T YPICAL APPLICATION
F EATURES
A PPLICATIONS
D ESCRIPTION Current Mode Boost,
Flyback and SEPIC Controller The L TC ®1871-1 is a wide input range, current mode, boost, fl yback 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 effi ciency. Higher output voltage applications are possible with the L TC1871-1 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 L TC1871-1 differs from the
L TC1871 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 L TC1871 datasheet.
The L TC1871-1 is available in the 10-lead MSOP package.
Effi ciency of Figure 1
n
High Effi ciency (No Sense Resistor Required)n  Wide Input Voltage Range: 2.5V to 36V n  Current Mode Control Provides Excellent  T ransient Response
n  High Maximum Duty Cycle (92% Typ)
n  ±2% RUN Pin Threshold with 100mV Hysteresis n  ±1% Internal Voltage Reference
n  Ultra Low Pulse Skip Threshold for Wide Input Range Applications
n  Micropower Shutdown: I Q
= 10μA n  Programmable Operating Frequency
(50kHz to 1MHz) with One External Resistor n  Synchronizable to an External Clock Up to 1.3 × f OSC
n  User-Controlled Pulse Skip or Burst Mode ® Operation
n  Internal 5.2V Low Dropout Voltage Regulator n  Output Overvoltage Protection
n  Capable of Operating with a Sense Resistor for High  Output Voltage Applications n  Small 10-Lead MSOP Package
n
Telecom Power Supplies
n  Portable Electronic Equipment
L , L T , L TC, L TM 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.
IN
OUT
C IN :  TAIYO YUDEN JMK325BJ226MM C OUT1:  PANASONIC EEFUEOJ151R
C OUT2:  TAIYO YUDEN JMK325BJ226MM
D1:  MBRB2515L
L1:  SUMIDA CEP125-H 1R0MH M1: FAIRCHILD FDS7760A
OUTPUT CURRENT (A)
30E F F I C I E N C Y  (%)
9010080507060400.001
0.1110
18711 F01b
0.01
P IN CONFIGURATION
A BSOLUTE MAXIMUM RATINGS 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 ,
F
B Voltages ....................................... –0.3V to 2.7V RUN, MODE/SYN
C 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)
L TC1871E-1 .........................................–40°C to 85°C  L TC1871I-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
(Note 1)
12345
RUN
I TH FB FREQ MODE/SYNC
109876
SENSE V IN INTV CC GATE GND
TOP VIEW
MS PACKAGE
10-LEAD PLASTIC MSOP T JMAX  = 125°C, θJA  = 120°C/W
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE L TC1871EMS-1#PBF L TC1871EMS-1#TRPBF L TCTV 10-Lead Plastic MSOP –40°C to 85°C L TC1871IMS-1#PBF L TC1871IMS-1#TRPBF L TCTV 10-Lead Plastic MSOP –40°C to 125°C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE L TC1871EMS-1L TC1871EMS-1#TR L TCTV 10-Lead Plastic MSOP –40°C to 85°C L TC1871IMS-1
L TC1871IMS-1#TR
L TCTV
10-Lead Plastic MSOP
–40°C to 125°C
Consult L TC Marketing for parts specifi ed with wider operating temperature ranges.
For more information on lead free part marking, go to: www.linear /leadfree/ For more information on tape and reel specifi cations, go to: www.linear /tapeandreel/
SYMBOL PARAMETER
CONDITIONS MIN TYP MAX UNITS
Main Control Loop
V IN(MIN)Minimum Input Voltage
2.5V I-Grade (Note 2)
●
2.5
V
I Q
Input Voltage Supply Current (Note 4)
Continuous Mode
V MODE/SYNC  = 5V , V FB  = 1.4V , V ITH  = 0.75V 5501000μA V MODE/SYNC  = 5V , V FB  = 1.4V , V ITH  = 0.75V ,
I-Grade (Note 2)
●5501000μA      Burst Mode Operation, No Load
V MODE/SYNC  = 0V , V ITH  = 0V (Note 5)250500μA V MODE/SYNC  = 0V , V ITH  = 0V (Note 5),I-Grade (Note 2)
●250500μA      Shutdown Mode
V RUN  = 0V
1020μA V RUN  = 0V , I-Grade (Note 2)
●10
20
μA
ELECTRICAL CHARACTERISTICS
The l  denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at T A  = 25°C. V IN  = 5V , V RUN  = 1.5V , R FREQ  = 80k, V MODE/SYNC  = 0V , unless otherwise specifi ed.
E LECTRICAL CHARACTERISTICS
The
l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at T A = 25°C. V IN = 5V, V RUN = 1.5V, R FREQ = 80k, V MODE/SYNC = 0V, unless oth
erwise specifi ed. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V RUN+Rising RUN Input Threshold Voltage  1.348V
V RUN–Falling RUN Input Threshold Voltage
●1.223
1.198
1.248  1.273
1.298
V
V
V RUN(HYST)RUN Pin Input Threshold Hysteresis50100150mV
I-Grade (Note 2)●35100175mV I RUN RUN Input Current160nA
V FB Feedback Voltage V ITH = 0.4V (Note 5)
●1.218
1.212
1.230  1.242
1.248
V
V
V ITH = 0.4V (Note 5), I-Grade (Note 2)●  1.205  1.255V I FB FB Pin Input Current V ITH = 0.4V (Note 5)1860nA
ΔV FB ΔV IN Line Regulation  2.5V ≤ V IN ≤ 30V0.0020.02%/V
2.5V ≤ V IN ≤ 30V, I-Grade (Note 2)●0.0020.03%/V
ΔV FB ΔV ITH Load Regulation V MODE/SYNC = 0V, V ITH = 0.5V to 0.9V (Note 5)●–1–0.1%
V MODE/SYNC = 0V, V ITH = 0.5V to 0.9V (Note 5)
I-Grade (Note 2)
●–1–0.1%
ΔV FB(OV)ΔFB Pin, Overvoltage Lockout V FB(OV) – V FB(NOM) in Percent  2.5610% g m Error Amplifi er T ransconductance I TH Pin Load = ±5μA (Note 5)650μmho V ITH(BURST)Burst Mode Operation I TH Pin Voltage Falling I TH Voltage (Note 5)195mV V SENSE(MAX)Maximum Current Sense Input Threshold Duty Cycle < 20%120150180mV
Duty Cycle < 20%, I-Grade (Note 2)●100200mV I SENSE(ON)SENSE Pin Current (GATE High)V SENSE = 0V3550μA I SENSE(OFF)SENSE Pin Current (GATE Low)V SENSE = 30V0.15μA Oscillator
f OSC Oscillator Frequency R FREQ = 80k250300350kHz
R FREQ = 80k, I-Grade (Note 2)●250300350kHz Oscillator Frequency Range501000kHz
I-Grade (Note 2)●501000kHz D MAX Maximum Duty Cycle879297%
I-Grade (Note 2)●879297%
f SYNC/f OSC Recommended Maximum Synchronized
Frequency Ratio f OSC = 300kHz (Note 6)  1.25  1.30 f OSC = 300kHz (Note 6), I-Grade (Note 2)●  1.25  1.30
t SYNC(MIN)MODE/SYNC Minimum Input Pulse Width V SYNC = 0V to 5V25ns t SYNC(MAX)MODE/SYNC Maximum Input Pulse Width V SYNC = 0V to 5V0.8/f OSC ns V IL(MODE)Low Level MODE/SYNC Input Voltage0.3V
I-Grade (Note 2)●0.3V V IH(MODE)High Level MODE/SYNC Input Voltage  1.2V
I-Grade (Note 2)●  1.2V R MODE/SYNC MODE/SYNC Input Pull-Down Resistance50kΩV FREQ Nominal FREQ Pin Voltage0.62V
E LECTRICAL CHARACTERISTICS 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 L TC1871E-1 is guaranteed to meet performance specifi cations from 0°C to 85°C junction temperature. Specifi cations over the –40°C to 85°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The L TC1871I-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 L TC1871-1 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 signifi cantly 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.
The l  denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T A  = 25°C. V IN  = 5V , V RUN  = 1.5V , R FREQ  = 80k, V MODE/SYNC  = 0V , unless otherwise specifi
ed.SYMBOL PARAMETER
CONDITIONS MIN TYP MAX UNITS
Low Dropout Regulator
V INTVCC INTV CC  Regulator Output Voltage V IN  = 7.5V
5.0  5.2  5.4V V IN  = 7.5V , I-Grade (Note 2)●
5.0
5.2  5.4V ΔV INTVCC    ΔV IN1INTV CC  Regulator Line Regulation 7.5V ≤ V IN  ≤ 15V 825mV ΔV INTVCC    ΔV IN2INTV CC  Regulator Line Regulation
15V ≤ V IN  ≤ 30V
70200
mV V LDO(LOAD)INTV CC  Load Regulation 0 ≤ I INTVCC  ≤ 20mA, V IN  = 7.5V –2
–0.2%V DROPOUT INTV CC  Regulator Dropout Voltage INTV CC  Load = 20mA 280mV
I INTVCC Bootstrap Mode INTV CC  Supply
RUN = 0V , SENSE = 5V 10
20μA I-Grade (Note 2)
●
30
μA
GATE Driver t r GATE Driver Output Rise Time C L  = 3300pF (Note 7)17100ns t f
GATE Driver Output Fall Time
C L  = 3300pF (Note 7)
8
100
ns
TYPICAL PERFORMANCE CHARACTERISTICS
FB Voltage vs Temp
FB Voltage Line Regulation
FB Pin Current vs Temperature
TEMPERATURE (°C)
–50F B  V O L T A G E  (V )
1.231.2415018711 G01
1.22
1.21
50100–25
2575125
1.25
V IN  (V)
01.229
F B  V O L T A
G E  (V )
1.230
1.231
510
152018711 G02
2530
35
TEMPERATURE (°C)
–500
F B  P I N  C U R R E N T  (n A )
10
20304060–25
250
501007518711 G03
125150
50
T YPICAL PERFORMANCE CHARACTERISTICS Shutdown Mode I Q  vs V IN
Shutdown Mode I Q  vs Temperature
Burst Mode I Q  vs V IN
Burst Mode I Q  vs Temperature
Dynamic I Q  vs Frequency
Gate Drive Rise and Fall Time vs C L
V IN  (V)
00
S H U T D O W N  M O D E  I Q  (μA )
10
2010
203040
18711 G04
30
TEMPERATURE (°C)
–500
S H U T D O W N  M O D E  I Q  (μA )
5
10
15
20
–25
255018711 G05
75100125
150
V IN  (V)
00
B u r s t  M o d e  I Q  (μA )
100
20030040060010
2018711 G06
3040
500
TEMPERATURE (°C)
–500
B u r s t  M o d e  I Q  (μA )
200
500
507518711 G07
100
400300
–25
25100125
150FREQUENCY (kHz)
00
I Q  (m A )
2
6
8108001818711 G08
44001200600
200
1000121416
C L  (pF)
bootstrapped00
T I M E  (n s )
1020
30406020004000
6000800018711 G09
10000
12000
50RUN Thresholds vs V IN
RUN Thresholds vs Temperature
R T  vs Frequency
V IN  (V)
01.2
R U N  T H R E S H O L D S  (V )
1.3
1.4
10
203040
18711 G10
1.5
TEMPERATURE (°C)
–50R U N  T H R E S H O L D S  (V )
1.301.35
15018711 G11
1.25
1.20
50100–25
2575
1251.40
FREQUENCY (kHz)
100R T  (k Ω)
3001000
18711 G12
10
100
2001000
900800700600500400
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency vs Temperature
Maximum Sense Threshold vs Temperature
SENSE Pin Current vs Temperature
INTV CC  Load Regulation
INTV CC  Line Regulation
INTV CC  Dropout Voltage vs Current, Temperature
RUN (Pin 1): The RUN pin provides the user with an accurate means for sensing the input voltage and pro-gramming the start-up threshold for the converter . The falling RUN pin threshold is nominally 1.248V and the comparator has 100mV of hysteresis for noise immunity. When the RUN pi
n is below this input threshold, the IC is shut down and the V IN  supply current is kept to a low value (typ 10μA). The Absolute Maximum Rating for the voltage on this pin is 7V .
I TH  (Pin 2): Error Amplifi er Compensation Pin. The current comparator input threshold increases with this control voltage. Nominal voltage range for this pin is 0V to 1.40V .
FB (Pin 3): Receives the feedback voltage from the external resistor divider across the output. Nominal voltage for this pin in regulation is 1.230V .
FREQ (Pin 4): A resistor from the FREQ pin to ground programs the operating frequency of the chip. The nominal voltage at the FREQ pin is 0.6V .
TEMPERATURE (°C)
–50275
G A T E  F R E Q U E N C Y  (k H z )
2802902953003253100
507518711 G13
285315320305–25
25100125
150TEMPERATURE (°C)
–50140
M A X  S E N S E  T H R E S H O L D  (m V )
145
150155
160–25
255018711 G14
75100125
150TEMPERATURE (°C)
–5025
S E N S E  P I N  C U R R E N T  (μA )
30
35
507518711 G15
–25
25100125
150INTV CC  LOAD (mA)
0I N T V C C  V O L T A G E  (V )
5.2305080
18711 G165.1
5.0
1020
4060
70V IN  (V)
05.1
I N T V C C  V O L T A G E  (V )
5.2
5.310203040
18711 G17
5.4
515
25
35INTV CC  LOAD (mA)
00
D R O P O U T  V O L T A G
E  (m V )50
1502002505003505
1018711 G18
10040045030015
20
PIN FUNCTIONS

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