LTC3522EUD [Linear]
Synchronous 400mA Buck-Boost and 200mA Buck Converters; 同步400毫安降压 - 升压至200mA降压转换器
| 型号： | LTC3522EUD |
| 厂家： | 
Linear |
| 描述： | Synchronous 400mA Buck-Boost and 200mA Buck Converters |
| 文件： | 总20页 (文件大小：260K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3522
Synchronous 400mA
Buck-Boost and 200mA
Buck Converters
FEATURES
DESCRIPTION
TheLTC®3522combinesa400mAbuck-boostDC/DCcon-
verterwitha200mAsynchronousbuckDC/DCconverterin
atiny3mm×3mmpackage.The1MHzswitchingfrequency
minimizes the solution footprint while maintaining high
efficiency. Both converters feature internal soft-start and
compensation, simplifying the design process.
■
Dual High Efficiency DC/DC Converters:
Buck-Boost (V : 2.2V to 5.25V, I : 400mA
OUT
OUT
OUT
for V > 3V, V
= 3.3V)
IN
Buck (V : 0.6V to V , I : 200mA)
OUT
IN OUT
■
■
■
2.4V to 5.5V Input Voltage Range
Pin Selectable Burst Mode® Operation
25μA Total Quiescent Current for Both Converters in
Burst Mode Operation
The buck converter is current mode controlled and utilizes
an internal synchronous rectifier for high efficiency. The
buck converter supports 100% duty cycle operation to
extend battery life. If the PWM pin is held low, the buck
converterautomaticallytransitionsfromBurstModeopera-
tion to PWM mode. With the PWM pin held high, the buck
converter remains in low noise, 1MHz PWM mode.
■
■
■
■
■
Independent Power Good Indicator Outputs
Integrated Soft-Start
Thermal and Overcurrent Protection
<1ꢀA Quiescent Current in Shutdown
Small 0.75mm × 3mm × 3mm QFN Package
The buck-boost converter provides continuous conduc-
tion operation to maximize efficiency and minimize noise.
At light loads, the buck-boost converter can be placed in
Burst Mode operation to improve efficiency and reduce
no-load standby current.
APPLICATIONS
■
Flash-Based MP3 Players
■
Medical Instruments
■
Digital Cameras
PDAs, Handheld PCs
Personal Navigation Devices
■
■
The LTC3522 provides a 1μA shutdown mode, overtem-
perature shutdown and current limit protection on both
converters.TheLTC3522isavailableina16-pinlowprofile
3mm × 3mm QFN package.
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 6404251 and 6166527.
TYPICAL APPLICATION
Efficiency vs VIN
100
BUCK-BOOST
98
V
IN
I
= 100mA
OUT
OUT
2.4V TO 4.2V
96
94
92
90
88
86
84
82
80
78
76
74
72
70
+
V
= 3.3V
4.7μF
Li-Ion
L1
L2
PV
PV
IN2
8.2μH
4.7μH
IN1
BUCK
V
OUT2
1.8V
I
= 100mA
OUT
SW2
SW1A
SW1B
OUT
V
= 1.8V
200mA
6.8μF
V
137k
OUT1
12pF
LTC3522
3.3V
300mA
(400mA
V
FB2
V
OUT1
1M
4.7μF
SHDN2
SHDN1
68.1k
ON
> 3V)
IN
OFF
PWM
FB1
PGOOD2
PGOOD1
432k
BURST
PWM
PGND1 GND PGND2
4.4
3522 TA01a
2.4
3.4
5.4
L1: COILCRAFT MSS6132-8.2μH
L2: COILCRAFT MSS6132-4.7μH
V
(V)
IN
3522 TA01b
3522f
1
LTC3522
ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER INFORMATION
(Note 1)
TOP VIEW
PV , PV Voltage.................................... –0.3V to 6V
IN1
IN2
SW1A, SW1B, SW2 Voltage
DC............................................................ –0.3V to 6V
Pulsed < 100ns........................................... –1V to 7V
Voltage, All Other Pins ................................. –0.3V to 6V
Operating Temperature Range (Note 2) ... –40°C to 85°C
Maximum Junction Temperature (Note 5) ............ 125°C
Storage Temperature Range................... –65°C to 125°C
16 15 14 13
FB2
PWM
1
2
3
4
12
V
OUT1
11 SW1A
17
GND
SW1B
10
9
PGOOD2
PGND2
5
6
7
8
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
= 125°C, θ = 68°C/W
T
JMAX
JA
EXPOSED PAD (PIN 17) IS GND AND MUST BE SOLDERED TO PCB GROUND
ORDER PART NUMBER
UD PART MARKING
LCRQ
LTC3522EUD
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. PVIN1 = PVIN2 = 3.6V, VOUT1 = 3.3V unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
5.5
1
UNITS
V
●
●
Input Voltage
2.4
Quiescent Current—Shutdown
Burst Mode Quiescent Current
Oscillator Frequency
V
V
= V
= 0V
SHDN2
0.01
25
ꢀA
ꢀA
MHz
V
SHDN1
= 1.1V, V = 0.66V, V = 0V
PWM
FB1
FB2
●
0.8
1.4
1.07
1.33
SHDN1, SHDN2, PWM Input High Voltage
SHDN1, SHDN2, PWM Input Low Voltage
Power Good Outputs Low Voltage
Power Good Outputs Leakage
Buck Converter
0.4
0.1
10
V
I
= I
= 1mA
PGOOD2
0.02
0.1
V
PGOOD1
V
= V
= 5.5V
PGOOD2
ꢀA
PGOOD1
Ω
Ω
PMOS Switch Resistance
NMOS Switch Resistance
NMOS Switch Leakage
PMOS Switch Leakage
Feedback Voltage
0.41
0.34
0.1
V
V
= 5V, PV = PV = 5V
5
10
ꢀA
ꢀA
V
SW2
IN1
IN2
= 0V, PV = PV = 5V
0.1
SW2
IN1
IN2
●
(Note 4)
0.582
0.594
1
0.606
50
Feedback Input Current
Peak Current Limit
nA
mA
%
(Note 3)
300
100
400
●
●
Maximum Duty Cycle
V
V
= 0.54V
= 0.66V
FB2
Minimum Duty Cycle
0
%
FB2
3522f
2
LTC3522
ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. PVIN1 = PVIN2 = 3.6V, VOUT1 = 3.3V unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
–7.7
2.5
MAX
UNITS
%
PGOOD Threshold
V
Falling
–11.3
–4.1
FB2
Power Good Hysteresis
Buck-Boost Converter
Output Voltage
%
●
2.2
5.25
V
Ω
PMOS Switch Resistance
NMOS Switch Resistance
NMOS Switch Leakage
PMOS Switch Leakage
Feedback Voltage
0.29
0.22
0.1
0.1
1
Ω
V
V
= V
= V
= 5V, PV = PV = 5V
5
10
ꢀA
ꢀA
V
SW1A
SW1A
SW1B
SW1B
IN1
IN2
= 0V, PV = PV = 5V
IN1
IN2
●
(Note 4)
(Note 3)
(Note 3)
0.97
1.03
50
Feedback Input Current
Average Current Limit
Burst Mode Current Limit
Reverse Current Limit
Maximum Duty Cycle
Minimum Duty Cycle
PGOOD Threshold
1
nA
A
0.65
230
0.85
340
250
80
mA
mA
%
●
●
V
V
V
= 0.9V
70
FB1
FB1
FB1
= 1.1V
Falling
0
%
–12
–10
2.5
–8
%
Power Good Hysteresis
%
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3522 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 4: The LTC3522 is tested in a proprietary non-switching test mode
that connects each FB pin to the output of the respective error amplifier.
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 impair device reliability.
Note 3: Current measurements are performed when the LTC3522 is not
switching. The current limit values in operation will be somewhat higher
due to the propagation delay of the comparators.
3522f
3
LTC3522
(TA = 25°C unless otherwise noted)
Buck Efficiency, Li-Ion to 2.5V
TYPICAL PERFORMANCE CHARACTERISTICS
Buck-Boost Efficiency,
Li-Ion to 3.3V
160
140
120
100
80
100
90
160
100
90
Burst Mode
OPERATION
Burst Mode
OPERATION
140
120
100
80
80
70
60
80
70
60
PWM Mode
PWM Mode
50
40
50
40
Burst Mode
POWER LOSS
60
60
Burst Mode
V
V
= 3.7V
= 4.2V
IN
IN
30
20
10
0
30
20
10
0
POWER LOSS
V
V
= 4.2V
= 2.7V
40
40
IN
IN
L: COILCRAFT
MSS6132-8.2μH
20
20
L: COILCRAFT
MSS6132-4.7μH
0
1000
0
1000
1
100
10
1
100
10
LOAD CURRENT (mA)
LOAD CURRENT (mA)
3522 G02
3522 G01
Buck Burst Mode Threshold
Buck-Boost Switch RDS(0N)
Buck Efficiency, Li-Ion to 1.8V
50
45
40
35
30
25
20
15
10
5
400
350
300
250
200
150
100
50
100
90
160
140
120
100
80
Burst Mode
OPERATION
L = 4.7μH
PMOS
(SWITCHES A AND D)
80
70
60
V
= 1.2V
V
OUT
PWM Mode
= 1.8V
OUT
50
40
NMOS
(SWITCHES B AND C)
Burst Mode
60
POWER LOSS
V
= 2.5V
4.9
OUT
V
V
= 4.2V
= 2.7V
30
20
10
0
IN
IN
40
L: COILCRAFT
MSS6132-8.2μH
20
0
1000
0
0
2.4
3.4
3.9
(V)
4.4
5.4
2.9
40 60
TEMPERATURE (°C)
1
100
–40 –20
0
20
80 100 120
10
V
LOAD CURRENT (mA)
IN
3522 G04
3522 G03
3522 G05
Switching Frequency vs
Temperature
Buck Switch RDS(0N)
Switching Frequency vs VIN
600
10
8
10
8
500
400
300
200
100
0
6
6
PMOS
4
4
2
2
NMOS
0
0
–2
–4
–6
–8
–10
–2
–4
–6
–8
–10
40 60
20
TEMPERATURE (°C)
4.4
5.4
–40 –20
0
80 100 120
2.5
3.4
3.9
(V)
4.9
2.9
–50 –30 –10 10 30 50 70 90 110
V
TEMPERATURE (°C)
IN
3522 G06
3522 G08
3522 G07
3522f
4
LTC3522
(TA = 25°C unless otherwise noted)
TYPICAL PERFORMANCE CHARACTERISTICS
Buck-Boost Feedback Voltage vs
Temperature
Buck Feedback Voltage vs
Temperature
Buck-Boost Maximum Load
Current, Burst Mode Operation
0.5
0.4
90
80
70
60
50
40
30
20
10
0
0.5
0.4
L = 4.7μH
V
V
= 3V
= 5V
OUT
OUT
0.3
0.3
0.2
0.2
0.1
0.1
0
0
–0.1
–0.2
–0.3
–0.4
–0.5
–0.1
–0.2
–0.3
–0.4
–0.5
–40 –20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
3522 G09
–40 –20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
3522 G09
2.4
2.9
3.4
3.9
(V)
4.4
4.9
5.4
V
IN
3522 G11
Buck-Boost Maximum Load
Current, PWM Mode
No Load Quiescent Current
vs VIN
Buck-Boost Burst to PWM
Transition
600
500
400
300
200
100
0
50
45
40
35
30
25
20
15
10
5
L = 4.7μH
BOTH CONVERTERS ENABLED
INDUCTOR
CURRENT
200mA/DIV
V
= 3.3V
OUT
V
OUT
100mV/DIV
V
= 5V
OUT
3522 G14
V
V
= 3.6V
50μs/DIV
IN
OUT
= 3.3V
L = 4.7μH
= 4.7μF
C
OUT
0
2.4
3.4
3.9
(V)
4.4
4.9
5.4
2.4
2.9
3.4
3.9
(V)
4.4
4.9
5.4
2.9
V
V
IN
IN
3522 G12
3522 G13
Buck Load Step, PWM Mode,
5mA to 200mA
Buck Load Step, Burst Mode
Operation, 5mA to 200mA
Buck-Boost Load Step,
0mA to 300mA
V
V
V
OUT
OUT
OUT
100mV/DIV
100mV/DIV
100mV/DIV
INDUCTOR
CURRENT
100mA/DIV
INDUCTOR
CURRENT
100mA/DIV
INDUCTOR
CURRENT
200mA/DIV
3522 G16
3522 G15
3522 G17
V
V
= 3.6V
100μs/DIV
V
V
= 3.6V
= 3V
100μs/DIV
IN
OUT
IN
OUT
V
V
= 3.6V
100μs/DIV
IN
OUT
= 1.8V
= 1.8V
L = 4.7μH
= 4.7μF
L = 4.7μH
= 4.7μF
L = 4.7μH
= 4.7μF
C
C
OUT
OUT
C
OUT
3522f
5
LTC3522
PIN FUNCTIONS
FB2 (Pin 1): Feedback Voltage for the Buck Converter De-
rived from a Resistor Divider on the Buck Output Voltage.
The buck output voltage is given by the following equation
where R1 is a resistor between FB2 and ground and R2 is
a resistor between FB2 and the buck output voltage:
FB1 (Pin 5): Feedback Voltage for the Buck-Boost Con-
verter Derived from a Resistor Divider on the Buck-Boost
Output Voltage. The buck-boost output voltage is given
by the following equation where R1 is a resistor between
FB1 and ground and R2 is a resistor between FB1 and the
buck-boost output voltage:
R2
R1
⎛
⎝
⎞
⎠
VOUT = 0.594V 1+
⎜
⎟
R2
⎠
R1
⎛
⎝
⎞
VOUT = 1V 1+
⎜
⎟
PWM (Pin 2): Logic Input Used to Choose Between Burst
and PWM Mode Operation for Both Converters. This pin
cannot be left floating.
PGOOD1 (Pin 6): This pin is an open-drain output which
will only pull low if the buck-boost converter is enabled
and one or more of the following conditions occurs: the
buck-boost output voltage is out of regulation, the part is
in overtemperature shutdown, the part is in undervoltage
lockout or the buck-boost converter is in current limit. See
the Operation section of this data sheet for details on the
functionality of this pin in PWM mode.
PWM = Low: Burst Mode operation is enabled on both
converters. The buck converter will operate in Burst
Mode operation at light current but will automatically
transition to PWM operation at higher currents. The
buck converter can supply its maximum output current
(200mA) in this mode. The buck-boost converter will
operateinvariablefrequencymodeandcanonlysupply
a reduced load current (typically 50mA).
SHDN1 (Pin 7): Buck-Boost Active-Low Shutdown Pin.
Forcing this pin above 1.4V enables the buck-boost con-
verter.Forcingthispinbelow0.4Vdisablesthebuck-boost
converter. This pin cannot be left floating.
PWM = High: Both converters are forced into low noise
1MHz PWM mode operation. The buck converter will
remain at constant frequency operation until its mini-
mumon-timeisreached. Thebuck-boostconverterwill
remain in PWM mode at all load currents.
PV (Pin8):HighCurrentPowerSupplyConnectionUsed
IN1
to Supply Switch A of the Buck-Boost Converter. This pin
shouldbebypassedbya4.7μForlargerceramiccapacitor.
The bypass capacitor should be placed as close to the pin
as possible and should have a short return path to ground.
GND (Pin 3): Small-Signal Ground Used as a Ground
Reference for the Internal Circuitry of the LTC3522.
Pins PV and PV must be connected together in the
IN1
IN2
PGOOD2 (Pin 4): This pin is an open-drain output which
will only pull low if the buck converter is enabled and one
ormoreofthefollowingconditionsoccurs:thebuckoutput
voltage is out of regulation, the part is in overtemperature
shutdown or the part is in undervoltage lockout.
application circuit.
PGND2 (Pin 9): High Current Ground Connection for the
Buck-BoostSwitchC. ThePCBtraceconnectingthispinto
ground should be made as short and wide as possible.
3522f
6
LTC3522
PIN FUNCTIONS
PV (Pin 15): High Current Power Supply Connection
SW1B (Pin 10): Buck-Boost Switch Node That Must be
IN2
Used to Supply the Buck Converter Power Switch. In ad-
dition this pin is the supply pin for the internal circuitry of
the LTC3522. This pin should be bypassed by a 4.7μF or
larger ceramic capacitor. The bypass capacitor should be
placed as close to the pin as possible and should have a
Connected to One Side of the Buck-Boost Inductor.
SW1A (Pin 11): Buck-Boost Switch Node That Must be
Connected to One Side of the Buck-Boost Inductor.
V
(Pin12):Buck-BoostOutputVoltageNode. Thispin
OUT1
should be connected to a low ESR output capacitor. The
capacitor should be placed as close to the IC as possible
and should have a short return to ground.
short return path to ground. Pins PV and PV must
IN1
IN2
be connected together in the application circuit.
SHDN2 (Pin 16): Buck Active-Low Shutdown Pin. Forcing
this pin above 1.4V enables the buck converter. Forcing
this pin below 0.4V disables the buck converter. This pin
cannot be left floating.
PGND1 (Pin 13): High Current Ground Connection for
Buck-BoostSwitchBandtheBuckConverterSynchronous
Rectifier. The PCB trace connecting this pin to ground
should be made as short and wide as possible.
Exposed Pad (Pin 17): The Exposed Pad must be electri-
cally connected to ground. Pins PGND1, PGND2, GND,
and the Exposed Pad must be connected together in the
application circuit.
SW2 (Pin 14): Buck Converter Switch Node That Must be
Connected to the Buck Inductor.
3522f
7
LTC3522
BLOCK DIAGRAM
8
11
10
12
PV
*
SW1A SW1B
V
OUT1
IN1
FILTER
PGOOD1
6
+
–
0.9V
+
–
A
D
0.85A
+
0.250A
0A
–
B
C
+
–
I
ZERO
V
OUT1
PGND1 PGND2
FB1
BUCK-BOOST
PWM
–
+
+
GATE
DRIVES
5
1.00V
LOGIC
SOFT-START
RAMP
SHDN1
PWM
7
2
PV
IN2
*
OSCILLATOR
UVLO
INTERNAL
CC
15
14
V
SW2
GATE
DRIVES
BUCK
PWM
LOGIC
SHDN2
16
PGND1
0A
+
–
ZERO CROSSING
1.00V
I
+
–
LIMIT
BANDGAP
0.594V
REFERENCE
AND OT
0.4A
SLOPE
COMPENSATION
0.9V
0.548V
SHUTDOWN
+
g
m
+
–
FB2
–
1
+
0.594V
+
PGOOD2
4
SOFT-START
RAMP
0.548V
+
–
GND
3
PGND1
13
PGND2
9
3522 BD
*PV AND PV MUST BE CONNECTED TOGETHER IN THE APPLICATION.
IN1
IN2
3522f
8
LTC3522
OPERATION
Characteristics section of this data sheet. Under dropout
and near dropout conditions, Burst Mode operation will
not be entered.
The LTC3522 combines a synchronous buck DC/DC
converter and a 4-switch buck-boost DC/DC converter
in a single 3mm × 3mm QFN 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 voltage. The buck converter provides a
high efficiency lower voltage output and supports 100%
duty cycle operation to extend battery life. In Burst Mode
operation, the combined quiescent current for both con-
verters is reduced to 25μA. Both converters operate from
the same internal 1MHz oscillator.
Dropout Operation
As the input voltage decreases to a value approaching the
output regulation voltage, the duty cycle increases toward
the maximum on-time. Further reduction of the supply
voltage will force the main switch to remain on for more
than one cycle until 100% duty cycle operation is reached
where the main switch remains on continuously. In this
dropout state, the output voltage will be determined by
the input voltage less the resistive voltage drop across the
main switch and series resistance of the inductor.
BUCK CONVERTER OPERATION
PWM Mode Operation
Slope Compensation
When the PWM pin is held high, the LTC3522 buck con-
verter uses a constant frequency, current mode control
architecture. Both the main (P-channel MOSFET) and
synchronous rectifier (N-channel MOSFET) switches are
internal. At the start of each oscillator cycle, the P-chan-
nel switch is turned on and remains on until the current
waveform with superimposed slope compensation ramp
exceeds the error amplifier output. At this point, the syn-
chronous rectifier is turned on and remains on until the
inductor current falls to zero or a new switching cycle is
initiated. As a result, the buck converter operates with
discontinuous inductor current at light loads which im-
proves 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 in order
to maintain regulation.
Currentmodecontrolrequirestheuseofslopecompensa-
tion to prevent sub-harmonic oscillations in the inductor
current waveform at high duty cycle operation. This is ac-
complishedinternallyontheLTC3522throughtheaddition
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 LTC3522 performs cur-
rent limiting prior to addition of the slope compensation
ramp and therefore achieves a peak inductor current limit
that is independent of duty cycle.
Short-Circuit Protection
When the output is shorted to ground, the error amplifier
will saturate high and the P-channel MOSFET switch will
turn on at the start of each cycle and remain on until the
current limit trips. During this minimum on-time, the in-
ductor current will increase rapidly and will decrease very
slowly during the remainder of the period due to the very
small reverse voltage produced by a hard output short.
To eliminate the possibility of inductor current runaway
in this situation, the buck converter switching frequency
is reduced to approximately 250kHz when the voltage on
FB2 falls below 0.3V.
Burst Mode Operation
When the PWM pin is forced low, the buck converter will
automatically transition between Burst Mode operation
at sufficiently light loads (below approximately 10mA)
and PWM mode at heavier loads. Burst Mode entry is
determined by the peak inductor current and therefore
the load current at which Burst Mode operation will be
entered depends on the input voltage, the output voltage
and the inductor value. Typical curves for Burst Mode
entry threshold are provided in the Typical Performance
3522f
9
LTC3522
OPERATION
Soft-Start
L
Thebuckconverterhasaninternalvoltagemodesoft-start
circuit with a nominal duration of 600μs. The converter
remains in regulation during soft-start and will therefore
respond to output load transients which occur during
this time. In addition, the output voltage rise time has
minimal dependency on the size of the output capacitor
or load current.
PV
SW1A
SW1B
V
OUT1
IN1
A
D
B
C
LTC3522
PGND1
PGND2
3522 F01
Figure 1. Buck-Boost Switch Topology
Error Amplifier and Compensation
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 modu-
lated 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, the AC switch pair remains on for longer durations
andthedurationoftheBDphasedecreasesproportionally.
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 phase. At this point, switch A remains on
continuously while switch pair CD is pulse width modu-
lated to obtain the desired output voltage. At this point,
the converter is operating solely in boost mode.
The LT3522 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.
PGOOD2 Comparator
The PGOOD2 pin is an open-drain output which indicates
the status of the buck converter. If the buck output volt-
age falls 7.7% below the regulation voltage, the PGOOD2
open-drain output will pull low. The output voltage must
rise2.5%abovethefallingthresholdbeforethepull-down
will turn off. In addition, there is a 60μs typical deglitch-
ing delay in the flag in order to prevent false trips due
to voltage transients on load steps. The PGOOD2 output
will also pull low during overtemperature shutdown and
undervoltage lockout to indicate these fault conditions.
The PGOOD2 output is only active if the buck converter
is enabled.
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.
BUCK-BOOST CONVERTER OPERATION
PWM Mode Operation
When the PWM pin is held high, the LTC3522 buck-boost
converteroperatesinaconstantfrequencyPWMmodewith
voltage mode control. A proprietary switching algorithm
allows the converter to switch between buck, buck-boost
and boost modes without discontinuity in inductor cur-
rent or loop characteristics. The switch topology for the
buck-boost converter is shown in Figure 1.
Error Amplifier and Compensation
The buck-boost converter utilizes a voltage mode error
amplifierwithaninternalcompensationnetworkasshown
in Figure 2.
Notice that resistor R2 of the external resistor divider
networkplaysanintegralroleindeterminingthefrequency
3522f
10
LTC3522
OPERATION
current limit will have a dependency on the duty cycle
(i.e., on the input and output voltages in the overcurrent
condition).
LTC3522
V
OUT1
V
OUT
1V
+
–
R2
R1
The speed of the average current limit circuit is limited by
thedynamicsoftheerroramplifier.Onahardoutputshort,
it would be possible for the inductor current to increase
substantially beyond current limit before the average cur-
rent limit circuit would react. For this reason, there is a
second current limit circuit which turns off switch A if the
current ever exceeds approximately 165% of the average
current limit value. This provides additional protection in
the case of an instantaneous hard output short.
FB1
GND
3522 F02
Figure 2. Buck-Boost Error Amplifier and Compensation
response of the compensation network. The ratio of R2 to
R1 must be set to program the desired output voltage but
this still allows the value of R2 to be adjusted to optimize
thetransientresponseoftheconverter.Increasingthevalue
of R2 generally leads to greater stability at the expense of
reduced transient response speed. Increasing the value of
R2canyieldsubstantialtransientresponseimprovementin
caseswherethephasemarginhasbeenreducedduetothe
use of a small value output capacitor or a large inductance
(particularly with large boost step-up ratios). Conversely,
decreasing the value of R2 increases the loop bandwidth
which can improve the speed of the converter’s transient
response. This can be useful in improving the transient
response if a large valued output capacitor is utilized. In
this case, the increased bandwidth created by decreasing
R2 is used to counteract the reduced converter bandwidth
caused by the large output capacitor.
Reverse Current Limit
The reverse current comparator on switch D monitors
the inductor current entering V
exceeds 250mA (typical) switch D will be turned off for
the remainder of the switching cycle.
. When this current
OUT1
Burst Mode Operation
With the PWM pin held low, the buck-boost converter
operatesutilizingavariablefrequencyswitchingalgorithm
designed to improve efficiency at light load and reduce
the standby current at zero load. In Burst Mode operation,
the inductor is charged with fixed peak amplitude current
pulses. These current pulses are repeated as often as
necessary to maintain the output regulation voltage. The
typicaloutputcurrentwhichcanbesuppliedinBurstMode
operaton is dependent upon the input and output voltage
as given by the following formula:
Current Limit Operation
0.11• V
IN
The buck-boost converter has two current limit circuits.
The primary current limit is an average current limit circuit
which injects an amount of current into the feedback node
which is proportional to the extent that the switch A cur-
rent exceeds the current limit value. Due to the high gain
of this loop, the injected current forces the error amplifier
outputtodecreaseuntiltheaveragecurrentthroughswitch
A decreases approximately to the current limit value. The
average current limit utilizes the error amplifier in an ac-
tive state and thereby provides a smooth recovery with
little overshoot once the current limit fault condition is
removed. Since the current limit is based on the average
current through switch A, the peak inductor current in
IOUT(MAX),BURST
=
A
( )
V + VOUT
IN
InBurstModeoperation,theerroramplifierisnotusedbut
is instead placed in a low current standby mode to reduce
supply current and improve light load efficiency.
Soft-Start
The buck-boost converter has an internal voltage mode
soft-start circuit with a nominal duration of 600μs. The
converter remains in regulation during soft-start and will
therefore respond to output load transients that occur
during this time. In addition, the output voltage rise time
3522f
11
LTC3522
OPERATION
has minimal dependency on the size of the output capaci-
tor or load. During soft-start, the buck-boost converter is
forced into PWM operation regardless of the state of the
PWM pin.
In such cases, the occurrence of current limit will cause
the PGOOD1 flag to fall indicating a fault state. There can
be cases, however, when the buck-boost converter is
continuously in current limit, causing the PGOOD1 output
to pull low, but the output voltage still remains slightly
above the PGOOD1 comparator trip point.
PGOOD1 Comparator
The PGOOD1 pin is an open-drain output which indicates
the status of the buck-boost converter. In Burst Mode
operation (PWM = Low), the PGOOD1 open-drain output
will pull low when the output voltage falls 10% below the
regulationvoltage.Thereisapproximately2.5%hysteresis
inthisthresholdwhentheoutputvoltageisreturninggood.
In addition, there is a 60μs typical deglitching delay to
prevent false trips due to short duration voltage transients
in response to load steps.
ThePGOOD1outputalsopullslowduringovertemperature
shutdown and undervoltage lockout. The PGOOD1 output
is only active if the buck-boost converter is enabled.
COMMON FUNCTIONS
Thermal Shutdown
If the die temperature exceeds 150°C (typical) both con-
verters 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 are reset during
thermal shutdown to provide a smooth recovery once the
overtemperature condition is eliminated. Both converters
will restart (if enabled) when the die temperature drops to
approximately 140°C.
In PWM mode, operation of the PGOOD1 comparator is
complicated by the fact that the feedback pin voltage is
driven to the reference voltage independent of the output
voltage through the action of the voltage mode error am-
plifier. Since the soft-start is voltage mode, the feedback
voltage will track the output voltage correctly during
soft-start, and the PGOOD1 output will correctly indicate
the point at which the buck-boost attains regulation at the
end of soft-start. Therefore, the PGOOD1 output can be
utilized for sequencing purposes. Once in regulation, the
feedback voltage will no longer track the output voltage
and the PGOOD1 pin will not directly respond to a loss
of regulation in the output. However, the only means
by which a loss of regulation can occur is if the current
limit has been reached thereby preventing the buck-boost
converter from delivering the required output current.
Undervoltage Lockout
If the supply voltage decreases below 2.3V (typical) then
both converters will be disabled and all power devices will
be turned off. The soft-start circuits for both converters
are reset during undervoltage lockout to provide a smooth
restartoncetheinputvoltagerisesabovetheundervoltage
lockout threshold.
3522f
12
LTC3522
APPLICATIONS INFORMATION
The basic LTC3522 application circuit is shown as the
typical application on the front page of this data sheet.
The external component selection is determined by the
desiredoutputvoltages,outputcurrentsandripplevoltage
requirementsofeachparticularapplication.However,basic
guidelines and considerations for the design process are
provided in this section.
the inductance value must be at least L
the following equation:
as given by
MIN
L
= 2.5 • V
(ꢀH)
MIN
OUT
Table 1 depicts the minimum required inductance for
several common output voltages.
Table 1. Buck Minimum Inductance
OUTPUT VOLTAGE
MINIMUM INDUCTANCE
Buck Inductor Selection
0.6V
0.8V
1.2V
2.0V
2.7V
3.3V
1.5μH
2.0μH
3.0μH
5.0μH
6.8μH
8.3μH
The choice of buck inductor value influences both the ef-
ficiency 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,
thereby offsetting this efficiency advantage.
Buck Output Capacitor Selection
A low ESR output capacitor should be utilized at the buck
output in order to minimize voltage ripple. Multi-layer
ceramic capacitors are an excellent choice as they have
low ESR and are available in small footprints. In addition
to controlling the ripple magnitude, the value of the output
capacitoralsosetstheloopcrossoverfrequencyandthere-
forecanimpactloopstability.Thereisbothaminimumand
maximumcapacitancevaluerequiredtoensurestabilityof
the loop. If the output capacitance is too small, the loop
cross-over 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
addition, the wider bandwidth produced by a small output
capacitor will make the loop more susceptible to switch-
ing noise. At the other extreme, if the output capacitor is
too large, the cross-over frequency can decrease too far
below the compensation zero and also lead to degraded
phase margin. Table 2 provides a guideline for the range
of allowable values of low ESR output capacitors. Larger
value output capacitors can be accommodated provided
they have sufficient ESR to stabilize the loop or by increas-
ing the value of the feedforward capacitor in parallel with
the upper resistor divider resistor.
Givenadesiredpeaktopeakcurrentripple,ΔI ,therequired
L
inductance can be calculated via the following expression,
where f represents the switching frequency in MHz:
⎛
⎞
VOUT
1
fΔIL
L =
VOUT 1–
μH
( )
⎜
⎝
⎟
V
⎠
IN
AreasonablechoiceforripplecurrentisΔI =80mAwhich
L
represents40%ofthemaximum200mAloadcurrent. The
DC current rating of the inductor should be at least equal
to the maximum load current plus half the ripple current
in order to prevent core saturation and loss of efficiency
duringoperation.Tooptimizeefficiencytheinductorshould
have a low series resistance.
In particularly space restricted applications it may be
advantageous to use a much smaller value inductor at
the expense of larger ripple current. In such cases, the
converter will operate in discontinuous conduction for a
wider range of output loads and efficiency will be reduced.
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%,
3522f
13
LTC3522
APPLICATIONS INFORMATION
Table 3. Buck Resistor Divider Values
Table 2. Buck Output Capacitor Range
V
R1
R2
0
C
FF
V
C
C
MAX
OUT
OUT
MIN
0.6V
0.8V
1.0V
1.2V
1.5V
1.8V
2.7V
3.3V
–
–
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
200k
118k
100k
78.7k
68.1k
63.4k
60.4k
69.8k
80.6k
102k
121k
137k
226k
274k
12pF
12pF
12pF
12pF
12pF
18pF
20pF
70μF
50μF
Buck Input Capacitor Selection
The PV pin provides current to the buck converter
IN2
Buck-Boost Output Voltage Programming
power switch and is also the supply pin for the IC’s inter-
nal circuitry. It is recommended that a low ESR ceramic
capacitor with a value of at least 4.7ꢀF 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.
The buck-boost output voltage is set by a resistive divider
according to the following formula:
R2
⎠
R1
⎛
⎝
⎞
VOUT = 1V 1+
⎜
⎟
Buck Output Voltage Programming
The external divider is connected to the output as shown
in Figure 4. The buck-boost converter utilizes voltage
mode control and the value of R2 plays an integral role
in the dynamics of the feedback loop. In general, a larger
value for R2 will increase stability and reduce the speed of
the transient response. A smaller value of R2 will reduce
stabilitybutincreasethetransientresponsespeed.Agood
starting point is to choose R2 = 1M, and then calculate
the required value of R1 to set the desired output voltage
according to the formula given above. If a large output
capacitorisused,thebandwidthoftheconverterisreduced.
In such cases R2 can be reduced to improve the transient
The output voltage is set by a resistive divider according
to the following formula:
R2
⎠
R1
⎛
⎝
⎞
VOUT = 0.594V 1+
⎜
⎟
Theexternaldividerisconnectedtotheoutputasshownin
Figure 3. It is recommended that a feedforward capacitor,
C ,beplacedinparallelwithresistorR2inordertoimprove
FF
the noise immunity of the feedback node. Table 3 provides
the recommended resistor and feedforward capacitor
combinations for common output voltage options.
2.2V ≤ V
≤ 5.25V
OUT
0.6V ≤ V
≤ 5.25V
OUT
R2
R2
C
FF
FB1
FB2
LTC3522
LTC3522
R1
R1
GND
GND
3522 F04
3522 F03
Figure 4. Setting the Buck-Boost Output Voltage
Figure 3. Setting the Buck Output Voltage
3522f
14
LTC3522
APPLICATIONS INFORMATION
response. If a large inductor or small output capacitor is
utilized the loop will be less stable and the phase margin
can be improved by increasing the value of R2.
Neglecting the capacitor ESR and ESL, the peak-to-peak
output voltage ripple can be calculated by the following
formulas, where f is the frequency in MHz, C
is the
OUT
capacitance in μF, L is the inductance in μH and I
is
LOAD
Buck-Boost Inductor Selection
the output current in Amps:
To achieve high efficiency, a low ESR inductor should be
utilized for the buck-boost converter. The inductor must
haveasaturationratinggreaterthantheworstcaseaverage
inductor current plus half the ripple current. The peak-to-
peakinductorcurrentripplewillbelargerinbuckandboost
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 f is the frequency in
MHz and L is the inductance in μH:
ILOAD VOUT – V
IN
COUT • VOUT • f
(
)
ΔVP-P(BOOST)
=
V – V
V
(
)
1
8 •L •COUT • f2
IN
OUT OUT
ΔVP-P(BUCK)
=
•
V
IN
Since the output current is discontinuous in boost mode,
the ripple in this mode will generally be much larger than
the magnitude of the ripple in buck mode. In addition to
controlling the ripple magnitude, the value of the output
capacitoralsoaffectsthelocationoftheresonantfrequency
in the open loop converter transfer function. If the output
capacitor is too small, the bandwidth of the converter
will extend high enough to degrade the phase margin.
To prevent this from happening, it is recommended that
a minimum value of 4.7μF be used for the buck-boost
output capacitor.
VOUT V – V
(
)
1
fL
IN
OUT
ΔIL,P-P,BUCK
=
•
V
IN
V VOUT – V
(
)
1
fL
IN
IN
ΔIL,P-P,BOOST
=
•
VOUT
In addition to affecting output current ripple, the size of
the inductor can also affect the stability of the feedback
loop. In boost mode, the converter transfer function has
a right half plane zero at a frequency that is inversely
proportional to the value of the inductor. As a result, a
large inductor can move this zero to a frequency that is
low enough to degrade the phase margin of the feedback
loop. It is recommended that the inductor value be chosen
less than 10μH if the buck-boost converter is to be used
in the boost region.
Buck-Boost Input Capacitor Selection
Thesupplycurrenttothebuck-boostconverterisprovided
bythePV pin.ItisrecommendedthatalowESRceramic
IN1
capacitor with a value of at least 4.7μF be located as close
to this pin as possible.
Inductor Style and Core Material
Differentinductorcorematerialsandstyleshaveanimpact
on the size and price of an inductor at any given peak
current rating. Toroid or shielded pot cores in ferrite or
permalloy materials are small and reduce emissions, but
generallycostmorethanpowderedironcoreinductorswith
similar electrical characteristics. The choice of inductor
styledependsupontheprice,sizing,andEMIrequirements
of a particular application. Table 4 provides a sampling
Buck-Boost Output Capacitor Selection
A low ESR output capacitor should be utilized at the buck-
boostconverteroutputinordertominimizeoutputvoltage
ripple. Multi-layer ceramic capacitors are an excellent
choice as they have low ESR and are available in small
footprints. The capacitor should be chosen large enough
to reduce the output voltage ripple to acceptable levels.
3522f
15
LTC3522
APPLICATIONS INFORMATION
of inductors that are well suited to many LTC3522 buck
converter applications.
PCB Layout Considerations
The LTC3522 switches large currents at high frequencies.
Special care should be given to the PCB layout to ensure
stable, noise-free operation. Figure 5 depicts the recom-
mended PCB layout to be utilized for the LTC3522. A few
key guidelines follow:
Table 4. Representative Surface Mount Inductors
MAX
MANUFACTURER PART NUMBER VALUE CURRENT DCR HEIGHT
Taiyo Yuden
NP035B-4R7M 4.7μH
NP035B-6R8M 6.8μH
MSS6132-472ML 4.7μH
MSS6132-822ML 8.2ꢀH
1.2A
1.0A
1.8A
0.047Ω 1.8mm
0.084Ω 1.8mm
0.056Ω 3.2mm
1. Allcirculatinghighcurrentpathsshouldbekeptasshort
as possible. This can be accomplished by keeping the
routes to all bold components in Figure 5 as short and
as wide as possible. Capacitor ground connections
should via down to the ground plane in the shortest
Coilcraft
1.35A 0.070Ω 3.2mm
Sumida
CDRH2D14NP- 4.7ꢀH
4R7N
1.0A
1.2A
0.9A
0.135Ω 1.55mm
0.110Ω 2.0mm
0.08Ω 1.8mm
CDRH2D18/
HPNP-4R7N
4.7ꢀH
route possible. The bypass capacitors on PV and
IN1
CDRH3D16NP- 4.7ꢀH
4R7N
PV shouldbeplacedasclosetotheICaspossibleand
IN2
should have the shortest possible paths to ground.
Cooper-
Bussmann
SD18-4R7
SD10-4R7
4.7ꢀH
4.7μH
1.54A 0.082Ω 1.8mm
1.08A 0.153Ω 1.0mm
2. Thesmall-signalgroundpad(GND)shouldhaveasingle
point connection to the power ground. A convenient
way to achieve this is to short the pin directly to the
Exposed Pad as shown in Figure 5.
Capacitor Vendor Information
BoththeinputandoutputcapacitorsusedwiththeLTC3522
must be low ESR and designed to handle the large AC cur-
rents generated by switching converters. The vendors in
Table 5 provide capacitors that are well suited to LTC3522
application circuits.
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
theoutputvoltagesensing, thegroundforeachresistor
divider should be returned directly to the small signal
ground pin (GND).
Table 5. Capacitor Vendor Information
REPRESENTATIVE PART
MANUFACTURER WEB SITE
NUMBERS
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.
Taiyo Yuden
TDK
www.t-yuden.com JMK107BJ105MA 4.7μF, 6.3V
www.component.
tdk.com
C2012X5R0J475K 4.7μF, 6.3V
GRM219R61A475K 4.7ꢀF
Murata
AVX
www.murata.com
6. Keep the connection from the resistor dividers to the
feedback pins FB1 and FB2 as short as possible and
away from the switch pin connections.
www.avxcorp.com SM055C475KHN480 4.7μF
3522f
16
LTC3522
APPLICATIONS INFORMATION
KELVIN TO
PAD
V
OUT
BUCK
V
OUT
UNINTERRUPTED GROUND PLANE MUST
EXIST UNDER ALL COMPONENTS
SHOWN IN BOLD AND UNDER TRACES
CONNECTING TO THOSE COMPONENTS
VIA TO
GROUND PLANE
MINIMIZE
TRACE
LENGTH
BUCK-BOOST
OUT
V
FB2
(1)
V
OUT1
(12)
KELVIN TO
PAD
V
DIRECT TIE
OUT
PWM
(2)
SW1A
(11)
BACK TO
GND PIN
GND
(3)
SW1B
(10)
VIA TO
GROUND
PLANE
PGOOD2
(4)
PGND2
(9)
MINIMIZE
TRACE
LENGTH
3522 F05
Figure 5. LTC3522 Recommended PCB Layout
3522f
17
LTC3522
TYPICAL APPLICATION
Li-Ion to 3V at 400mA and 1.2V at 200mA
V
IN
2.4V TO 4.2V
+
C3
4.7μF
Li-Ion
L2
4.7μH
L1
6.8μH
PV
PV
IN2
IN1
V
OUT2
1.2V
SW2
SW1A
SW1B
C1
10μF
200mA
12pF
499k
102k
100k
V
OUT1
LTC3522
COMBINED
PGOOD
OUTPUT
3V
FB2
V
OUT1
300mA
C2
4.7μF
1M
(400mA, V > 3V)
IN
FB1
SHDN2
SHDN1
499k
PGOOD2
PGOOD1
ON
OFF
PWM
BURST
PWM
PGND1 GND1 PGND2
3522 TA02
C1: MURATA GRM219R61A475K (0805 PACKAGE)
C2, C3: MURATA GRM21BR60J106K (0805 PACKAGE)
L1: TAIYO YUDEN NPO35B-6R8M
L2: TAIYO YUDEN NPO35B-4R7M
Buck-Boost Converter Efficiency vs Load Current
Buck Converter Efficiency vs Load Current
100
100
Burst Mode
90
90
Burst Mode
OPERATION
OPERATION
80
80
70
70
60
PWM Mode
PWM Mode
60
50
40
50
40
30
20
V
V
= 4.2V
= 2.7V
V
V
= 4.2V
= 2.7V
IN
IN
IN
IN
30
1
100
10
LOAD CURRENT (mA)
1000
1
100
10
LOAD CURRENT (mA)
1000
3522 TA02b
3522 TA02c
3522f
18
LTC3522
PACKAGE DESCRIPTION
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691)
0.70 0.05
3.50 0.05
2.10 0.05
1.45 0.05
(4 SIDES)
PACKAGE OUTLINE
0.25 0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 × 45° CHAMFER
R = 0.115
TYP
0.75 0.05
3.00 0.10
(4 SIDES)
15 16
PIN 1
TOP MARK
(NOTE 6)
0.40 0.10
1
2
1.45 0.10
(4-SIDES)
(UD16) QFN 0904
0.200 REF
0.25 0.05
0.50 BSC
0.00 – 0.05
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
3522f
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.
19
LTC3522
TYPICAL APPLICATION
3V at 400mA and 1.8V at 200mA with Sequenced Start-Up
V
IN
2.4V TO 4.2V
+
C3
4.7μF
Li-Ion
L2
4.7μH
L1
8.2μH
PV
PV
IN1
IN2
SW1A
SW1B
V
OUT2
1.8V
SW2
C1
6.8μF
200mA
12pF
499k
137k
V
OUT1
LTC3522
3V
FB2
V
OUT1
FB1
300mA
(400mA, V > 3V)
C2
4.7μF
1M
IN
68.1k
499k
PGOOD1
PGOOD1
PWM
ON
PWM
SHDN2
PGOOD2
SHDN1
OFF
BURST
499k
C1: TDK C3216X5R0J685M
PGND1 GND1 PGND2
3522 TA03A
C2, C3: TAIYO YUDEN JMK212BJ106MG
L1: COOPER BUSSMANN SD18-8R2
L2: COOPER BUSSMANN SD18-4R7
Sequenced Start-Up Waveforms
V
OUT2
1V/DIV
V
OUT1
2V/DIV
PGOOD2
5V/DIV
PGOOD1
5V/DIV
3522 TA03b
200μs/DIV
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC3410/LTC3410B 300mA (I ), 2.25MHz Synchronous Buck DC/DC Converter V : 2.5V to 5.5V, V
= 0.8V to V , I = 26ꢀA, I < 1ꢀA,
IN Q SD
OUT
IN
OUT(RANGE)
OUT(RANGE)
OUT(RANGE)
OUT(RANGE)
SC70 Package
LTC3440
LTC3441
LTC3442
LTC3455
LTC3456
LTC3530
LTC3532
600mA (I ), 2MHz Synchronous Buck-Boost
V : 2.5V to 5.5V, V
= 2.5V to 5.5V, I = 25ꢀA, I < 1ꢀA,
Q SD
OUT
IN
DC/DC Converter
MS, DFN Packages
600mA (I ), 2MHz Synchronous Buck-Boost
V : 2.5V to 5.5V, V
= 2.4V to 5.25V, I = 25ꢀA, I < 1ꢀA,
Q SD
OUT
IN
DC/DC Converter
DFN Package
1.2A (I ), 2MHz Synchronous Buck-Boost
V : 2.4V to 5.5V, V
= 2.4V to 5.25V, I = 35ꢀA, I < 1ꢀA,
Q SD
OUT
IN
DC/DC Converter
DFN Package
Dual DC/DC Converter with USB Power Manager and Li-Ion
Battery Charger
96% Efficiency, Seamless Transition Between Inputs, I = 110ꢀA,
Q
I
< 2ꢀA, QFN Package
SD
2-Cell Multi-Output DC/DC Converter with USB Power
Manager
92% Efficiency, Seamless Transition Between Inputs, I = 180ꢀA,
Q
I
< 1ꢀA, QFN Package
SD
600mA (I ), 2MHz Synchronous Buck-Boost
V : 1.8V to 5.5V, V
= 1.8V to 5.5V, I = 40ꢀA, I < 1ꢀA,
OUT(RANGE) Q SD
OUT
IN
DC/DC Converter
DFN, MSOP Packages
500mA (I ), 2MHz Synchronous Buck-Boost
V : 2.4V to 5.5V, V
= 2.4V to 5.25V, I = 35ꢀA, I < 1ꢀA,
Q SD
OUT
IN
OUT(RANGE)
DC/DC Converter
DFN, MSOP Packages
LTC3544/LTC3544B 300mA, 200mA ×2, 100mA, 2.25MHz Quad Output
V : 2.25V to 5.5V, V
= 0.8V, I = 70ꢀA, I < 1ꢀA,
Q SD
IN
OUT(MIN)
Synchronous Step-Down DC/DC Converter
3mm × 3mm QFN Packages
3522f
LT 0507 • PRINTED IN USA
20 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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