FEATURES
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LTC3535
Dual Channel 550mA 1MHz
Synchronous Step-Up
DC/DC Converter
DESCRIPTION
The LTC
®
3535 is a dual channel, synchronous, fixed fre-
quency step-up DC/DC converter with output disconnect.
Extended battery life in single AA/AAA powered products
is realized with a 680mV start-up voltage and operation
down to 500mV once started.
A switching frequency of 1MHz minimizes solution foot-
print by allowing the use of tiny, low profile inductors
and ceramic capacitors. The current mode PWM design
is internally compensated, reducing external parts count.
The LTC3535 features Burst Mode operation at light load
conditions allowing it to maintain high efficiency over a
wide range of load. Anti-ring circuitry reduces EMI by
damping the inductor in discontinuous mode. Additional
features include a low shutdown current of under 1μA and
thermal shutdown.
The LTC3535 is housed in a 3mm
×
3mm
×
0.75mm
DFN package.
, LT LTC, LTM and Burst Mode are registered trademarks of Linear Technology
,
Corporation. All other trademarks are the property of their respective owners.
Two Independent Step-Up Converters
Each Channel Delivers 3.3V at 100mA from a Single
Alkaline/NiMH Cell or 3.3V at 200mA from Two Cells
V
IN
Start-Up Voltage: 680mV
1.5V to 5.25V V
OUT
Range
Up to 94% Efficiency
Output Disconnect
1MHz Fixed Frequency Operation
V
IN
> V
OUT
Operation
Integrated Soft-Start
Current Mode Control with Internal Compensation
Burst Mode
®
Operation with 9μA I
Q
Each Channel
Internal Synchronous Rectifier
Logic Controlled Shutdown (I
Q
< 1μA)
Anti-Ring Control
Low Profile (3mm
×
3mm
×
0.75mm)
12-Lead DFN Package
APPLICATIONS
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Medical Instruments
Noise Canceling Headphones
Wireless Mice
Bluetooth Headsets
TYPICAL APPLICATION
4.7μH
100
90
80
EFFICIENCY (%)
70
60
50
40
30
1M
4.7μH
3535 TA01
Efficiency vs Load Current
SW1
V
OUT1
1.8V
100mA
511k
V
OUT
= 1.8V
V
IN1
V
IN
0.8V
TO 1.5V
2.2μF
OFF ON
OFF ON
SHDN1
V
OUT1
V
OUT2
10μF
FB1
FB2
1.78M
10μF
V
OUT2
3.3V
50mA
V
OUT
= 3.3V
LTC3535
V
IN2
SHDN2
1M
GND SW2 GND
20
10
V
IN
= 1.2V
0
0.01
0.1
10
100
1
LOAD CURRENT (mA)
1000
3535 TA01b
3535f
1
LTC3535
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
V
OUT1
SW1
GND
V
OUT2
SW2
GND
1
2
3
4
5
6
13
12 FB1
11
SHDN1
10
V
IN1
9 FB2
8
SHDN2
7
V
IN2
V
IN1,2
Voltage ............................................... –0.3V to 6V
SW1,2 Voltage
DC............................................................ –0.3V to 6V
Pulsed <100ns ......................................... –0.3V to 7V
SHDN1,2,
FB1,2 Voltage .............................. –0.3V to 6V
V
OUT1,2
......................................................... –0.3V to 6V
Operating Temperature Range
(Notes 2, 5) .............................................. –40°C to 85°C
Junction Temperature ........................................... 125°C
Storage Temperature Range................... –65°C to 150°C
DD PACKAGE
12-LEAD (3mm 3mm) PLASTIC DFN
θ
JA
= 45°C/W,
θ
JC(PAD)
= 10°C/W,
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3535EDD#PBF
TAPE AND REEL
LTC3535EDD#TRPBF
PART MARKING
LDWV
PACKAGE DESCRIPTION
12-Lead (3mm
×
3mm) Plastic DFN
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
(For each channel) The
l
denotes the specifications which apply over the specified
operating temperature range of –40°C to 85°C, otherwise specifications are at T
A
= 25°C. V
IN
= 1.2V V
OUT
= 3.3V unless otherwise noted.
,
PARAMETER
Minimum Start-Up Input Voltage
Input Voltage Range
Output Voltage Adjust Range
Feedback Pin Voltage
Feedback Pin Input Current
Quiescent Current—Shutdown
Quiescent Current—Active
Quiescent Current—Burst
N-Channel MOSFET Switch Leakage Current
P-Channel MOSFET Switch Leakage Current
N-Channel MOSFET Switch On Resistance
P-Channel MOSFET Switch On Resistance
N-Channel MOSFET Current Limit
Current Limit Delay to Output
Maximum Duty Cycle
(Note 3)
V
FB
= 1.15V
l
CONDITIONS
I
LOAD
= 1mA
After Start-Up. (Minimum Voltage is Load Dependent)
l
l
l
MIN
0.5
1.5
1.165
TYP
0.68
MAX
0.8
5
5.25
UNITS
V
V
V
V
nA
μA
μA
μA
μA
μA
Ω
Ω
mA
ns
%
1.195
1
0.01
250
9
0.1
0.1
0.4
0.6
1.225
50
1
500
18
5
10
V
FB
= 1.30V
V
SHDN
= 0V, Not Including Switch Leakage, V
OUT
= 0V
Measured on V
OUT
, Non-Switching
Measured on V
OUT
, FB > 1.230V
V
SW
= 5V
V
SW
= 5V, V
OUT
= 0V
V
OUT
= 3.3V
V
OUT
= 3.3V
l
550
87
750
60
90
3535f
2
LTC3535
ELECTRICAL CHARACTERISTICS
(For each channel) The
l
denotes the specifications which apply over the specified
,
operating temperature range of –40°C to 85°C, otherwise specifications are at T
A
= 25°C. V
IN
= 1.2V V
OUT
= 3.3V unless otherwise noted.
PARAMETER
Minimum Duty Cycle
Switching Frequency
SHDN
Pin Input High Voltage
SHDN
Pin Input Low Voltage
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 LTC3535 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:
Specification is guaranteed by design and not 100% tested in
production.
CONDITIONS
V
FB
= 1.3V
l
l
MIN
0.75
0.8
TYP
1
MAX
0
1.25
0.3
UNITS
%
MHz
V
V
Note 4:
Current measurements are made when the output is not switching.
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
60°C/W.
TYPICAL PERFORMANCE CHARACTERISTICS
(Each Channel) T
A
= 25°C, unless otherwise noted.
Efficiency vs Load Current
and V
IN
for V
OUT
= 1.8V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
0.1
V
IN
= 1.0V
V
IN
= 1.2V
V
IN
= 1.5V
1
10
100
LOAD CURRENT (mA)
0.1
POWER LOSS
1
10
EFFICIENCY
100
POWER LOSS (mW)
EFFICIENCY (%)
1000
100
90
80
70
60
50
POWER LOSS
40
30
20
10
0
0.01
0.1
V
IN
= 1.2V
V
IN
= 1.8V
V
IN
= 2.4V
V
IN
= 3.0V
1
10
100
LOAD CURRENT (mA)
1
10
100
POWER LOSS (mW)
Efficiency vs Load Current
and V
IN
for V
OUT
= 3.3V
EFFICIENCY
1000
100
90
80
70
I
IN
(μA)
60
50
40
30
20
No-Load Input Current vs V
IN
V
OUT
= 5V
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
0.1
0.01
1000
3535 G01
0.01
1000
3535 G02
10
0.5
1.0
1.5
2.0
2.5
V
IN
(V)
3.0
3.5
4.0
4.5
3535 G04
3535f
3
LTC3535
TYPICAL PERFORMANCE CHARACTERISTICS
(Each Channel) T
A
= 25°C, unless otherwise noted.
Efficiency vs Load Current
and V
IN
for V
OUT
= 5V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
0.1
POWER LOSS
1
10
EFFICIENCY
350
100
POWER LOSS (mW)
300
I
OUT
(mA)
250
200
V
OUT
= 5V
150
100
0.1
50
0
0.5
L = 4.7μH
1.0
1.5
2.0
2.5
V
IN
(V)
3535 G03
3535 G05
Maximum Output Current vs V
IN
1000
400
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
1000
LOAD (Ω)
10000
Minimum Load Resistance
During Start-Up vs V
IN
V
OUT
= 3.3V
100
V
IN
= 1.2V
V
IN
= 2.4V
V
IN
= 3.6V
V
IN
= 4.2V
1
10
100
LOAD CURRENT (mA)
0.01
1000
3.0
3.5
4.0
4.5
10
0.65
0.75
0.85
0.95
V
IN
(V)
1.05
1.15
3526 G06
Start-Up Delay Time vs V
IN
100
90
80
LOAD CURRENT (mA)
70
DELAY (μs)
60
50
40
30
20
10
0
1.0
1.5
2.0
2.5 3.0
V
IN
(V)
3.5
4.0
4.5
0
25
20
15
10
5
30
Burst Mode Threshold Current
vs V
IN
V
OUT
= 1.8V
L = 4.7μH
40
LEAVE BURST
LOAD CURRENT (mA)
35
30
25
20
15
10
5
1
1.25
V
IN
(V)
1.5
3535 G08a
Burst Mode Threshold Current
vs V
IN
V
OUT
= 2.5V
L = 4.7μH
LEAVE BURST
ENTER BURST
ENTER BURST
0
1
1.25
1.5
V
IN
(V)
1.75
2
3535 G08b
3535 G07
Burst Mode Threshold Current
vs V
IN
40
35
LOAD CURRENT (mA)
30
25
20
15
10
5
0
1.0
1.5
2.0
V
IN
(V)
2.5
3.0
3535 G08c
Burst Mode Threshold Current
vs V
IN
50
3
V
OUT
= 5V
L = 4.7μH
FREQUENCY CHANGE (%)
40
LOAD CURRENT (mA)
LEAVE BURST
2
1
0
–1
–2
Oscillator Frequency Change
vs V
OUT
NORMALIZED TO V
OUT
= 3.3V
V
OUT
= 3.3V
L = 4.7μH
LEAVE BURST
30
ENTER BURST
ENTER BURST
20
10
0
1.0
1.5
2.0
2.5 3.0
V
IN
(V)
3.5
4.0
4.5
–3
1.5
2.0
2.5
3.0 3.5
V
OUT
(V)
4.0
4.5
5.0
3535 G08d
3535 G09
3535f
4
LTC3535
TYPICAL PERFORMANCE CHARACTERISTICS
(Each Channel) T
A
= 25°C, unless otherwise noted.
R
DS(ON)
vs V
OUT
0.90
0.85
0.80
0.75
0.70
R
DS(ON)
(Ω)
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
1.5
2.0
2.5
3.0 3.5
V
OUT
(V)
4.0
4.5
5.0
NMOS
PMOS
FREQUECNY CHANGE (%)
10
8
6
4
2
0
–2
–4
–6
–8
–10
–50
–30
–10 10
30
50
TEMPERATURE (°C)
70
90
0.7
–50
–30
–10 10
30
50
TEMPERATURE (°C)
70
90
NORMALIZED R
DS(ON)
1.2
1.1
1.0
0.9
0.8
Oscillator Frequency Change
vs Temperature
NORMALIZED TO 25°C
1.3
R
DS(ON)
Change vs Temperature
NORMALIZED TO 25°C
3535 G10
3535 G11
3535 G12
V
FB
vs Temperature
0.50
0.25
CHANGE IN V
FB
(%)
0
–0.25
–0.50
–0.75
–1.00
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
0.80
NORMALIZED TO 25°C
0.75
Start-Up Voltage vs Temperature
10.0
Burst Mode Quiescent Current
vs V
OUT
MEASURED ON V
OUT
9.5
1mA LOAD
0.70
V
IN
(V)
I
Q
(μA)
75
100
3526 G14
9.0
8.5
8.0
7.5
7.0
1.5
0.65
0.60
NO LOAD
0.55
0.50
–50
80
100
25
0
25
50
TEMPERATURE (°C)
2.0
2.5
3.0 3.5
V
OUT
(V)
4.0
4.5
5.0
3535 G13
3535 G15
Fixed Frequency Switching
Waveform and V
OUT
Ripple
SW PIN
2V/DIV
V
OUT
10mV/DIV
AC COUPLED
V
IN
= 1.2V
500ns/DIV
V
OUT
= 3.3V AT 100mA
C
OUT
= 10μF
3535 G16
Burst Mode Waveforms
SW PIN
2V/DIV
V
OUT
20mV/DIV
AC COUPLED
INDUCTOR
CURRENT
0.2A/DIV
V
IN
= 1.2V
V
OUT
= 3.3V
C
OUT
= 10μF
10μs/DIV
3535 G17
V
OUT
and I
IN
During Soft-Start
V
OUT
1V/DIV
INPUT
CURRENT
0.2A/DIV
SHDN PIN
1V/DIV
V
OUT
= 3.3V
C
OUT
= 10μF
200μs/DIV
3535 G18
3535f
5
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