LTC3522
Synchronous 400mA
Buck-Boost and 200mA
Buck Converters
FEATURES
■
DESCRIPTION
The LTC
®
3522 combines a 400mA buck-boost DC/DC con-
verter with a 200mA synchronous buck DC/DC converter in
a tiny 3mm
×
3mm package. The 1MHz switching frequency
minimizes the solution footprint while maintaining high
efficiency. Both converters feature internal soft-start and
compensation, simplifying the design process.
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
converter automatically transitions from Burst Mode opera-
tion to PWM mode. With the PWM pin held high, the buck
converter remains in low noise, 1MHz PWM mode.
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.
The LTC3522 provides a 1μA shutdown mode, overtem-
perature shutdown and current limit protection on both
converters. The LTC3522 is available in a 16-pin low profile
3mm
×
3mm QFN package.
■
■
■
■
■
■
■
■
Dual High Efficiency DC/DC Converters:
Buck-Boost (V
OUT
: 2.2V to 5.25V, I
OUT
: 400mA
for V
IN
> 3V, V
OUT
= 3.3V)
Buck (V
OUT
: 0.6V to V
IN
, I
OUT
: 200mA)
2.4V to 5.5V Input Voltage Range
Pin Selectable Burst Mode
®
Operation
25μA Total Quiescent Current for Both Converters in
Burst Mode Operation
Independent Power Good Indicator Outputs
Integrated Soft-Start
Thermal and Overcurrent Protection
<1μA Quiescent Current in Shutdown
Small 0.75mm
×
3mm
×
3mm QFN Package
APPLICATIONS
■
■
■
■
■
Flash-Based MP3 Players
Medical Instruments
Digital Cameras
PDAs, Handheld PCs
Personal Navigation Devices
, 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 V
IN
V
IN
2.4V TO 4.2V
V
OUT2
1.8V
200mA
+
Li-Ion
4.7μF
L1
8.2μH
12pF
PV
IN1
PV
IN2
SW2
SW1A
SW1B
LTC3522
V
OUT1
L2
4.7μH
V
OUT1
3.3V
300mA
(400mA
4.7μF
V
IN
> 3V)
EFFICIENCY (%)
6.8μF
137k
FB2
68.1k
OFF
PWM
BURST
PWM
ON
SHDN2
SHDN1
FB1
PGOOD2
PGOOD1
3522 TA01a
1M
432k
PGND1 GND PGND2
L1: COILCRAFT MSS6132-8.2μH
L2: COILCRAFT MSS6132-4.7μH
100
98
96
94
92
90
88
86
84
82
80
78
76
74
72
70
2.4
BUCK-BOOST
I
OUT
= 100mA
V
OUT
= 3.3V
BUCK
I
OUT
= 100mA
V
OUT
= 1.8V
3.4
V
IN
(V)
4.4
5.4
3522 TA01b
3522fa
1
LTC3522
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
SHDN2
PGND1
12 V
OUT1
17
11 SW1A
10 SW1B
9
5
FB1
6
PGOOD1
7
SHDN1
8
PV
IN1
PGND2
PV
IN2
SW2
16 15 14 13
FB2 1
PWM 2
GND 3
PGOOD2 4
PV
IN1
, PV
IN2
Voltage .................................... –0.3V to 6V
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
UD PACKAGE
16-LEAD (3mm
×
3mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 68°C/W
EXPOSED PAD (PIN 17) IS GND AND MUST BE SOLDERED TO PCB GROUND
ORDER INFORMATION
LEAD FREE FINISH
LTC3522EUD#PBF
TAPE AND REEL
LTC3522EUD#TRPBF
PART MARKING
LCRQ
PACKAGE DESCRIPTION
16-Lead (3mm
×
3mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
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
PARAMETER
Input Voltage
Quiescent Current—Shutdown
Burst Mode Quiescent Current
Oscillator Frequency
SHDN1, SHDN2,
PWM Input High Voltage
SHDN1, SHDN2,
PWM Input Low Voltage
Power Good Outputs Low Voltage
Power Good Outputs Leakage
Buck Converter
PMOS Switch Resistance
NMOS Switch Resistance
NMOS Switch Leakage
PMOS Switch Leakage
Feedback Voltage
Feedback Input Current
Peak Current Limit
(Note 3)
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. PV
IN1
= PV
IN2
= 3.6V, V
OUT1
= 3.3V unless otherwise noted.
CONDITIONS
●
MIN
2.4
●
●
TYP
0.01
25
MAX
5.5
1
1.33
0.4
UNITS
V
μA
μA
MHz
V
V
V
μA
Ω
Ω
V
SHDN1
= V
SHDN2
= 0V
V
FB1
= 1.1V, V
FB2
= 0.66V, V
PWM
= 0V
0.8
1.4
1.07
I
PGOOD1
= I
PGOOD2
= 1mA
V
PGOOD1
= V
PGOOD2
= 5.5V
0.02
0.1
0.41
0.34
0.1
10
V
SW2
= 5V, PV
IN1
= PV
IN2
= 5V
V
SW2
= 0V, PV
IN1
= PV
IN2
= 5V
(Note 4)
●
0.1
0.1
0.582
300
0.594
1
400
5
10
0.606
50
μA
μA
V
nA
mA
3522fa
2
LTC3522
ELECTRICAL CHARACTERISTICS
PARAMETER
Maximum Duty Cycle
Minimum Duty Cycle
PGOOD Threshold
Power Good Hysteresis
Buck-Boost Converter
Output Voltage
PMOS Switch Resistance
NMOS Switch Resistance
NMOS Switch Leakage
PMOS Switch Leakage
Feedback Voltage
Feedback Input Current
Average Current Limit
Burst Mode Current Limit
Reverse Current Limit
Maximum Duty Cycle
Minimum Duty Cycle
PGOOD Threshold
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 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.
(Note 3)
V
FB1
= 0.9V
V
FB1
= 1.1V
V
FB1
Falling
●
●
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. PV
IN1
= PV
IN2
= 3.6V, V
OUT1
= 3.3V unless otherwise noted.
CONDITIONS
V
FB2
= 0.54V
V
FB2
= 0.66V
V
FB2
Falling
●
●
MIN
100
TYP
MAX
0
UNITS
%
%
%
%
–11.3
–7.7
2.5
–4.1
2.2
0.29
0.22
5.25
V
Ω
Ω
V
SW1A
= V
SW1B
= 5V, PV
IN1
= PV
IN2
= 5V
V
SW1A
= V
SW1B
= 0V, PV
IN1
= PV
IN2
= 5V
(Note 4)
(Note 3)
●
0.1
0.1
0.97
0.65
230
70
–12
1
1
0.85
340
250
80
0
–10
2.5
5
10
1.03
50
μA
μA
V
nA
A
mA
mA
%
%
–8
%
%
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.
3522fa
3
LTC3522
TYPICAL PERFORMANCE CHARACTERISTICS
Buck-Boost Efficiency,
Li-Ion to 3.3V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
1
Burst Mode
POWER LOSS
V
IN
= 4.2V
V
IN
= 2.7V
PWM Mode
100
80
60
40
Burst Mode
OPERATION
160
140
120
POWER LOSS (mW)
EFFICIENCY (%)
100
(T
A
= 25°C unless otherwise noted)
Buck Efficiency, Li-Ion to 2.5V
Burst Mode
90 OPERATION
160
140
120
POWER LOSS (mW)
PWM Mode
100
80
Burst Mode
POWER LOSS
60
40
20
0
1000
3522 G02
80
70
60
50
40
30
20
10
0
1
100
10
LOAD CURRENT (mA)
V
IN
= 3.7V
V
IN
= 4.2V
L: COILCRAFT
MSS6132-8.2μH
20
L: COILCRAFT
MSS6132-4.7μH
0
1000
100
10
LOAD CURRENT (mA)
3522 G01
Buck Efficiency, Li-Ion to 1.8V
100
Burst Mode
OPERATION
90
160
140
LOAD CURRENT (mA)
120
POWER LOSS (mW)
PWM Mode
100
80
Burst Mode
POWER LOSS
V
IN
= 4.2V
V
IN
= 2.7V
L: COILCRAFT
MSS6132-8.2μH
1
100
10
LOAD CURRENT (mA)
60
40
20
0
1000
3522 G03
Buck Burst Mode Threshold
50
45
40
35
30
25
20
15
10
5
0
2.4
2.9
3.4
4.4
3.9
V
IN
(V)
4.9
5.4
3522 G04
Buck-Boost Switch R
DS(0N)
400
350
PMOS
(SWITCHES A AND D)
L = 4.7μH
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
V
OUT
= 1.2V
R
DS(ON)
(mΩ)
V
OUT
= 1.8V
300
250
200
150
100
50
0
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3522 G05
NMOS
(SWITCHES B AND C)
V
OUT
= 2.5V
Buck Switch R
DS(0N)
600
500
CHANGE FROM 25°C (%)
PMOS
R
DS(ON)
(mΩ)
400
NMOS
300
200
100
0
–40 –20
10
8
Switching Frequency vs
Temperature
10
8
CHANGE FROM V
IN
= 3.6V (%)
6
4
2
0
–2
–4
–6
–8
–10
90 110
3522 G07
Switching Frequency vs V
IN
6
4
2
0
–2
–4
–6
–8
0
20 40 60 80
TEMPERATURE (°C)
100 120
3522 G06
–10
–50 –30 –10 10 30 50 70
TEMPERATURE (°C)
2.5
2.9
3.4
4.4
3.9
V
IN
(V)
4.9
5.4
3522 G08
3522fa
4
LTC3522
TYPICAL PERFORMANCE CHARACTERISTICS
Buck-Boost Feedback Voltage vs
Temperature
CHANGE IN FEEDBACK VOLTAGE FROM 20°C (%)
CHANGE IN FEEDBACK VOLTAGE FROM 20°C (%)
0.5
0.4
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
–40 –20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
3522 G09
(T
A
= 25°C unless otherwise noted)
Buck-Boost Maximum Load
Current, Burst Mode Operation
90
80
MAXIMUM LOAD CURRENT (mA)
70
60
50
40
30
20
10
V
OUT
= 5V
L = 4.7μH
V
OUT
= 3V
Buck Feedback Voltage vs
Temperature
0.5
0.4
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
–40 –20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
3522 G09
0
2.4
2.9
3.4
3.9
4.4
V
IN
(V)
4.9
5.4
3522 G11
Buck-Boost Maximum Load
Current, PWM Mode
600
500
LOAD CURRENT (mA)
400
300
V
OUT
= 5V
200
100
0
2.4
2.9
3.4
3.9
4.4
V
IN
(V)
4.9
5.4
3522 G12
No Load Quiescent Current
vs V
IN
50
45
BOTH CONVERTERS ENABLED
INDUCTOR
CURRENT
200mA/DIV
Buck-Boost Burst to PWM
Transition
L = 4.7μH
V
OUT
= 3.3V
QUIESCENT CURRENT (μA)
40
35
30
25
20
15
10
5
0
2.4
2.9
3.4
4.4
3.9
V
IN
(V)
4.9
5.4
3522 G13
V
OUT
100mV/DIV
3522 G14
V
IN
= 3.6V
V
OUT
= 3.3V
L = 4.7μH
C
OUT
= 4.7μF
50μs/DIV
Buck-Boost Load Step,
0mA to 300mA
V
OUT
100mV/DIV
V
OUT
100mV/DIV
Buck Load Step, PWM Mode,
5mA to 200mA
V
OUT
100mV/DIV
Buck Load Step, Burst Mode
Operation, 5mA to 200mA
INDUCTOR
CURRENT
200mA/DIV
V
IN
= 3.6V
V
OUT
= 3V
L = 4.7μH
C
OUT
= 4.7μF
100μs/DIV
3522 G15
INDUCTOR
CURRENT
100mA/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
L = 4.7μH
C
OUT
= 4.7μF
100μs/DIV
3522 G16
INDUCTOR
CURRENT
100mA/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
L = 4.7μH
C
OUT
= 4.7μF
100μs/DIV
3522 G17
3522fa
5
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