LTC3100EUD-PBF [Linear]
1.5MHz Synchronous Dual Channel DC/DC Converter and 100mA LDO; 1.5MHz的同步双通道DC / DC转换器和LDO百毫安
| 型号： | LTC3100EUD-PBF |
| 厂家： | 
Linear |
| 描述： | 1.5MHz Synchronous Dual Channel DC/DC Converter and 100mA LDO |
| 文件： | 总24页 (文件大小：411K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3100
1.5MHz Synchronous Dual
Channel DC/DC Converter
and 100mA LDO
FEATURES
DESCRIPTION
The LTC®3100 combines a high efficiency 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.Thestep-downconvertercanbepoweredbytheoutput
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.
n
Extremely Compact Triple-Rail Solution
Burst Mode® Operation, I = 15μA
n
Q
n
1.5MHz Fixed Frequency Operation
n
Power Good Indicators
n
700mA Synchronous Step-Up DC/DC
0.65V to 5V V Range
IN
1.5V to 5.25V V
Range
OUT
94% Peak Efficiency
V > V
Operation
IN
OUT
Aswitchingfrequencyof1.5MHzminimizessolutionfoot-
print by allowing the use of tiny, low profile 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 efficiency
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.
Output Disconnect
n
n
n
250mA Synchronous Step-Down DC/DC
1.8V to 5.5V V Range
IN
OUT
0.6V to 5.5V V
Range
LDO (V Internally Tied to V
)
BST
IN
0.6V to 5.25V V
Range
OUT
200mV Dropout Voltage at 100mA
Available in a 16-Lead 3mm × 3mm QFN Package
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.
APPLICATIONS
n
Bar Code Readers
Medical Instruments
n
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.
TYPICAL APPLICATION
Efficiency and Power Loss
vs Load Current, VIN = 2.4V
Two-Cell, Triple Output Converter
3.3μH
3.3V AT 100mA
BOOST
V
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
10μF
1.87M
1.07M
V
BATT
SWBST
V
V
BST
1M
INBK
s2
1.6V TO 3.2V
V
FBBST
INBST
2.2μF
BOOST_GOOD
3V AT 50mA
LTC3100
PGBST
V
V
LDO
LDO
102k
2.2μF
10μF
1
FBLDO
25.5k
BOOST
FF EN_BURST
MODE
0.1
0.01
BUCK
4.7μH
1.8V AT 200mA
V
PL, BOOST
PL, BUCK
SWBK
FBBK
BUCK
OFF ON
BOOST
RUNBST
RUNLDO
RUNBK
2M
1M
0.01
0.1
1
10
100
1000
OFF ON
LDO
1M
LOAD CURRENT (mA)
3100 TA01b
OFF ON
BUCK
GND
PGBK
3100 TA01a
BUCK_GOOD
3100fa
1
LTC3100
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
V
and V
Voltage .............................. –0.3 to 6V
INBST
INBK
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
16 15 14 13
SWBST
1
2
3
4
12 FBBST
11 FBLDO
V
BST
17
V
RUNLDO
FBBK
10
9
LDO
V
, V ...................................................... –0.3 to 6V
BST LDO
SWBK
Operating Temperature (Notes 2, 5).........–40°C to 85°C
Storage Temperature Range...................–65°C to 125°C
5
6
7
8
UD PACKAGE
16-LEAD (3mm s 3mm) PLASTIC QFN
T
= 125°C, θ = 68°C/W, 4-LAYER BOARD
JA
JMAX
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB (NOTE 6)
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3100EUD#PBF
LTC3100EUD#TRPBF
LDJR
–40°C to 85°C
16-Lead (3mm × 3mm) Plastic QFN
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
ELECTRICAL CHARACTERISTICS: STEP-UP CONVERTER The l denotes the specifications
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.
PARAMETER
CONDITIONS
= 1mA
MIN
TYP
MAX
0.90
5
UNITS
V
l
l
l
l
Minimum Start-Up Voltage
Input Voltage Range
Output Voltage Adjust Range
Feedback Voltage
I
0.65
LOAD
After Start-Up (Minimum Voltage Is Load Dependent)
0.5
1.5
V
5.25
1.218
50
V
1.182
1.200
1
V
Feedback Input Current
FBBST = 1.2V
nA
μA
μA
Quiescent Current (V ): Shutdown
RUNBST = 0V, Not Including Switch Leakage, V
= 0V, V = 0V
INBK
0.01
300
1
IN
BST
Quiescent Current: Active
Measured on V
(Note 4), RUNBK = 0V, RUNLDO = 0V
500
BST
Quiescent Current: Burst Mode
Operation
Measured on V , FBBST > 1.25V
BST
MODE = 1V, RUNLDO = 0V
MODE = 1V, RUNLDO = 1V
15
28
25
45
μA
μA
N-Channel MOSFET Switch Leakage SWBST = 5V, V = 5V
0.1
5
μA
BST
Current
P-Channel MOSFET Switch Leakage SWBST = 0V, V
Current
= 5V
0.1
10
μA
BST
3100fa
2
LTC3100
ELECTRICAL CHARACTERISTICS: STEP-UP CONVERTER The l denotes the specifications
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.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
N-Channel MOSFET Switch-On
Resistance
V
BST
= 3.3V
0.3
Ω
P-Channel MOSFET Switch-On
Resistance
V
BST
= 3.3V
0.4
Ω
l
l
l
l
l
l
N-Channel MOSFET Current Limit
Maximum Duty Cycle
Minimum Duty Cycle
700
87
850
90
mA
%
V
V
= 1.15V
= 1.3V
FBBST
0
%
FBBST
Switching Frequency
1.2
0.9
1.5
1.8
MHz
V
RUNBST Input High Voltage
RUNBST Input Low Voltage
RUNBST Input Current
Soft-Start Time
0.3
2
V
RUNBST = 1.2V
0.8
0.8
–8
μA
ms
%
PGBST Threshold, Falling
PGBST Hysteresis
Referenced to Feedback Voltage
Referenced to Feedback Voltage
5mA Load
3
%
PGBST Voltage Low
65
mV
μA
PGBST Leakage Current
PGBST = 5.5V
0.01
10
ELECTRICAL CHARACTERISTICS: STEP-DOWN CONVERTER The l denotes the
specifications 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.
PARAMETER
CONDITIONS
MIN
1.8
TYP
MAX
5.5
5.5
610
30
UNITS
V
l
l
l
Input Voltage Range
Output Voltage Adjust Range
Feedback Voltage
0.61
590
V
600
1
mV
nA
Feedback Input Current
Quiescent Current: Shutdown
FBBK = 600mV
Measured on V
Not Including Switch Leakage
, RUNBK = 0V, V
= 0V, V = 0V
BST
0.01
1
μA
INBK
INBST
Quiescent Current: Active
Measured on V (Note 4), RUNBST = 0V
240
16
350
30
μA
μA
INBK
Quiescent Current: Burst Mode Operation
Measured on V , FBBK = 620mV, MODE = OPEN,
INBK
RUNBST = 0V
N-Channel MOSFET Switch Leakage Current
V
= SWBK = 5V
0.1
0.1
5
5
μA
μA
Ω
INBK
P-Channel MOSFET Switch Leakage Current SWBK = 0V, V
= 5V
INBK
N-Channel MOSFET Switch-On Resistance
P-Channel MOSFET Switch-On Resistance
P-Channel MOSFET Current Limit
Maximum Duty Cycle
V
INBK
V
INBK
= 3.3V
= 3.3V
0.45
0.55
450
Ω
l
l
l
l
340
100
mA
%
FBBK < 590mV
FBBK > 610mV
Minimum Duty Cycle
0
%
Switching Frequency
1.2
1.5
1.8
MHz
3100fa
3
LTC3100
ELECTRICAL CHARACTERISTICS: STEP-DOWN CONVERTER The l denotes the
specifications 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.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
l
l
RUNBK Input High Voltage
RUNBK Input Low Voltage
RUNBK Input Current
Soft-Start Time
0.9
0.3
2
V
RUNBK = 1.2V
0.8
1.3
–8
μA
ms
%
PGBK Threshold, Falling
PGBK Hysteresis
Referenced to Feedback Voltage
Referenced to Feedback Voltage
5mA Load
3
%
PGBK Voltage Low
PGBK Leakage Current
65
mV
μA
PGBK = 5.5V
0.01
10
ELECTRICAL CHARACTERISTICS: LDO REGULATOR The l denotes the specifications 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.
PARAMETER
CONDITIONS
MIN
1.8
TYP
MAX
5.25
5.25
618
UNITS
V
l
l
l
l
Input Voltage Range
Output Voltage Adjust Range
Feedback Voltage
(Note 3)
0.618
582
V
600
120
1
mV
mA
nA
%/V
%
Maximum Output Current
Feedback Input Current
Line Regulation
100
FBLDO = 600mV
30
V
= 3.3V to 5.25V
0.1
0.1
130
35
IN
Load Regulation
From 10mA to 100mA Load
= 100mA
l
l
Dropout Voltage
I
200
160
mV
dB
mA
ms
V
OUT
Ripple Rejection (PSRR)
Short-Circuit Current Limit
Soft-Start Time
Frequency = 1.5MHz at I
= 50mA, C
= 2.2μF (Note 3)
LOAD
OUT
FBLDO < 582mV
120
0.3
l
l
RUNLDO Input High Voltage
RUNLDO Input Low Voltage
RUNLDO Input Current
Quiescent Current—Active
0.9
0.3
2
V
RUNLDO = 1.2V
0.8
26
μA
μA
RUNLDO = 3.3V, Measured on V
RUNBST = RUNBK = 0V, V
40
BST
= 0V
INBK
ELECTRICAL CHARACTERISTICS: COMMON CIRCUITRY The l denotes the specifications
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.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
l
MODE Input High Voltage
MODE Input Low Voltage
MODE Input Current
0.9
V
V
0.3
MODE = 0V
MODE = 5V
–3.3
1.7
–5
3
μA
μA
3100fa
4
LTC3100
ELECTRICAL CHARACTERISTICS
Note 4: Current measurements are made when the output is not switching.
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 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 thermal resistance much higher than
68°C/W.
Note 2: The LTC3100E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Specification is guaranteed by design and not 100% tested in
production.
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise specified.
Step-Up DC/DC Converter
Efficiency vs Load Current
and VIN for VO = 1.8V
Efficiency vs Load Current
and VIN for VO = 3.3V
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
1
1
V
V
V
= 1.2V
= 2.4V
= 3V
IN
IN
IN
V
IN
= 1.2V
= 1.5V
IN
0.1
0.01
0.1
0.01
V
PL, V = 1.2V
IN
PL, V = 1.2V
IN
PL, V = 2.4V
IN
PL, V = 1.5V
IN
PL, V = 3V
IN
0.01
0.1
1
10
100
1000
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
3100 G01
3100 G02
Efficiency vs Load Current
and VIN for VO = 5V
3.3V, 100mA Efficiency vs VIN
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
100
90
80
70
60
50
40
30
20
10
0
1
V
V
V
= 1.8V
= 2.4V
= 3.6V
IN
IN
IN
0.1
0.01
PL, V = 1.8V
IN
PL, V = 2.4V
IN
V
BST
= 3.3V AT 100mA
PL, V = 3.6V
IN
3.6
3.8
4
4.2
0.01
0.1
1
10
100
1000
2.2 2.4 2.6 2.8
3
3.4
1.8
2
3.2
(V)
LOAD CURRENT (mA)
V
INBST
3100 G03
3100 G04
3100fa
5
LTC3100
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise specified.
Step-Up DC/DC Converter
No-Load Input Current vs VIN,
Mode = Open, LDO and Buck Off
Maximum Load Current During
Start-Up vs VIN
Maximum Output Current vs VIN
600
500
400
300
200
100
0
180
160
140
120
100
80
1000
100
V
= 3.3V
OUT
V
= 1.8V
OUT
V
= 5V
OUT
10
1
60
V
= 5V
OUT
40
20
V
= 3.3V
V
= 1.8V
OUT
OUT
0
0.7
0.8
V
0.9
1
1.1
1.2
1.3
0
1
1.5
2
2.5
(V)
3
3.5
4
4.5
0.5
1.0 1.5 2.0 2.5
V
4.5
3.0 3.5 4.0
(V)
V
V
(V)
INBST
INBST
INBST
3100 G07
3100 G06
= 1.8V, RESISTIVE LOAD
= 1.8V, CONSTANT-CURRENT LOAD
= 3.3V, RESISTIVE LOAD
= 3.3V, CONSTANT-CURRENT LOAD
= 5V, RESISTIVE LOAD
= 5V, CONSTANT-CURRENT LOAD
3100 G05
BST
V
BST
V
BST
V
BST
V
BST
V
BST
Burst Mode Threshold
Current vs VIN
Start-Up Voltage vs Temperature
60
50
40
30
0.85
L = 3.3μH
0.80
0.75
0.70
0.65
0.60
0.55
0.50
V
= 3.3V
OUT
V
= 1.8V
OUT
V
= 5V
OUT
20
10
0
3.0
(V)
4.0
4.5
1.0 1.5
2.0 2.5
3.5
–45
–15
0
15 30 45 60 75 90
–30
TEMPERATURE (°C)
V
INBST
3100 G09
3100 G08
Output Voltage Ripple in Fixed
Frequency and Burst Mode Operation
VOUT and IIN During Soft-Start
V
C
= 20μF
BST OUT
0.5μs/DIV
100mA LOAD
20mV/DIV
I
IN
200mA/DIV
20μs/DIV
5mA LOAD
20mV/DIV
V
BST
1V/DIV
3100 G10
3100 G11
500μs/DIV
3100fa
6
LTC3100
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise specified.
Step-Up DC/DC Converter
Load Step Response, 50mA-150mA
Fixed Frequency Mode
Load Step Response, 5mA-100mA
Burst Mode Operation Enabled
V
C
= 10μF
V
C
= 20μF
BST OUT
BST OUT
I
I
OUT
OUT
100mA/DIV
100mA/DIV
V
V
BST
BST
50mV/DIV
50mV/DIV
3100 G12
3100 G13
100μs/DIV
100μs/DIV
LDO Regulator
Dropout Voltage vs VOUT
and Temperature (IOUT = 100mA)
Ripple Rejection
Soft-Start Time
0.250
0.225
0.200
0.175
0.150
0.125
0.100
0.075
0.050
40
35
30
25
20
15
10
5
LDO C
= 2.2μF
OUT
VLDO = 1.5V
RUNLDO
2V/DIV
VLDO = 2.5V
VLDO
1V/DIV
VLDO = 5V
3100 G16
V
= 3V
= 50mA
= 2.2μF
OUT
OUT
VLDO = 3.3V
100μs/DIV
I
C
OUT
0
0.1
–15
0
15 30 45
90
–45 –30
60 75
1
10
100
1000
10000
TEMPERATURE (°C)
FREQUENCY (Hz)
6105 G14
3100 G15
Burst Mode Operation
Ripple Rejection
Load Step Response, 10mA-60mA
LDO C
= 2.2μF
LDO C
= 2.2μF
OUT
OUT
BOOST RIPPLE
20mV/DIV
50mA/DIV
VLDO
100mV/DIV
LDO RIPPLE
20mV/DIV
3100 G18
3100 G17
200μs/DIV
5μs/DIV
3100fa
7
LTC3100
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise specified.
Step-Down DC/DC Converter
Efficiency vs Load Current and VIN
for VO = 1.2V
Efficiency vs Load Current and VIN
for VO = 1.8V
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
1
1
V
V
V
= 2.4V
= 3.3V
= 5V
V
V
V
= 1.8V
= 2.4V
= 3.3V
IN
IN
IN
IN
IN
IN
0.1
0.01
0.1
0.01
PL, V = 2.4V
IN
PL, V = 1.8V
IN
PL, V = 3.3V
IN
PL, V = 5V
IN
PL, V = 2.4V
IN
PL, V = 3.3V
IN
0.01
0.1
1
10
100
1000
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
3100 G20
3100 G19
No-Load Input Current
vs VINBK (Mode = Open)
Burst Mode Operation Threshold
Current vs VIN
VOUT and IIN During Soft-Start
20
15
10
5
80
STARTUP, 200mA LOAD
V
V
C
= 2.4V
IN
70
60
50
40
30
20
10
0
= 1.2V
= 10μF
V
OUT
= 1.2V
OUT
OUT
INPUT
CURRENT
50mA/DIV
V
OUT
= 1.5V
V
OUT
0.5V/DIV
V
OUT
3100 G23
= 1.8V
V
= 2.5V
4
2ms/DIV
OUT
0
2.5
3
3.5
(V)
4
4.5
5
1.5
2
2.5
3
3.5
4.5
5
2
V
V
INBK
(V)
INBK
3100 G21
3100 G22
Load Step Response,
Fixed Frequency Mode
10mA to 100mA
Load Step Response,
Burst Mode Operation Enabled
10mA to 100mA
Output Voltage Ripple in Fixed
Frequency and Burst Mode Operation
C
OUT
= 10μF
C
OUT
= 10μF
C
OUT
= 10μF
100mA/DIV
50mV/DIV
50mA/DIV
50mV/DIV
50mV/DIV
50mV/DIV
3100 G24
3100 G25
3100 G26
5μs/DIV
200μs/DIV
200μs/DIV
3100fa
8
LTC3100
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise specified.
RUN Pin Threshold Voltage
Start-Up Delay Times vs VIN
450
400
350
300
250
200
150
100
50
0.625
0.600
0.575
0.550
0.525
0.500
BUCK
RISING
BOOST
FALLING
LDO
0
1.5
2
2.5
V
3
3.5
5
0.5
1
4
4.5
1.5
2
2.5
3
3.5
5
1
4
4.5
(V)
V
IN
(V)
IN
3100 G28
3100 G27
PIN FUNCTIONS
SWBST (Pin 1): Switch Pin for the Boost Converter.
Connect the boost inductor between SWBST and V
nect a pull-up resistor from this pin to a positive supply
less than 6V.
.
INBST
Keep PCB trace lengths as short and wide as possible to
reduce EMI. If the inductor current falls to zero, an internal
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.
anti-ringing switch is connected from SWBST to V
to minimize EMI.
INBST
RUNBK (Pin 8): Logic-Controlled Shutdown Input for the
Buck Converter. There is an internal 4MΩ pull-down on
this pin.
V
BST
(Pin 2): Output Voltage for the Boost Converter
(which is the drain of the internal synchronous rectifier)
and Input Voltage for the LDO. PCB trace length from V
BST
RUNBK = High: Normal operation
RUNBK = Low: Shutdown
to the output filter capacitor (10μF minimum) should be
as short and wide as possible.
FBBK (Pin 9): Feedback Input to the g Error Amplifier
V
(Pin3):OutputVoltageoftheLDORegulator.Connect
m
LDO
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:
a 1μF ceramic capacitor between V
values of capacitance may be used for higher PSRR or
improved transient response.
and GND. Larger
LDO
R6
R5
⎛
⎞
SWBK (Pin 4): Switch Pin for the Buck Converter. Connect
the buck inductor between SWBK and the buck output
filter capacitor. Keep PCB trace lengths as short and wide
as possible to reduce EMI.
VOUT_BUCK = 0.600V • 1+
⎜
⎝
⎟
⎠
RUNLDO (Pin 10): Logic-Controlled Shutdown Input for
the LDO Regulator. There is an internal 4MΩ pull-down
on this pin.
V
(Pin 5): Input Voltage for the Buck Converter. Con-
INBK
nect a minimum of 4.7μF ceramic decoupling capacitor
from this pin to ground.
RUNLDO = High: Normal operation
RUNLDO = Low: Shutdown
PGBK (Pin 6): Open-Drain Output That Pulls Low When
FBBK Is More Than 8% Below Its Regulated Voltage. Con-
3100fa
9
LTC3100
PIN FUNCTIONS
FBLDO (Pin 11): Feedback Input to the g Error Amplifier
RUNBST (Pin 14): Logic-Controlled Shutdown Input for
the Boost Converter. There is an internal 4MΩ pull-down
on this pin.
m
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:
RUNBST = High: Normal operation
RUNBST = Low: Shutdown
R4
R3
⎛
⎞
VOUT_LDO = 0.600V • 1+
⎜
⎝
⎟
⎠
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.
FBBST (Pin 12): Feedback Input to the g Error Amplifier
m
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:
V
(Pin 16): Input Voltage for the Boost Converter.
INBST
R2
R1
⎛
⎞
Connect a minimum of 1μF ceramic decoupling capacitor
VOUT_BOOST = 1.20V • 1+
⎜
⎝
⎟
⎠
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.
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 V
, V
or
INBST BST
V
.
INBK
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 fixed frequency mode regardless
of load current.
3100fa
10
LTC3100
BLOCK DIAGRAM
L1, 3.3μH
V
BATT1
, 0.65V TO 5V
V
, 1.5V TO 5.25V
R2
BOOST
C
IN
2.2μF
16
1
2
V
SWBST
V
BST
C
OUT
10μF
INBST
FBBST
PGBST
V
BST
12
15
R1
V
WELL
SWITCH
SEL
V
BEST
V
INBK
V
VB
–
+
GATE
DRIVERS
AND
ANTI-CROSS
CONDUCTION
BEST
1.1V
V
OF 3
+
–
BEST
I
ZERO
COMPARATOR
WELL
SWITCH
V
REF
VREF_GD
V
REF
3
V
LDO
V
VREF_GD
LDO
SLOPE
COMPARATOR
0.15Ω
0.6V TO 5V
I
PK
3
COMPARATOR
–
+
START_OSC
IPK
R4
START-UP
ERROR
AMPLIFIER/
SLEEP
100mA
ERROR
AMPLIFIER
C
OUT
1μF
I
ZERO
FBLDO
I
LIM
11
COMPARATOR
–
+
–
+
LOGIC
CLK
TSD
–
+
FB
1.5MHz
OSC
0.6V
RUNLDO
10
R3
MODE
CONTROL
1.2V
GATE
THERMAL
SHUTDOWN
TSD
SET
CONTROL
I
BURST
OFF ON
CLAMP
4M
RUNBST
14
OFF ON
FROM V , V
SHUTDOWN
BST BATT1
BATT2
V
INBK
OR V
I
PK
COMPARATOR
–
+
5
4
SOFT-START
4M
I
REF
SENSE
LIM
WAKE
C
IN
4.7μF
I
V
BST
1M
UVLO
MODE
13
LEVEL
SHIFT
L1
3.3μH
GATE
DRIVERS
AND
V
BUCK
SWBK
0.6V TO 5V
ANTI-CROSS
CONDUCTION
CLK
TSD
SHUTDOWN
LOGIC
RUNLDO
SHUTDOWN
R6
RUNBK
I
ZERO
COMPARATOR
C
OUT
8
6
SHUTDOWN
4.7μF
LOGIC
–
+
OFF ON
4M
R5
ERROR
SLOPE
3
AMPLIFIER
PGBK
I
FBBK
SENSE
COMPARATOR
–
+
9
–
+
–
+
PWM
0.6V
0.55V
PAD
GND
7
3100 BD
PGND
3100fa
11
LTC3100
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 filter-
ing. Both converters have internal soft-start and internal
loop compensation, simplifying the design process and
minimizing the number of external components.
requirement for a large input capacitor. The limiting fac-
tor for the application becomes the ability of the power
source to supply sufficient 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
With its low R
and low gate charge internal MOSFET
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.
Thesoft-startcircuitryisresetintheeventofacommanded
shutdown or an overtemperature shutdown.
DS(ON)
switchesandsynchronousrectifiers,theLTC3100achieves
high efficiency over a wide range of load current. Burst
Modeoperationmaintainshighefficiencyatverylightloads,
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, theLTC3100isveryflexible. Thetwoconverters
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).
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 V
IN
Operation can be best understood by referring to the
Block Diagram.
or V , as long as it is limited to less than the absolute
OUT
maximum rating.
BOOST CONVERTER
Low Voltage Start-Up
Error Amplifier
The error amplifier 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
The LTC3100 boost converter includes an independent
start-up oscillator designed to start up at an input voltage
of0.65V(typical).Soft-startandinrushcurrentlimitingare
provided during start-up, as well as in normal mode.
internally.AvoltagedividerfromV togroundprograms
When either V
or V
exceeds 1.4V (typical), the
BST
INBST
BST
theoutputvoltage(viaFBBST)from1.5Vto5.25V, accord-
IC enters normal operating mode. Once the output volt-
age exceeds the input by 0.24V, the IC powers itself from
ing to the formula:
V
instead of V
. At this point, the internal circuitry
R2
R1
⎛
⎞
BST
INBST
VBST = 1.20V • 1+
⎜
⎝
⎟
⎠
has no dependency on the input voltage, eliminating the
3100fa
12
LTC3100
OPERATION
Current Sensing
SW pin during discontinuous current mode operation.
The ringing of the resonant circuit formed by L and C
SW
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
summedsignaliscomparedtotheerroramplifieroutputto
provide a peak current control command for the PWM.
(capacitance on SWBST pin) is low energy, but can cause
EMI radiation.
PGOOD Comparator
ThePGBSTpinisanopen-drainoutputwhichindicatesthe
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
Current Limit
The current limit comparator shuts off the N-channel
MOSFETswitchonceitsthresholdisreached. Peakswitch
current is no less than 700mA, independent of input or
output voltage, unless V
falls below 1V, in which case
OUT
the current limit is cut in half to minimize power dissipa-
tion into a short-circuit.
PGBST pull-down switch resistance is 13Ω when V or
BST
Slope Compensation
V
equals 3.3V.
INBST
Currentmodecontrolrequirestheuseofslopecompensa-
tion to prevent subharmonic oscillations in the inductor
current waveform at high duty cycle operation. This is ac-
complishedinternallyontheLTC3100throughtheaddition
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.
Output Disconnect
The LTC3100 boost converter is designed to allow true
output disconnect by eliminating body diode conduction
of the internal P-channel MOSFET rectifier. This allows for
V
to go to 0V during shutdown, drawing no current
OUT
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
Zero Current Comparator
The zero current comparator monitors the boost inductor
currenttotheoutputandshutsoffthesynchronousrectifier
once this current reduces to approximately 30mA. This
prevents the inductor current from reversing in polarity,
improving efficiency at light loads.
connected between SWBST and V . The output discon-
nect feature also allows V
any reverse current into the battery.
BST
to be pulled high without
OUT
V > V Operation
IN
OUT
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.
Synchronous Rectifier
To control inrush current and to prevent the inductor
current from running away when V
is close to V ,
OUT
IN
the P-channel MOSFET synchronous rectifier is only fully
enabled when V > (V + 0.24V).
OUT
IN
Burst Mode Operation (for Boost and Buck Converters)
Anti-Ringing Control
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
The anti-ring circuitry connects a resistor across the
boost inductor to prevent high frequency ringing on the
3100fa
13
LTC3100
OPERATION
buckconverters.Inthiscase,bothconverterswillremainin
fixedfrequencyoperation,evenatlightloadcurrents.Ifthe
load is very light, they will exhibit pulse-skip operation.
BUCK CONVERTER OPERATION
Thebuckconverterprovidesahighefficiency,lowervoltage
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.
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 fixed frequency operation when the
load current increases. Refer to the Typical Performance
Characteristics section to see the output load Burst Mode
PWM Mode Operation
WhentheMODEpinisheldlow,theLTC3100buckconverter
usesaconstant-frequency, currentmodecontrolarchitec-
ture.Boththemain(P-channelMOSFET)andsynchronous
rectifier (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
withsuperimposedslopecompensationrampexceedsthe
error amplifier output. At this point, the synchronous
rectifier is turned on and remains on until the inductor
current falls to zero or a new switching cycle is initiated.
Asaresult,thebuckconverteroperateswithdiscontinuous
inductor current at light loads which improves efficiency.
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.
thresholdvsV andV . Thetwoconverterscanenteror
IN
OUT
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 amplifier
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
consumesonly15μAofquiescentcurrentfromV . Once
BST
theoutputvoltagehasdroopedslightly,switchingresumes
again. This maximizes efficiency at very light loads by
minimizing switching and quiescent losses. Burst Mode
operation output ripple is typically 1% peak-to-peak.
Burst Mode Operation
Burst Mode operation for the boost converter is inhibited
When the MODE pin is forced high, or left open, the buck
converterwillautomaticallytransitionbetweenBurstMode
operation at sufficiently light loads (below approximately
10mA)andPWMmodeatheavierloads.BurstModeopera-
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
ModeoperationentrythresholdareprovidedintheTypical
PerformanceCharacteristicssectionofthisdatasheet.The
during start-up, and until soft-start is complete and V
BST
is at least 0.24V greater than V
.
INBST
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).
quiescentcurrentonV
inBurstModeoperationisonly
INBK
Schottky Diode
15μA. If the boost converter is enabled and V
or V
INBST
BST
Although it is not required, adding a Schottky diode from
are at a higher potential than V
, some of the quiescent
INBK
SWBST to V will improve efficiency by about 2%. Note
current will be supplied by the boost converter, reducing
the burst quiescent current on V to just 9μA.
BST
that this defeats the boost output disconnect and short-
INBK
circuit protection features.
3100fa
14
LTC3100
OPERATION
Dropout Operation
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.
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.
Error Amplifier and Compensation
The LTC3100 buck converter utilizes an internal transcon-
ductance error amplifier. 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.
Slope Compensation
Currentmodecontrolrequirestheuseofslopecompensa-
tion to prevent subharmonic oscillations in the inductor
current waveform at high duty cycle operation. This is ac-
complishedinternallyontheLTC3100throughtheaddition
of a compensating ramp to the current sense signal. In
some current mode ICs, current limiting is performed by
clamping the error amplifier voltage to a fixed 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.
Undervoltage Lockout
IftheV
supplyvoltagedecreasesbelow1.6V(typical),
INBK
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-
glitchingdelayinordertopreventfalsetripsduetovoltage
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
Short-Circuit Protection
When the buck output is shorted to ground, the error am-
plifierwillsaturatehighandtheP-channelMOSFETswitch
will turn on at the start of each cycle and remain on until
the current limit trips. During this minimum on-time, the
inductorcurrentwillincreaserapidlyandwilldecreasevery
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.
resistance is 13Ω when V
= 3.3V.
INBK
Schottky Diode
Although it is not required, adding a Schottky diode from
SWBK to the ground plane will improve efficiency by
about 2%.
Soft-Start
Thebuckconverterhasaninternalvoltagemodesoft-start
circuit with a nominal duration of 1.3ms. The converter
remains in regulation during soft-start and will therefore
3100fa
15
LTC3100
OPERATION
LDO REGULATOR OPERATION
COMMON FUNCTIONS
Oscillator
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 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.
the boost output (V
pin), and can share the same filter
BST
capacitor. The LDO can be operated independently of the
boost (or buck) converter, providing a sufficient voltage
is present on V
.
BST
MODE Control
Soft-Start and Current Limit
The MODE pin is used to force fixed 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.
TheLDOhasanindependentcurrentlimitcircuitthatlimits
output current to 120mA (typical). To minimize loading on
theboostconverteroutputwhenenablingtheLDO,theLDO
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 V
pin.
LDO
Reverse Current Blocking
Note: Leaving the pin open, or connecting it to the high-
The LDO is designed to prevent any reverse current from est of V
or V , will result in the lowest Burst Mode
INBK
BST
V
back to the V
pin, both in normal operation and quiescent current.
is pulled above V
LDO
BST
in shutdown. If V
and V
is
LDO
BST
BST
Overtemperature Shutdown
above 1V, there will be a small (1μA typical) current from
to ground.
V
LDO
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.
3100fa
16
LTC3100
APPLICATIONS INFORMATION
PC Board Layout Guidelines
should be placed as close to the IC as possible and
should have the shortest possible paths to ground.
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
depictstherecommendedPCboardlayout.Alargeground
pin copper area will help to lower the chip temperature.
A multilayer board with a separate ground plane is ideal,
but not absolutely necessary.
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
theviasextendtoagroundplaneregionontheexposed
bottom surface of the PC board.
A few key guidelines follow:
1. All circulating high current paths should be kept as
shortaspossible.Capacitorgroundconnectionsshould
via down to the ground plane in the shortest route pos-
4. Keep the connection from the resistor dividers to the
feedback pins as short as possible and away from the
switch pin connections.
sible. The bypass capacitors on all V and V
pins
IN
OUT
16 15 14 13
SWBST
1
2
3
4
12 FBBST
11 FBLDO
LTC3100
V
BST
RUNLDO
10
V
LDO
SWBK
9
FBBK
5
6
7
8
V
BUCK
3100 F01
Figure 1. Recommended Component Placement for Two-Layer PC Board
3100fa
17
LTC3100
APPLICATIONS INFORMATION
COMPONENT SELECTION
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.
Boost Output Voltage Programming
The boost output voltage is set by a resistive divider ac-
cording to the following formula:
Table 1. Recommended Boost Inductors
VENDOR
PART/STYLE
R2
R1
⎛
⎞
VOUT = 1.200V • 1+
Coilcraft
(847) 639-6400
www.coilcraft.com
LPS4012, LPS4018
MSS4020, MSS5131
⎜
⎝
⎟
⎠
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
immunityofthefeedbacknode,improvetransientresponse
and reduce output ripple in Burst Mode operation. A value
of 33pF will generally suffice.
Coiltronics
FDK
SD14, SD3814, SD3118
MIPSA2520
MIPW3226
Murata
www.murata.com
LQH43C
Sumida
(847) 956-0666
www.sumida.com
CDRH2D18, CDRH2D16
CDRH3D14, CDRH3D16
CDRH4D14, CDRH4D16
Boost Inductor Selection
Taiyo-Yuden
www.t-yuden.com
NR3015
NP03SB
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.
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
The minimum boost inductance value is given by:
Boost Input and Output Capacitor Selection
V
• VOUT(MAX) − V
(
)
IN(MIN)
IN(MIN)
TheinternalloopcompensationoftheLTC3100boostcon-
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.Multilayerceramiccapacitorsareanexcellentchoice
as they have extremely low ESR and are available in small
footprints. A 4.7μF to 10μF output capacitor is sufficient
for most fixed 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.
L >
1.5 • RIPPLE • VOUT(MAX)
Where:
RIPPLE = Allowable Inductor Current Ripple (Amps Peak-
to-Peak)
V
V
= Minimum Input Voltage
IN(MIN)
= Maximum Output Voltage
OUT(MAX)
The inductor current ripple is typically set for 20% to
40% of the maximum inductor current. High frequency
ferritecoreinductormaterialsreducefrequencydependent
power losses compared to cheaper powdered iron types,
improving efficiency. The inductor should have low DCR
(series resistance of the winding) to reduce the I R power
losses, and must not saturate at peak inductor current
levels. Molded chokes and some chip inductors usually
2
3100fa
18
LTC3100
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-
can be calculated via the following expression, where f
represents the switching frequency in MHz:
⎛
⎞
⎟
⎠
1
VOUT
L =
• 1−
μH
(
)
⎜
⎝
fΔIL
V
IN
sible to the device. A 2.2μF input capacitor on the V
INBST
pin is sufficient 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.
AreasonablechoiceforripplecurrentisΔI =100mAwhich
L
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.Tooptimizeefficiencytheinductorshouldhave
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
conductionforawiderrangeofoutputloadsandefficiency
will be reduced.
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
voltageapplied.Thiseffectisparticularlybadforcapacitors
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.
In addition, there is a minimum inductor value required
to maintain stability of the current loop (given the fixed
internal slope compensation). Specifically, if the buck
converter is going to be utilized at duty cycles over 40%,
Table 2.Capacitor Vendor Information
the inductance value must be at least L
following equation:
as given by the
MIN
SUPPLIER
AVX
PHONE
WEB SITE
www.avxcorp.com
www.murata.com
(803) 448-9411
(714) 852-2001
(408) 573-4150
(847) 803-6100
L
= 2.5 • V
(μH)
OUT
MIN
Murata
Taiyo-Yuden
TDK
www.t-yuden.com
Table 3 depicts the minimum required inductance for
several common output voltages.
www.component.tdk.com
Table 3.Buck Minimum Inductance
Buck Inductor Selection
OUTPUT VOLTAGE
MINIMUM INDUCTANCE
The choice of buck inductor value influences both the
efficiency and the magnitude of the output voltage ripple.
Largerinductancevalueswillreduceinductorcurrentripple
and will therefore lead to lower output voltage ripple. For
a fixed DC resistance, a larger value inductor will yield
higher efficiency by lowering the peak current to be closer
to the average. However, a larger value inductor within the
samefamilywillgenerallyhaveagreaterseriesresistance,
therebyoffsettingthisefficiencyadvantage.Givenadesired
0.6V
0.8V
1.2V
2V
1.5μH
2μH
3μH
5μH
2.7V
3.3V
6.8μH
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).
peak to peak current ripple, ΔI , the required inductance
L
3100fa
19
LTC3100
APPLICATIONS INFORMATION
Table 4. Recommended Buck Inductors
the value of the feedforward capacitor in parallel with the
upper resistor divider resistor.
VENDOR
PART/STYLE
Coilcraft
(847) 639-6400
www.coilcraft.com
LPS3008, LPS3010, LPS3015
Note that even X5R and X7R type ceramic capacitors have
a DC bias effect which reduces their capacitance with a DC
voltageapplied.Thiseffectisparticularlybadforcapacitors
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.
Coiltronics
FDK
SD3114, SD3118, SD3112
MIPF2016
MIPF2520, MIPS2520
Murata
www.murata.com
LQH32C
LQM31P
Table 5. Buck Output Capacitor Range
Sumida
(847) 956-0666
www.sumida.com
CDRH2D11, CDRH2D09
CMD4D06-4R7MC
CMD4D06-3R3MC
V
C
C
MAX
OUT
MIN
0.6V
0.8V
1.2V
1.8V
2.7V
3.3V
15μF
15μF
10μF
6.8μF
6.8μF
6.8μF
300μF
230μF
150μF
90μF
Taiyo-Yuden
NR3010, NR3012
www.t-yuden.com
TDK
www.tdk.com
VLF3010, VLF3012
LEMC3225, LBC2518
Toko
(408) 432-8282
www.tokoam.com
D3010
70μF
DB3015
50μF
D312, D301F
Würth
(201) 785-8800
www.we-online.com
WE-TPC Type XS, S
Buck Input Capacitor Selection
The V pin provides current to the buck converter
INBK
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 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
outputcapacitoralsosetstheloopcrossoverfrequencyand
thereforecanimpactloopstability.Thereisbothaminimum
andmaximumcapacitancevaluerequiredtoensurestabil-
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 amplifier will degrade the phase margin. In ad-
dition, the wider bandwidth produced by a small output
capacitorwillmaketheloopmoresusceptibletoswitching
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 sufficient ESR to stabilize the loop or by increasing
Buck Output Voltage Programming
The output voltage is set by a resistive divider according
to the following formula:
R6
R5
⎛
⎞
VOUT = 0.600V • 1+
⎜
⎝
⎟
⎠
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 suffice.
3100fa
20
LTC3100
APPLICATIONS INFORMATION
LDO Output Capacitor Selection
LDO Output Voltage Programming
The LDO is designed to be stable with a minimum 1μF
output capacitor. No series resistor is required when using
lowESRcapacitors.Formostapplications,a2.2μFceramic
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.
The output voltage is set by a resistive divider according
to the following formula:
R4
R3
⎛
⎞
VOUT = 0.600V • 1+
⎜
⎝
⎟
⎠
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
L1
3.3μH
3.5V
1
5
2
C1
10μF
s2
R2
V
BATT
SWBST
V
V
BST
INBK
1M
0.9V TO 1.5V
16
12
V
FBBST
INBST
+
R1
523k
C
IN
V
, 1V/DIV
BST
I/O
2.2μF
LTC3100
V
, 1V/DIV
+3.3V AT 50mA
V_I/O
3
V
LDO
R4
C2
115k
V
, 1V/DIV
CORE
2.2μF
11
FBLDO
SWBK
R3
25.5k
13
120mA AT V
220mA AT V
= 0.9V
= 1.2V
BATT
BATT
L2
3.3μH
FF EN_BURST
OFF ON
MODE
3100 TA02b
1ms/DIV
4
14
10
8
V_CORE = 1.2V
RUNBST
RUNLDO
RUNBK
R6
1M
C3
10μF
9
FBBK
PGBST
PGBK
R7
1M
R8
1M
15
16
R5
1M
GND
7
BOOST_GOOD
BUCK_GOOD
3100fa
21
LTC3100
TYPICAL APPLICATIONS
Li-Ion Input, Triple Output Converter
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
L1
V
= 3.6V
IN
3.3μH
+5V AT 200mA
V
BOOST
1
5
2
C1
10μF
s2
R2
V
2.5V TO 5V
IN
SWBST
V
V
BST
INBK
2M
Li-Ion
16
12
FBBST
V
INBST
C
IN
4.7μF
R1
634k
+3.3V AT
50mA
V_I/O
3
V
LDO
1
R4
115k
C2
2.2μF
LTC3100
11
FBLDO
SWBK
1.8V BUCK
5V BOOST
BUCK POWER LOSS
BOOST POWER LOSS
0.1
0.01
R3
25.5k
13
14
10
8
+1.8V AT
250mA
V_CORE
L2
MODE
4.7μH
4
OFF ON
RUNBST
RUNLDO
RUNBK
C
FF2
R6
976k
BOOST
0.01
0.1
1
10 100
LOAD CURRENT (mA)
1000
C3
10μF
10pF
9
FBBK
OFF ON
OFF ON
R7
100k
R8
100k
LDO
3100 TA03b
15
16
R5
487k
PGBST
PGBK
GND
7
BUCK
3100 TA03a
BOOST_GOOD
BUCK_GOOD
Single-Cell/Two-Cell or USB Input to 3.3V/1.8V Converter
Efficiency vs Load Current
MBR0520
USB
INPUT
3.3V AT: 100mA FOR V
= 1.2V
BATT
BATT
100
300mA FOR V
= 2.4V
3.3V OUTPUT
C1
L1
250mA FOR USB INPUT
90
80
70
60
50
40
30
20
10
0
4.7μF 3.3μH
V
OUT
V
1
5
2
V
= 2.4V
BATT
C2
IN
R1
0.9V TO
10μF
SWBST
V
V
INBK
BST
FBBST
1.07M
3.3V
16
12
3
V
= 1.2V
IN
V
INBST
C4
R2
324k
4.7μF
V
LDO
R3
301k
R5
V
= 5V USB
IN
200k
LTC3100
11
FBLDO
1.8V AT 50mA
R6
100k
VLDO
C4
2.2μF
L2
10μH
13
14
10
8
4
MODE
SWBK
FBBK
0.01
0.1
1
10
100
1000
C3
10μF
9
LOAD CURRENT (mA)
RUNBST
RUNLDO
RUNBK
R7
64.9k
3100 TA04b
15
16
PGBST
PGBK
GND
7
R4
20k
3100 TA04a
3100fa
22
LTC3100
PACKAGE DESCRIPTION
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691)
0.70 p0.05
3.50 p 0.05
2.10 p 0.05
1.45 p 0.05
(4 SIDES)
PACKAGE OUTLINE
0.25 p0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 s 45o CHAMFER
R = 0.115
TYP
0.75 p 0.05
3.00 p 0.10
(4 SIDES)
15 16
PIN 1
TOP MARK
(NOTE 6)
0.40 p 0.10
1
2
1.45 p 0.10
(4-SIDES)
(UD16) QFN 0904
0.200 REF
0.25 p 0.05
0.00 – 0.05
0.50 BSC
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
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.
23
LTC3100
TYPICAL APPLICATION
Single-Cell to 1.2V/1.8V Converter
Efficiency vs Load Current
(VBUCK
)
L1
3.3μH
100
90
80
70
60
50
40
30
20
10
0
2.4V
1
5
2
C1
10μF
s2
R2
V
BATT
SWBST
V
V
BST
INBK
1M
0.9V TO 1.6V
16
V
INBST
+
C
2.2μF
R1
1M
12
3
IN
FBBST
1.8V AT
50mA
VLDO
V
LDO
R4
200k
C2
2.2μF
LTC3100
11
4
FBLDO
SWBK
R3
100k
V
IN
V
IN
V
IN
= 0.9V
= 1.2V
= 1.5V
13
14
10
8
1.2V AT: 120mA FOR V
250mA FOR V
= 0.9V
= 1.2V
L2
3.3μH
MODE
BATT
BATT
VBUCK
RUNBST
RUNLDO
RUNBK
OFF ON
0.01
0.1
1
10
100
(mA)
1000
R6
1M
C3
10μF
R7
LOAD CURRENT ON V
BUCK
9
FBBK
3100 TA05b
15
6
R5
1M
100k
PGBST
PGBK
GND
7
3100 TA05a
BUCK_GOOD
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC3442
1.2A (I ), 2MHz Synchronous Buck-Boost
V : 2.4V to 5.5V, V
: 2.4V to 5.25V, I = 35μA, I < 1μA,
OUT(RANGE) Q SD
OUT
IN
DC/DC Converter
DFN Package
LTC3455
LTC3456
LTC3520
LTC3522
Dual DC/DC Converter with USB Power Manager and Li-Ion 96% Efficiency, Seamless Transition Between Inputs, I = 110μA,
Q
Battery Charger
I
< 2μA, QFN Package
SD
2-Cell Multi-Output DC/DC Converter with USB Power
Manager
92% Efficiency, Seamless Transition Between Inputs, I = 180μA,
Q
SD
I
< 1μA, QFN Package
Synchronous 1A Buck-Boost and 600mA Step-Down
DC/DC Converter
V : 2.2V to 5.5V, V
= 0.6V, I = 55μA, I < 1μA,
OUT(MIN) Q SD
IN
4mm × 4mm QFN Package
Synchronous 400mA Buck-Boost and 200mA Step-Down
DC/DC Converter
V : 2.4V to 5.5V, V
= 0.6V, I = 25μA, I < 1μA,
Q SD
IN
OUT(MIN)
3mm × 3mm QFN-16 Package
LTC3527/LTC3527-1 Dual (400mA/800mA) Synchronous Boost Converter
V : 0.5V to 5V, V : 1.5V to 5.25V, I = 12μA, I < 2μA,
IN
OUT
Q
SD
3mm × 3mm QFN Package
LTC3530
600mA (I ), 2MHz Synchronous Buck-Boost
V : 1.8V to 5.5V, V
: 1.8V to 5.5V, I = 40μA, I < 1μA,
OUT(RANGE) Q SD
OUT
IN
DC/DC Converter
DFN and MSOP Packages
LTC3532
500mA (I ), 2MHz Synchronous Buck-Boost
V : 2.4V to 5.5V, V
: 2.4V to 5.25V, I = 35μA, I < 1μA,
OUT(RANGE) Q SD
OUT
IN
DC/DC Converter
DFN and MSOP Packages
LTC3537
600mA (I ), 2.2MHz Synchronous Boost Converter with V : 0.68V to 5V, V
= 5.5V, I = 30μA, I < 1μA,
OUT(MAX) Q SD
SW
IN
100mA LDO
3mm × 3mm QFN Package
LTC3538
600mA (I ), 2MHz Synchronous Buck-Boost
V : 2.4V to 5.5V, V
: 1.5V to 5.5V, I = 35μA, I < 1μA,
OUT(RANGE) Q SD
OUT
IN
DC/DC Converter
DFN Package
LTC3544/LTC3544B
LTC3545
V : 2.25V to 5.5V, V
= 0.8V, I = 70μA, I < 1μA,
Q SD
300mA, 200mA ×2, 100mA, 2.25MHz Quad Output
IN
OUT(MIN)
QFN Package
Synchronous Step-Down DC/DC Converter
V : 2.25V to 5.5V, V
= 0.6V, I = 58μA, I < 1μA,
Q SD
Triple Output, 3mA × 800mA, 2.25MHz Synchronous
Step-Down DC/DC Converter
IN
OUT(MIN)
QFN Package
3100fa
LT 1108 REV A • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
24
●
●
© LINEAR TECHNOLOGY CORPORATION 2008
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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