FEATURES
■
LTC3520
Synchronous 1A
Buck-Boost and 600mA
Buck Converters
DESCRIPTION
The LTC
®
3520 combines 1A buck-boost and 600mA
synchronous buck DC/DC converters in a tiny 4mm
×
4mm package. A programmable switching frequency
allows the efficiency to be optimized while minimizing
the solution footprint. Both converters feature soft-start
and current limit protection. The uncommitted gain block
can be configured as an LDO or utilized as a battery-good
comparator.
The buck converter is current mode controlled with internal
synchronous rectification to improve efficiency. Pin-select-
able Burst Mode operation can be enabled to improve light
load efficiency, or the buck converter can be operated in
low noise PWM mode for sensitive applications.
The buck-boost converter provides continuous conduc-
tion operation to maximize efficiency and minimize noise.
At light loads, use of Burst Mode operation will improve
efficiency.
The LTC3520 provides a <1µA shutdown mode and over-
temperature shutdown on both converters. The LTC3520
is available in a low profile (0.75mm) 24-lead 4mm
×
4mm QFN package.
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■
■
■
■
Dual High Efficiency DC/DC Converters:
Buck-Boost (V
OUT
: 2.2V to 5.25V, I
OUT
= 1A at
V
OUT
= 3.3V, V
IN
≥ 3V)
Buck (V
OUT
: 0.8V to V
IN
, I
OUT
= 600mA)
2.2V to 5.5V Input Voltage Range
Pin-Selectable Burst Mode
®
Operation
Uncommitted Gain Block for LDO Controller,
Battery Good Indication or Sequencing
Programmable 100kHz to 2MHz Switching Frequency
55µA Total Quiescent Current for Both Converters in
Burst Mode Operation
Thermal and Overcurrent Protection
<1µA Quiescent Current in Shutdown
24-Lead 4mm
×
4mm QFN Package
APPLICATIONS
■
■
■
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Portable Media Players
Digital Cameras
Handheld PCs, PDAs
GPS Receivers
, 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 5481178, 6166527, 6304066, 6404251, 6580258.
TYPICAL APPLICATION
3.3V at 500mA, 1.8V at 600mA and 1.5V at 200mA Converter
V
IN
2.2V TO
5.5V
V
OUT2
1.8V
600mA
22µF
4.7µH
255k
PV
IN1
PV
IN2
PV
IN3
SV
IN
SW1A
SW1B
V
OUT1
SW2
V
C1
FB2
200k
0.01µF
SS2
54.9k
R
T
PWM1
BURST
PWM
PWM2
SD3
OFF ON
SD2
SD1
PGND1 SGND PGND2
A
IN
110k
3520 TA01
Efficiency vs V
IN
100
V
OUT1
3.3V
500mA
1A FOR
V
IN
≥
3V
4.7µH
95
EFFICIENCY (%)
90
85
80
75
70
2.2
BUCK-BOOST
I
OUT
= 150mA
BUCK
I
OUT
= 250mA
470pF
56pF
1M
15k
10k
47µF
10µF
27pF
FB1
0.01µF
LTC3520
SS1
V
OUT2
A
OUT
V
OUT
1.5V
200mA
4.7µF
309k
33pF
100k
2.7
3.2
4.2
3.7
V
IN
(V)
4.7
5.2
3520f
1
LTC3520
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
PGND1
V
OUT1
18 FB1
17 SS1
25
16 SGND
15 V
C1
14 FB2
13 SS2
7
SD2
8
SD3
9 10 11 12
PV
IN2
PGND2
SW2
PWM2
SW1A
SW1B
PV
IN3
SV
IN
1
A
OUT
2
A
IN
3
R
T
4
PWM1 5
SD1 6
PV
IN1
PV
IN1
, PV
IN2
, PV
IN3
, SV
IN
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 150°C
24 23 22 21 20 19
UF PACKAGE
24-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 37°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3520EUF#PBF
TAPE AND REEL
LTC3520EUF#TRPBF
PART MARKING
3520
PACKAGE DESCRIPTION
24-Lead (4mm
×
4mm) 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 in Shutdown
Undervoltage Lockout
Burst Mode Quiescent Current, Both Converters
Oscillator Frequency
Buck Converter
PMOS Switch Resistance
NMOS Switch Resistance
NMOS Switch Leakage
PMOS Switch Leakage
CONDITIONS
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, S
VIN
= P
VIN1
= P
VIN2
= P
VIN3
= 3.6V, V
OUT1
= 3.3V, R
T
= 54.9k, unless
otherwise noted.
MIN
●
TYP
0.01
2
55
MAX
5.5
1
2.2
1.2
UNITS
V
µA
V
µA
MHz
Ω
Ω
2.2
V
⎯
S
⎯
D
⎯
1
= V
⎯
S
⎯
D
⎯
2
= V
⎯
S
⎯
D
⎯
3
= 0V
SV
IN
Rising
V
FB1
= V
FB2
= 0.88V, V
⎯
S
⎯
D
⎯
3
= 0V
R
T
= 54.9k
●
●
0.8
1
0.32
0.18
V
SW2
= 5V, S
VIN
= P
VIN1
= P
VIN2
= P
VIN3
= 5V
V
SW2
= 0V, S
VIN
= P
VIN1
= P
VIN2
= P
VIN3
= 5V
0.1
0.1
5
10
µA
µA
3520f
2
LTC3520
ELECTRICAL CHARACTERISTICS
PARAMETER
Feedback Voltage (FB2 Pin)
Feedback Input Current (FB2 Pin)
PMOS Current Limit
Maximum Duty Cycle
Minimum Duty Cycle
Soft-Start Charging Current
⎯
SD
⎯
2 Input High Voltage
⎯
⎯
SD
⎯
2 Input Low Voltage
⎯
⎯
SD
⎯
2 Input Current
⎯
Buck-Boost Converter
Output Voltage
PMOS Switch Resistance
NMOS Switch Resistance
NMOS Switch Leakage
PMOS Switch Leakage
Feedback Voltage (FB1 Pin)
Feedback Input Current (FB1 Pin)
Forward Current Limit
Reverse Current Limit
Burst Mode Operation Current Limit
Error Amplifier Gain
Error Amplifier Sink Current
Error Amplifier Source Current
Maximum Duty Cycle
Minimum Duty Cycle
Soft-Start Charging Current
⎯
S
⎯
D
⎯
1, PWM1 Input High Voltage
⎯
SD
⎯
1, PWM1 Input Low Voltage
⎯
⎯
SD
⎯
1, PWM1 Input Current
⎯
Gain Block
Quiescent Current
A
IN
Pin Threshold Voltage
A
IN
Pin Input Bias Current
A
OUT
Sink Current
A
OUT
Source Current
A
OUT
Pin Voltage
Open Loop Gain
V
AIN
= 0.72V, V
AOUT
= 1.8V
V
AIN
= 0.88V, V
AOUT
= 1.8V
V
AIN
= 0.72V, I
AOUT
= 1mA
V
AIN
= 0.88V, V
⎯
S
⎯
D
⎯
1
= V
⎯
S
⎯
D
⎯
2
= 0V
●
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, S
VIN
= P
VIN1
= P
VIN2
= P
VIN3
= 3.6V, V
OUT1
= 3.3V, R
T
= 54.9k, unless
otherwise noted.
CONDITIONS
(Note 4)
(Note 3)
V
FB2
= 0.72V
V
FB2
= 0.88V
●
MIN
0.771
0.8
100
TYP
0.790
1
1.25
MAX
0.809
50
UNITS
V
nA
A
%
●
●
●
0
6
1.4
0.4
0.01
2.2
0.20
0.15
1
5.25
%
µA
V
V
µA
V
Ω
Ω
V
SW1A
= V
SW1B
= 5V, S
VIN
= P
VIN1
= P
VIN2
= P
VIN3
= 5V
V
SW1A
= V
SW1B
= 0V, S
VIN
= P
VIN1
= P
VIN2
= P
VIN3
= 5V
●
0.1
0.1
0.766
1.4
0.782
1
2
560
325
80
500
14
5
10
0.798
50
µA
µA
V
nA
A
mA
mA
dB
µA
µA
%
%
(Note 3)
(Note 3)
(Note 3)
●
Boost (% Switch C is On)
Buck (% Switch A is On)
●
●
70
100
80
0
6
%
µA
V
1.4
0.4
0.01
45
0.770
0.786
1
17
18
25
80
150
0.802
50
1
V
µA
µA
V
nA
mA
µA
mV
dB
3520f
3
LTC3520
ELECTRICAL CHARACTERISTICS
PARAMETER
Propagation Delay
⎯
SD
⎯
3 Input High Voltage
⎯
⎯
S
⎯
D
⎯
3 Input Low Voltage
⎯
SD
⎯
3 Input Current
⎯
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 LTC3520 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 LTC3520 is not
switching. The current limit values in operation will be somewhat higher
due to the propagation delay of the comparators.
0.01
CONDITIONS
A
OUT
Falling
1.4
0.4
1
The
●
denotes the specifications which apply over the full operating temp-
erature range, otherwise specifications are at T
A
= 25°C, V
IN
= 3.6V, V
OUT1
= 3.3V, V
OUT2
= 1.8V, R
T
= 54.9k, unless otherwise noted.
MIN
TYP
11
MAX
UNITS
µs
V
V
µA
Note 4:
The LTC3520 is tested in a proprietary non-switching test mode
that internally connects the FB2 pin to the output of the buck converter
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.
TYPICAL PERFORMANCE CHARACTERISTICS
(T
A
= 25°C, unless otherwise specified)
Buck-Boost Efficiency
Lithium-Ion to 3.3V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
1
100
10
LOAD CURRENT (mA)
Burst Mode
OPERATION
POWER LOSS
L = COILCRAFT
MSS6132-4.7µH
150
100
50
0
1000
3520 G01
Buck Efficiency
Lithium-Ion to 2.7V
300
100
90 Burst Mode OPERATION
250
POWER LOSS (mW)
200
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
1
100
10
LOAD CURRENT (mA)
L = SUMIDA
CDRH3D16NP-4R7N
Burst Mode
OPERATION
POWER LOSS
PWM MODE
500
400
300
200
100
0
1000
3520 G02
V
IN
= 4.2V
V
IN
= 2.7V
800
700
600
POWER LOSS (mW)
PWM MODE
Burst Mode
OPERATION
3520f
4
LTC3520
TYPICAL PERFORMANCE CHARACTERISTICS
Buck Efficiency
Lithium-Ion to 1.8V
100
Burst Mode
90 OPERATION
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
1
100
10
LOAD CURRENT (mA)
L = SUMIDA
CDRH3D16NP-4R7N
R
BURST
= 249k
Burst Mode
OPERATION
POWER LOSS
V
IN
= 4.2V
V
IN
= 3V
500
400
300
200
100
0
1000
3520 G03
Switching Frequency vs R
T
800
PWM MODE
700
600
POWER LOSS (mW)
SWITCHING FREQUENCY (kHz)
10000
1000
100
10
100
R
T
(k)
1000
3520 G04
LDO Load
Transient Response
LDO V
OUT
100mV/DIV
V
OUT
V
IN
= 5V
200mV/DIV
V
OUT
V
IN
= 2.2V
500mV/DIV
LOAD
CURRENT
100mA/DIV
(20mA TO
210mA STEP)
50µs/DIV
C
OUT
= 4.7µF
V
IN
= 3.6V
V
OUT
= 1.5V LDO INPUT VOLTAGE = 1.8V
3520 G05
Buck-Boost Load
Transient Response
LOAD CURRENT
500mA/DIV
C
OUT
= 47µF
L = 4.7µH
V
IN
= 3.3V
200µs/DIV
3520 G06
Buck Load Transient
Response (PWM Mode)
BUCK V
OUT
100mV/DIV
BUCK V
OUT
100mV/DIV
Buck Load Transient
Response (Burst Mode Operation)
LOAD CURRENT
500mA/DIV
(50mA TO
500mA STEP)
100µs/DIV
3520 G07
LOAD CURRENT
200mA/DIV
(5mA TO
300mA STEP)
100µs/DIV
C
OUT
= 22µF
R
BURST
= 249k
3520 G08
V
IN
= 3.6V
V
OUT
= 1.8V
C
OUT
= 10µF
V
IN
= 3.6V
V
OUT
= 1.8V
3520f
5
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