FEATURES
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LTC1871-7
High Input Voltage,
Current Mode Boost,
Flyback and SEPIC Controller
DESCRIPTION
The LTC
®
1871-7 is a current mode, boost, flyback and
SEPIC controller optimized for driving 6V-rated MOSFETs
in high voltage applications. The LTC1871-7 works equally
well in low or high power applications and requires few
components to provide a complete power supply solution.
The switching frequency can be set with an external resistor
over a 50kHz to 1MHz range, and can be synchronized to
an external clock using the MODE/SYNC pin. Burst Mode
operation at light loads, a low minimum operating supply
voltage of 6V and a low shutdown quiescent current of
10μA make the LTC1871-7 well suited for battery-operated
systems. For applications requiring constant frequency
operation, Burst Mode operation can be defeated using
the MODE/SYNC pin. The LTC1871-7 is available in the
10-lead MSOP package.
PARAMETER
INTV
CC
INTV
CC
UV
+
INTV
CC
UV
–
LTC1871-7
7.0V
5.6V
4.6V
LTC1871
5.2V
2.1V
1.9V
Optimized for High Input Voltage Applications
Wide Chip Supply Voltage Range: 6V to 36V
Internal 7V Low Dropout Voltage Regulator
Optimized for 6V-Rated MOSFETs
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
Output Overvoltage Protection
Can be Used in a No R
SENSE
™ Mode for V
DS
< 36V
Small 10-Lead MSOP Package
APPLICATIONS
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n
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Telecom Power Supplies
42V Automotive Systems
24V Industrial Controls
IP Phone Power Supplies
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.
TYPICAL APPLICATION
V
IN
36V TO 72V
604k
26.7k
2.2μF
100V
X7R
3:1
100k
D1
9.1V
2.2nF
3.4k
FB
12.4k
FREQ
MODE/SYNC
110k
120k
RUN
I
TH
LTC1871-7
INTV
CC
GATE
GND
4.7μF
X5R
0.1μF
X5R
SENSE
V
IN
Q1
FMMT625
10Ω
D3
10BQ060
V
OUT
12V
0.4A
47μF
16V
X5R
Figure 1. Small, Nonisolated 12V Flyback Telecom Housekeeping Supply
18717fc
•
T1
VP1-0076
M1
FDC2512
0.12Ω
•
D2
4148
18717 F01
1
LTC1871-7
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 9V
INTV
CC
Output Current .......................................... 50mA
GATE Voltage ............................ –0.3V to V
INTVCC
+ 0.3V
I
TH
, FB Voltages ....................................... –0.3V to 2.7V
RUN Voltage ............................................... –0.3V to 7V
MODE/SYNC Voltage.................................... –0.3V to 9V
FREQ Voltage ............................................ –0.3V to 1.5V
SENSE Pin Voltage .................................... –0.3V to 36V
Operating Temperature Range (Note 2)
LTC1871E-7 ......................................... –40°C to 85°C
LTC1871I-7 ........................................ –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
LT1871EMS-7#PBF
LT1871IMS-7#PBF
LEAD BASED FINISH
LT1871EMS-7
LT1871IMS-7
TAPE AND REEL
LT1871EMS-7#TRPBF
LT1871IMS-7#TRPBF
TAPE AND REEL
LT1871EMS-7#TR
LT1871IMS-7#TR
PART MARKING
LTG4
LTBTR
PART MARKING
LTG4
LTBTR
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
= 8V, 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
= 0.2V (Note 5)
V
MODE/SYNC
= 0V, V
ITH
= 0.2V (Note 5),
I-Grade (Note 2)
Shutdown Mode
V
RUN
= 0V
V
RUN
= 0V, I-Grade (Note 2)
●
●
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
6
6
TYP
MAX
UNITS
V
V
Main Control Loop
550
600
280
280
12
12
1000
1100
500
600
25
25
μA
μA
μA
μA
μA
μA
18717fc
2
LTC1871-7
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
= 8V, 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
= 0.2V (Note 5)
V
ITH
= 0.2V (Note 5), I-Grade (Note 2)
●
●
●
TYP
1.348
1.248
100
100
5
1.230
MAX
1.273
1.298
150
175
60
1.242
1.248
1.255
60
0.02
0.02
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
= 0.2V (Note 5)
6V ≤ V
IN
≤ 30V
6V ≤ 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
600
0.3
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
V
150
35
0.1
180
200
70
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
V
INTVCC
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
INTV
CC
Regulator Output Voltage
V
IN
= 8V
V
IN
= 8V, I-Grade (Note 2)
●
●
●
92
92
1.25
1.25
25
0.8/f
OSC
97
98.5
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
6.5
6.5
7
7
7.5
7.5
kΩ
V
V
V
18717fc
Low Dropout Regulator
3
LTC1871-7
ELECTRICAL CHARACTERISTICS
SYMBOL
UVLO
PARAMETER
INTVCC Undervoltage Lockout Threshold
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 8V, V
RUN
= 1.5V, R
FREQ
= 80k, V
MODE/SYNC
= 0V, unless otherwise specified.
CONDITIONS
Rising INTV
CC
Falling INTV
CC
UVLO Hysteresis
8V ≤ V
IN
≤ 15V
15V ≤ V
IN
≤ 30V
0 ≤ I
INTVCC
≤ 20mA, V
IN
= 8V
V
IN
= 6V, INTV
CC
Load = 20mA
C
L
= 3300pF (Note 7)
C
L
= 3300pF (Note 7)
–2
MIN
TYP
5.6
4.6
1.0
8
70
–0.2
280
17
8
100
100
25
200
MAX
UNITS
V
V
V
mV
mV
%
mV
ns
ns
ΔV
INTVCC
ΔV
IN1
ΔV
INTVCC
ΔV
IN2
V
LDO(LOAD)
V
DROPOUT
GATE Driver
t
r
t
f
INTV
CC
Regulator Line Regulation
INTV
CC
Regulator Line Regulation
INTV
CC
Load Regulation
INTV
CC
Regulator Dropout Voltage
GATE Driver Output Rise Time
GATE Driver Output Fall Time
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-7 is guaranteed to meet performance specifications
from 0°C to 70°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-7 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
• 120°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 LTC1871-7 is tested in a feedback loop that servos V
FB
to the
reference voltage with the I
TH
pin forced to a voltage between 0V and 1.4V
(the no load to full load operating voltage range for the I
TH
pin is 0.3V to
1.23V).
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)
25
30
35
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
0
25 50 75 100 125 150
TEMPERATURE (°C)
18717 G01
1.229
0
5
10
15
20
V
IN
(V)
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
18717 G03
18717 G02
18717fc
4
LTC1871-7
TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Mode I
Q
vs V
IN
30
20
Shutdown Mode I
Q
vs Temperature
V
IN
= 8V
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)
400
300
200
100
20
10
10
5
0
0
10
20
V
IN
(V)
30
40
18717 G04
0
–50 –25
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
18717 G05
0
10
20
V
IN
(V)
30
40
18717 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)
= 600μA + 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)
18717 G07
0
0
200
400
800
600
FREQUENCY (kHz)
1000
1200
0
0
2000
4000
6000 8000
C
L
(pF)
10000 12000
18717 G09
18717 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)
18717 G11
1.30
100
1.3
1.25
1.2
0
10
20
V
IN
(V)
30
40
18717 G10
1.20
–50 –25
10
0 100 200 300 400 500 600 700 800 900 1000
FREQUENCY (kHz)
18717 G12
18717fc
5
