FEATURES
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LTC1871-1
Wide Input Range, No R
SENSE
™
Current Mode Boost,
Flyback and SEPIC Controller
DESCRIPTION
The LTC
®
1871-1 is a wide input range, current mode, boost,
flyback or SEPIC controller that drives an N-channel power
MOSFET and requires very few external components. It
eliminates the need for a current sense resistor by utilizing
the power MOSFET’s on-resistance, thereby maximizing
efficiency. Higher output voltage applications are possible
with the LTC1871-1 by connecting the SENSE pin to a
resistor in the source of the power MOSFET.
The IC’s operating frequency can be set with an external
resistor over a 50kHz to 1MHz range, and can be synchro-
nized to an external clock using the MODE/SYNC pin.
The LTC1871-1 differs from the LTC1871 by having a
lower pulse skip threshold, making it ideal for applica-
tions requiring constant frequency operation at light
loads. The lower pulse skip threshold also helps maintain
constant frequency operation in applications with a wide
input voltage range. For applications requiring primary-
to-secondary side isolation, please refer to the LTC1871
datasheet.
The LTC1871-1 is available in the 10-lead MSOP package.
L,
LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
No R
SENSE
is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
High Efficiency (No Sense Resistor Required)
Wide Input Voltage Range: 2.5V to 36V
Current Mode Control Provides Excellent
Transient Response
High Maximum Duty Cycle (92% Typ)
±2% RUN Pin Threshold with 100mV Hysteresis
±1% Internal Voltage Reference
Ultra Low Pulse Skip Threshold for Wide Input
Range Applications
Micropower Shutdown: I
Q
= 10μA
Programmable Operating Frequency
(50kHz to 1MHz) with One External Resistor
Synchronizable to an External Clock Up to 1.3 × f
OSC
User-Controlled Pulse Skip or Burst Mode
®
Operation
Internal 5.2V Low Dropout Voltage Regulator
Output Overvoltage Protection
Capable of Operating with a Sense Resistor for High
Output Voltage Applications
Small 10-Lead MSOP Package
APPLICATIONS
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Telecom Power Supplies
Portable Electronic Equipment
TYPICAL APPLICATION
V
IN
3.3V
L1
1μH
D1
RUN
I
TH
R
C
22k
C
C1
6.8nF
C
C2
47pF
R2
37.4k
1%
R1
12.1k
1%
FB
FREQ
R
T
80.6k
1%
MODE/SYNC
LTC1871-1
INTV
CC
GATE
GND
C
VCC
4.7μF
X5R
SENSE
V
IN
V
OUT
5V
7A
(10A PEAK)
C
OUT2
22μF
6.3V
X5R
×2
GND
100
90
80
EFFICIENCY (%)
70
60
50
40
30
0.001
Burst Mode
OPERATION
Efficiency of Figure 1
+
M1
C
OUT1
150μF
6.3V
×4
PULSE-SKIP
MODE
+
C
IN
22μF
6.3V
×2
18711 F01a
C
IN
:
TAIYO YUDEN JMK325BJ226MM
C
OUT1
: PANASONIC EEFUEOJ151R
C
OUT2
: TAIYO YUDEN JMK325BJ226MM
D1: MBRB2515L
L1: SUMIDA CEP125-H 1R0MH
M1: FAIRCHILD FDS7760A
0.01
0.1
1
OUTPUT CURRENT (A)
10
18711 F01b
Figure 1. High Efficiency 3.3V Input, 5V Output Boost Converter (Bootstrapped)
18711fb
1
LTC1871-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
RUN
I
TH
FB
FREQ
MODE/
SYNC
1
2
3
4
5
10
9
8
7
6
SENSE
V
IN
INTV
CC
GATE
GND
V
IN
Voltage ............................................... – 0.3V to 36V
INTV
CC
Voltage............................................ –0.3V to 7V
INTV
CC
Output Current .......................................... 50mA
GATE Voltage ............................ –0.3V to V
INTVCC
+ 0.3V
I
TH
, FB Voltages ....................................... –0.3V to 2.7V
RUN, MODE/SYNC Voltages ....................... –0.3V to 7V
FREQ Voltage ............................................ –0.3V to 1.5V
SENSE Pin Voltage .................................... –0.3V to 36V
Operating Junction Temperature Range (Note 2)
LTC1871E-1 ......................................... –40°C to 85°C
LTC1871I-1 ........................................ –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
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 120°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC1871EMS-1#PBF
LTC1871IMS-1#PBF
LEAD BASED FINISH
LTC1871EMS-1
LTC1871IMS-1
TAPE AND REEL
LTC1871EMS-1#TRPBF
LTC1871IMS-1#TRPBF
TAPE AND REEL
LTC1871EMS-1#TR
LTC1871IMS-1#TR
PART MARKING
LTCTV
LTCTV
PART MARKING
LTCTV
LTCTV
PACKAGE DESCRIPTION
10-Lead Plastic MSOP
10-Lead Plastic MSOP
PACKAGE DESCRIPTION
10-Lead Plastic MSOP
10-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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
IN
= 5V, V
RUN
= 1.5V, R
FREQ
= 80k, V
MODE/SYNC
= 0V, unless otherwise specified.
SYMBOL
V
IN(MIN)
I
Q
PARAMETER
Minimum Input Voltage
I-Grade (Note 2)
Input Voltage Supply Current
Continuous Mode
(Note 4)
V
MODE/SYNC
= 5V, V
FB
= 1.4V, V
ITH
= 0.75V
V
MODE/SYNC
= 5V, V
FB
= 1.4V, V
ITH
= 0.75V,
I-Grade (Note 2)
Burst Mode Operation, No Load
V
MODE/SYNC
= 0V, V
ITH
= 0V (Note 5)
V
MODE/SYNC
= 0V, V
ITH
= 0V (Note 5),
I-Grade (Note 2)
Shutdown Mode
V
RUN
= 0V
V
RUN
= 0V, I-Grade (Note 2)
●
●
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
2.5
2.5
TYP
MAX
UNITS
V
V
Main Control Loop
550
550
250
250
10
10
1000
1000
500
500
20
20
μA
μA
μA
μA
μA
μA
18711fb
2
LTC1871-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
RUN+
V
RUN–
V
RUN(HYST)
I
RUN
V
FB
PARAMETER
Rising RUN Input Threshold Voltage
Falling RUN Input Threshold Voltage
●
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 5V, V
RUN
= 1.5V, R
FREQ
= 80k, V
MODE/SYNC
= 0V, unless otherwise specified.
CONDITIONS
MIN
1.223
1.198
50
I-Grade (Note 2)
RUN Input Current
Feedback Voltage
V
ITH
= 0.4V (Note 5)
V
ITH
= 0.4V (Note 5), I-Grade (Note 2)
●
●
●
TYP
1.348
1.248
100
100
1
1.230
MAX
1.273
1.298
150
175
60
1.242
1.248
1.255
60
0.02
0.03
UNITS
V
V
V
mV
mV
nA
V
V
V
nA
%/V
%/V
%
%
RUN Pin Input Threshold Hysteresis
35
1.218
1.212
1.205
I
FB
ΔV
FB
ΔV
IN
ΔV
FB
ΔV
ITH
ΔV
FB(OV)
g
m
V
ITH(BURST)
V
SENSE(MAX)
I
SENSE(ON)
I
SENSE(OFF)
Oscillator
f
OSC
FB Pin Input Current
Line Regulation
Load Regulation
V
ITH
= 0.4V (Note 5)
2.5V ≤ V
IN
≤ 30V
2.5V ≤ V
IN
≤ 30V, I-Grade (Note 2)
V
MODE/SYNC
= 0V, V
ITH
= 0.5V to 0.9V (Note 5)
V
MODE/SYNC
= 0V, V
ITH
= 0.5V to 0.9V (Note 5)
I-Grade (Note 2)
●
●
●
18
0.002
0.002
–1
–1
2.5
–0.1
–0.1
6
650
195
120
●
ΔFB
Pin, Overvoltage Lockout
Error Amplifier Transconductance
Burst Mode Operation I
TH
Pin Voltage
Maximum Current Sense Input Threshold
SENSE Pin Current (GATE High)
SENSE Pin Current (GATE Low)
Oscillator Frequency
Oscillator Frequency Range
V
FB(OV)
– V
FB(NOM)
in Percent
I
TH
Pin Load = ±5μA (Note 5)
Falling I
TH
Voltage (Note 5)
Duty Cycle < 20%
Duty Cycle < 20%, I-Grade (Note 2)
V
SENSE
= 0V
V
SENSE
= 30V
R
FREQ
= 80k
R
FREQ
= 80k, I-Grade (Note 2)
I-Grade (Note 2)
●
●
●
●
10
%
μmho
mV
150
35
0.1
180
200
50
5
350
350
1000
1000
mV
mV
μA
μA
kHz
kHz
kHz
kHz
%
%
100
250
250
50
50
87
300
300
D
MAX
f
SYNC/
f
OSC
t
SYNC(MIN)
t
SYNC(MAX)
V
IL(MODE)
V
IH(MODE)
R
MODE/SYNC
V
FREQ
Maximum Duty Cycle
I-Grade (Note 2)
Recommended Maximum Synchronized
Frequency Ratio
MODE/SYNC Minimum Input Pulse Width
MODE/SYNC Maximum Input Pulse Width
Low Level MODE/SYNC Input Voltage
I-Grade (Note 2)
High Level MODE/SYNC Input Voltage
I-Grade (Note 2)
MODE/SYNC Input Pull-Down Resistance
Nominal FREQ Pin Voltage
●
●
92
92
1.25
1.25
25
0.8/f
OSC
97
97
1.30
1.30
87
f
OSC
= 300kHz (Note 6)
f
OSC
= 300kHz (Note 6), I-Grade (Note 2)
V
SYNC
= 0V to 5V
V
SYNC
= 0V to 5V
ns
ns
0.3
0.3
V
V
V
V
1.2
1.2
50
0.62
kΩ
V
18711fb
3
LTC1871-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
INTVCC
ΔV
INTVCC
ΔV
IN1
ΔV
INTVCC
ΔV
IN2
V
LDO(LOAD)
V
DROPOUT
I
INTVCC
GATE Driver
t
r
t
f
GATE Driver Output Rise Time
GATE Driver Output Fall Time
C
L
= 3300pF (Note 7)
C
L
= 3300pF (Note 7)
17
8
100
100
ns
ns
INTV
CC
Load Regulation
INTV
CC
Regulator Dropout Voltage
Bootstrap Mode INTV
CC
Supply
0 ≤ I
INTVCC
≤ 20mA, V
IN
= 7.5V
INTV
CC
Load = 20mA
RUN = 0V, SENSE = 5V
I-Grade (Note 2)
●
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 5V, V
RUN
= 1.5V, R
FREQ
= 80k, V
MODE/SYNC
= 0V, unless otherwise specified.
PARAMETER
INTV
CC
Regulator Output Voltage
INTV
CC
Regulator Line Regulation
INTV
CC
Regulator Line Regulation
CONDITIONS
V
IN
= 7.5V
V
IN
= 7.5V, I-Grade (Note 2)
7.5V ≤ V
IN
≤ 15V
15V ≤ V
IN
≤ 30V
–2
●
MIN
5.0
5.0
TYP
5.2
5.2
8
70
–0.2
280
10
MAX
5.4
5.4
25
200
UNITS
V
V
mV
mV
%
mV
Low Dropout Regulator
20
30
μA
μA
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 LTC1871E-1 is guaranteed to meet performance specifications
from 0°C to 85°C junction temperature. Specifications over the – 40°C
to 85°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC1871I-1 is guaranteed over the full –40°C to 125°C operating junction
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
• 110°C/W)
Note 4:
The dynamic input supply current is higher due to power MOSFET
gate charging (Q
G
• f
OSC
). See Applications Information.
Note 5:
The LTC1871-1 is tested in a feedback loop which servos V
FB
to
the reference voltage with the I
TH
pin forced to the midpoint of its voltage
range (0.3V ≤ V
ITH
≤ 1.2V, midpoint = 0.75V).
Note 6:
In a synchronized application, the internal slope compensation
gain is increased by 25%. Synchronizing to a significantly higher ratio will
reduce the effective amount of slope compensation, which could result in
subharmonic oscillation for duty cycles greater than 50%.
Note 7:
Rise and fall times are measured at 10% and 90% levels.
TYPICAL PERFORMANCE CHARACTERISTICS
FB Voltage vs Temp
1.25
1.231
FB Voltage Line Regulation
60
50
FB PIN CURRENT (nA)
FB Pin Current vs Temperature
1.24
FB VOLTAGE (V)
FB VOLTAGE (V)
40
30
20
10
1.23
1.230
1.22
1.21
–50 –25
1.229
0
25 50 75 100 125 150
TEMPERATURE (°C)
18711 G01
0
5
10
15
20
V
IN
(V)
25
30
35
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
18711 G03
18711 G02
18711fb
4
LTC1871-1
TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Mode I
Q
vs V
IN
30
20
Shutdown Mode I
Q
vs Temperature
V
IN
= 5V
600
500
Burst Mode I
Q
vs V
IN
SHUTDOWN MODE I
Q
(μA)
SHUTDOWN MODE I
Q
(μA)
15
Burst Mode I
Q
(μA)
0
25 50 75 100 125 150
TEMPERATURE (°C)
18711 G05
20
400
300
200
100
10
10
5
0
0
10
20
V
IN
(V)
30
40
18711 G04
0
–50 –25
0
0
10
20
V
IN
(V)
30
40
18711 G06
Burst Mode I
Q
vs Temperature
500
18
16
400
Burst Mode I
Q
(μA)
14
12
Dynamic I
Q
vs Frequency
C
L
= 3300pF
I
Q(TOT)
= 550μA + Qg • f
60
50
40
TIME (ns)
Gate Drive Rise and
Fall Time vs C
L
I
Q
(mA)
300
10
8
6
RISE TIME
30
20
FALL TIME
10
200
100
4
2
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
18711 G07
0
0
200
400
800
600
FREQUENCY (kHz)
1000
1200
0
0
2000
4000
6000 8000
C
L
(pF)
10000 12000
18711 G09
18711 G08
RUN Thresholds vs V
IN
1.5
1.40
RUN Thresholds vs Temperature
1000
R
T
vs Frequency
RUN THRESHOLDS (V)
1.4
RUN THRESHOLDS (V)
1.35
R
T
(kΩ)
0
25 50 75 100 125 150
TEMPERATURE (°C)
18711 G11
1.30
100
1.3
1.25
1.2
0
10
20
V
IN
(V)
30
40
18711 G10
1.20
–50 –25
10
0 100 200 300 400 500 600 700 800 900 1000
FREQUENCY (kHz)
18711 G12
18711fb
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