Linear Technology LTC3129-1 User manual

LTC3129-1
1
31291fc
For more information www.linear.com/LTC3129-1
Typical applicaTion
FeaTures DescripTion
15V, 200mA Synchronous
Buck-Boost DC/DC Converter
with 1.3µA Quiescent Current
The LT C
®
3129-1 is a high efficiency, 200mA buck-boost
DC/DC converter with a wide VIN and VOUT range. It
includes an accurate RUN pin threshold to allow predict-
able regulator turn-on and a maximum power point control
(MPPC)capabilitythat ensures maximumpower extraction
fromnon-ideal power sourcessuch as photovoltaic panels.
The LTC3129-1 employs an ultralow noise, 1.2MHz PWM
switching architecture that minimizes solution footprint by
allowing the use of tiny, low profile inductors and ceramic
capacitors. Built-in loop compensation and soft-start
simplify the design. For high efficiency operation at light
loads, automatic Burst Mode operation can be selected,
reducing the quiescent current to just 1.3µA. To further
reduce part count and improve light load efficiency, the
LTC3129-1 includes an internal voltage divider to provide
eight selectable fixed output voltages.
Additional features include a power good output, less than
10nA of shutdown current and thermal shutdown.
The LTC3129-1 is available in thermally enhanced
3mm×3mm QFN and 16-lead MSOP packages. For an
adjustable output voltage, see the functionally equivalent
LTC3129.
L, LT , LT C , LT M , Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective owners.
applicaTions
nRegulates VOUT Above, Below or Equal to VIN
nWide VIN Range: 2.42V to 15V, 1.92V to 15V After
Start-Up (Bootstrapped)
nFixed Output Voltage with Eight User-Selectable
Settings from 2.5V to 15V
n200mA Output Current in Buck Mode
nSingle Inductor
n1.3µA Quiescent Current
nProgrammable Maximum Power Point Control
n1.2MHz Ultralow Noise PWM
nCurrent Mode Control
nPin Selectable Burst Mode
®
Operation
nUp to 95% Efficiency
nAccurate RUN Pin Threshold
nPower Good Indicator
n10nA Shutdown Current
nThermally Enhanced 3mm ×3mm QFN and
16-Lead MSOP Packages
nIndustrial Wireless Sensor Nodes
nPost-Regulator for Harvested Energy
nSolar Panel Post-Regulator/Charger
nIntrinsically Safe Power Supplies
nWireless Microphones
nAvionics-Grade Wireless Headsets
BST1
VOUT
VOUT
5V AT
100mA VIN < VOUT
200mA VIN > VOUT
SW1 SW2
LTC3129-1
22nF
BST2
PGOOD
GND
VCC
VCC
VIN
VIN
2.42V TO 15V
RUN
MPPC
PWM
VS1
VS2
VS3
22nF 10µH
10µF
10µF
2.2µF
31291 TA01a
PGND
AA OR AAA
BATTERIES
Efficiency and Power Loss vs Load
100
OUTPUT CURRENT (mA)
0.01
EFFICIENCY (%)
POWER LOSS (mW)
70
80
90
50
30
20
60
40
10
0
1000
100
0.1
10
1
0.01
3129 TA01b
0.1 100 1000101
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 15V
EFFICIENCY
POWER LOSS
VOUT = 5V

LTC3129-1
2
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For more information www.linear.com/LTC3129-1
absoluTe MaxiMuM raTings
VIN, VOUT Voltages ..................................... –0.3V to 18V
SW1 DC Voltage.............................. –0.3V to (VIN + 0.3V)
SW2 DC Voltage............................–0.3V to (VOUT + 0.3V)
SW1, SW2 Pulsed (<100ns) Voltage ..............–1V to 19V
BST1 Voltage ..................... (SW1 – 0.3V) to (SW1 + 6V)
BST2 Voltage .....................(SW2 – 0.3V) to (SW2 + 6V)
RUN, PGOOD Voltage................................. –0.3V to 18V
VCC, PWM, MPPC, VS1, VS2,
VS3 Voltages ............................................... –0.3V to 6V
PGOOD Sink Current..............................................15mA
Operating Junction Temperature Range
(Notes 2, 5)............................................ –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
MSE Lead Temperature (Soldering, 10 sec).......... 300°C
(Notes 1, 8)
16 15 14 13
5678
TOP VIEW
UD PACKAGE
16-LEAD (3mm ×3mm) PLASTIC QFN
9
10
11
12
4
3
2
1
BST1
VIN
VCC
RUN
VOUT
PGOOD
PWM
VS1
SW1 PGND SW2 BST2
MPPC
GND
VS3 VS2
17
PGND
TJMAX = 125°C, θJC = 7.5°C/W, θJA = 68°C/W (NOTE 6)
EXPOSED PAD (PIN 17) IS PGND, MUST BE SOLDERED TO PCB
1
2
3
4
5
6
7
8
VCC
RUN
MPPC
GND
VS3
VS2
VS1
PWM
16
15
14
13
12
11
10
9
VIN
BST1
SW1
PGND
SW2
BST2
VOUT
PGOOD
TOP VIEW
MSE PACKAGE
16-LEAD PLASTIC MSOP
17
PGND
TJMAX = 125°C, θJC = 10°C/W, θJA = 40°C/W (NOTE 6)
EXPOSED PAD (PIN 17) IS PGND, MUST BE SOLDERED TO PCB
pin conFiguraTion
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3129EUD-1#PBF LTC3129EUD-1#TRPBF LGDS 16-Lead (3mm ×3mm) Plastic QFN –40°C to 125°C
LTC3129IUD-1#PBF LTC3129IUD-1#TRPBF LGDS 16-Lead (3mm ×3mm) Plastic QFN –40°C to 125°C
LTC3129EMSE-1#PBF LTC3129EMSE-1#TRPBF 31291 16-Lead Plastic MSOP –40°C to 125°C
LTC3129IMSE-1#PBF LTC3129IMSE-1#TRPBF 31291 16-Lead Plastic MSOP –40°C to 125°C
Consult LT C 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/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.

LTC3129-1
3
31291fc
For more information www.linear.com/LTC3129-1
elecTrical characTerisTics
The ldenotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA= 25°C (Note 2). Unless otherwise noted, VIN = 12V, VOUT = 5V.
PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Start-Up Voltage l2.25 2.42 V
Input Voltage Range VCC > 2.42V (Back-Driven) l1.92 15 V
VIN UVLO Threshold (Rising) VCC > 2.42V (Back-Driven) l1.8 1.9 2.0 V
VIN UVLO Hysteresis l80 100 130 mV
VOUT Voltages VS1 = VS2 = VS3 = 0V
VS1 = VCC, VS2 = VS3 = 0V
VS2 = VCC, VS1 = VS3 = 0V
VS1 = VS2 = VCC, VS3 = 0V
VS1 = VS2 = 0V, VS3 = VCC
VS2 = 0V, VS1 = VS3 = VCC
VS1 = 0V, VS2 = VS3 = VCC
VS1 = VS2 = VS3 = VCC
l
l
l
l
l
l
l
l
2.425
3.2175
3.998
4.875
6.727
7.995
11.64
14.50
2.5
3.3
4.1
5.0
6.9
8.2
12
15.0
2.575
3.383
4.203
5.125
7.073
8.405
12.40
15.50
V
V
V
V
V
V
V
V
Quiescent Current (VIN) – Shutdown RUN = 0V, Including Switch Leakage 10 100 nA
Quiescent Current (VIN) UVLO Either VIN or VCC Below Their UVLO Threshold, or
RUN Below the Threshold to Enable Switching
1.9 3 µA
Quiescent Current – Burst Mode Operation Measured on VIN, VOUT > VREG
PWM = 0V, RUN = VIN
1.3 2.0 µA
N-Channel Switch Leakage on VIN and VOUT SW1 = 0V, VIN = 15V
SW2 = 0V, VOUT = 15V
RUN = 0V
10 50 nA
N-Channel Switch On-Resistance VCC = 4V 0.75 Ω
Inductor Average Current Limit VOUT > UV Threshold (Note 4)
VOUT < UV Threshold (Note 4)
l
l
220
80
275
130
350
200
mA
mA
Inductor Peak Current Limit (Note 4) l400 500 680 mA
Maximum Boost Duty Cycle VOUT < VREG as Set by VS1-VS3. Percentage of
Period SW2 is Low in Boost Mode (Note 7)
l85 89 95 %
Minimum Duty Cycle VOUT > VREG as Set by VS1-VS3. Percentage of
Period SW1 is High in Buck Mode (Note 7)
l0 %
Switching Frequency PWM = VCC l1.0 1.2 1.4 MHz
SW1 and SW2 Minimum Low Time (Note 3) 90 ns
MPPC Voltage l1.12 1.175 1.22 V
MPPC Input Current MPPC = 5V 1 10 nA
RUN Threshold to Enable VCC l0.5 0.9 1.15 V
RUN Threshold to Enable Switching (Rising) VCC > 2.4V l1.16 1.22 1.28 V
RUN (Switching) Threshold Hysteresis 50 80 120 mV
RUN Input Current RUN = 15V 1 10 nA
VS1, VS2, VS3 Input High l1.2 V
VS1, VS2, VS3 Input Low l0.4 V
VS1, VS2, VS3 Input Current VS1, VS2, VS3 = VCC = 5V 1 10 nA
PWM Input High l1.6 V
PWM Input Low l0.5 V
PWM Input Current PWM = 5V 0.1 1 µA
Soft-Start Time 3 ms
VCC Voltage VIN > 4.85V l3.4 4.1 4.7 V
VCC Dropout Voltage (VIN – VCC) VIN = 3.0V, Switching
VIN = 2.0V (VCC in UVLO)
35
0
60
2
mV
mV

LTC3129-1
4
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For more information www.linear.com/LTC3129-1
elecTrical 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 LTC3129-1 is tested under pulsed load conditions such
that TJ≈ TA. The LTC3129E-1 is guaranteed to meet specifications
from 0°C to 85°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3129I-1 is guaranteed over the full –40°C to 125°C operating junction
temperature range. The junction temperature (TJ, in °C) is calculated from
the ambient temperature (TA, in °C) and power dissipation (PD, in watts)
according to the formula:
TJ= TA+ (PD • θJA),
where θJA (in °C/W) is the package thermal impedance.
Note that the maximum ambient temperature consistent with these
specifications is determined by specific operating conditions in
conjunction with board layout, the rated thermal package thermal
resistance and other environmental factors.
PARAMETER CONDITIONS MIN TYP MAX UNITS
VCC UVLO Threshold (Rising) l2.1 2.25 2.42 V
VCC UVLO Hysteresis 60 mV
VCC Current Limit VCC = 0V l4 20 60 mA
VCC Back-Drive Voltage (Maximum) l5.5 V
VCC Input Current (Back-Driven) VCC = 5.5V (Switching) 2 4 mA
VCC Leakage to VIN if VCC>VIN VCC = 5.5V, VIN = 1.8V, Measured on VIN –27 µA
VOUT UV Threshold (Rising) l0.95 1.15 1.35 V
VOUT UV Hysteresis 150 mV
VOUT Current – Shutdown RUN = 0V, VOUT = 15V Including Switch Leakage 10 100 nA
VOUT Current – Sleep PWM = 0V, VOUT ≥ VREG VOUT/27 µA
VOUT Current – Active PWM = VCC, VOUT = 15V (Note 4) 5 9 µA
PGOOD Threshold, Falling Referenced to Programmed VOUT Voltage –5.5 –7.5 –10 %
PGOOD Hysteresis Referenced to Programmed VOUT Voltage 2.5 %
PGOOD Voltage Low ISINK = 1mA 250 300 mV
PGOOD Leakage PGOOD = 15V 1 50 nA
The ldenotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA= 25°C (Note 2). Unless otherwise noted, VIN = 12V, VOUT = 5V.
Note 3: Specification is guaranteed by design and not 100% tested in
production.
Note 4: Current measurements are made when the output is not switching.
Note 5: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may result in device degradation or failure.
Note 6: Failure to solder the exposed backside of the package to the PC
board ground plane will result in a much higher thermal resistance.
Note 7: Switch timing measurements are made in an open-loop test
configuration. Timing in the application may vary somewhat from these
values due to differences in the switch pin voltage during non-overlap
durations when switch pin voltage is influenced by the magnitude and
duration of the inductor current.
Note 8: Voltage transients on the switch pin(s) beyond the DC limits
specified in the Absolute Maximum Ratings are non-disruptive to normal
operation when using good layout practices as described elsewhere in the
data sheet and Application Notes and as seen on the product demo board.

LTC3129-1
5
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For more information www.linear.com/LTC3129-1
Typical perForMance characTerisTics
Efficiency, VOUT = 2.5V
TA= 25°C, unless otherwise noted.
Power Loss, VOUT = 2.5V Efficiency, VOUT = 3.3V
Power Loss, VOUT = 3.3V
Efficiency, VOUT = 5V Power Loss, VOUT = 5V
OUTPUT CURRENT (mA)
0.01
EFFICIENCY (%)
100
90
70
50
40
80
60
30
20
10
0100.1
31291 G01
10001 100
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
BURST
PWM
OUTPUT CURRENT (mA)
0.01
POWER LOSS (mW)
1000
100
10
1
0.1
0.01 100.1
31291 G02
10001 100
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
BURST
PWM
OUTPUT CURRENT (mA)
0.01
EFFICIENCY (%)
100
90
70
50
40
80
60
30
20
10
0100.1
31291 G03
10001 100
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
PWM
BURST
OUTPUT CURRENT (mA)
0.01
POWER LOSS (mW)
1000
100
10
1
0.1
0.01 100.1
31291 G04
10001 100
BURST
PWM
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
OUTPUT CURRENT (mA)
0.01
POWER LOSS (mW)
1000
100
10
0.1
0.01
1
100.1
31291 G04b
10001 100
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
PWM
BURST
Efficiency, VOUT = 4.1V Power Loss, VOUT = 4.1V
OUTPUT CURRENT (mA)
0.01
EFFICIENCY (%)
100
90
70
50
40
80
60
30
20
10
0100.1
31291 G05
10001 100
BURST
PWM
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
OUTPUT CURRENT (mA)
0.01
POWER LOSS (mW)
1000
100
10
1
0.1
0.01 100.1
31291 G06
10001 100
PWM
BURST VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
Efficiency, VOUT = 6.9V
OUTPUT CURRENT (mA)
0.01
EFFICIENCY (%)
100
90
80
70
60
30
20
10
0
50
40
100.1
31291 G04a
10001 100
BURST
PWM
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
OUTPUT CURRENT (mA)
0.01
EFFICIENCY (%)
100
90
80
70
60
30
20
10
0
50
40
100.1
31291 G06a
10001 100
BURST
PWM
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V

LTC3129-1
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For more information www.linear.com/LTC3129-1
Typical perForMance characTerisTics
TA= 25°C, unless otherwise noted.
Maximum Output Current
vs VIN and VOUT
No Load Input Current
vs VIN and VOUT (PWM = 0V)Power Loss, VOUT = 15V
VIN (V)
2
IOUT (mA)
250
200
150
100
50
0133 4
31291 G11
1510 1411 1285 96 7
VOUT = 2.5V
VOUT = 3.3V
VOUT = 4.1V
VOUT = 5V
VOUT = 6.9V
VOUT = 8.2V
VOUT = 12V
VOUT = 15V
OUTPUT CURRENT (mA)
0.01
POWER LOSS (mW)
1000
100
10
0.1
0.01
1
100.1
31291 G06b
10001 100
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
PWM
BURST
OUTPUT CURRENT (mA)
0.01
EFFICIENCY (%)
100
90
80
70
60
30
20
10
0
50
40
100.1
31291 G06c
10001 100
BURST
PWM
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
OUTPUT CURRENT (mA)
0.01
POWER LOSS (mW)
1000
100
10
0.1
0.01
1
100.1
31291 G06d
10001 100
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
PWM
BURST
Efficiency, VOUT = 12V Power Loss, VOUT = 12V Efficiency, VOUT = 15V
Power Loss, VOUT = 6.9V Efficiency, VOUT = 8.2V Power Loss, VOUT = 8.2V
OUTPUT CURRENT (mA)
0.01
EFFICIENCY (%)
100
90
70
50
40
80
60
30
20
10
0100.1
31291 G07
10001 100
BURST
PWM
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
OUTPUT CURRENT (mA)
0.01
EFFICIENCY (%)
100
90
70
50
40
80
60
30
20
10
0100.1
31291 G09
10001 100
PWM
BURST
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
OUTPUT CURRENT (mA)
0.01
POWER LOSS (mW)
1000
100
10
1
0.1
0.01 100.1
31291 G08
10001 100
PWM
BURST
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
OUTPUT CURRENT (mA)
0.01
POWER LOSS (mW)
1000
100
10
1
0.1
0.01 100.1
31291 G10
10001 100
BURST
VIN = 2.5V
VIN = 3.6V
VIN = 5V
VIN = 10V
VIN = 15V
PWM
VIN (V)
2
IIN (µA)
5
4
3
2
1
012 14
31291 G12
16104 86
VOUT = 2.5V
VOUT = 3.3V
VOUT = 4.1V
VOUT = 5V
VOUT = 6.9V
VOUT = 8.2V
VOUT = 12V
VOUT = 15V

LTC3129-1
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For more information www.linear.com/LTC3129-1
Accurate RUN Threshold
vs Temperature (Normalized to 25°C)
Maximum Output vs Temperature
(Normalized to 25°C)
VCC Dropout Voltage vs Temperature
(PWM Mode, Switching)
VCC Dropout Voltage vs VIN
(PWM Mode, Switching)
Fixed Frequency PWM
Waveforms
Typical perForMance characTerisTics
TA= 25°C, unless otherwise noted.
Burst Mode Threshold
vs VIN and VOUT Switch RDS(ON) vs Temperature
Output Voltage vs Temperature
(Normalized to 25°C)
TEMPERATURE (°C)
–45
R
DS(ON)
(Ω)
1.3
1.2
1.1
1.0
0.8
0.7
0.6
0.5
0.9
0.4 –20
31291 G14
130
55 10580305
VCC = 2.5V
VCC = 3V
VCC = 4V
VCC = 5V
TEMPERATURE (°C)
–45
CHANGE IN V
OUT
(%)
1.0
0.5
0
–0.5
–1.0 –20
31291 G15
130
55 10580305
Average Input Current Limit
vs MPPC Voltage
TEMPERATURE (°C)
–45
DROPOUT (mV)
60
50
30
20
40
0
10
–20
31291 G20
130
55 10580305
VIN (V)
2
DROPOUT (mV)
60
50
30
20
40
0
10
2.25
31291 G21
4
3 3.5 3.753.252.752.5
L = 10µH
VIN = 7V
VOUT = 5V
IOUT = 200mA
SW2
5V/DIV
SW1
5V/DIV
31291 G22
500ns/DIV
IL
200mA/DIV
TEMPERATURE (°C)
–45
CHANGE IN RUN THRESHOLD (%)
2
0
–1
1
–2 –20
31291 G17
13055 10580305
MPPC PIN VOLTAGE (V)
1.13
PERCENTAGE OF FULL INPUT CURRENT (%)
100
90
70
60
50
40
30
20
10
80
01.135
31291 G18
1.171.1651.161.1551.145 1.151.14
TEMPERATURE (°C)
–45
CHANGE IN MAXIMUM OUTPUT CURRENT (%)
15
10
0
–5
5
–15
–10
–20
31291 G19
13055 10580305
VIN (V)
2
LOAD (mA)
80
70
60
40
30
20
10
50
04
3129 G13
1610 141286
VOUT = 2.5V
VOUT = 3.3V
VOUT = 4.1V
VOUT = 5V
VOUT = 6.9V
VOUT = 8.2V
VOUT = 12V
VOUT = 15V

LTC3129-1
8
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For more information www.linear.com/LTC3129-1
Typical perForMance characTerisTics
TA= 25°C, unless otherwise noted.
Step Load Transient Response in
Burst Mode Operation
PGOOD Response to a Drop
On VOUT MPPC Response to a Step Load
L = 10µH
VIN = 7V
VOUT = 5V
COUT = 22µF
IOUT = 5mA to 125mA STEP
31291 G28
500µs/DIV
IVOUT
100mA/DIV
VOUT
100mV/DIV
VOUT = 5V
31291 G29
1ms/DIV
PGOOD
2V/DIV
VOUT
2V/DIV
VIN = 5VOC
VMPPC SET TO 3.5V
CIN = 22µF, RIN = 10Ω,
VOUT = 5V, COUT = 22µF
IOUT = 25mA to 125mA STEP
31291 G30
2ms/DIV
IVOUT
100mA/DIV
VOUT
2V/DIV
VIN
2V/DIV
Fixed Frequency Ripple on VOUT Burst Mode Waveforms Burst Mode Ripple on VOUT
Start-Up Waveforms
Step Load Transient Response in
Fixed Frequency
L = 10µH
VIN = 7V
VOUT = 5V
IOUT = 200mA
COUT = 10µF
31291 G23
200ns/DIV
IL
200mA/DIV
VOUT
20mV/DIV
VIN = 7V
VOUT = 5V
IOUT = 50mA
COUT = 22µA
31291 G26
1ms/DIV
IVIN
200mA/DIV
VOUT
5V/DIV
VCC
5V/DIV
RUN
5V/DIV
L = 10µH
VIN = 7V
VOUT = 5V
COUT = 10µF
IOUT = 50mA to 150mA STEP
31291 G27
500µs/DIV
IVOUT
100mA/DIV
VOUT
100mV/DIV
L = 10µH
VIN = 7V
VOUT = 5V
IOUT = 5mA
COUT = 22µF
31291 G24
50µs/DIV
IL
200mA/DIV
SW2
5V/DIV
SW1
5V/DIV
L = 10µH
VIN = 7V
VOUT = 5V
IOUT = 5mA
COUT = 22µF
31291 G25
100µs/DIV
IL
100mA/DIV
VOUT
100mV/DIV

LTC3129-1
9
31291fc
For more information www.linear.com/LTC3129-1
BST1 (Pin 1/Pin 15): Boot-Strapped Floating Supply for
High Side NMOS Gate Drive. Connect to SW1 through a
22nF capacitor, as close to the part as possible. The value
is not critical. Any value from 4.7nF to 47nF may be used.
VIN (Pin2/Pin16): Input Voltagefor the Converter.Connect
a minimum of 4.7µF ceramic decoupling capacitor from
this pin to the ground plane, as close to the pin as possible.
VCC (Pin 3/Pin 1): Output Voltage of the Internal Voltage
Regulator. This is the supply pin for the internal circuitry.
Bypass this output with a minimum of 2.2µF ceramic ca-
pacitor close to the pin. This pin may be back-driven by
an external supply, up to a maximum of 5.5V.
RUN (Pin 4/Pin 2): Input to the Run Comparator. Pull
this pin above 1.1V to enable the VCC regulator and above
1.28V to enable the converter. Connecting this pin to a
resistor divider from VIN to ground allows programming a
VIN start threshold higher than the 1.8V(typical) VIN UVLO
threshold. In this case, the typical VIN turn-on threshold is
determinedby VIN = 1.22V • [1+(R3/PinR4)](see Figure 2).
MPPC (Pin 5/Pin 3): Maximum Power Point Control
Programming Pin. Connect this pin to a resistor divider
from VIN to ground to enable the MPPC functionality.
If the VOUT load is greater than what the power source
can provide, the MPPC will reduce the inductor current
to regulate VIN to a voltage determined by: VIN = 1.175V
• [1 + (R5/R6)] (see Figure 3). By setting the VIN regula-
tion voltage appropriately, maximum power transfer from
the limited source is assured. Note this pin is very noise
sensitive,therefore minimize trace length andstray capaci-
tance. Please refer to the Applications Information section
for more detail on programming the MPPC for different
sources. If this function is not needed, tie the pin to VCC.
GND (Pin 6/Pin 4): Signal Ground. Provide a short direct
PCB path between GND and the ground plane where the
exposed pad is soldered.
VS3 (Pin 7/Pin 5): Output Voltage Select Pin. Connect this
pin to ground or VCC to program the output voltage (see
Table 1). This pin should not float or go below ground.
If this pin is externally driven above VCC,a1M resistor
should be added in series.
VS2 (Pin 8/Pin 6): Output Voltage Select Pin. Connect this
pin to ground or VCC to program the output voltage (see
Table 1). This pin should not float or go below ground.
VS1 (Pin 9/Pin 7): Output Voltage Select Pin. Connect this
pin to ground or VCC to program the output voltage (see
Table 1). This pin should not float or go below ground.
PWM (Pin 10/Pin 8): Mode Select Pin.
PWM = Low (ground): Enables automatic Burst Mode
operation.
PWM = High (tie to VCC): Fixed frequency PWM
operation.
This pin should not be allowed to float. It has internal 5M
pull-down resistor.
PGOOD (Pin 11/Pin 9): Open drain output that pulls to
ground when FB drops too far below its regulated voltage.
Connect a pull-up resistor from this pin to a positive sup-
ply. This pin can sink up to the absolute maximum rating
of 15mA when low. Refer to the Operation section of the
data sheet for more detail.
VOUT (Pin 12/Pin 10): Output voltage of the converter, set
by the VS1-VS3 programming pins according to Table 1.
Connect a minimum value of 4.7µF ceramic capacitor from
this pin to the ground plane, as close to the pin as possible.
BST2 (Pin 13/Pin 11): Boot-Strapped Floating Supply for
High Side NMOS Gate Drive. Connect to SW2 through a
22nF capacitor, as close to the part as possible. The value
is not critical. Any value from 4.7nF to 47nF may be used
SW2 (Pin 14/Pin 12): Switch Pin. Connect to one side of
the inductor. Keep PCB trace lengths as short and wide
as possible to reduce EMI.
pin FuncTions
(QFN/MSOP)

LTC3129-1
10
31291fc
For more information www.linear.com/LTC3129-1
pin FuncTions
(QFN/MSOP)
PGND (Pin 15/Pin 13, Exposed Pad Pin 17/Pin 17): Power
Ground. Provide a short direct PCB path between PGND
and the ground plane. The exposed pad must also be
soldered to the PCB ground plane. It serves as a power
ground connection, and as a means of conducting heat
away from the die.
SW1 (Pin 16/Pin 14): Switch Pin. Connect to one side of
the inductor. Keep PCB trace lengths as short and wide
as possible to reduce EMI.
Table 1. VOUT Program Settings
VS3 PIN VS2 PIN VS1 PIN VOUT
0 0 0 2.5V
0 0 VCC 3.3V
0 VCC 0 4.1V
0 VCC VCC 5V
VCC 0 0 6.9V
VCC 0 VCC 8.2V
VCC VCC 0 12V
VCC VCC VCC 15V
block DiagraM
31291 BD
LDO
VREF
START
VREF
VCC
VCC
VCC_GD
START
START
4.1V
1.175V
VREF
+
–
SD
UVLO
+
–
–
+
+
–
–
+THERMAL
SHUTDOWN
+
–
–
+
PWM
600mV
–7.5%
OSC
GND
SLEEP
100mV
RESET
ENABLE
ILIM
IZERO
ISENSE
20mA
ISENSE
VREF_GD
500mA
PGND
CLAMP
+
–
1.175V
FB
–
+
–
+
–
+
–
+
DRIVER
DRIVER
DRIVER
DRIVER
ISENSE
ISENSE
DRV_C
1.1V
UV
VS1
VOUT
VCC
VOUT
VS2
VS3DRV_D
DRV_B
DRV_A
ISENSE
LOGIC
PGOOD
SOFT-START
+
–
MPPC
RUN
VCC
VIN
VIN
BST1 SW1 SW2
D
C
A
B
BST2
PWM
SLEEP
VIN
0.9V
1.22V
1.175V
5M
1.175V
VC
VOUT
SELECT
INPUTS