LTC3100
1
3100fa
SWBST VINBK VBST
LTC3100
FBBST
3.3μH
1.87M
1.07M
3.3V AT 100mA
10μF
s2
2.2μF
VLDO
VINBST
FBLDO
SWBK
PGBK
PGBST
102k
25.5k
BOOST
LDO
BUCK
VBATT
1.6V TO 3.2V
2.2μF
FBBK
2M
1M
10μF
3100 TA01a
MODE
RUNBST
RUNLDO
RUNBK GND
FF EN_BURST
OFF ON
OFF ON
OFF ON
4.7μH
VBOOST
3V AT 50mA
VLDO
1.8V AT 200mA
VBUCK
BOOST_GOOD
BUCK_GOOD
1M
1M
The LTC
®
3100 combines a high effi ciency 700mA syn-
chronous step-up converter, a 250mA synchronous
step-down converter and a 100mA LDO regulator. The
LTC3100 features a wide input voltage range of 0.65V to
5V. The step-down converter can be powered by the output
of the step-up converter or from a separate power source
between 1.8V and 5.5V. The LDO can also be used as a
sequencing switch on the output of the boost.
A switching frequency of 1.5MHz minimizes solution foot-
print by allowing the use of tiny, low profi le inductors and
ceramic capacitors. The switching regulators use current
mode control and are internally compensated, reducing
external parts count. Each converter automatically transi-
tions to Burst Mode operation to maintain high effi ciency
over the full load range. Burst Mode operation can be
disabled for low noise applications. The integrated LDO
provides a third low noise, low dropout supply.
Anti-ringing circuitry reduces EMI by damping the boost
inductor in discontinuous mode. Additional features
include shutdown current of under 1μA and overtem-
perature shutdown. The LTC3100 is housed in a 16-lead
3mm × 3mm 0.75mm QFN package.
TYPICAL APPLICATION
FEATURES
APPLICATIONS
DESCRIPTION
1.5MHz Synchronous Dual
Channel DC/DC Converter
and 100mA LDO
Two-Cell, Triple Output Converter
n Extremely Compact Triple-Rail Solution
n Burst Mode
®
Operation, IQ = 15μA
n 1.5MHz Fixed Frequency Operation
n Power Good Indicators
n 700mA Synchronous Step-Up DC/DC
0.65V to 5V VIN Range
1.5V to 5.25V VOUT Range
94% Peak Effi ciency
V
IN > VOUT Operation
Output Disconnect
n 250mA Synchronous Step-Down DC/DC
1.8V to 5.5V VIN Range
0.6V to 5.5V VOUT Range
n LDO (VIN Internally Tied to VBST)
0.6V to 5.25V VOUT Range
200mV Dropout Voltage at 100mA
n Available in a 16-Lead 3mm × 3mm QFN Package
n Bar Code Readers
n Medical Instruments
n Low Power Portable Electronic Devices
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
Effi ciency and Power Loss
vs Load Current, VIN = 2.4V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
POWER LOSS (mW)
50
80
0.01 10 100 1000
0
10
0.1 1
100
70
90
40
60
20
100
0.01
1000
1
10
0.1
3100 TA01b
BOOST
BUCK
PL, BOOST
PL, BUCK
LTC3100
2
3100fa
PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS
VINBST and VINBK Voltage .............................. –0.3 to 6V
SWBST, SWBK DC Voltage ............................. –0.3 to 6V
SWBST, SWBK Pulsed (< 100ns) Voltage ...... –0.3 to 7V
FBBST, FBBK, FBLDO, PGBST, PGBK Voltage . –0.3 to 6V
MODE, RUNBST, RUNBK, RUNLDO Voltage ... –0.3 to 6V
VBST
, VLDO ...................................................... –0.3 to 6V
Operating Temperature (Notes 2, 5) .........–40°C to 85°C
Storage Temperature Range ...................–65°C to 125°C
(Note 1)
16 15 14 13
5 6 7
17
8
TOP VIEW
UD PACKAGE
16-LEAD (3mm s 3mm) PLASTIC QFN
9
10
11
12
4
3
2
1SWBST
VBST
VLDO
SWBK
FBBST
FBLDO
RUNLDO
FBBK
VINBST
PGBST
RUNBST
MODE
VINBK
PGBK
GND
RUNBK
TJMAX = 125°C, θJA = 68°C/W, 4-LAYER BOARD
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB (NOTE 6)
ELECTRICAL CHARACTERISTICS: STEP-UP CONVERTER
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Start-Up Voltage ILOAD = 1mA l0.65 0.90 V
Input Voltage Range After Start-Up (Minimum Voltage Is Load Dependent) l0.5 5 V
Output Voltage Adjust Range l1.5 5.25 V
Feedback Voltage l1.182 1.200 1.218 V
Feedback Input Current FBBST = 1.2V 1 50 nA
Quiescent Current (VIN): Shutdown RUNBST = 0V, Not Including Switch Leakage, VBST = 0V, VINBK = 0V 0.01 1 μA
Quiescent Current: Active Measured on VBST (Note 4), RUNBK = 0V, RUNLDO = 0V 300 500 μA
Quiescent Current: Burst Mode
Operation
Measured on VBST
, FBBST > 1.25V
MODE = 1V, RUNLDO = 0V
MODE = 1V, RUNLDO = 1V
15
28
25
45
μA
μA
N-Channel MOSFET Switch Leakage
Current
SWBST = 5V, VBST= 5V 0.1 5 μA
P-Channel MOSFET Switch Leakage
Current
SWBST = 0V, VBST = 5V 0.1 10 μA
The l denotes the specifi cations
which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VINBST = 1.2V, VBST = 3.3V,
TA = 25°C, unless otherwise noted.
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3100EUD#PBF LTC3100EUD#TRPBF LDJR 16-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/
LTC3100
3
3100fa
PARAMETER CONDITIONS MIN TYP MAX UNITS
N-Channel MOSFET Switch-On
Resistance
VBST = 3.3V 0.3 Ω
P-Channel MOSFET Switch-On
Resistance
VBST = 3.3V 0.4 Ω
N-Channel MOSFET Current Limit l700 850 mA
Maximum Duty Cycle VFBBST = 1.15V l87 90 %
Minimum Duty Cycle VFBBST = 1.3V l0%
Switching Frequency l1.2 1.5 1.8 MHz
RUNBST Input High Voltage l0.9 V
RUNBST Input Low Voltage l0.3 V
RUNBST Input Current RUNBST = 1.2V 0.8 2 μA
Soft-Start Time 0.8 ms
PGBST Threshold, Falling Referenced to Feedback Voltage –8 %
PGBST Hysteresis Referenced to Feedback Voltage 3 %
PGBST Voltage Low 5mA Load 65 mV
PGBST Leakage Current PGBST = 5.5V 0.01 10 μA
ELECTRICAL CHARACTERISTICS: STEP-DOWN CONVERTER
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Voltage Range l1.8 5.5 V
Output Voltage Adjust Range l0.61 5.5 V
Feedback Voltage l590 600 610 mV
Feedback Input Current FBBK = 600mV 1 30 nA
Quiescent Current: Shutdown Measured on VINBK, RUNBK = 0V, VINBST = 0V, VBST = 0V
Not Including Switch Leakage
0.01 1 μA
Quiescent Current: Active Measured on VINBK (Note 4), RUNBST = 0V 240 350 μA
Quiescent Current: Burst Mode Operation Measured on VINBK, FBBK = 620mV, MODE = OPEN,
RUNBST = 0V
16 30 μA
N-Channel MOSFET Switch Leakage Current VINBK = SWBK = 5V 0.1 5 μA
P-Channel MOSFET Switch Leakage Current SWBK = 0V, VINBK = 5V 0.1 5 μA
N-Channel MOSFET Switch-On Resistance VINBK = 3.3V 0.45 Ω
P-Channel MOSFET Switch-On Resistance VINBK = 3.3V 0.55 Ω
P-Channel MOSFET Current Limit l340 450 mA
Maximum Duty Cycle FBBK < 590mV l100 %
Minimum Duty Cycle FBBK > 610mV l0%
Switching Frequency l1.2 1.5 1.8 MHz
The l denotes the
specifi cations which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VINBK = 3.3V,
TA = 25°C, unless otherwise noted.
ELECTRICAL CHARACTERISTICS: STEP-UP CONVERTER
The l denotes the specifi cations
which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VINBST = 1.2V, VBST = 3.3V,
TA = 25°C, unless otherwise noted.
LTC3100
4
3100fa
PARAMETER CONDITIONS MIN TYP MAX UNITS
RUNBK Input High Voltage l0.9 V
RUNBK Input Low Voltage l0.3 V
RUNBK Input Current RUNBK = 1.2V 0.8 2 μA
Soft-Start Time 1.3 ms
PGBK Threshold, Falling Referenced to Feedback Voltage –8 %
PGBK Hysteresis Referenced to Feedback Voltage 3 %
PGBK Voltage Low 5mA Load 65 mV
PGBK Leakage Current PGBK = 5.5V 0.01 10 μA
ELECTRICAL CHARACTERISTICS: STEP-DOWN CONVERTER
The l denotes the
specifi cations which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VINBK = 3.3V,
TA = 25°C, unless otherwise noted.
ELECTRICAL CHARACTERISTICS: LDO REGULATOR
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Voltage Range l1.8 5.25 V
Output Voltage Adjust Range (Note 3) l0.618 5.25 V
Feedback Voltage l582 600 618 mV
Maximum Output Current l100 120 mA
Feedback Input Current FBLDO = 600mV 1 30 nA
Line Regulation VIN = 3.3V to 5.25V 0.1 %/V
Load Regulation From 10mA to 100mA Load 0.1 %
Dropout Voltage IOUT = 100mA l130 200 mV
Ripple Rejection (PSRR) Frequency = 1.5MHz at ILOAD = 50mA, COUT = 2.2μF (Note 3) 35 dB
Short-Circuit Current Limit FBLDO < 582mV l120 160 mA
Soft-Start Time 0.3 ms
RUNLDO Input High Voltage l0.9 V
RUNLDO Input Low Voltage l0.3 V
RUNLDO Input Current RUNLDO = 1.2V 0.8 2 μA
Quiescent Current—Active RUNLDO = 3.3V, Measured on VBST
RUNBST = RUNBK = 0V, VINBK = 0V
26 40 μA
The l denotes the specifi cations which
apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VBST = 3.3V, VLDO = 3V, TA = 25°C, unless
otherwise noted.
ELECTRICAL CHARACTERISTICS: COMMON CIRCUITRY
PARAMETER CONDITIONS MIN TYP MAX UNITS
MODE Input High Voltage l0.9 V
MODE Input Low Voltage l 0.3 V
MODE Input Current MODE = 0V
MODE = 5V
–3.3
1.7
–5
3
μA
μA
The l denotes the specifi cations
which apply over the full operating temperature range. Extended commercial grade: –40°C to 85°C, VBST or VINBK = 3.3V, TA = 25°C,
unless otherwise noted.
LTC3100
5
3100fa
Effi ciency vs Load Current
and VIN for VO = 1.8V
Effi ciency vs Load Current
and VIN for VO = 3.3V
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 LTC3100E is guaranteed to meet performance specifi cations
from 0°C to 85°C. Specifi cations over –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Specifi cation 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 specifi ed 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 thermal resistance much higher than
68°C/W.
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise specifi ed.
Step-Up DC/DC Converter
LOAD CURRENT (mA)
30
EFFICIENCY (%)
POWER LOSS (mW)
50
80
0.01 10 100 1000
0
10
0.1 1
100
70
90
40
60
20
100
0.01
1000
1
10
0.1
3100 G01
VIN = 1.2V
VIN = 1.5V
PL, VIN = 1.2V
PL, VIN = 1.5V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
POWER LOSS (mW)
50
80
0.01 10 100 1000
0
10
0.1 1
100
70
90
40
60
20
100
0.01
1000
1
10
0.1
3100 G02
VIN = 1.2V
VIN = 2.4V
VIN = 3V
PL, VIN = 1.2V
PL, VIN = 2.4V
PL, VIN = 3V
ELECTRICAL CHARACTERISTICS
3.3V, 100mA Effi ciency vs VIN
Effi ciency vs Load Current
and VIN for VO = 5V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
POWER LOSS (mW)
50
80
0.01 10 100 1000
0
10
0.1 1
100
70
90
40
60
20
100
0.01
1000
1
10
0.1
3100 G03
VIN = 1.8V
VIN = 2.4V
VIN = 3.6V
PL, VIN = 1.8V
PL, VIN = 2.4V
PL, VIN = 3.6V
VINBST (V)
EFFICIENCY (%)
40
90
100
2.2 2.6 3
20
70
30
80
10
0
60
50
1.8 22.4 3.4 4.2
2.8 3.2 3.8 4
3.6
3100 G04
VBST = 3.3V AT 100mA
LTC3100
6
3100fa
Maximum Load Current During
Start-Up vs VIN
VINBST (V)
0.7
1
LOAD CURRENT (mA)
100
1000
0.9 1.10.8 1 1.2 1.3
10
3100 G07
VBST = 1.8V, RESISTIVE LOAD
VBST = 1.8V, CONSTANT-CURRENT LOAD
VBST = 3.3V, RESISTIVE LOAD
VBST = 3.3V, CONSTANT-CURRENT LOAD
VBST = 5V, RESISTIVE LOAD
VBST = 5V, CONSTANT-CURRENT LOAD
TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Output Current vs VIN
Burst Mode Threshold
Current vs VIN Start-Up Voltage vs Temperature
VOUT and IIN During Soft-Start
Output Voltage Ripple in Fixed
Frequency and Burst Mode Operation
TA = 25°C, unless otherwise specifi ed.
Step-Up DC/DC Converter
No-Load Input Current vs VIN,
Mode = Open, LDO and Buck Off
VINBST (V)
0
OUTPUT CURRENT (mA)
400
600
123
200
300
100
0
500
0.5 1.5 44.5
2.5 3.5
3100 G06
VOUT = 1.8V
VOUT = 3.3V
VOUT = 5V
VINBST (V)
1.0
LOAD CURRENT (mA)
40
50
60
2.5 3.5
3100 G08
30
20
1.5 2.0 3.0 4.0 4.5
10
0
L = 3.3μH
VOUT = 1.8V
VOUT = 3.3V
VOUT = 5V
TEMPERATURE (°C)
–45
INPUT VOLTAGE (V)
0.70
0.85
–15 15 45
0.60
0.65
0.55
0.50
0.80
0.75
–30 075 90
30 60
3100 G09
3100 G10
500μs/DIV
IIN
200mA/DIV
VBST
1V/DIV
3100 G11
0.5μs/DIV
100mA LOAD
20mV/DIV
20μs/DIV
5mA LOAD
20mV/DIV
VBST COUT = 20μF
VINBST (V)
1.0
0
INPUT CURRENT (μA)
20
60
80
100
3.0
180
3100 G05
40
2.0
1.5 3.5 4.0
2.5 4.5
120
140
160
VOUT = 5V
VOUT = 3.3V
VOUT = 1.8V
LTC3100
7
3100fa
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step Response, 5mA-100mA
Burst Mode Operation Enabled
Dropout Voltage vs VOUT
and Temperature (IOUT = 100mA) Soft-Start Time
Burst Mode Operation
Ripple Rejection Load Step Response, 10mA-60mA
TA = 25°C, unless otherwise specifi ed.
LDO Regulator
Load Step Response, 50mA-150mA
Fixed Frequency Mode
Ripple Rejection
Step-Up DC/DC Converter
3100 G12
100μs/DIV
IOUT
100mA/DIV
VBST
50mV/DIV
VBST COUT = 10μF
3100 G13
100μs/DIV
IOUT
100mA/DIV
VBST
50mV/DIV
VBST COUT = 20μF
TEMPERATURE (°C)
–45
DROPOUT VOLTAGE (VBST_VLDO)
0.200
0.225
60
0.175
0.150
–15 15
–30 030 75
45 90
0.075
0.050
0.125
0.250
0.100
6105 G14
VLDO = 1.5V
VLDO = 2.5V
VLDO = 5V
VLDO = 3.3V
FREQUENCY (Hz)
15
PSRR (dB)
25
35
0.1 100 1000 10000
0
5
110
40
20
30
10
3100 G15
VOUT = 3V
IOUT = 50mA
COUT = 2.2μF
3100 G16
100μs/DIV
RUNLDO
2V/DIV
VLDO
1V/DIV
LDO COUT = 2.2μF
3100 G17
5μs/DIV
BOOST RIPPLE
20mV/DIV
LDO RIPPLE
20mV/DIV
LDO COUT = 2.2μF
3100 G18
200μs/DIV
50mA/DIV
VLDO
100mV/DIV
LDO COUT = 2.2μF
LTC3100
8
3100fa
Step-Down DC/DC Converter
TYPICAL PERFORMANCE CHARACTERISTICS
Effi ciency vs Load Current and VIN
for VO = 1.2V
Effi ciency vs Load Current and VIN
for VO = 1.8V
No-Load Input Current
vs VINBK (Mode = Open)
Burst Mode Operation Threshold
Current vs VIN VOUT and IIN During Soft-Start
TA = 25°C, unless otherwise specifi ed.
Output Voltage Ripple in Fixed
Frequency and Burst Mode Operation
Load Step Response,
Burst Mode Operation Enabled
10mA to 100mA
Load Step Response,
Fixed Frequency Mode
10mA to 100mA
LOAD CURRENT (mA)
30
EFFICIENCY (%)
POWER LOSS (mW)
50
80
0.01 10 100 1000
0
10
0.1 1
100
70
90
40
60
20
100
0.01
1000
1
10
0.1
3100 G19
VIN = 1.8V
VIN = 2.4V
VIN = 3.3V
PL, VIN = 1.8V
PL, VIN = 2.4V
PL, VIN = 3.3V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
POWER LOSS (mW)
50
80
0.01 10 100 1000
0
10
0.1 1
100
70
90
40
60
20
100
0.01
1000
1
10
0.1
3100 G20
VIN = 2.4V
VIN = 3.3V
VIN = 5V
PL, VIN = 2.4V
PL, VIN = 3.3V
PL, VIN = 5V
VINBK (V)
1.5
INPUT CURRENT (μA)
2.5 3.5
23 4 4.5 5
5
0
15
20
10
3100 G21
VINBK (V)
LOAD CURRENT (mA)
60
70
50
40
2.5 3.5
23 4 4.5 5
10
0
30
80
20
3100 G22
VOUT = 2.5V
VOUT
= 1.8V
VOUT = 1.2V
VOUT = 1.5V
3100 G24
5μs/DIV
50mV/DIV
50mV/DIV
COUT = 10μF
3100 G25
200μs/DIV
100mA/DIV
50mV/DIV
COUT = 10μF
3100 G26
200μs/DIV
50mA/DIV
50mV/DIV
COUT = 10μF
3100 G23
2ms/DIV
INPUT
CURRENT
50mA/DIV
VOUT
0.5V/DIV
STARTUP, 200mA LOAD
VIN = 2.4V
VOUT = 1.2V
COUT = 10μF
LTC3100
9
3100fa
RUN Pin Threshold Voltage Start-Up Delay Times vs VIN
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise specifi ed.
PIN FUNCTIONS
SWBST (Pin 1): Switch Pin for the Boost Converter.
Connect the boost inductor between SWBST and VINBST.
Keep PCB trace lengths as short and wide as possible to
reduce EMI. If the inductor current falls to zero, an internal
anti-ringing switch is connected from SWBST to VINBST
to minimize EMI.
VBST (Pin 2): Output Voltage for the Boost Converter
(which is the drain of the internal synchronous rectifi er)
and Input Voltage for the LDO. PCB trace length from VBST
to the output fi lter capacitor (10μF minimum) should be
as short and wide as possible.
VLDO (Pin 3): Output Voltage of the LDO Regulator. Connect
a 1μF ceramic capacitor between VLDO and GND. Larger
values of capacitance may be used for higher PSRR or
improved transient response.
SWBK (Pin 4): Switch Pin for the Buck Converter. Connect
the buck inductor between SWBK and the buck output
fi lter capacitor. Keep PCB trace lengths as short and wide
as possible to reduce EMI.
VINBK (Pin 5): Input Voltage for the Buck Converter. Con-
nect a minimum of 4.7μF ceramic decoupling capacitor
from this pin to ground.
PGBK (Pin 6): Open-Drain Output That Pulls Low When
FBBK Is More Than 8% Below Its Regulated Voltage. Con-
nect a pull-up resistor from this pin to a positive supply
less than 6V.
GND (Pin 7): Signal Ground. Provide a short, direct PCB
path between GND and the PC board ground plane con-
nected to the Exposed Pad.
RUNBK (Pin 8): Logic-Controlled Shutdown Input for the
Buck Converter. There is an internal 4MΩ pull-down on
this pin.
RUNBK = High: Normal operation
RUNBK = Low: Shutdown
FBBK (Pin 9): Feedback Input to the gm Error Amplifi er
for the Buck Converter. Connect the resistor divider tap
to this pin. The output voltage can be adjusted from 0.6V
to 5.5V by:
VV
R
R
OUT BUCK_.•=+
⎛
⎝
⎜⎞
⎠
⎟
0 600 1 6
5
RUNLDO (Pin 10): Logic-Controlled Shutdown Input for
the LDO Regulator. There is an internal 4MΩ pull-down
on this pin.
RUNLDO = High: Normal operation
RUNLDO = Low: Shutdown
VIN (V)
THRESHOLD (V)
0.550
0.575
0.600
4 4.5
0.525
1.5 2.5
12 3 3.5 5
0.500
0.625
3100 G27
FALLING
RISING
VIN (V)
0.5
DELAY TIME (μs)
300
350
400
4
250
200
1.5 2.5
123 4.5
3.5 5
50
0
150
450
100
3100 G28
LDO
BOOST
BUCK
LTC3100
10
3100fa
PIN FUNCTIONS
FBLDO (Pin 11): Feedback Input to the gm Error Amplifi er
for the LDO Regulator. Connect the resistor divider tap to
this pin. The output voltage can be adjusted from 0.6V
to 5.25V by:
VV
R
R
OUT LDO_.•=+
⎛
⎝
⎜⎞
⎠
⎟
0 600 1 4
3
FBBST (Pin 12): Feedback Input to the gm Error Amplifi er
for the Boost Converter. Connect the resistor divider tap
to this pin. The output voltage can be adjusted from 1.5V
to 5.25V by:
VV
R
R
OUT BOOST_.•=+
⎛
⎝
⎜⎞
⎠
⎟
120 1 2
1
MODE (Pin 13): Logic-Controlled Mode Select Pin for
Both the Boost and Buck Converters. There is an internal
1MΩ pull-up on this pin to the higher of VINBST, VBST or
VINBK.
MODE = Float or High: Enables Burst Mode operation for
both the boost and the buck.
MODE = Low: Disables Burst Mode operation. Both con-
verters will operate in fi xed frequency mode regardless
of load current.
RUNBST (Pin 14): Logic-Controlled Shutdown Input for
the Boost Converter. There is an internal 4MΩ pull-down
on this pin.
RUNBST = High: Normal operation
RUNBST = Low: Shutdown
PGBST (Pin 15): Open-Drain Output That Pulls to Ground
When FBBST Is More Than 8% Below Its Regulated Volt-
age. Connect a pull-up resistor from this pin to a positive
supply less than 6V.
VINBST (Pin 16): Input Voltage for the Boost Converter.
Connect a minimum of 1μF ceramic decoupling capacitor
from this pin to ground.
Exposed Pad (Pin 17): The Exposed Pad must be soldered
to the PCB ground plane. It serves as the power ground
connection, and as a means of conducting heat away
from the die.
LTC3100
11
3100fa
BLOCK DIAGRAM
3100 BD
THERMAL
SHUTDOWN
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
MODE
CONTROL
1.5MHz
OSC
GATE
CONTROL
VREF
VREF_GD
WELL
SWITCH
WELL
SWITCH
START-UP START_OSC
CLK
TSD
VBEST
VBEST GATE
DRIVERS
AND
ANTI-CROSS
CONDUCTION
GATE
DRIVERS
AND
ANTI-CROSS
CONDUCTION
SHUTDOWN
LOGIC
LOGIC
LOGIC
SHUTDOWN
CIN
4.7μF
4M
CIN
2.2μF
VBATT1, 0.65V TO 5V
4M
4M
COUT
10μF
VBOOST, 1.5V TO 5.25V
R2
R1
COUT
4.7μF
L1
3.3μH
L1, 3.3μH
VBUCK
0.6V TO 5V
IZERO
COMPARATOR
IZERO
COMPARATOR
IZERO ILIM
ISET
R6
FBBST
PGBST
VLDO
VBEST OF 3
VBST
VREF_GD
BURST
VINBK
VSEL
PAD
FBLDO
100mA
0.15Ω
0.6V
RUNLDO
FROM VBST, VBATT1
OR VBATT2
VINBK
SWBK
FBBK
VINBST
VREF
SWBST VBST
0.55V
GND
PGND
0.6V
VB
1.2V
FB
IPK
SLOPE
COMPARATOR
IPK
COMPARATOR
IPK
COMPARATOR ILIM REF
ISENSE
ISENSE
WAKE
SOFT-START
ERROR
AMPLIFIER
R5
COUT
1μF
VLDO
0.6V TO 5V
R4
R3
3
3
8
6
13
14
16 1 2
12
15
3
11
10
5
4
9
7
OFF ON
OFF ON
OFF ON
RUNBST
ERROR
AMPLIFIER
ERROR
AMPLIFIER/
SLEEP
COMPARATOR
TSD
1.1V
MODE
SLOPE
COMPARATOR
CLK
TSD
RUNLDO
RUNBK
PWM
PGBK
UVLO
SHUTDOWN
SHUTDOWN
LEVEL
SHIFT
CLAMP
VBST
1M
LTC3100
12
3100fa
OPERATION
The LTC3100 includes an 700mA synchronous step-up
(boost) converter, a 250mA synchronous step-down
(buck) converter and a 100mA low dropout (LDO) linear
regulator housed in a 16-lead 3mm × 3mm QFN package.
Both converters utilize current mode PWM control for
exceptional line and load regulation and operate from the
same 1.5MHz oscillator. The current mode architecture
with adaptive slope compensation also provides excellent
transient load response, requiring minimal output fi lter-
ing. Both converters have internal soft-start and internal
loop compensation, simplifying the design process and
minimizing the number of external components.
With its low RDS(ON) and low gate charge internal MOSFET
switches and synchronous rectifi ers, the LTC3100 achieves
high effi ciency over a wide range of load current. Burst
Mode operation maintains high effi ciency at very light loads,
but can be disabled for noise-sensitive applications.
With separate power inputs for the boost and buck con-
verters, along with independent enable and power good
functions, the LTC3100 is very fl exible. The two converters
can operate from the same input supply, or from two dif-
ferent sources, or can even be cascaded by powering the
buck converter from the output of the boost converter. By
using the LDO as well, three different output voltages can
be generated from a single alkaline/NiMH cell (or the LDO
can be used for power sequencing the boost output).
Operation can be best understood by referring to the
Block Diagram.
BOOST CONVERTER
Low Voltage Start-Up
The LTC3100 boost converter includes an independent
start-up oscillator designed to start up at an input voltage
of 0.65V (typical). Soft-start and inrush current limiting are
provided during start-up, as well as in normal mode.
When either VINBST or VBST exceeds 1.4V (typical), the
IC enters normal operating mode. Once the output volt-
age exceeds the input by 0.24V, the IC powers itself from
VBST instead of VINBST
. At this point, the internal circuitry
has no dependency on the input voltage, eliminating the
requirement for a large input capacitor. The limiting fac-
tor for the application becomes the ability of the power
source to supply suffi cient energy to the output at low
input voltages, and maximum duty cycle of the converter,
which is clamped at 90% (typical). Note that at low input
voltages, even small input voltage drops due to series
resistance become critical, and greatly limit the power
delivery capability of the converter.
LOW NOISE FIXED FREQUENCY OPERATION
Soft-Start
The internal soft-start circuitry ramps the peak boost
inductor current from zero to its peak value of 700mA in
approximately 800μs, allowing start-up into heavy loads.
The soft-start circuitry is reset in the event of a commanded
shutdown or an overtemperature shutdown.
Oscillator
An internal oscillator sets the switching frequency to
1.5MHz. The oscillator allows a maximum duty cycle of
90% (typical) for the boost converter.
Shutdown
The boost converter is shut down by pulling the RUNBST
pin below 0.3V, and activated by pulling the RUNBST pin
above 0.9V. Note that RUNBST can be driven above VIN
or VOUT, as long as it is limited to less than the absolute
maximum rating.
Error Amplifi er
The error amplifi er is a transconductance type. The
non-inverting input is internally connected to the 1.20V
reference and the inverting input is connected to FBBST.
Clamps limit the minimum and maximum error amp out-
put voltage for improved large signal transient response.
Power converter control loop compensation is provided
internally. A voltage divider from VBST to ground programs
the output voltage (via FBBST) from 1.5V to 5.25V, accord-
ing to the formula:
VV
R
R
BST =+
⎛
⎝
⎜⎞
⎠
⎟
120 1 2
1
.•
LTC3100
13
3100fa
Current Sensing
Lossless current sensing converts the peak current signal
of the N-channel MOSFET switch into a voltage which
is summed with the internal slope compensation. The
summed signal is compared to the error amplifi er output to
provide a peak current control command for the PWM.
Current Limit
The current limit comparator shuts off the N-channel
MOSFET switch once its threshold is reached. Peak switch
current is no less than 700mA, independent of input or
output voltage, unless VOUT falls below 1V, in which case
the current limit is cut in half to minimize power dissipa-
tion into a short-circuit.
Slope Compensation
Current mode control requires the use of slope compensa-
tion to prevent subharmonic oscillations in the inductor
current waveform at high duty cycle operation. This is ac-
complished internally on the LTC3100 through the addition
of a compensating ramp to the current sense signal. The
LTC3100 performs current limiting prior to addition of the
slope compensation ramp and therefore achieves a peak
inductor current limit that is independent of duty cycle.
Zero Current Comparator
The zero current comparator monitors the boost inductor
current to the output and shuts off the synchronous rectifi er
once this current reduces to approximately 30mA. This
prevents the inductor current from reversing in polarity,
improving effi ciency at light loads.
Synchronous Rectifi er
To control inrush current and to prevent the inductor
current from running away when VOUT is close to VIN,
the P-channel MOSFET synchronous rectifi er is only fully
enabled when VOUT > (VIN + 0.24V).
Anti-Ringing Control
The anti-ring circuitry connects a resistor across the
boost inductor to prevent high frequency ringing on the
SW pin during discontinuous current mode operation.
The ringing of the resonant circuit formed by L and CSW
(capacitance on SWBST pin) is low energy, but can cause
EMI radiation.
PGOOD Comparator
The PGBST pin is an open-drain output which indicates the
status of the boost converter output voltage. If the boost
output voltage falls 8% below the regulation voltage, the
PGBST open-drain output will pull low. The output voltage
must rise 3% above the falling threshold before the pull-
down will turn off. In addition, there is a 60μs (typical)
deglitching delay in order to prevent false trips due to
voltage transients on load steps. The PGBST output will
also pull low if the boost converter is disabled. The typical
PGBST pull-down switch resistance is 13Ω when VBST or
VINBST equals 3.3V.
Output Disconnect
The LTC3100 boost converter is designed to allow true
output disconnect by eliminating body diode conduction
of the internal P-channel MOSFET rectifi er. This allows for
VOUT to go to 0V during shutdown, drawing no current
from the input source. It also allows for inrush current
limiting at turn-on, minimizing surge currents seen by the
input supply. Note that to obtain the advantages of output
disconnect, there must not be an external Schottky diode
connected between SWBST and VBST
. The output discon-
nect feature also allows VOUT to be pulled high without
any reverse current into the battery.
VIN > VOUT Operation
The LTC3100 boost converter will maintain voltage regu-
lation even when the input voltage is above the desired
output voltage. Note that the output current capability is
slightly reduced in this mode of operation. Refer to the
Typical Performance Characteristics section.
Burst Mode Operation (for Boost and Buck Converters)
Burst Mode operation for both converters can be enabled
or disabled using the MODE pin. If MODE is grounded,
Burst Mode operation is disabled for both the boost and
OPERATION
LTC3100
14
3100fa
buck converters. In this case, both converters will remain in
fi xed frequency operation, even at light load currents. If the
load is very light, they will exhibit pulse-skip operation.
If MODE is raised above 0.9V, or left open, Burst Mode
operation will be enabled for both converters. In this case,
either converter may enter Burst Mode operation at light
load, and return to fi xed frequency operation when the
load current increases. Refer to the Typical Performance
Characteristics section to see the output load Burst Mode
threshold vs VIN and VOUT. The two converters can enter or
leave Burst Mode operation independent of each other.
In Burst Mode operation, each converter still switches at
a frequency of 1.5MHz, using the same error amplifi er
and loop compensation for peak current mode control.
This control method eliminates any output transient
when switching between modes. In Burst Mode opera-
tion, energy is delivered to the output until it reaches the
nominal regulation value, then the LTC3100 transitions to
sleep mode where the outputs are off and the LTC3100
consumes only 15μA of quiescent current from VBST
. Once
the output voltage has drooped slightly, switching resumes
again. This maximizes effi ciency at very light loads by
minimizing switching and quiescent losses. Burst Mode
operation output ripple is typically 1% peak-to-peak.
Burst Mode operation for the boost converter is inhibited
during start-up, and until soft-start is complete and VBST
is at least 0.24V greater than VINBST.
Short-Circuit Protection
The LTC3100 output disconnect feature allows output
short-circuit while maintaining a maximum internally set
current limit. To reduce power dissipation under short-
circuit conditions, the boost peak switch current limit is
reduced to 400mA (typical).
Schottky Diode
Although it is not required, adding a Schottky diode from
SWBST to VBST will improve effi ciency by about 2%. Note
that this defeats the boost output disconnect and short-
circuit protection features.
BUCK CONVERTER OPERATION
The buck converter provides a high effi ciency, lower voltage
output and supports 100% duty cycle operation to extend
battery life. The buck converter uses the same 1.5MHz
oscillator used by the boost converter.
PWM Mode Operation
When the MODE pin is held low, the LTC3100 buck converter
uses a constant-frequency, current mode control architec-
ture. Both the main (P-channel MOSFET) and synchronous
rectifi er (N-channel MOSFET) switches are internal. At
the start of each oscillator cycle, the P-channel switch
is turned on and remains on until the current waveform
with superimposed slope compensation ramp exceeds the
error amplifi er output. At this point, the synchronous
rectifi er is turned on and remains on until the inductor
current falls to zero or a new switching cycle is initiated.
As a result, the buck converter operates with discontinuous
inductor current at light loads which improves effi ciency.
At extremely light loads, the minimum on-time of the main
switch will be reached and the buck converter will begin
turning off for multiple cycles (pulse-skipping) in order
to maintain regulation.
Burst Mode Operation
When the MODE pin is forced high, or left open, the buck
converter will automatically transition between Burst Mode
operation at suffi ciently light loads (below approximately
10mA) and PWM mode at heavier loads. Burst Mode opera-
tion entry is determined by the peak inductor current and
therefore the load current at which Burst Mode operation
will be entered depends on the input voltage, the output
voltage and the inductor value. Typical curves for Burst
Mode operation entry threshold are provided in the Typical
Performance Characteristics section of this data sheet. The
quiescent current on VINBK in Burst Mode operation is only
15μA. If the boost converter is enabled and VINBST or VBST
are at a higher potential than VINBK, some of the quiescent
current will be supplied by the boost converter, reducing
the burst quiescent current on VINBK to just 9μA.
OPERATION
LTC3100
15
3100fa
Dropout Operation
As the input voltage decreases to a value approaching the
output regulation voltage, the duty cycle increases toward
the maximum on-time. Further reduction of the supply
voltage will force the main switch to remain on for more
than one cycle until 100% duty cycle operation is reached
where the main switch remains on continuously. In this
dropout state, the output voltage will be determined by
the input voltage less the resistive voltage drop across the
main switch and series resistance of the inductor.
Slope Compensation
Current mode control requires the use of slope compensa-
tion to prevent subharmonic oscillations in the inductor
current waveform at high duty cycle operation. This is ac-
complished internally on the LTC3100 through the addition
of a compensating ramp to the current sense signal. In
some current mode ICs, current limiting is performed by
clamping the error amplifi er voltage to a fi xed maximum.
This leads to a reduced output current capability at low
step-down ratios. In contrast, the LTC3100 performs cur-
rent limiting prior to addition of the slope compensation
ramp and therefore achieves a peak inductor current limit
that is independent of duty cycle.
Short-Circuit Protection
When the buck output is shorted to ground, the error am-
plifi er will saturate high and the P-channel MOSFET switch
will turn on at the start of each cycle and remain on until
the current limit trips. During this minimum on-time, the
inductor current will increase rapidly and will decrease very
slowly during the remainder of the period due to the very
small reverse voltage produced by a hard output short.
To eliminate the possibility of inductor current runaway
in this situation, the buck converter switching frequency
is reduced to approximately 375kHz when the voltage on
FBBK falls below 0.3V.
Soft-Start
The buck converter has an internal voltage mode soft-start
circuit with a nominal duration of 1.3ms. The converter
remains in regulation during soft-start and will therefore
respond to output load transients which occur during
this time. In addition, the output voltage rise time has
minimal dependency on the size of the output capacitor
or load current.
Error Amplifi er and Compensation
The LTC3100 buck converter utilizes an internal transcon-
ductance error amplifi er. Compensation of the feedback
loop is performed internally to reduce the size of the
application circuit and simplify the design process. The
compensation network has been designed to allow use of
a wide range of output capacitors while simultaneously
ensuring rapid response to load transients.
Undervoltage Lockout
If the VINBK supply voltage decreases below 1.6V (typical),
the buck converter will be disabled. The soft-start for the
buck converter will be reset during undervoltage lockout
to provide a smooth restart once the input voltage rises
above the undervoltage lockout threshold.
PGOOD Comparator
The PGBK pin is an open-drain output which indicates the
status of the buck converter output voltage. If the buck
output voltage falls 8% below the regulation voltage, the
PGBK open-drain output will pull low. The output voltage
must rise 3% above the falling threshold before the pull-
down will turn off. In addition, there is a 60μs typical de-
glitching delay in order to prevent false trips due to voltage
transients on load steps. The PGBK output will also pull
low during overtemperature shutdown and undervoltage
lockout to indicate these fault conditions, or if the buck
converter is disabled. The typical PGBK pull-down switch
resistance is 13Ω when VINBK = 3.3V.
Schottky Diode
Although it is not required, adding a Schottky diode from
SWBK to the ground plane will improve effi ciency by
about 2%.
OPERATION
LTC3100
16
3100fa
LDO REGULATOR OPERATION
The LDO regulator utilizes an internal 1.3Ω (typical)
P-channel MOSFET pass device to supply up to 100mA
of load current with a typical dropout voltage of 130mV.
The input voltage to the LDO is internally connected to
the boost output (VBST pin), and can share the same fi lter
capacitor. The LDO can be operated independently of the
boost (or buck) converter, providing a suffi cient voltage
is present on VBST
.
Soft-Start and Current Limit
The LDO has an independent current limit circuit that limits
output current to 120mA (typical). To minimize loading on
the boost converter output when enabling the LDO, the LDO
current limit is soft-started over a 500μs period. Therefore
the rise time of the LDO output voltage will depend on the
amount of capacitance on the VLDO pin.
Reverse Current Blocking
The LDO is designed to prevent any reverse current from
VLDO back to the VBST pin, both in normal operation and
in shutdown. If VLDO is pulled above VBST and VBST is
above 1V, there will be a small (1μA typical) current from
VLDO to ground.
COMMON FUNCTIONS
Oscillator
The 1.5MHz oscillator is shared by the boost and buck
converters. It will be oscillating if either converter is en-
abled. If both converters are enabled, the boost N-channel
MOSFET switch will be turned on coincident with the buck
P-channel MOSFET switch.
MODE Control
The MODE pin is used to force fi xed frequency opera-
tion (MODE < 0.3V) or to enable Burst Mode operation
(MODE > 0.9V) for both the boost and buck converters.
With Burst Mode operation enabled, the two converters
will automatically enter or leave Burst Mode operation
independently, based on their respective load conditions.
There is an internal 1MΩ pull-up on MODE, in the event
that the pin is left open.
Note: Leaving the pin open, or connecting it to the high-
est of VINBK or VBST, will result in the lowest Burst Mode
quiescent current.
Overtemperature Shutdown
If the die temperature exceeds 150°C (typical) both con-
verters and the LDO regulator will be disabled. All power
devices will be turned off and all switch nodes will be high
impedance. The soft-start circuits for both converters
and the LDO are reset during overtemperature shutdown
to provide a smooth recovery once the overtemperature
condition is eliminated. Both converters and the LDO will
restart (if enabled) when the die temperature drops to
approximately 130°C.
OPERATION
LTC3100
17
3100fa
PC Board Layout Guidelines
The LTC3100 switches large currents at high frequen-
cies. Special care should be given to the PC board layout
to ensure stable, noise-free operation. You will not get
advertised performance with a careless layout. Figure 1
depicts the recommended PC board layout. A large ground
pin copper area will help to lower the chip temperature.
A multilayer board with a separate ground plane is ideal,
but not absolutely necessary.
A few key guidelines follow:
1. All circulating high current paths should be kept as
short as possible. Capacitor ground connections should
via down to the ground plane in the shortest route pos-
sible. The bypass capacitors on all VIN and VOUT pins
APPLICATIONS INFORMATION
Figure 1. Recommended Component Placement for Two-Layer PC Board
should be placed as close to the IC as possible and
should have the shortest possible paths to ground.
2. To prevent large circulating currents from disrupting
the output voltage sensing, the ground for each resis-
tor divider should be returned directly to the ground
plane near the IC.
3. Use of vias in the die attach pad of the IC will enhance
the thermal environment of the converter, especially if
the vias extend to a ground plane region on the exposed
bottom surface of the PC board.
4. Keep the connection from the resistor dividers to the
feedback pins as short as possible and away from the
switch pin connections.
16
LTC3100
3100 F01
15 14 13
56 8
7
12
11
10
9
1
2
3
4
FBBST
VINBST
PGBST
RUNBST
MODE
VINBK
PGBK
GND
RUNBK
SWBST
VBST
VLDO
VBUCK
SWBK
FBLDO
RUNLDO
FBBK
LTC3100
18
3100fa
APPLICATIONS INFORMATION
COMPONENT SELECTION
Boost Output Voltage Programming
The boost output voltage is set by a resistive divider ac-
cording to the following formula:
VV
R
R
OUT =+
⎛
⎝
⎜⎞
⎠
⎟
1 200 1 2
1
.•
The external divider is connected to the output as shown
in the Block Diagram. A feedforward capacitor may be
placed in parallel with resistor R2 to improve the noise
immunity of the feedback node, improve transient response
and reduce output ripple in Burst Mode operation. A value
of 33pF will generally suffi ce.
Boost Inductor Selection
The LTC3100 boost converter can utilize small surface
mount and chip inductors due to the fast 1.5MHz switch-
ing frequency. Inductor values between 2.2μH and 4.7μH
are suitable for most applications. Larger values of induc-
tance will allow slightly greater output current capability
by reducing the inductor ripple current. Increasing the
inductance above 10μH will increase size while providing
little improvement in output current capability.
The minimum boost inductance value is given by:
LVV V
RIPPLE V
IN MIN OUT MAX IN MIN
>−
()
() ( ) ()
•
.• •15 OOUT MAX()
Where:
RIPPLE = Allowable Inductor Current Ripple (Amps Peak-
to-Peak)
VIN(MIN) = Minimum Input Voltage
VOUT(MAX) = Maximum Output Voltage
The inductor current ripple is typically set for 20% to
40% of the maximum inductor current. High frequency
ferrite core inductor materials reduce frequency dependent
power losses compared to cheaper powdered iron types,
improving effi ciency. The inductor should have low DCR
(series resistance of the winding) to reduce the I2R power
losses, and must not saturate at peak inductor current
levels. Molded chokes and some chip inductors usually
do not have enough core area to support the peak induc-
tor currents of 800mA seen on the LTC3100. To minimize
radiated noise, use a shielded inductor. See Table 1 for
suggested components and suppliers.
Table 1. Recommended Boost Inductors
VENDOR PART/STYLE
Coilcraft
(847) 639-6400
www.coilcraft.com
LPS4012, LPS4018
MSS4020, MSS5131
Coiltronics SD14, SD3814, SD3118
FDK MIPSA2520
MIPW3226
Murata
www.murata.com
LQH43C
Sumida
(847) 956-0666
www.sumida.com
CDRH2D18, CDRH2D16
CDRH3D14, CDRH3D16
CDRH4D14, CDRH4D16
Taiyo-Yuden
www.t-yuden.com
NR3015
NP03SB
TDK
www.tdk.com
VLP
VLF, VLCF
Toko
(408) 432-8282
www.tokoam.com
D518LC
D52LC
DP418C
Würth
(201) 785-8800
www.we-online.com
WE-TPC Type S, M
Boost Input and Output Capacitor Selection
The internal loop compensation of the LTC3100 boost con-
verter is designed to be stable with output capacitor values
of 4.7μF or greater. Low ESR (equivalent series resistance)
capacitors should be used to minimize the output voltage
ripple. Multilayer ceramic capacitors are an excellent choice
as they have extremely low ESR and are available in small
footprints. A 4.7μF to 10μF output capacitor is suffi cient
for most fi xed frequency applications. For applications
where Burst Mode operation is enabled, a minimum value
of 20μF is recommended. Larger values may be used to
obtain very low output ripple and to improve transient
response. X5R and X7R dielectric materials are preferred
for their ability to maintain capacitance over wide voltage
and temperature ranges. Y5V types should not be used.
Case sizes smaller than 0805 are not recommended due
to their increased DC bias effect.
LTC3100
19
3100fa
APPLICATIONS INFORMATION
Low ESR input capacitors reduce input switching noise
and reduce the peak current drawn from the battery. It
follows that ceramic capacitors are also a good choice for
input decoupling and should be located as close as pos-
sible to the device. A 2.2μF input capacitor on the VINBST
pin is suffi cient for most applications. Larger values may
be used without limitations. For applications where the
power source is more than a few inches away, a larger
bulk decoupling capacitor is recommended on the input
to the boost converter.
Table 2 shows a list of several ceramic capacitor manu-
facturers. Consult the manufacturers directly for detailed
information on their selection of capacitors.
Note that even X5R and X7R type ceramic capacitors have
a DC bias effect which reduces their capacitance with a DC
voltage applied. This effect is particularly bad for capacitors
in the smallest case sizes. Consult the manufacturer’s data
for the capacitor you select to be assured of having the
necessary capacitance in your application.
Table 2.Capacitor Vendor Information
SUPPLIER PHONE WEB SITE
AVX (803) 448-9411 www.avxcorp.com
Murata (714) 852-2001 www.murata.com
Taiyo-Yuden (408) 573-4150 www.t-yuden.com
TDK (847) 803-6100 www.component.tdk.com
Buck Inductor Selection
The choice of buck inductor value infl uences both the
effi ciency and the magnitude of the output voltage ripple.
Larger inductance values will reduce inductor current ripple
and will therefore lead to lower output voltage ripple. For
a fi xed DC resistance, a larger value inductor will yield
higher effi ciency by lowering the peak current to be closer
to the average. However, a larger value inductor within the
same family will generally have a greater series resistance,
thereby offsetting this effi ciency advantage. Given a desired
peak to peak current ripple, ΔIL, the required inductance
can be calculated via the following expression, where f
represents the switching frequency in MHz:
LfI
V
VH
L
OUT
IN
=Δ−
⎛
⎝
⎜⎞
⎠
⎟
()
11• μ
A reasonable choice for ripple current is ΔIL = 100mA which
represents 40% of the maximum 250mA load current.
The DC current rating of the inductor should be at least
450mA to avoid saturation under overload or short-circuit
conditions. To optimize effi ciency the inductor should have
a low series resistance. In particularly space restricted ap-
plications it may be advantageous to use a much smaller
value inductor at the expense of larger ripple current. In
such cases, the converter will operate in discontinuous
conduction for a wider range of output loads and effi ciency
will be reduced.
In addition, there is a minimum inductor value required
to maintain stability of the current loop (given the fi xed
internal slope compensation). Specifi cally, if the buck
converter is going to be utilized at duty cycles over 40%,
the inductance value must be at least LMIN as given by the
following equation:
L
MIN = 2.5 • VOUT (μH)
Table 3 depicts the minimum required inductance for
several common output voltages.
Table 3.Buck Minimum Inductance
OUTPUT VOLTAGE MINIMUM INDUCTANCE
0.6V 1.5μH
0.8V 2μH
1.2V 3μH
2V 5μH
2.7V 6.8μH
3.3V 8.3μH
Larger values of inductor will also provide slightly greater
output current capability before reaching current limit (by
reducing the peak-to-peak ripple current).
LTC3100
20
3100fa
APPLICATIONS INFORMATION
Table 4. Recommended Buck Inductors
VENDOR PART/STYLE
Coilcraft
(847) 639-6400
www.coilcraft.com
LPS3008, LPS3010, LPS3015
Coiltronics SD3114, SD3118, SD3112
FDK MIPF2016
MIPF2520, MIPS2520
Murata
www.murata.com
LQH32C
LQM31P
Sumida
(847) 956-0666
www.sumida.com
CDRH2D11, CDRH2D09
CMD4D06-4R7MC
CMD4D06-3R3MC
Taiyo-Yuden
www.t-yuden.com
NR3010, NR3012
TDK
www.tdk.com
VLF3010, VLF3012
LEMC3225, LBC2518
Toko
(408) 432-8282
www.tokoam.com
D3010
DB3015
D312, D301F
Würth
(201) 785-8800
www.we-online.com
WE-TPC Type XS, S
Buck Output Capacitor Selection
A low ESR output capacitor should be utilized at the buck
output in order to minimize voltage ripple. Multilayer ce-
ramic capacitors are an excellent choice as they have low
ESR and are available in small footprints. In addition to
controlling the output ripple magnitude, the value of the
output capacitor also sets the loop crossover frequency and
therefore can impact loop stability. There is both a minimum
and maximum capacitance value required to ensure stabil-
ity of the loop. If the output capacitance is too small, the
loop crossover frequency will increase to the point where
switching delay and the high frequency parasitic poles of
the error amplifi er will degrade the phase margin. In ad-
dition, the wider bandwidth produced by a small output
capacitor will make the loop more susceptible to switching
noise. At the other extreme, if the output capacitor is too
large, the crossover frequency can decrease too far below
the compensation zero and also lead to degraded phase
margin. Table 5 provides a guideline for the range of al-
lowable values of low ESR output capacitors. Larger value
output capacitors can be accommodated provided they
have suffi cient ESR to stabilize the loop or by increasing
the value of the feedforward capacitor in parallel with the
upper resistor divider resistor.
Note that even X5R and X7R type ceramic capacitors have
a DC bias effect which reduces their capacitance with a DC
voltage applied. This effect is particularly bad for capacitors
in the smallest case sizes. Consult the manufacturer’s data
for the capacitor you select to be assured of having the
necessary capacitance in your application.
Table 5. Buck Output Capacitor Range
VOUT CMIN CMAX
0.6V 15μF 300μF
0.8V 15μF 230μF
1.2V 10μF 150μF
1.8V 6.8μF 90μF
2.7V 6.8μF 70μF
3.3V 6.8μF 50μF
Buck Input Capacitor Selection
The VINBK pin provides current to the buck converter
power switch and is also the supply pin for the buck’s
internal control circuitry. It is recommended that a low
ESR ceramic capacitor with a value of at least 4.7μF be
used to bypass this pin. The capacitor should be placed
as close to the pin as possible and have a short return to
ground. For applications where the power source is more
than a few inches away, a larger bulk decoupling capacitor
is recommended.
Buck Output Voltage Programming
The output voltage is set by a resistive divider according
to the following formula:
VV
R
R
OUT =+
⎛
⎝
⎜⎞
⎠
⎟
0 600 1 6
5
.•
The external divider is connected to the output as shown
in the Block Diagram. It is recommended that a feedfor-
ward capacitor be placed in parallel with resistor R6 to
improve the noise immunity of the feedback node and
reduce output ripple in Burst Mode operation. A value of
10pF will generally suffi ce.
LTC3100
21
3100fa
APPLICATIONS INFORMATION
LDO Output Capacitor Selection
The LDO is designed to be stable with a minimum 1μF
output capacitor. No series resistor is required when using
low ESR capacitors. For most applications, a 2.2μF ceramic
capacitor is recommended. Larger values will improve
transient response, and raise the power supply rejection
ratio (PSRR) of the LDO. Refer to the Typical Performance
Characteristics for the allowable range of output capacitor
to ensure loop stability.
LDO Output Voltage Programming
The output voltage is set by a resistive divider according
to the following formula:
VV
R
R
OUT =+
⎛
⎝
⎜⎞
⎠
⎟
0 600 1 4
3
.•
The external divider is connected to the output as shown
in the Block Diagram. For improved transient response,
a feedforward capacitor may be placed in parallel with
resistor R4.
TYPICAL APPLICATIONS
Single-Cell Boost and Buck with Voltage Sequencing Output Voltages During Soft-Start
for Sequenced Converter
SWBST VINBK VBST
LTC3100
FBBST
L1
3.3μH 3.5V
R2
1M
R1
523k
C1
10μF
s2
CIN
2.2μF
VLDO
VINBST
FBLDO
SWBK
PGBK
PGBST
R4
115k
R3
25.5k
VBATT
0.9V TO 1.5V
C2
2.2μF
FBBK
12
3
11
4
16
15
9
R6
1M
R5
1M
C3
10μF
MODE
RUNBST
RUNLDO
RUNBK GND
16
13
14
10
8
152
7
FF EN_BURST
OFF ON
L2
3.3μH
+3.3V AT 50mA
V_I/O
120mA AT VBATT = 0.9V
220mA AT VBATT = 1.2V
V_CORE = 1.2V
BOOST_GOOD
BUCK_GOOD
R7
1M
R8
1M
+
3100 TA02b
1ms/DIV
VCORE, 1V/DIV
VBST, 1V/DIV
VI/O, 1V/DIV
LTC3100
22
3100fa
SWBST VINBK VBST
LTC3100
FBBST
BOOST
L1
3.3μH
R2
2M
R1
634k
C1
10μF
s2
C2
2.2μF
CIN
4.7μF
VLDO
VINBST
FBLDO
SWBK
PGBK
PGBST
VIN 2.5V TO 5V
Li-Ion
FBBK
12
3
11
4
16
15
9
R6
976k
R5
487k
C3
10μF
3100 TA03a
MODE
RUNBST
RUNLDO
RUNBK GND
16
13
14
10
8
152
7
OFF ON
LDO
BUCK OFF ON
OFF ON
L2
4.7μH
+5V AT 200mA
VBOOST
R4
115k
R3
25.5k
+3.3V AT
50mA
V_I/O
+1.8V AT
250mA
V_CORE
BOOST_GOOD
BUCK_GOOD
R7
100k
R8
100k
CFF2
10pF
SWBST VINBK VBST
LTC3100
FBBST
R1
1.07M
R2
324k
R3
301k
C2
10μF
R4
20k
C1
4.7μF
C4
4.7μF
VLDO
VINBST
FBLDO
SWBK
PGBK
PGBST
VBATT
0.9V TO
3.3V
USB
INPUT
FBBK
12
3
11
4
16
15
9
R5
200k
R6
100k
C3
10μF
3100 TA04a
MODE
RUNBST
RUNLDO
RUNBK GND
16
13
14
10
8
152
7
L2
10μH
1.8V AT 50mA
VLDO
VOUT
R7
64.9k
L1
3.3μH
MBR0520
C4
2.2μF
3.3V AT: 100mA FOR VBATT = 1.2V
300mA FOR VBATT = 2.4V
250mA FOR USB INPUT
TYPICAL APPLICATIONS
Li-Ion Input, Triple Output Converter Effi ciency vs Load Current
Single-Cell/Two-Cell or USB Input to 3.3V/1.8V Converter Effi ciency vs Load Current
LOAD CURRENT (mA)
30
EFFICIENCY (%)
POWER LOSS (mW)
50
80
0.01 10 100 1000
0
10
0.1 1
100
70
90
40
60
20
100
0.01
1000
1
10
0.1
3100 TA03b
1.8V BUCK
5V BOOST
BUCK POWER LOSS
BOOST POWER LOSS
VIN = 3.6V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
50
80
0.01 10 100 1000
0
10
0.1 1
100
70
90
40
60
20
3100 TA04b
VIN = 1.2V
3.3V OUTPUT
VIN = 2.4V
VIN = 5V USB
LTC3100
23
3100fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PACKAGE DESCRIPTION
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691)
3.00 p 0.10
(4 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1.45 p 0.05
(4 SIDES)
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
PIN 1
TOP MARK
(NOTE 6)
0.40 p 0.10
BOTTOM VIEW—EXPOSED PAD
1.45 p 0.10
(4-SIDES)
0.75 p 0.05 R = 0.115
TYP
0.25 p 0.05
1
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 s 45o CHAMFER
15 16
2
0.50 BSC
0.200 REF
2.10 p 0.05
3.50 p 0.05
0.70 p0.05
0.00 – 0.05
(UD16) QFN 0904
0.25 p0.05
0.50 BSC
PACKAGE OUTLINE
LTC3100
24
3100fa
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
LT 1108 REV A • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
LTC3442 1.2A (IOUT), 2MHz Synchronous Buck-Boost
DC/DC Converter
VIN: 2.4V to 5.5V, VOUT(RANGE): 2.4V to 5.25V, IQ = 35μA, ISD < 1μA,
DFN Package
LTC3455 Dual DC/DC Converter with USB Power Manager and Li-Ion
Battery Charger
96% Effi ciency, Seamless Transition Between Inputs, IQ = 110μA,
ISD < 2μA, QFN Package
LTC3456 2-Cell Multi-Output DC/DC Converter with USB Power
Manager
92% Effi ciency, Seamless Transition Between Inputs, IQ = 180μA,
ISD < 1μA, QFN Package
LTC3520 Synchronous 1A Buck-Boost and 600mA Step-Down
DC/DC Converter
VIN: 2.2V to 5.5V, VOUT(MIN) = 0.6V, IQ = 55μA, ISD < 1μA,
4mm × 4mm QFN Package
LTC3522 Synchronous 400mA Buck-Boost and 200mA Step-Down
DC/DC Converter
VIN: 2.4V to 5.5V, VOUT(MIN) = 0.6V, IQ = 25μA, ISD < 1μA,
3mm × 3mm QFN-16 Package
LTC3527/LTC3527-1 Dual (400mA/800mA) Synchronous Boost Converter VIN: 0.5V to 5V, VOUT: 1.5V to 5.25V, IQ = 12μA, ISD < 2μA,
3mm × 3mm QFN Package
LTC3530 600mA (IOUT), 2MHz Synchronous Buck-Boost
DC/DC Converter
VIN: 1.8V to 5.5V, VOUT(RANGE): 1.8V to 5.5V, IQ = 40μA, ISD < 1μA,
DFN and MSOP Packages
LTC3532 500mA (IOUT), 2MHz Synchronous Buck-Boost
DC/DC Converter
VIN: 2.4V to 5.5V, VOUT(RANGE): 2.4V to 5.25V, IQ = 35μA, ISD < 1μA,
DFN and MSOP Packages
LTC3537 600mA (ISW), 2.2MHz Synchronous Boost Converter with
100mA LDO
VIN: 0.68V to 5V, VOUT(MAX) = 5.5V, IQ = 30μA, ISD < 1μA,
3mm × 3mm QFN Package
LTC3538 600mA (IOUT), 2MHz Synchronous Buck-Boost
DC/DC Converter
VIN: 2.4V to 5.5V, VOUT(RANGE): 1.5V to 5.5V, IQ = 35μA, ISD < 1μA,
DFN Package
LTC3544/LTC3544B 300mA, 200mA ×2, 100mA, 2.25MHz Quad Output
Synchronous Step-Down DC/DC Converter
VIN: 2.25V to 5.5V, VOUT(MIN) = 0.8V, IQ = 70μA, ISD < 1μA,
QFN Package
LTC3545 Triple Output, 3mA × 800mA, 2.25MHz Synchronous
Step-Down DC/DC Converter
VIN: 2.25V to 5.5V, VOUT(MIN) = 0.6V, IQ = 58μA, ISD < 1μA,
QFN Package
Single-Cell to 1.2V/1.8V Converter Effi ciency vs Load Current
(VBUCK)
SWBST VINBK VBST
LTC3100
FBBST
R2
1M
R1
1M
C1
10μF
s2
C2
2.2μF
VLDO
VINBST
FBLDO
SWBK
PGBK
PGBST
FBBK
12
3
11
4
6
15
9
R6
1M
R5
1M
C3
10μF
3100 TA05a
MODE
RUNBST
RUNLDO
RUNBK GND
16
13
14
10
8
152
7
OFF ON
L2
3.3μH
R4
200k
R3
100k
VLDO
1.8V AT
50mA
2.4V
VBUCK
BUCK_GOOD
R7
100k
CIN
2.2μF
VBATT
0.9V TO 1.6V
L1
3.3μH
+
1.2V AT: 120mA FOR VBATT = 0.9V
250mA FOR VBATT = 1.2V
LOAD CURRENT ON VBUCK (mA)
30
EFFICIENCY (%)
50
80
0.01 10 100 1000
0
10
0.1 1
100
70
90
40
60
20
3100 TA05b
VIN = 0.9V
VIN = 1.2V
VIN = 1.5V
