LTC3127EMSETRPBF [Linear]
1A Buck-Boost DC/DC Converter with Programmable Input Current Limit; 1A降压 - 升压型DC / DC转换器与可编程输入电流限制
| 型号： | LTC3127EMSETRPBF |
| 厂家： | 
Linear |
| 描述： | 1A Buck-Boost DC/DC Converter with Programmable Input Current Limit |
| 文件： | 总20页 (文件大小：366K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3127
1A Buck-Boost DC/DC
Converter with Programmable
Input Current Limit
FeaTures
DescripTion
TheLTC®3127isawideV range,highlyefficient,1.35MHz
n
Programmable (0.2A to 1A) ±±4 Accꢀrate Average
IN
Inpꢀt Cꢀrrent Limit
Regꢀlated Oꢀtpꢀt with Inpꢀt Voltages Above,
Below or Eqꢀal to the Oꢀtpꢀt
1.8V to 5.5V (Inpꢀt) and 1.8V to 5.25V (Oꢀtpꢀt)
Voltage Range
0.6A Continꢀoꢀs Oꢀtpꢀt Cꢀrrent: V > 1.8V
1A Continꢀoꢀs Oꢀtpꢀt Cꢀrrent: V > 3V
fixedfrequencybuck-boostDC/DCconverterthatoperates
from input voltages above, below or equal to the output
voltage. The LTC3127 features programmable average
input current limit, making it ideal for power-limited input
sources. The input current limit is programmed with a
single resistor and is accurate from 0.2A to 1A of average
input current.
n
n
n
n
n
n
n
n
n
n
IN
IN
Single Indꢀctor
The topology incorporated provides a continuous
transfer function through all operating modes. Other
features include <1μA shutdown current, pin-selectable
Burst Mode operation and thermal overload protection.
The LTC3127 is housed in thermally enhanced 10-lead
(3mm × 3mm × 0.75mm) DFN packages and 12-lead
MSOP packages.
Synchronous Rectification: Up to 96% Efficiency
Burst Mode® Operation: I = 35μA (Pin Selectable)
Q
Output Disconnect in Shutdown
<1μA Shutdown Current
Small, Thermally Enhanced 10-Lead (3mm × 3mm ×
0.75mm) DFN and 12-Lead MSOP Packages
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
and PowerPath and ThinSOT are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
applicaTions
n
USB Powered GSM Modems
n
Supercap Charger
n
Handheld Test Instruments
PC Card Modems
n
n
Wireless Terminals
Typical applicaTion
USB or Li-Ion (500mA Maximꢀm Inpꢀt Cꢀrrent) to 3.3V
Efficiency vs VIN
100
L1
4.7µH
300mA LOAD
90
SW2
SW1
1A LOAD
USB OR Li-Ion
2.9V to 5.5V
V
3.3V
OUT
V
V
OUT
IN
80
70
60
50
MODE
320k
182k
SHDN
PROG
FB
2.2mF
OFF ON
V
C
10µF
SGND PGND
499k
32.4k
100pF
V
= 3.3V
OUT
L = 4.7µH
F = 1.35MHz
3127 TA01
2.5
3
3.5
4
4.5
5
5.5
L1: COILCRAFT XPL4020-472ML
V
(V)
IN
3127 TA01a
3127f
ꢀ
LTC3127
(Note 1)
absoluTe MaxiMuM raTings
V , V
Voltage .......................................... –0.3 to 6V
PROG Voltage ................................................ –0.3 to 6V
Operating Junction Temperature Range
(Note 2)....................................................–40°C to 85°C
Maximum Junction Temperature (Note 5) ........... 125°C
Storage Temperature Range ..................–65°C to 125°C
IN OUT
SW1, SW2 DC Voltage ................................... –0.3 to 6V
SW1, SW2 Pulsed (<100ns) Voltage .............. –0.3 to 7V
MODE, FB, V Voltage.................................... –0.3 to 6V
SHDN Voltage ............................................... –0.3 to 6V
C
pin conFiguraTion
TOP VIEW
TOP VIEW
10 SW2
PGND
SW1
1
2
3
4
5
6
12 PGND
11 SW2
SW1
1
2
3
4
5
V
IN
9
8
7
6
V
V
OUT
C
13
PGND
V
10
9
V
V
11
PGND
IN
OUT
C
SHDN
MODE
PROG
SHDN
MODE
PROG
FB
8
FB
SGND
7
SGND
MSE PACKAGE
DD PACKAGE
12-LEAD PLASTIC MSOP
10-LEAD (3mm s 3mm) PLASTIC DFN
T
= 125°C, θ = 40°C/W (NOTE 6)
JA
EXPOSED PAD (PIN 11) IS PGND, MUST BE SOLDERED TO PCB
JMAX
T
= 125°C, θ = 43°C/W (NOTE 6)
JA
EXPOSED PAD (PIN 11) IS PGND, MUST BE SOLDERED TO PCB
JMAX
orDer inForMaTion
LEAD FREE FINISH
LTC3127EDD#PBF
LTC3127EMSE#PBF
TAPE AND REEL
PART MARKING
LDYD
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3127EDD#TRPBF
LTC3127EMSE#TRPBF
–40°C to 85°C
–40°C to 85°C
10-Lead (3mm × 3mm) Plastic DFN
3127
12-Lead Plastic MSOP
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/
3127f
ꢁ
LTC3127
elecTrical characTerisTics The l denotes the specifications which apply over the fꢀll operating
temperatꢀre range, otherwise specifications are at TJ = 25°C. VIN = 3.6V, VOUT = 3.3V, ꢀnless otherwise noted.
PARAMETER
CONDITIONS
MIN
1.8
TYP
MAX
5.5
UNITS
V
l
l
l
Input Operating Range
Output Voltage Adjust
1.8
5.25
1.225
50
V
Feedback Voltage
1.165
1.195
1
V
Feedback Input Current
Quiescent Current—Burst Mode Operation
Quiescent Current—Shutdown
Quiescent Current—Active
Input Current Limit
V
V
V
V
= 1.25V
nA
µA
µA
µA
mA
mA
mA
A
FB
> 1.225, V
= V (Note 4)
35
FB
MODE
IN
= 0V, Including SW Leakage
0.1
400
500
500
500
2.5
0.3
0.1
4
SHDN
> 1.225V, V
= 0V (Note 4)
MODE
FB
R
PROG
= 32.4k (Note 3)
480
465
430
2
520
540
540
l
l
l
0°C to 85°C (Note 3)
–40°C to 85°C (Note 3)
Peak Current Limit
Reverse-Current Limit
0.15
0.45
4
A
P-Channel MOSFET Leakage
N-Channel MOSFET On-Resistance
Switches A and D
µA
Switch B
Switch C
140
170
mΩ
mΩ
P-Channel MOSFET On-Resistance
Maximum Duty Cycle
Switch A
Switch D
160
190
mΩ
mΩ
l
l
Boost( % Switch C On)
Buck (% Switch A On)
80
100
90
%
%
l
l
l
l
Minimum Duty Cycle
Frequency Accuracy
0
%
MHz
V
1
1.35
1.7
SHDN Input High Voltage
SHDN Input Low Voltage
SHDN Input Current
1.2
0.3
1
V
V
V
= 5.5V
= 5.5V
0.01
0.01
µA
V
SHDN
l
l
MODE Input High Voltage
MODE Input Low Voltage
MODE Input Current
1.2
0.3
1
V
µA
MODE
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 3: Specification is guaranteed when the inductor current is in
continuous conduction.
Note ±: Current measurements are made when the output is not
switching.
Note 2: The LTC3127 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. Note that the maximum
ambient temperature is determined by specific operating conditions in
conjunction with board layout, the rated package thermal resistance and
other environmental factors.
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
40°C/W.
3127f
ꢂ
LTC3127
(TJ = 25°C, ꢀnless otherwise noted )
Typical perForMance characTerisTics
Efficiency vs Load Cꢀrrent
Efficiency vs Load Cꢀrrent
Efficiency vs Load Cꢀrrent
100
100
90
100
90
PWM
V
= 5V
OUT
V
OUT
= 1.8V
V
= 3.3V
OUT
90
80
70
BURST
80
80
BURST
BURST
70
70
60
50
60
50
60
50
PWM
PWM
40
30
20
10
0
40
30
20
10
0
40
30
20
10
0
V
V
V
= 4.5V
= 5V
V
V
V
= 1.8V
= 3.6V
= 5V
V
V
V
= 2.9V
= 3.6V
= 4.3V
IN
IN
IN
IN
IN
IN
IN
IN
IN
= 5.5V
0.1
1
10
100
1000 10000
0.1
1
10
100
1000
0.1
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
3127 G03
3127 G01
3127 G02
Average Inpꢀt Cꢀrrent Limit
vs VIN (Normalized)
Average Inpꢀt Cꢀrrent Limit
vs Temperatꢀre (Normalized)
Qꢀiescent Cꢀrrent vs VIN (Fixed
Freqꢀency Mode–Not Switching)
2
1
430
410
390
370
350
330
310
290
270
2
1
V
= 3.3V
PROG
V
= 3.3V
PROG
OUT
OUT
R
= 32.4k
R
= 32.4k
0
0
–1
–2
–3
–4
–5
–1
–2
–3
–4
–5
2.6
3
3.4 3.8 4.2
5.4
15 30 45 60 75 90
1.8 2.2
4.6
5
–45
–15
0
–30
1.8
2.6
3
3.4 3.8 4.2 4.6
(V)
5
5.4
2.2
TEMPERATURE (°C)
V
IN
(V)
V
IN
3127 G05
3127 G04
3127 G06
Bꢀrst Mode Qꢀiescent Cꢀrrent
vs VIN
No Load Inpꢀt Cꢀrrent vs VIN in
Bꢀrst Mode Operation
38
37
36
35
34
33
32
52.5
52.0
51.5
51.0
50.5
50.0
49.5
49.0
48.5
V
OUT
= 3.3V
1.8
2.6
3
3.4 3.8 4.2 4.6
(V)
5
5.4
1.8 2.2
2.6
3
3.4 3.8 4.2
4.6
5
5.4
2.2
V
IN
V
IN
(V)
3127 G07
3127 G08
3127f
ꢃ
LTC3127
(TJ = 25°C, ꢀnless otherwise noted )
Typical perForMance characTerisTics
Feedback Voltage vs Temperatꢀre
(Normalized)
VOUT Regꢀlation vs Load Cꢀrrent
(Normalized)
NMOS RDS(ON) vs VIN
0.20
0.00
300
250
200
150
100
0.40
0.30
L = 4.7µH
V
OUT
= 3.3V
V
V
= 3.3V
OUT
IN
= 3.6V
0.20
0.10
–0.20
–0.40
–0.60
–0.80
0
–0.10
–0.20
–0.30
–0.40
–0.50
–0.60
SWC
SWB
50
70
90
–50 –30 –10 10
30
1.8
2.4
3
3.6
(V)
4.2
4.8
5.4
0
200
600
LOAD CURRENT (mA)
800
1000
400
TEMPERATURE (°C)
V
IN
3127 G09
3127 G10
3127 G11
Load Transient Response in Fixed
Freqꢀency Mode, No Load to 1A,
Not in Inpꢀt Cꢀrrent Limit
Maximꢀm Load Cꢀrrent vs VIN
PMOS RDS(ON) vs VIN
2250
2000
1750
1500
1250
1000
750
325
275
225
175
125
R
PROG
= 90k
I
LOAD
1A/DIV
I
IN
V
OUT
= 2.4V
V
OUT
= 3.3V
1A/DIV
V
OUT
50mV/DIV
V
OUT
= 5V
I
SWD
L
1A/DIV
500
3127 G14
SWA
200µs/DIV
250
V
= 3.6V
PROG
V
C
= 3.3V
IN
OUT
OUT
0
R
= 90k
= 4.4mF
2.6
3
3.4 3.8 4.2
5.4
1.8 2.2
4.6
5
1.8
2.4
3
3.6
(V)
4.2
4.8
5.4
R3 = 499k
C1 = 100pF
V
V
IN
(V)
IN
3127 G13
3127 G12
Load Transient Response in Fixed
Freqꢀency Mode, No Load to 1A,
in Inpꢀt Cꢀrrent Limit
Bꢀrst Mode Operation
MODE = 0V
I
LOAD
1A/DIV
I
L
500mA/DIV
I
IN
500mA/DIV
V
OUT
V
OUT
100mV/DIV
20mV/DIV
3127 G15
3127 G16
200µs/DIV
5µs/DIV
V
= 3.6V
PROG
V
C
= 3.3V
V
= 3.6V
V
C
= 3.3V
IN
OUT
OUT
IN
OUT
OUT
R
= 32.4k
= 4.4mF
R
= 32.4k
PROG
= 4.4mF
R3 = 499k
C1 = 100pF
R3 = 499k
C1 = 100pF
3127f
ꢄ
LTC3127
(TJ = 25°C, ꢀnless otherwise noted )
Operation to Fixed Freqꢀency Mode
Typical perForMance characTerisTics
Load Transient Response in
Transition from Bꢀrst Mode
Bꢀrst Mode Operation, No Load
to 1A, Not in Inpꢀt Cꢀrrent Limit
I
LOAD
1A/DIV
I
IN
200mA/DIV
I
IN
1A/DIV
V
V
OUT
20mV/DIV
OUT
50mV/DIV
MODE
5V/DIV
MODE
5V/DIV
3127 G17
3127 G18
200µs/DIV
100µs/DIV
V
= 3.6V
PROG
V
C
= 3.3V
IN
OUT
OUT
V
= 3.6V
PROG
V
C
= 3.3V
IN
OUT
OUT
R
= 90k
= 4.4mF
R
= 32.4k
= 4.4mF
R3 = 499k
C1 = 100pF
R3 = 499k
C1 = 100pF
Load Transient Response in
Bꢀrst Mode Operation, No Load
to 1A, in Inpꢀt Cꢀrrent Limit
Start-Up Waveform
I
LOAD
1A/DIV
I
V
IN
OUT
500mA/DIV
1V/DIV
V
OUT
100mV/DIV
I
IN
500mA/DIV
MODE
5V/DIV
SHDN
5V/DIV
3127 G20
3127 G19
5ms/DIV
200µs/DIV
V
= 3.6V
PROG
V
C
= 3.3V
V
= 3.6V
PROG
V
C
= 3.3V
OUT
IN
OUT
OUT
IN
R
= 32.4k
= 4.4mF
R
= 32.4k
= 4.4mF
OUT
R3 = 499k
C1 = 100pF
R3 = 499k
C1 = 100pF
3127f
ꢅ
LTC3127
(DD Package)
pin FuncTions
SW1 (Pin 1): Switch Pin Where Internal Switches A and
B Are Connected. Connect inductor from SW1 to SW2.
Minimize trace length to reduce EMI.
SGND (Pin 6): Signal Ground for the IC. Terminate the
PROG resistor, compensation components and the output
voltage divider to SGND.
V
(Pin 2): Input Supply Pin. Internal V for the IC. A
FB(Pin7):FeedbackPin.Connectresistordividertaphere.
The output voltage can be adjusted from 1.8V to 5.25V.
The feedback reference voltage is 1.195V.
IN
CC
10μF or greater ceramic capacitor should be placed as
close to V and PGND as possible.
IN
SHDN (Pin 3): Logic-Controlled Shutdown Input.
SHDN = High: Normal Operation
SHDN = Low: Shutdown
R2
R1
VOUT = 1.195 • 1+
V
V (Pin 8): Error Amplifier Output. Place compensation
components from this pin to SGND.
C
MODE (Pin ±): Pulse Width Modulation/Burst Mode
Selection Input.
V
(Pin9):OutputoftheSynchronousRectifier.Connect
OUT
theoutputfiltercapacitorfromthispintoGND.Aminimum
value of 22µF is recommended. Output capacitors must
be low ESR.
MODE = High: Burst Mode Operation
MODE = Low: PWM Operation Only. Forced continuous
conduction mode.
SW2 (Pin 10): Switch Pin Where Internal Switches C and
D Are Connected. Minimize trace length to reduce EMI.
PROG (Pin 5): Sets the Average Input Current Limit
Threshold. Connect a resistor from PROG to ground. See
below for component value selection.
PGND(ExposedPadPin11):PowerGround.Theexposed
pad mꢀst be soldered to the PCB groꢀnd plane.
R
PROG
= 54.92 • I
(A) + 4.94 (kΩ)
LIMIT
3127f
ꢆ
LTC3127
block DiagraM
L
SW1
SW2
V
IN
V
OUT
C
IN
–
+
V
C
I
I
ZERO
AMP
PEAK
AMP
R2
R1
R3
C
OUT
PWM
COMPARATOR
AND LOGIC
–
+
FB
1.195V
SHDN
+
–
MODE
SAMPLE/HOLD
AND RESET
PROG
–
+
V
CLAMP
R
PROG
SGND
3127 BD
3127f
ꢇ
LTC3127
operaTion
The LTC3127 is an average input current controlled buck-
boostDC/DCconverterofferedinbothathermallyenhanced
3mm × 3mm DFN package and a thermally enhanced 12-
lead MSOP package. The buck-boost converter utilizes a
proprietary switching algorithm which allows its output
voltage to be regulated above, below or equal to the input
the AC switch pair remains on for longer durations and
the duration of the BD phase decreases proportionally. As
the input voltage drops below the output voltage, the AC
phase will eventually increase to the point that there is no
longer any BD switching. At this point, switch A remains
oncontinuouslywhileswitchpairCDispulsewidthmodu-
lated to obtain the desired output voltage. At this point,
the converter is operating solely in boost mode.
voltage. The low R
, low gate charge synchronous
DS(ON)
switches efficiently provide high frequency PWM control.
High efficiency is achieved at light loads when Burst Mode
operation is commanded.
This switching algorithm provides a seamless transition
between operating modes and eliminates discontinuities
in average inductor current, inductor current ripple, and
loop transfer function throughout all three operational
modes. These advantages result in increased efficiency
and stability in comparison to the traditional 4-switch
buck-boost converter. In forced PWM mode operation,
the inductor is forced to have continuous conduction.
This allows for a constant switching frequency and better
noise performance.
PWM Mode Operation
The LTC3127 uses fixed frequency, average input cur-
rent PWM control. The MODE pin can be used to select
automatic Burst Mode operation (MODE connected to
V ) or to disable Burst Mode operation and select forced
IN
continuousconductionoperationforlownoiseapplications
(MODE grounded).
A proprietary switching algorithm allows the converter
to switch between buck, buck-boost and boost modes
without discontinuity in inductor current or loop charac-
teristics.Theswitchtopologyforthebuck-boostconverter
is shown in Figure 1.
Error Amplifier and Compensation
The buck-boost converter utilizes two control loops. The
outer voltage loop determines the amount of current re-
quired to regulate the output voltage. The voltage loop is
externally compensated and can be configured with either
integral compensation or proportional control. The inner
currentloopisinternallycompensatedandforcestheinput
current to equal the commanded current.
When the input voltage is significantly greater than the
output voltage, the buck-boost converter operates in
buck mode. Switch D turns on continuously and switch C
remains off. Switches A and B are pulse width modulated
to produce the required duty cycle to support the output
regulation voltage. As the input voltage decreases, switch
A remains on for a larger portion of the switching cycle.
When the duty cycle reaches approximately 85%, the
switch pair AC begins turning on for a small fraction of the
switching period. As the input voltage decreases further,
When V is compensated via proportional control, the
C
dominant pole of the output capacitor is used to ensure
stability with a minimum of 1000µF of capacitance on the
outputwhena499kresistorisused. Thereisnomaximum
capacitance limitation with proportional compensation.
L
V
SW1
SW2
V
OUT
IN
A
D
B
C
LTC3127
PGND
PGND
3127 F01
Figꢀre 1. Bꢀck-Boost Switch Topology
3127f
ꢈ
LTC3127
operaTion
Integral compensation is required if an output capacitor
less than 1000µF but greater than 44µF is used, otherwise
using proportional compensation is recommended.
This causes poles and zeros to occur at the following
locations:
f
@ DC
POLE2
When compensating the converter with integral compen-
sation it is important to consider that the total bandwidth
of the network must be below 15kHz. The inner current
loop of the LTC3127 eliminates one of the double poles
caused by the inductor. The output capacitor causes a
dominant pole and also a zero, and the resistor divider
sets the gain.
1
fPOLE3
fZERO2
=
2 • π • RA • C2
1
=
2 • π • RA • C1
The poles and zeros of the compensation should be deter-
mined by looking at where f lands at the minimum
POLE1
R2
GDC = 1+
R1
load where the LTC3127 will be continuously conducting,
which places the dominant pole at its lowest frequency.
Aftersettingthepolesandzerosforthecompensation, the
phase margin of the system should be greater than 45°
andthegainmarginshouldbegreaterthan3dB. Following
these two criteria will help to ensure stability.
1
fPOLE1
=
2 • π • RLOAD • COUT
1
fZERO1
=
2 • π • RESR • COUT
Cꢀrrent Limit Operation
Using the compensation network show in Figure 2, the
voltage loop compensation can be approximated with the
following transfer function:
The buck-boost converter has two current limit circuits.
The primary current limit is an average input current
limit circuit that clamps the output of the outer voltage
loop. This limits the amount of input current that can be
commanded, and the inner current loop regulates to that
clamped value.
gm • (C1• RA • s + 1)
s • (C1• C2 •RA • s + C1+ C2)
HCOMP(s) =
–6
where g = 150 • 10
m
V
OUT
V
LTC3127
PWM
OUT
–
1.195V
MEASURED
R2
+
–
+ INPUT CURRENT
FB
C
OUT
V
C
R1
R
A
C2
SGND
C1
3127 F02
Figꢀre 2. Bꢀck-Boost External Compensation
3127f
ꢀ0
LTC3127
operaTion
The input current limit is set by the R
resistor placed
Anti-Ringing Control
PROG
on the PROG pin to SGND. The resistor value can be
calculated using the following formula:
Theanti-ringingcontrolconnectsaresistorfromSW1and
SW2 to PGND to prevent high frequency ringing during
discontinuous current mode operation in Burst Mode.
Although the ringing of the resonant circuit formed by L
and CSW (capacitance on SW pin) is low energy, it can
cause EMI radiation.
R
PROG
= 54.92 • I
(A) + 4.94 (kΩ)
LIMIT
Where I
is the average input current limit in amps.
LIMIT
A secondary 2.5A (typical) current limit forces switches
B and D on and A and C off if tripped. This current limit
is not affected by the value of R
.
Shꢀtdown
PROG
Shutdown of the converter is accomplished by pulling
Reverse Cꢀrrent Limit
SHDN below 0.3V and enabled by pulling SHDN above
The reverse current comparator on switch D monitors
the inductor current supplied from the output. When this
current exceeds 300mA (typical) switch D will be turned
off for the remainder of the switching cycle.
1.2V. Note that SHDN can be driven above V or V
,
IN
OUT
as long as it is limited to less than the absolute maximum
rating.
Thermal Shꢀtdown
Bꢀrst Mode Operation
Ifthedietemperatureexceeds150°C(typical)theLTC3127
will be disabled. All power devices will be turned off and
both switch nodes will be high impedance. The LTC3127
will restart (if enabled) when the die temperature drops
to approximately 140°C.
When the MODE pin is held high the LTC3127 will func-
tion in Burst Mode operation as long as the load current
is typically less than 35mA. In Burst Mode operation, the
LTC3127 still switches at a fixed frequency of 1.35MHz,
usingthesameerroramplifiersandloopcompensationfor
average input current mode control. This control method
eliminates any output transient when switching between
modes. In Burst Mode operation, energy is delivered to
the output until the output voltage reaches the nominal
regulation value. At this point, the LTC3127 transitions to
sleep mode where the output switches are shut off and the
LTC3127 consumes only 35μA of quiescent current from
Thermal Regꢀlator
To help prevent the part from going into thermal shutdown
when charging very large capacitive loads, the LTC3127 is
equipped with a thermal regulator. If the die temperature
exceeds 130°C (typical) the average current limit is lowered
to help reduce the amount of power being dissipated in the
package.Thecurrentlimitwillbeapproximately0Ajustbefore
thermalshutdown.Thecurrentlimitwillreturntoitsfullvalue
when the die temperature drops back below 130°C.
V . When the output voltage droops slightly, switching
IN
resumes. This maximizes efficiency at very light loads by
minimizing switching and quiescent losses.
Undervoltage Lockoꢀt
Zero Cꢀrrent Comparator
If the input supply voltage drops below 1.7V (typical),
the LTC3127 will be disabled and all power devices will
be turned off.
The zero current comparator monitors the inductor cur-
rent to the output and shuts off the synchronous rectifier
when this current reduces to approximately 30mA. This
prevents the inductor current from reversing in polarity,
improving efficiency at light loads. This comparator is
only active in Burst Mode operation.
3127f
ꢀꢀ
LTC3127
applicaTions inForMaTion
The LTC3127 can utilize small surface mount inductors
due to its fast 1.35MHz switching frequency. Inductor
values between 2.2μH and 4.7μH are suitable for most
applications.Largervaluesofinductancewillallowslightly
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.
A typical LTC3127 application circuit is shown on the front
page of this data sheet. The external component selection
is determined by the desired output voltage, input current
andripplevoltagerequirementsforeachparticularapplica-
tion. However, basic guidelines and considerations for the
design process are provided in this section.
Bꢀck-Boost Oꢀtpꢀt Voltage Programming
The buck-boost output voltage is set by a resistive divider
according to the following formula:
The inductor current ripple is typically set for 20% to
40% of the maximum inductor current. High frequency
ferrite core inductor materials reduce frequency depen-
dent power losses compared to cheaper powdered iron
types, improving efficiency. The inductor should have
low ESR (series resistance of the windings) to reduce the
I2R power losses, and must be able to support the peak
inductor current without saturating. Molded chokes and
somechipinductorsusuallydonothaveenoughcorearea
to support the peak inductor currents of 2.5A seen on
the LTC3127. To minimize radiated noise, use a shielded
inductor. See Table 1 and the reference schematics for
suggested components and suppliers.
R2
R1
VOUT =1.195V • 1+
V
The external divider is connected to the output as shown
inFigure3.Thebuck-boostconverterutilizesinputcurrent
mode control, and the output divider resistance does not
play a role in the stability.
1.8V b V
b 5.25V
OUT
R2
FB
LTC3127
GND
Table 1. Recommended Indꢀctors
R1
VENDOR
Coilcraft
847-639-6400
www.coilcraft.com
PART/STYLE
LPO2506
LPS4012, LPS4018
MSS6122
MSS4020
MOS6020
DS1605, DO1608
XPL4020
3127 F03
Figꢀre 3. Setting the Bꢀck-Boost Oꢀtpꢀt Voltage
Bꢀck-Boost Indꢀctor Selection
Coiltronics
SD52, SD53
To achieve high efficiency, a low ESR inductor should
be utilized for the buck-boost converter. The inductor
must have a saturation rating greater than the worst case
average inductor current plus half the ripple current.
The peak-to-peak inductor current ripple will be larger
in buck and boost mode than in the buck-boost region.
The peak-to-peak inductor current ripple for each mode
can be calculated from the following formulas, where L
is the inductance in μH:
www.cooperet.com
SD3114, SD3118
Murata
714-852-2001
www.murata.com
LQH55D
Sumida
847-956-0666
www.sumida.com
CDH40D11
Taiyo-Yuden
www.t-yuden.com
NP04SB
NR3015
NR4018
TDK
VLP, LTF
VLF, VLCF
VOUT (V − VOUT
)
IN
847-803-6100
www.component.tdk.com
∆IL,P−P,BUCK
=
(A)
V • L • (1.35MHz)
IN
Würth Elektronik
201-785-8800
www.we-online.com
WE-TPC Type S, M, MH
V (VOUT − V )
VOUT • L • (1.35MHz)
IN
IN
∆IL,P−P,BOOST
=
(A)
3127f
ꢀꢁ
LTC3127
applicaTions inForMaTion
Oꢀtpꢀt and Inpꢀt Capacitor Selection
The total output voltage droop is given by:
= V + V (V)
When selecting output capacitors for large pulsed loads,
the magnitude and duration of the pulse current, together
with the droop voltage specification, determine the choice
of the output capacitor. Both the ESR of the capacitor and
the charge stored in the capacitor each cycle contribute
to the output voltage droop. The droop due to the charge
is approximately:
V
DROOP
DROOP_LOAD
DROOP_ESR
HighcapacitancevaluesandlowESRcanleadtoinstability
in typical internally compensated buck-boost convert-
ers. Using proportional compensation, the LTC3127 is
stable with low ESR output capacitor values greater than
1000µF.
Multilayer ceramic capacitors are an excellent choice for
input decoupling of the step-up converter as they have
extremely low ESR and are available in small footprints.
Input capacitors should be located as close as possible to
the device. While a 10µF input capacitor is sufficient for
most applications, larger values may be used to improve
input decoupling without limitation. Consult the manufac-
turers directly for detailed information on their selection
of ceramic capacitors. Although ceramic capacitors are
recommended, low ESR tantalum capacitors may be used
as well.
VDROOP_LOAD
=
V •IIN(MAX) • h
IN
I
−
− I
• D • T
STANDBY
PULSE
VOUT
COUT
(V)
where
I
= pulsed load current
PULSE
I
I
= static load current in standby mode
STANDBY
IN(MAX)
When using a large capacitance to help with pulsed load
applications,themaximumloadforagivendutycycle,and
the minimum capacitance can be calculated by:
= programmed input current limit in amps
T = period of the load pulse
D = load pulse’s duty cycle
V •IIN(MAX) • h
IN
ILOAD(MAX)
=
(A)
V
= amount the output falls out of regulation in volts
DROOP
D • VOUT
h = the efficiency of the converter at the input current
limit point
COUT(MIN)
=
The preceding equation is a worst-case approximation
assuming all the pulsing energy comes from the output
capacitor.
V •IIN(MAX) • h
IN
I
−
−I
STANDBY
PULSE
VOUT
Thedroopduetothecapacitorequivalentseriesresistance
(ESR) is:
D • T
VDROOP
•
(F)
VDROOP_ESR
V •IIN(MAX) • h
IN
Table 2. Capacitor Vendor Information
= I
−
− I
• ESR (V)
STANDBY
PULSE
VOUT
SUPPLIER
Vishay
PHONE
WEB SITE
www.vishay.com
402-563-6866
803-448-9411
516-998-4100
843-267-0720
800-394-2112
AVX
www.avxcorp.com
www.cooperbussmann.com
www.cap-xx.com
Low ESR and high capacitance are critical to main-
taining low output droop. Table 2 and the Typical Applica-
tions schematics show a list of several reservoir capacitor
manufacturers.
Cooper Bussmann
CAP-XX
Panasonic
www.panasonic.com
3127f
ꢀꢂ
LTC3127
applicaTions inForMaTion
Capacitor Selection Example
Step 2: Calculate the minimum output capacitance re-
quired.
In this example, a pulsed load application requires that
V
droops less than 300mV. The application is a Li-Ion
OUT
3V • 500mA • 0.9
3.6V
COUT(MIN) ≥ 1.5A −
battery input to a 3.6V output. The pulsed load is a no-load
to a 1.5A step with a frequency of 217Hz and a duty cycle
of 12.5%. The input current limit is set to 500mA. In order
to meet the 300mV droop requirement, the amount of
0.125 • 4.6ms
•
= 2.15mF
300mV
capacitance must be calculated at the highest V to V
IN
OUT
Step 3: For this application a 2.2mF Vishay Tantamount
tantalum,lowESRcapacitorisselected.Thiscapacitorhas
a maximum ESR of 0.04Ω. With the selected capacitor,
the amount of droop must be calculated:
step-up ratio. All of the following calculations assume a
minimum V of 3V and an efficiency of 90%.
IN
Given the application, the following is known:
V = 3V
IN
VDROOP_LOAD
=
V
I
= 3.6V
OUT
3V • 500mA • 0.9
3.6V
= 500mA
1.5A −
− 0A • 0.125 • 4.6ms
IN(MAX)
I
I
= 1.5A
PULSE
2.2mF
= 0A
STANDBY
= 0.294V
h = 0.9
VDROOP_ESR
=
D = 0.125
T = 1/217Hz = 4.6ms
3V • 500mA • 0.9
3.6V
1.5A −
− 0A • 0.04Ω
V
= 300mV
DROOP
= 0.045V
Step 1: Check to make sure the application can provide
enough current to recover from the pulsed load using the
I
equation:
LOAD(MAX)
VDROOP = VDROOP_LOAD + VDROOP_ESR = 0.339V
3V • 500mA • 0.9
ILOAD(MAX)
=
= 3A
Due to the ESR of the capacitor, the total droop is greater
than 300mV. In this case, if the higher droop cannot be
accepted, a larger valued, lower ESR capacitor can be
selected.
0.125 • 3.6V
The maximum load that can be pulsed at this V to V
combination is 3A.
IN
OUT
3127f
ꢀꢃ
LTC3127
applicaTions inForMaTion
PCB Layoꢀt Considerations
venient way to achieve this is to short the pin directly
to the Exposed Pad as shown in Figure 4.
The LTC3127 switches large currents at high frequencies.
Special care should be given to the PCB layout to ensure
stable, noise-free operation. Figure 4 depicts the recom-
mended PCB layout to be utilized for the LTC3127. A few
key guidelines follow:
3. The components shown in bold and their connections
should all be placed over a complete ground plane.
4. To prevent large circulating currents from disrupting
the output voltage sensing, the ground for the resistor
1.Allcirculatinghighcurrentpathsshouldbekeptasshort
as possible. This can be accomplished by keeping the
routes to all bold components in Figure 4 as short and
as wide as possible. Capacitor ground connections
should via down to the ground plane in the shortest
divider and R
should be returned directly to the
PROG
small signal ground pin (SGND).
5. Use of vias in the die attach pad will enhance the ther-
mal environment of the converter especially if the vias
extend to a ground plane region on the exposed bottom
surface of the PCB.
route possible. The bypass capacitor on V should be
IN
placed as close to the IC as possible and should have
the shortest possible path to ground.
6. Keep the connections to the FB and PROG pins as
short as possible and away from the switch pin con-
nections.
2. The small-signal ground pad (SGND) should have a
single point connection to the power ground. A con-
VIA TO
GROUND
VIA TO
GROUND
SW1
SW2
10
1
V
C
OUT
V
9
8
7
6
2
IN
V
SHDN
3
PGND
MODE
PROG
4
5
FB
SGND
3127 F04
Figꢀre ±. Recommended PCB Layoꢀt
3127f
ꢀꢄ
LTC3127
Typical applicaTions
USB (500mA Max), 3.8V GSM Pꢀlsed Load
L1
4.7µH
SW1
SW2
V
V
OUT
IN
V
V
OUT
IN
3.8V
USB
MODE
PWM BURST
2.15M
1M
LTC3127
FB
C1
2.2mF
C2
2.2mF
OFF ON
SHDN
V
C
PROG
10µF
SGND
PGND
100pF
499k
32.4k
C1, C2: VISHAY TANTAMOUNT
TANTALUM, LOW ESR CAPACITORS
L1: COILCRAFT XPL4020-472ML
3127 TA02
PCMCIA/Compact Flash (3.3V or 5V/500mA Max), 3.8V GPRS, Class 10 Pꢀlsed Load
L1
4.7µH
SW1
SW2
V
IN
V
OUT
3.3V OR
5V
V
V
IN
OUT
3.8V
2.15M
1M
MODE
PWM BURST
OFF ON
LTC3127
FB
C3
2.2mF
SHDN
PROG
V
C
C2
2.2mF
10µF
SGND
PGND
C1
2.2mF
100pF
499k
32.4k
C1, C2, C3: VISHAY TANTAMOUNT
TANTALUM, LOW ESR CAPACITORS
L1: COILCRAFT XPL4020-472ML
3127 TA03
3127f
ꢀꢅ
LTC3127
Typical applicaTions
Stacked Sꢀpercapacitor Charger (1000mA Max Inpꢀt Cꢀrrent)
L1
4.7µH
SW1
SW2
V
V
V
OUT
5V
IN
V
OUT
IN
1.8V to 5.5V
PWM BURST
MODE
100k
3.16M
1M
C1
100F
LTC3127
FB
SHDN
OFF ON
V
C
PROG
10µF
100k
C2
100F
SGND
PGND
100pF
499k
60.4k
L1: COILCRAFT XPL4020-472ML
3127 TA04
General Pꢀrpose Forced Continꢀoꢀs Condꢀction Application with 500µs Start-Up
L1
4.7µH
SW1
SW2
V
V
OUT
3.3V
IN
V
V
IN
OUT
3V TO 4.3V
33pF
316k
182k
FB
MODE
SHDN
PROG
PWM BURST
OFF ON
LTC3127
V
C
22µF
s 2
10µF
SGND
PGND
47k
3300pF
60.4k
0.01µF
L1: COILCRAFT XPL4020-472ML
3127 TA05
3127f
ꢀꢆ
LTC3127
package DescripTion
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699 Rev B)
0.70 p0.05
3.55 p0.05
2.15 p0.05 (2 SIDES)
1.65 p0.05
PACKAGE
OUTLINE
0.25 p 0.05
0.50
BSC
2.38 p0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.125
0.40 p 0.10
TYP
6
10
3.00 p0.10
(4 SIDES)
1.65 p 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD) DFN REV B 0309
5
1
0.25 p 0.05
0.50 BSC
0.75 p0.05
0.200 REF
2.38 p0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
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
3127f
ꢀꢇ
LTC3127
package DescripTion
MSE Package
12-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1666 Rev B)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 p 0.102
(.112 p .004)
2.845 p 0.102
(.112 p .004)
0.889 p 0.127
(.035 p .005)
1
6
0.35
REF
5.23
(.206)
MIN
1.651 p 0.102
(.065 p .004)
3.20 – 3.45
(.126 – .136)
0.12 REF
DETAIL “B”
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
DETAIL “B”
12
4.039 p 0.102
7
NO MEASUREMENT PURPOSE
0.65
(.0256)
BSC
0.42 p 0.038
(.0165 p .0015)
(.159 p .004)
TYP
(NOTE 3)
0.406 p 0.076
RECOMMENDED SOLDER PAD LAYOUT
(.016 p .003)
12 11 10 9 8 7
REF
DETAIL “A”
0.254
(.010)
3.00 p 0.102
(.118 p .004)
(NOTE 4)
0o – 6o TYP
4.90 p 0.152
(.193 p .006)
GAUGE PLANE
0.53 p 0.152
(.021 p .006)
1
2 3 4 5 6
DETAIL “A”
0.86
(.034)
REF
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.1016 p 0.0508
(.004 p .002)
MSOP (MSE12) 0608 REV B
0.650
(.0256)
BSC
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
3127f
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.
ꢀꢈ
LTC3127
Typical applicaTion
Single Sꢀpercapacitor Charger (1000mA Max Inpꢀt Cꢀrrent)
L1
4.7µH
SW1
SW2
V
V
OUT
IN
V
V
OUT
IN
2.5V
1.8V TO 5V
1.05M
1M
MODE
PWM BURST
C1
100F
LTC3127
FB
SHDN
OFF ON
PROG
10µF
V
C
SGND
PGND
60.4k
C1: COOPER BUSSMANN POWERSTOR
B-SERIES, B1860-2R5107-R
L1: COILCRAFT XPL4020-472ML
100pF
499k
3127 TA06
relaTeD parTs
PART NUMBER
DESCRIPTION
COMMENTS
95% Efficiency, V : 1.8V to 5.5V, V
LTC3101
Wide V , 1MHz Multioutput DC/DC Converter and
: 1.8V to 5.25V, I = 35µA,
Q
IN
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
PowerPath™ Controller
I
< 1µA, 4mm × 4mm QFN-24 Package
SD
LTC3125
LTC3606B
LTC3440
1.2A I , 1.6MHz, Synchronous Boost DC/DC
94% Efficiency, V : 1.8V to 5.5V, V
= 5.25V, I = 15µA, I < 1µA,
Q SD
OUT
IN
Converter With Adjustable Input Current Limit
2mm × 3mm DFN-8 Package
800mA I , Synchronous Step-Down DC/DC
95% Efficiency, V : 2.5V to 5.5V, V
= 0.6V, I = 420µA, I < 1µA,
Q SD
OUT
IN
Converter with Average Input Current Limit
3mm × 3mm DFN-8 Package
600mA I , 2MHz, Synchronous Buck-Boost
95% Efficiency, V : 2.5V to 5.5V, V : 2.5V to 5.5V, I = 25µA,
IN OUT Q
OUT
DC/DC Converter
I
SD
< 1µA, 3mm × 3mm DFN-10 and MSOP-10 Packages
LTC3441/LTC3441-2/ 1.2A I , 2MHz, Synchronous Buck-Boost DC/DC
95% Efficiency, V : 2.4V to 5.5V, V : 2.4V to 5.25V, I = 50µA,
IN OUT Q
SD
OUT
LTC3441-3
Converter
I
< 1µA, 3mm × 4mm DFN-12 Package
LTC3520
1A 2MHz, Synchronous Buck-Boost and 600mA
Buck Converter
95% Efficiency, V : 2.2V to 5.5V, V
= 5.25V, I = 55µA, I < 1µA,
OUT(MAX) Q SD
IN
4mm × 4mm QFN-24 Package
LTC3530
LTC3532
LTC3533
LTC3538
LTC3534
600mA I , 2MHz, Synchronous Buck-Boost
95% Efficiency, V : 1.8V to 5.5V, V : 1.8V to 5.25V, I = 40µA,
IN OUT Q
SD
OUT
DC/DC Converter
I
< 1µA, 3mm × 3mm DFN-10 and MSOP-10 Packages
500mA I , 2MHz, Synchronous Buck-Boost
95% Efficiency, V : 2.4V to 5.5V, V : 2.4V to 5.25V, I = 35µA,
IN OUT Q
OUT
DC/DC Converter
I
SD
< 1µA, 3mm × 3mm DFN-10 and MSOP-10 Packages
2A I , 2MHz, Synchronous Buck-Boost DC/DC
95% Efficiency, V : 1.8V to 5.5V, V : 1.8V to 5.25V, I = 40µA,
IN OUT Q
OUT
Converter
I
SD
< 1µA, 3mm × 4mm DFN-14 Package
800mA I , 1MHz, Synchronous Buck-Boost
95% Efficiency, V : 2.4V to 5.5V, V : 1.8V to 5.25V, I = 35µA,
IN OUT Q
OUT
DC/DC Converter
I
SD
< 1µA, 2mm × 3mm DFN-8 Package
500mA I , 1MHz, Synchronous Buck-Boost
95% Efficiency, V : 2.4V to 7V, V : 1.8V to 2V, I = 25µA,
IN OUT Q
OUT
DC/DC Converter
I
SD
< 1µA, 3mm × 3mm DFN-16 and SSOP-16 Packages
3127f
LT 0210 • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
ꢁ0
●
●
LINEAR TECHNOLOGY CORPORATION 2010
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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Linear
LTC3129EUD#PBF
LTC3129 - 15V, 200mA Synchronous Buck-Boost DC/DC Converter with 1.3µA Quiescent Current; Package: QFN; Pins: 16; Temperature Range: -40°C to 85°C
Linear
LTC3129EUD-1#PBF
LTC3129-1 - 15V, 200mA Synchronous Buck-Boost DC/DC Converter with 1.3µA Quiescent Current; Package: QFN; Pins: 16; Temperature Range: -40°C to 85°C
Linear
LTC3130EMSE#PBF
LTC3130 - 25V, 600mA Buck-Boost DC/DC Converter with 1.6µA Quiescent Current; Package: MSOP; Pins: 16; Temperature Range: -40°C to 85°C
Linear
LTC3130EMSE#TRPBF
LTC3130 - 25V, 600mA Buck-Boost DC/DC Converter with 1.6µA Quiescent Current; Package: MSOP; Pins: 16; Temperature Range: -40°C to 85°C
Linear
LTC3130EMSE-1#PBF
LTC3130 - 25V, 600mA Buck-Boost DC/DC Converter with 1.6µA Quiescent Current; Package: MSOP; Pins: 16; Temperature Range: -40°C to 85°C
Linear
LTC3130EUDC#PBF
LTC3130 - 25V, 600mA Buck-Boost DC/DC Converter with 1.6µA Quiescent Current; Package: QFN; Pins: 20; Temperature Range: -40°C to 85°C
Linear
LTC3130EUDC#TRPBF
LTC3130 - 25V, 600mA Buck-Boost DC/DC Converter with 1.6µA Quiescent Current; Package: QFN; Pins: 20; Temperature Range: -40°C to 85°C
Linear
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