FEATURES
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LTC1871
Wide Input Range, No R
SENSE
™
Current Mode Boost,
Flyback and SEPIC Controller
DESCRIPTION
The LTC
®
1871 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. In-
tended for low to medium power applications, it eliminates
the need for a current sense resistor by utilizing the power
MOSFET’s on-resistance, thereby maximizing efficiency.
The IC’s operating frequency can be set with an external
resistor over a 50kHz to 1MHz range, and can be syn-
chronized to an external clock using the MODE/SYNC
pin. Burst Mode operation at light loads, a low minimum
operating supply voltage of 2.5V and a low shutdown
quiescent current of 10μA make the LTC1871 ideally suited
for battery-operated systems.
For applications requiring constant frequency opera-
tion, Burst Mode operation can be defeated using the
MODE/SYNC pin. Higher output voltage boost, SEPIC
and flyback applications are possible with the LTC1871
by connecting the SENSE pin to a resistor in the source
of the power MOSFET.
The LTC1871 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
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
n
n
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
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
1871 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
0.1
1
0.01
OUTPUT CURRENT (A)
10
1871 F01b
Figure 1. High Efficiency 3.3V Input, 5V Output Boost Converter (Bootstrapped)
1871fe
1
LTC1871
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 Temperature Range (Note 2)
LTC1871E............................................. –40°C to 85°C
LTC1871I............................................ –40°C to 125°C
LTC1871H .......................................... –40°C to 150°C
Junction Temperature (Note 3)
LTC1871E/LTC1871I ......................................... 125°C
LTC1871H ......................................................... 150°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#PBF
LTC1871IMS#PBF
LTC1871HMS#PBF
LEAD BASED FINISH
LTC1871EMS
LTC1871IMS
LTC1871HMS
TAPE AND REEL
LTC1871EMS#TRPBF
LTC1871IMS#TRPBF
LTC1871HMS#TRPBF
TAPE AND REEL
LTC1871EMS#TR
LTC1871IMS#TR
LTC1871HMS#TR
PART MARKING
LTSX
LTBFC
LTCXS
PART MARKING
LTSX
LTBFC
LTCXS
PACKAGE DESCRIPTION
10-Lead Plastic MSOP
10-Lead Plastic MSOP
10-Lead Plastic MSOP
PACKAGE DESCRIPTION
10-Lead Plastic MSOP
10-Lead Plastic MSOP
10-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 150°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 150°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/
1871fe
2
LTC1871
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN(MIN)
I
Q
PARAMETER
Minimum Input Voltage
I-Grade or H-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 or H-Grade (Note 2)
Burst Mode Operation, No Load
V
MODE/SYNC
= 0V, V
ITH
= 0.2V (Note 5)
V
MODE/SYNC
= 0V, V
ITH
= 0.2V (Note 5),
I-Grade or H-Grade (Note 2)
Shutdown Mode
V
RUN+
V
RUN–
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
= V
INTVCC
= 5V, V
RUN
= 1.5V, R
FREQ
= 80k, V
MODE/SYNC
= 0V, unless
otherwise specified.
CONDITIONS
MIN
2.5
2.5
550
550
250
250
10
●
TYP
MAX
UNITS
V
V
Main Control Loop
1000
1000
500
500
20
20
1.273
1.298
1.315
150
175
300
60
1.242
1.248
1.255
60
0.02
0.02
μA
μA
μA
μA
μA
μA
V
V
V
V
mV
mV
mV
nA
V
V
V
nA
%/V
%/V
%
%
V
RUN
= 0V
V
RUN
= 0V, I-Grade or H-Grade (Note 2)
10
1.348
1.223
1.198
1.179
50
100
100
1
35
35
1.218
1.212
1.205
18
0.002
1.230
1.248
H-Grade (Note 2)
V
RUN(HYST)
RUN Pin Input Threshold Hysteresis
I-Grade (Note 2)
H-Grade (Note 2)
I
RUN
V
FB
RUN Input Current
Feedback Voltage
V
ITH
= 0.2V (Note 5)
V
ITH
= 0.2V (Note 5), I-Grade or H-Grade (Note 2)
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
Oscillator Frequency
R
FREQ
= 80k
R
FREQ
= 80k, I-Grade (Note 2)
R
FREQ
= 80k, H-Grade (Note 2)
Oscillator Frequency Range
I-Grade or H-Grade (Note 2)
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)
Load Regulation
FB Pin Input Current
Line Regulation
V
ITH
= 0.2V (Note 5)
2.5V ≤ V
IN
≤ 30V
2.5V ≤ V
IN
≤ 30V, I-Grade or H-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 or H-Grade (Note 2)
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 or H-Grade (Note 2)
V
SENSE
= 0V
V
SENSE
= 30V
●
●
●
●
●
●
●
●
0.002
–1
–1
2.5
–0.1
–0.1
6
650
0.3
120
150
35
0.1
250
300
300
300
10
%
μmho
V
180
200
50
5
350
350
360
1000
1000
mV
mV
μA
μA
kHz
kHz
kHz
kHz
kHz
1871fe
●
100
●
●
●
250
240
50
50
3
LTC1871
ELECTRICAL CHARACTERISTICS
SYMBOL
D
MAX
f
SYNC/
f
OSC
t
SYNC(MIN)
t
SYNC(MAX)
V
IL(MODE)
V
IH(MODE)
R
MODE/SYNC
V
FREQ
V
INTVCC
PARAMETER
Maximum Duty Cycle
I-Grade or H-Grade (Note 2)
Recommended Maximum Synchronized
Frequency Ratio
MODE/SYNC Minimum Input Pulse Width
Low Level MODE/SYNC Input Voltage
I-Grade or H-Grade (Note 2)
High Level MODE/SYNC Input Voltage
I-Grade or H-Grade (Note 2)
MODE/SYNC Input Pull-Down Resistance
Nominal FREQ Pin Voltage
INTV
CC
Regulator Output Voltage
V
IN
= 7.5V
V
IN
= 7.5V, I-Grade (Note 2)
V
IN
= 7.5V, H-Grade (Note 2)
ΔV
INTVCC
Δ
V
IN1
ΔV
INTVCC
Δ
V
IN2
V
LDO(LOAD)
V
DROPOUT
I
INTVCC
INTV
CC
Load Regulation
INTV
CC
Regulator Dropout Voltage
Bootstrap Mode INTV
CC
Supply
Current in Shutdown
0 ≤ I
INTVCC
≤ 20mA, V
IN
= 7.5V
V
IN
= 5V, INTV
CC
Load = 20mA
RUN = 0V, SENSE = 5V
I-Grade (Note 2)
H-Grade (Note 2)
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
●
●
●
●
●
●
●
●
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
INTVCC
= 5V, V
RUN
= 1.5V, R
FREQ
= 80k, V
MODE/SYNC
= 0V, unless
otherwise specified.
CONDITIONS
MIN
87
87
f
OSC
= 300kHz (Note 6)
f
OSC
= 300kHz (Note 6), I-Grade or H-Grade (Note 2)
V
SYNC
= 0V to 5V
TYP
92
92
1.25
1.25
25
0.8/f
OSC
0.3
0.3
1.2
1.2
50
0.62
5.0
5.0
4.95
5.2
5.2
5.2
8
70
–2
–0.2
280
10
20
30
50
5.4
5.4
5.45
25
200
MAX
97
97
1.30
1.30
ns
ns
V
V
V
V
kΩ
V
V
V
V
mV
mV
%
mV
μA
μA
μA
UNITS
%
%
MODE/SYNC Maximum Input Pulse Width V
SYNC
= 0V to 5V
Low Dropout Regulator
INTV
CC
Regulator Line Regulation
INTV
CC
Regulator Line Regulation
7.5V ≤ V
IN
≤ 15V
15V ≤ V
IN
≤ 30V
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 is guaranteed to meet performance specifications
from 0°C to 85°C operating temperature. Specifications over the – 40°C to
85°C operating temperature range are assured by design, characterization
and correlation with statistical process controls. The LTC1871I is
guaranteed over the full –40°C to 125°C operating temperature range
and the LTC1871H is guaranteed over the full –40°C to 150°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
• 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 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.
1871fe
4
LTC1871
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)
1871 G01
0
5
10
15
20
V
IN
(V)
25
30
35
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1871 G03
1871 G02
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)
1871 G05
20
400
300
200
100
10
10
5
0
0
10
20
V
IN
(V)
30
40
1871 G04
0
–50 –25
0
0
10
20
V
IN
(V)
30
40
1871 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)
1871 G07
0
0
200
400
800
600
FREQUENCY (kHz)
1000
1200
0
0
2000
4000
6000 8000
C
L
(pF)
10000 12000
1871 G09
1871 G08
1871fe
5
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