lockout
Thresholds vs Temperature
5.10
V
TURN(ON)
4.5
V
TURN(OFF)
4.0
I
RUN(HYST)
5.00
4.90
3.5
4.80
4.70
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G07
3.0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G08
38055fb
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LTC3805-5
TYPICAL PERFORMANCE CHARACTERISTICS
Start-Up I
CC
Supply Current
vs Temperature
50
START-UP SUPPLY CURRENT (μA)
48
46
44
42
40
38
36
34
32
30
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G09
I
CC
Supply Current
vs Temperature
360
350
SUPPLY CURRENT (μA)
340
330
320
310
300
–50 –25
V
CLAMP
(V)
9.60
9.55
9.50
9.45
9.40
9.35
9.30
9.25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G10
V
CC
Shunt Regulator Voltage
vs Temperature
V
CLAMP25mA
V
CLAMP1mA
9.20
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G11
Peak Current Sense Voltage
vs Temperature
100.8
PEAK CURRENT SENSE VOLTAGE (mV)
OVERCURRENT THRESHOLD (mV)
100.6
100.4
100.2
100.0
99.8
99.6
99.4
99.2
99.0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G12
Overcurrent Threshold
vs Temperature
104
INTERNAL SOFT-START TIME (ms)
2.20
2.15
2.10
2.05
2.00
1.95
Internal Soft-Start Time
vs Temperature
102
100
98
96
94
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G13
1.90
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G14
External Soft-Start Current
vs Temperature
5.4
5.3
I
SS
SOFT-START CURRENT (μA)
5.2
5.1
5.0
4.9
4.8
4.7
4.6
4.5
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G15
External Timeout Current
vs Temperature
2.1
I
FTO
EXTERNAL TIMEOUT CURRENT (μA)
2.0
1.9
1.8
1.7
1.6
1.5
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
38055 G16
38055fb
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