LTC1871
Wide Input Range, No R
SENSE
TM
Current Mode Boost, Flyback and SEPIC Controller
FEATURES
s
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DESCRIPTIO
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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
The LTC
®
1871 is a wide input range, current mode, boost,
flyback and SEPIC controller that drives an N-channel
power MOSFET and requires very few external compo-
nents. Intended for low to medium power applications, it
eliminates the need for a current sense resistor by utiliz-
ing the power MOSFET’s on-resistance, thereby maximiz-
ing efficiency.
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.
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 operation,
Burst Mode operation can be defeated using the MODE/
SYNC pin. Higher output voltage boost, SEPIC and fly-
back 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
No R
SENSE
is a trademark of Linear Technology Corporation.
APPLICATIO S
s
s
Telecom Power Supplies
Portable Electronic Equipment
TYPICAL APPLICATIO
V
IN
3.3V
L1
1µH
D1
90
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
80
EFFICIENCY (%)
70
60
50
40
30
0.001
100
+
M1
C
OUT1
150µF
6.3V
×4
+
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
Figure 1. High Efficiency 3.3V Input, 5V Output Boost Converter (Bootstrapped)
U
Efficiency of Figure 1
Burst Mode
OPERATION
PULSE-SKIP
MODE
0.01
0.1
1
OUTPUT CURRENT (A)
10
1871 F01b
U
U
1
LTC1871
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
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) .. – 40°C to 85°C
Junction Temperature (Note 3) ............................ 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
LTC1871EMS
MS PACKAGE
10-LEAD PLASTIC MSOP
MS PART MARKING
LTSX
T
JMAX
= 125°C,
θ
JA
= 120°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes 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.
SYMBOL
V
IN(MIN)
I
Q
PARAMETER
Minimum Input Voltage
Input Voltage Supply Current
Continuous Mode
Burst Mode Operation, No Load
Shutdown Mode
Rising RUN Input Threshold Voltage
Falling RUN Input Threshold Voltage
q
CONDITIONS
MIN
2.5
TYP
MAX
UNITS
V
Main Control Loop
(Note 4)
V
MODE/SYNC
= 5V, V
FB
= 1.4V, V
ITH
= 0.75V
V
MODE/SYNC
= 0V, V
ITH
= 0.2V (Note 5)
V
RUN
= 0V
1.223
1.198
50
V
ITH
= 0.2V (Note 5)
q
550
250
10
1.348
1.248
100
1
1.218
1.212
1.230
18
0.002
q
1000
500
20
1.273
1.298
150
60
1.242
1.248
60
0.02
V
RUN+
V
RUN–
V
RUN(HYST)
I
RUN
V
FB
I
FB
∆V
FB
∆V
IN
∆V
FB
∆V
ITH
∆V
FB(OV)
g
m
V
ITH(BURST)
I
SENSE(ON)
I
SENSE(OFF)
RUN Pin Input Threshold Hysteresis
RUN Input Current
Feedback Voltage
FB Pin Input Current
Line Regulation
Load Regulation
∆FB
Pin, Overvoltage Lockout
Error Amplifier Transconductance
Burst Mode Operation I
TH
Pin Voltage
SENSE Pin Current (GATE High)
SENSE Pin Current (GATE Low)
V
ITH
= 0.2V (Note 5)
2.5V
≤
V
IN
≤
30V
V
MODE/SYNC
= 0V, V
TH
= 0.5V to 0.90V (Note 5)
V
FB(OV)
– V
FB(NOM)
in Percent
I
TH
Pin Load =
±5µA
(Note 5)
Falling I
TH
Voltage (Note 5)
Duty Cycle < 20%
V
SENSE
= 0V
V
SENSE
= 30V
120
–1
2.5
– 0.1
6
650
0.3
150
35
0.1
180
50
5
10
V
SENSE(MAX)
Maximum Current Sense Input Threshold
2
U
µA
µA
µA
V
V
V
mV
nA
V
V
nA
%/V
%
%
µmho
V
mV
µA
µA
W
U
U
W W
W
LTC1871
The
q
denotes 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.
SYMBOL
Oscillator
f
OSC
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
∆V
INTVCC
∆V
IN1
∆V
INTVCC
∆V
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
Oscillator Frequency
Oscillator Frequency Range
Maximum Duty Cycle
Recommended Maximum Synchronized
Frequency Ratio
MODE/SYNC Minimum Input Pulse Width
MODE/SYNC Maximum Input Pulse Width
Low Level MODE/SYNC Input Voltage
High Level MODE/SYNC Input Voltage
MODE/SYNC Input Pull-Down Resistance
Nominal FREQ Pin Voltage
INTV
CC
Regulator Output Voltage
INTV
CC
Regulator Line Regulation
INTV
CC
Regulator Line Regulation
INTV
CC
Load Regulation
INTV
CC
Regulator Dropout Voltage
Bootstrap Mode INTV
CC
Supply
Current in Shutdown
V
IN
= 7.5V
7.5V
≤
V
IN
≤
15V
15V
≤
V
IN
≤
30V
0
≤
I
INTVCC
≤
20mA, V
IN
= 7.5V
V
IN
= 5V, INTV
CC
Load = 20mA
RUN = 0V, SENSE = 5V
–2
5.0
1.2
50
0.62
5.2
8
70
– 0.2
280
10
20
5.4
25
200
f
OSC
= 300kHz (Note 6)
V
SYNC
= 0V to 5V
V
SYNC
= 0V to 5V
R
FREQ
= 80k
250
50
87
92
1.25
25
0.8/f
OSC
0.3
300
350
1000
97
1.30
ns
ns
V
V
kΩ
V
V
mV
mV
%
mV
µA
kHz
kHz
%
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ELECTRICAL CHARACTERISTICS
Low Dropout Regulator
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
The LTC1871E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the – 40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
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 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.
3
LTC1871
TYPICAL PERFOR A CE CHARACTERISTICS
FB Voltage vs Temp
1.25
FB PIN CURRENT (nA)
0
5
10
15
20
V
IN
(V)
25
30
35
1.24
FB VOLTAGE (V)
FB VOLTAGE (V)
1.23
1.22
1.21
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1871 G01
Shutdown Mode I
Q
vs V
IN
30
SHUTDOWN MODE I
Q
(µA)
SHUTDOWN MODE I
Q
(µA)
20
Burst Mode I
Q
(µA)
10
0
0
10
20
V
IN
(V)
30
Burst Mode I
Q
vs Temperature
500
18
16
400
14
12
Burst Mode I
Q
(µA)
TIME (ns)
I
Q
(mA)
300
200
100
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1871 G07
4
U W
1871 G04
FB Voltage Line Regulation
1.231
60
50
40
30
20
10
1.229
FB Pin Current vs Temperature
1.230
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1871 G03
1871 G02
Shutdown Mode I
Q
vs Temperature
20
V
IN
= 5V
600
500
Burst Mode I
Q
vs V
IN
15
400
300
200
100
10
5
40
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1871 G05
0
0
10
20
V
IN
(V)
30
40
1871 G06
Dynamic I
Q
vs Frequency
C
L
= 3300pF
I
Q(TOT)
= 550µA + Qg • f
Gate Drive Rise and Fall Time
vs C
L
60
50
40
RISE TIME
30
20
FALL TIME
10
10
8
6
4
2
0
0
200
400
600
800
FREQUENCY (kHz)
1000
1200
0
0
2000
4000
6000 8000
C
L
(pF)
10000 12000
1871 G09
1871 G08
LTC1871
TYPICAL PERFOR A CE CHARACTERISTICS
RUN Thresholds vs V
IN
1.5
1.40
RUN THRESHOLDS (V)
1.4
RUN THRESHOLDS (V)
R
T
(kΩ)
0
25 50 75 100 125 150
TEMPERATURE (°C)
1871 G11
1.3
1.2
0
10
20
V
IN
(V)
30
Frequency vs Temperature
325
320
160
GATE FREQUENCY (kHz)
155
310
305
300
295
290
285
280
275
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1871 G13
150
SENSE PIN CURRENT (µA)
315
MAX SENSE THRESHOLD (mV)
INTV
CC
Load Regulation
5.4
V
IN
= 7.5V
DROPOUT VOLTAGE (mV)
5.2
INTV
CC
VOLTAGE (V)
INTV
CC
VOLTAGE (V)
5.1
5.0
0
10
20
30 40
50 60
INTV
CC
LOAD (mA)
70
80
U W
1871 G10
1871 G16
RUN Thresholds vs Temperature
1000
R
T
vs Frequency
1.35
1.30
100
1.25
40
1.20
–50 –25
10
0 100 200 300 400 500 600 700 800 900 1000
FREQUENCY (kHz)
1871 G12
Maximum Sense Threshold
vs Temperature
35
SENSE Pin Current vs Temperature
GATE HIGH
V
SENSE
= 0V
30
145
140
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1871 G14
25
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1871 G15
INTV
CC
Line Regulation
500
450
INTV
CC
Dropout Voltage
vs Current, Temperature
150°C
400
350
300
250
200
150
100
50
25°C
125°C
75°C
5.3
5.2
0°C
–50°C
5.1
0
5
10
15
20 25
V
IN
(V)
30
0
35
40
0
5
10
15
INTV
CC
LOAD (mA)
20
1871 G18
1871 G17
5
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