LTC3523/LTC3523-2
Synchronous 600mA Step-Up
and 400mA Step-Down
DC/DC Converters
FEATURES
n
DESCRIPTION
The LTC
®
3523/LTC3523-2 combine a 600mA step-up
DC/DC converter with a 400mA synchronous step-down
DC/DC converter in a tiny 3mm
×
3mm package. The
1.2MHz/2.4MHz switching frequencies minimize the
solution footprint while maintaining high efficiency. Both
converters feature soft-start and internal compensation,
simplifying the design.
Both the step-up and step-down converters are current
mode controlled and utilize an internal synchronous rec-
tifier for high efficiency. The step-up supports 0% duty
cycle operation and the step-down converter supports
100% duty cycle operation to extend battery run time.
If the MODE pin is held high, both converters automati-
cally transition between Burst Mode operation and PWM
operation improving light load efficiency. Fixed, low noise
1.2MHz/2.4MHz PWM operation is selected when MODE
is grounded.
The LTC3523/LTC3523-2 provide a sub-3μA shutdown
mode, overtemperature shutdown and current limit pro-
tection on both converters. The LTC3523/LTC3523-2 are
housed in a 16-lead 3mm
×
3mm
×
0.75mm QFN package.
L,
LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
n
n
n
n
n
n
n
n
n
n
Dual High Efficiency DC/DC Converters:
Step-Up (V
OUT
= 1.8V to 5.25V, I
SW
= 600mA)
Step-Down (V
OUT
= 0.615V to 5.5V, I
OUT
= 400mA)
1.8V to 5.5V Input Voltage Range
Up to 94% Efficiency
Pin Selectable Burst Mode
®
Operation
45μA Quiescent Current in Burst Mode Operation
1.2MHz (LTC3523) or 2.4MHz (LTC3523-2)
Switching Frequency
Independent Power Good Indicator Outputs
Integrated Soft-Start
Thermal and Overcurrent Protection
<3μA Quiescent Current in Shutdown
Small 16-Lead 3mm
×
3mm
×
0.75mm QFN Package
APPLICATIONS
n
n
n
n
Digital Cameras
Medical Instruments
Industrial Handhelds
GPS Navigators
TYPICAL APPLICATION
LTC3523 Efficiency and Power
Loss vs Load Current
V
IN
1.8V TO 3.2V
2-CELL
ALKALINE
+
47μF
4.7μH
V
IN1
V
IN2
V
BAT
SW2
10pF
V
OUT
10μF
634k
365k
FB1
PGOOD1
SHDN1
LTC3523
FB2
MODE
PGOOD2
SHDN2
V
IN
511k
511k
4.7μH
SW1
V
OUT2
STEP-DOWN
OUTPUT
10μF 1.2V
200mA
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
OFF ON
OFF ON
3523 TA01a
1000
EFFICIENCY
100
POWER LOSS (mW)
V
OUT1
STEP-UP
OUTPUT
3.3V
200mA
P0WER LOSS
V
IN
= 2.4V
V
OUT1
= 3.3V
V
OUT2
= 1.2V
f
OSC
= 1.2MHz
STEP-UP
STEP-DOWN
1
10
100
LOAD CURRENT (mA)
10
GND1 GND2 GND3
1
0
0.1
0.1
1000
3523 TA01b
3523fb
1
LTC3523/LTC3523-2
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
SHDN1
SHDN2
12 FB2
17
11 PGOOD2
10 MODE
9
5
SW1
6
GND1
7
GND2
8
SW2
V
IN2
GND3
V
BAT
V
IN1
, V
IN2
, V
BAT
, V
OUT
Voltages .................... –0.3V to 6V
SHDN1,
PGOOD1, PGOOD2, FB1 Voltages .. –0.3V to 6V
SHDN2,
FB2, MODE Voltages ...... –0.3V to (V
IN2
+ 0.3V)
SW1 Voltage
DC.............................................................. 0.3V to 6V
Pulse < 100ns .......................................... –0.3V to 7V
SW2 Voltage Pulse < 100ns ......... –0.3V to (V
IN2
+ 0.3V)
Operating Temperature Range
(Notes 2, 3) .............................................. –40°C to 85°C
Storage Temperature Range................... –65°C to 125°C
16 15 14 13
FB1 1
V
IN1
2
PG00D1 3
V
OUT
4
UD PACKAGE
16-LEAD (3mm 3mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 68°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3523EUD#PBF
LTC3523EUD-2#PBF
TAPE AND REEL
LTC3523EUD#TRPBF
LTC3523EUD-2#TRPBF
PART MARKING
LCYC
LDDR
PACKAGE DESCRIPTION
16-Lead (3mm
×
3mm) Plastic DFN
16-Lead (3mm
×
3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
–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
Minimum Start-Up Voltage
Frequency
Quiescent Current–Shutdown
Quiescent Current –Sleep
Quiescent Current V
OUT
– Sleep
SHDN1, SHDN2
Input High
SHDN1, SHDN2
Input Low
SHDN1, SHDN2
Input Current
PGOOD1, PGOOD2 Threshold
PGOOD1, PGOOD2 Low Voltage
PGOOD1, PGOOD2 Leakage
MODE Input High
MODE Input Low
LTC3523
LTC3523-2
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN1
= V
IN2
= V
BAT
= 2.4V, V
OUT
= 3.3V, unless otherwise specified.
CONDITIONS
l
l
l
MIN
0.9
1.8
TYP
1.6
1.2
2.4
0.5
45
15
MAX
1.8
1.5
2.65
3
UNITS
V
MHz
MHz
μA
μA
μA
V
V
SHDN1
= V
SHDN2
= 0V, V
OUT
= 0V, V
IN1
= V
IN2
= V
BAT
Measured from V
SUPPLY
, V
IN1
= V
IN2
= V
BAT
= 2.4V
Measured from V
OUT
= 3.3V (Note 4)
1
0.35
V
SHDN
= 5.5V
Referenced to the Feedback Voltage
I
PGOOD
= 1mA
V
PGOOD
= 5.25V
1.0
0.35
–6
1.4
–9
0.35
0.01
1
2
–14
V
μA
%
V
μA
V
V
3523fb
2
LTC3523/LTC3523-2
ELECTRICAL CHARACTERISTICS
PARAMETER
MODE Leakage Current
Soft-Start Time
Step-Up Converter
Input Voltage Range
Output Voltage Adjust Range
Feedback Voltage FB1
Feedback Input Current FB1
N-Channel Switch Leakage
P-Channel Switch Leakage
N-Channel Switch On Resistance
P-Channel Switch On Resistance
Peak Inductor Current
Current Limit Delay to Output
Maximum Duty Cycle
Minimum Duty Cycle
Step-Down Converter
Input Voltage Range
Output Voltage Range
Feedback Voltage FB2
Feedback Input Current FB2
Reference Voltage Line Regulation
Output Voltage Line Regulation
Output Voltage Load Regulation
Maximum Duty Cycle
Peak Inductor Current
N-Channel Switch On Resistance
P-Channel Switch On Resistance
SW Leakage
(Note 7)
V
IN2
= 2.4V
V
IN2
= 2.4V
V
SHDN2
= 0V, V
SW2
= 0V or 5V, V
IN2
= 5.5V
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN1
= V
IN2
= V
BAT
= 2.4V, V
OUT
= 3.3V, unless otherwise specified.
CONDITIONS
V
MODE
= 5.5V
MIN
TYP
0.01
500
1.8
1.8
1.16
1.20
0
0.20
0.20
0.36
0.22
0.33
0.31
l
l
l
MAX
1
UNITS
μA
μs
5.25
5.25
1.23
50
2
2
V
V
V
nA
μA
μA
Ω
Ω
Ω
Ω
mA
ns
%
(Note 6)
V
FB1
= 1.25V
V
SW
= 5.5V
V
SW
= 5.5V, V
OUT
= 0V
V
OUT
= 3.3V
V
OUT
= 5V
V
OUT
= 3.3V, I
SW
= 100mA
V
OUT
= 5V, I
SW
= 100mA
(Note 7)
(Note 6)
V
FB
= 1V
V
FB
= 1.5V
l
l
600
80
1000
40
87
0
%
V
V
mV
nA
%/V
%/V
%
%
mA
Ω
Ω
1.8
0.615
585
600
0
0.04
0.04
1.0
100
400
650
0.33
0.58
0.20
5.5
5.5
615
50
(Note 6)
V
FB2
= 0.625V
I
OUT
= 100mA (Notes 5, 6)
I
OUT
= 100mA, 1.6V < V
IN
< 5.5V (Note 6)
I
OUT
= 0mA to 600mA (Note 6)
l
l
2
μA
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 LTC3523/LTC3523-2 are 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 control.
Note 3:
The LTC3523/LTC3523-2 include an overtemperature
shutdown that is intended to protect the device during momentary
overload conditions. Junction temperature will exceed 125°C when the
overtemperature shutdown is active. Continuous operation above the
specified maximum operating junction temperature may impair device
reliability.
Note 4:
Current is measured into the V
OUT
pin since the supply is
bootstrapped to the output for the step-up. The current will reflect to the
input supply by: (V
OUT
/V
IN
) • Efficiency. The outputs are not switching in
sleep.
Note 5:
The LTC3523/LTC3523-2 are tested in a propriety test mode that
connects FB2 to the output of the error amplifier.
Note 6:
Specification is guaranteed by design and not 100% tested in
production.
Note 7:
Current measurements are performed when the LTC3523/
LTC3523-2 are not switching. The current limit values in operation will be
somewhat higher due to the propagation delay of the comparator.
3523fb
3
LTC3523/LTC3523-2
TYPICAL PERFORMANCE CHARACTERISTICS
(T
A
= 25°C unless otherwise noted)
Normalized FBx Reference vs
Temperature
1.00125
NORMALIZED FBx VOLTAGE (V)
NORMALIZED FREQUENCY (Hz)
1.05
V
OUT_BST
2V/DIV
I
L_BST
200mA/DIV
1.00
SHDN1
2V/DIV
V
OUT
= 3.3V
V
IN
= 2.4V
C
OUT
= 10μF
L1 = 4.7μH
0.95
–45
200μs/DIV
3523 G03
Normalized Oscillator Frequency
vs Temperature
Inrush Current Control for the
Step-Up Converter
1.00000
0.99875
0.99750
0.99625
0.99500
–45
–25
15
35
55
–5
TEMPERATURE (°C)
75
3523 G01
–25
15
35
55
–5
TEMPERATURE (°C)
75
3523 G02
Inrush Current Control for the
Step-Down Converter
V
OUT_BCK
1V/DIV
I
L_BCK
200mA/DIV
SHDN2
2V/DIV
V
OUT
= 1.2V
V
IN
= 2.4V
C
OUT
= 10μF
L1 = 4.7μH
200μs/DIV
3523 G04
Load Transient Response Step-Up
OUTPUT
RIPPLE
20mV/DIV
LOAD
CURRENT
20mA/DIV
OUTPUT
RIPPLE
20mV/DIV
Load Transient Response
Step-Down
LOAD
CURRENT
20mA/DIV
V
OUT
= 3.3V
500μs/DIV
V
IN
= 2.4V
C
OUT
= 10μF
L1 = 4.7μH
20mA TO 70mA STEP
3523 G05
V
OUT
= 1.2V
500μs/DIV
V
IN
= 2.4V
C
OUT
= 47μF
L1 = 4.7μH
C
F
= 68pF
10mA TO 30mA STEP
3523 G06
Current Limit vs Temperature
1.2
1.0
CURRENT LIMIT (A)
0.8
0.6
0.4
0.2
0
–45
BUCK CURRENT
LIMIT
BOOST CURRENT
LIMIT
0.80
0.70
0.60
RDS(ON) (Ω)
0.50
0.40
0.30
0.20
0.10
–25
55
35
–5
15
TEMPERATURE (°C)
75
3523 G07
R
DS(ON)
vs Input Voltage for the
Step-Down Converter
0.50
0.45
0.40
PMOS
R
DS(0N)
(Ω)
0.35
0.30
0.25
0.20
0.15
0.10
0.05
1
1.5
2
2.5 3 3.5 4
INPUT VOLTAGE (V)
4.5
5
0
R
DS(ON)
vs Output Voltage for the
Step-Up Converter
PMOS
NMOS
NMOS
0
1
1.5
2
2.5 3
3.5 4
OUTPUT VOLTAGE (V)
4.5
5
3523 G08
3532 G09
3523fb
4
LTC3523/LTC3523-2
TYPICAL PERFORMANCE CHARACTERISTICS
(T
A
= 25°C unless otherwise noted)
Normalized R
DS(ON)
vs
Temperature
1.3
1.2
NORMALIZED R
DS(ON)
(Ω)
INPUT CURRENT (μA)
1.1
1.0
0.9
NMOS
0.8
0.7
0.6
0.5
–45
–25
–5
55
35
15
TEMPERATURE (°C)
75
3523 G10
Step-Up No-Load Input Current
vs V
IN
500
450
400
350
300
250
200
150
100
50
0
1.5
2
V
OUT
= 2.8V
3.5
3
2.5
4
INPUT VOLTAGE (V)
4.5
5
V
OUT
= 3.3V
MODE
2V/DIV
V
OUT
= 5V
V
OUT_BST
50mV/DIV
V
OUT_BCK
20mV/DIV
Mode Transition Response
PMOS
V
OUT1
= 3.3V
200μs/DIV
V
OUT2
= 1.2V
V
IN
= 2.4V
I
OUT1
= 20mA
I
OUT2
= 25mA
C
OUT1
= C
OUT2
= 10μF
L1 = L2 = 4.7μH
3523 G12
3523 G11
Maximum I
OUT
vs V
IN
for the
Step-Up Converter
500
MAXIMUM OUTPUT CURRENT (mA)
450
400
350
300
250
200
150
100
50
0
1
2
3
4
INPUT VOLTAGE (V)
5
3523 G13
Maximum I
OUT
vs V
IN
for the
Step-Down Converter
450
MAXIMUM OUTPUT CURRENT (mA)
400
350
300
250
200
150
100
50
0
1
1.5
2
2.5 3 3.5 4
INPUT VOLTAGE (V)
4.5
5
V
OUT
= 1.8V
V
OUT
= 2.5V
V
OUT
= 1.2V
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 5V
3523 G14
PIN FUNCTIONS
FB1 (Pin 1):
Step-Up Converter Feedback Input to the Er-
ror Amplifier. Connect resistor divider tap to this pin. The
output voltage can be adjusted from 1.8V to 5.25V by:
⎛
R1
⎞
V
OUT(STEP-UP)
=
1.2V •
⎜
1
+ ⎟
⎝
R2
⎠
See Block Diagram.
V
IN1
(Pin 2):
Step-Up Converter Power Voltage Input. This
pin can be connected to a different supply than V
IN2
. This
pin must be connected to a valid supply voltage.
PGOOD1 (Pin 3):
Step-Up Converter Power Good Com-
parator Output. This open-drain output is pulled low when
V
FB1
< –9% of its regulation voltage.
V
OUT
(Pin 4):
Step-Up Converter Output Voltage Sense Input
and Drain of the Internal Synchronous Rectifier MOSFET.
Driver bias is derived from V
OUT
. PCB trace length from
V
OUT
to the output filter capacitor(s) should be as short
and wide as possible.
3523fb
5
京公网安备 11010802033920号
EEWORLD
