LTC3535EDD-TRPBF [Linear]
Dual Channel 550mA 1MHz Synchronous Step-Up DC/DC Converter; 双通道550毫安1MHz同步升压型DC / DC转换器
| 型号： | LTC3535EDD-TRPBF |
| 厂家： | 
Linear |
| 描述： | Dual Channel 550mA 1MHz Synchronous Step-Up DC/DC Converter |
| 文件： | 总16页 (文件大小：248K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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.
FEATURES
n
Two Independent Step-Up Converters
n
Each Channel Delivers 3.3V at 100mA from a Single
Alkaline/NiMH Cell or 3.3V at 200mA from Two Cells
n
V Start-Up Voltage: 680mV
IN
n
1.5V to 5.25V V
Range
OUT
n
n
n
n
n
n
n
n
n
n
n
Up to 94% Efficiency
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.
Output Disconnect
1MHz Fixed Frequency Operation
V > V
Operation
IN
OUT
Integrated Soft-Start
Current Mode Control with Internal Compensation
Burst Mode® Operation with 9μA I Each Channel
Q
Internal Synchronous Rectifier
Logic Controlled Shutdown (I < 1μA)
Q
Anti-Ring Control
Low Profile (3mm × 3mm × 0.75mm)
12-Lead DFN Package
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.
APPLICATIONS
n
Medical Instruments
n
Noise Canceling Headphones
n
Wireless Mice
Bluetooth Headsets
n
TYPICAL APPLICATION
Efficiency vs Load Current
4.7μH
100
V
SW1
OUT1
V
V
= 1.8V
= 3.3V
OUT
OUT
V
V
V
1.8V
90
80
70
60
50
40
30
20
10
0
IN1
OUT1
OUT2
100mA
10μF
OFF ON
OFF ON
SHDN1
V
IN
511k
V
0.8V
OUT2
10μF
3.3V
TO 1.5V
LTC3535
50mA
2.2μF
V
IN2
FB1
FB2
1.78M
1M
SHDN2
1M
GND SW2 GND
4.7μH
3535 TA01
V
IN
= 1.2V
10
100
0.01
1000
0.1
1
LOAD CURRENT (mA)
3535 TA01b
3535f
1
LTC3535
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
V
Voltage............................................... –0.3V to 6V
IN1,2
SW1,2 Voltage
1
2
3
4
5
6
12 FB1
V
OUT1
SHDN1
SW1
11
10
9
DC............................................................ –0.3V to 6V
Pulsed <100ns......................................... –0.3V to 7V
SHDN1,2, FB1,2 Voltage .............................. –0.3V to 6V
V
IN1
GND
13
FB2
V
OUT2
SHDN2
8
SW2
7
V
IN2
GND
V
......................................................... –0.3V to 6V
OUT1,2
DD PACKAGE
12-LEAD (3mm s 3mm) PLASTIC DFN
Operating Temperature Range
(Notes 2, 5).............................................. –40°C to 85°C
Junction Temperature ........................................... 125°C
Storage Temperature Range................... –65°C to 150°C
θ
= 45°C/W, θ
= 10°C/W,
JC(PAD)
JA
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
12-Lead (3mm × 3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
LTC3535EDD#PBF
LTC3535EDD#TRPBF
LDWV
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 TA = 25°C. VIN = 1.2V, VOUT = 3.3V unless otherwise noted.
PARAMETER
CONDITIONS
= 1mA
MIN
TYP
MAX
0.8
5
UNITS
V
Minimum Start-Up Input Voltage
Input Voltage Range
I
0.68
LOAD
l
l
l
After Start-Up. (Minimum Voltage is Load Dependent)
0.5
1.5
V
Output Voltage Adjust Range
Feedback Pin Voltage
5.25
1.225
50
V
1.165
1.195
1
V
Feedback Pin Input Current
V
V
= 1.30V
nA
μA
μA
μA
μA
μA
Ω
FB
Quiescent Current—Shutdown
Quiescent Current—Active
= 0V, Not Including Switch Leakage, V
SHDN
= 0V
0.01
250
9
1
OUT
Measured on V , Non-Switching
500
18
OUT
Quiescent Current—Burst
Measured on V , FB > 1.230V
OUT
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
V
V
V
V
= 5V
0.1
0.1
0.4
0.6
750
60
5
SW
= 5V, V
= 0V
10
SW
OUT
= 3.3V
= 3.3V
OUT
OUT
Ω
l
l
550
87
mA
ns
%
(Note 3)
= 1.15V
V
FB
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 TA = 25°C. VIN = 1.2V, VOUT = 3.3V unless otherwise noted.
PARAMETER
CONDITIONS
V = 1.3V
FB
MIN
TYP
MAX
0
UNITS
%
l
l
Minimum Duty Cycle
Switching Frequency
SHDN Pin Input High Voltage
SHDN Pin Input Low Voltage
0.75
0.8
1
1.25
MHz
V
0.3
V
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 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.
Note 3: Specification is guaranteed by design and not 100% tested in
production.
TYPICAL PERFORMANCE CHARACTERISTICS (Each Channel) TA = 25°C, unless otherwise noted.
Efficiency vs Load Current
and VIN for VOUT = 1.8V
Efficiency vs Load Current
and VIN for VOUT = 3.3V
No-Load Input Current vs VIN
100
90
1000
100
10
100
90
1000
100
10
100
90
80
70
60
50
40
30
20
10
EFFICIENCY
EFFICIENCY
V
OUT
= 5V
80
80
70
70
V
= 3.3V
OUT
V
60
50
60
50
= 2.5V
OUT
POWER LOSS
POWER LOSS
V
OUT
= 1.8V
40
30
20
10
0
1
40
30
20
10
0
1
V
= 1.2V
= 1.8V
= 2.4V
= 3.0V
IN
IN
IN
IN
0.1
0.01
0.1
0.01
V
V
V
= 1.0V
= 1.2V
= 1.5V
IN
IN
IN
V
V
V
2.5 3.0
(V)
0.5 1.0 1.5 2.0
3.5 4.0 4.5
0.01
0.1
1
10
100
1000
0.01
0.1
1
10
100
1000
V
LOAD CURRENT (mA)
LOAD CURRENT (mA)
IN
3535 G01
3535 G02
3535 G04
3535f
3
LTC3535
TYPICAL PERFORMANCE CHARACTERISTICS (Each Channel) TA = 25°C, unless otherwise noted.
Minimum Load Resistance
During Start-Up vs VIN
Efficiency vs Load Current
and VIN for VOUT = 5V
Maximum Output Current vs VIN
10000
1000
100
90
1000
100
10
400
350
300
250
200
150
100
50
V
OUT
= 3.3V
V
OUT
= 3.3V
EFFICIENCY
V
OUT
= 2.5V
80
V
OUT
= 1.8V
70
60
50
POWER LOSS
V
OUT
= 5V
40
30
20
10
0
1
100
V
= 1.2V
= 2.4V
= 3.6V
= 4.2V
IN
IN
IN
IN
0.1
0.01
V
V
V
L = 4.7μH
10
0
2.5 3.0
0.65
0.75
0.85
0.95
(V)
1.05
1.15
0.5 1.0 1.5 2.0
3.5 4.0 4.5
0.01
0.1
1
10
100
1000
V
IN
(V)
LOAD CURRENT (mA)
V
IN
3535 G03
3526 G06
3535 G05
Burst Mode Threshold Current
vs VIN
Burst Mode Threshold Current
vs VIN
Start-Up Delay Time vs VIN
100
90
80
70
60
50
40
30
20
10
0
30
25
40
35
30
25
V
= 1.8V
V
= 2.5V
OUT
OUT
LEAVE BURST
L = 4.7μH
LEAVE BURST
L = 4.7μH
20
15
ENTER BURST
ENTER BURST
20
15
10
5
10
5
0
0
1.0
2.0 2.5 3.0
(V)
3.5 4.0 4.5
1
1.25
(V)
1.5
1.5
1.25
1.5
(V)
1.75
1
2
V
IN
V
IN
V
IN
3535 G07
3535 G08a
3535 G08b
Burst Mode Threshold Current
vs VIN
Burst Mode Threshold Current
vs VIN
Oscillator Frequency Change
vs VOUT
40
35
30
25
20
15
10
5
3
2
1
0
50
NORMALIZED TO V
= 3.3V
OUT
V
= 3.3V
OUT
V
= 5V
OUT
LEAVE BURST
L = 4.7μH
L = 4.7μH
LEAVE BURST
40
30
ENTER BURST
ENTER BURST
20
10
0
–1
–2
–3
0
3.5
(V)
4.5
5.0
1.5 2.0
2.5 3.0
V
4.0
1.0
1.5
2.0
(V)
2.5
3.0
3.0
(V)
4.0
4.5
1.0 1.5
2.0 2.5
V
3.5
V
IN
OUT
IN
3535 G09
3535 G08c
3535 G08d
3535f
4
LTC3535
TYPICAL PERFORMANCE CHARACTERISTICS (Each Channel) TA = 25°C, unless otherwise noted.
Oscillator Frequency Change
RDS(ON) vs VOUT
vs Temperature
RDS(ON) Change vs Temperature
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
10
8
1.3
1.2
1.1
1.0
0.9
0.8
0.7
NORMALIZED TO 25°C
NORMALIZED TO 25°C
6
4
2
PMOS
NMOS
(V)
0
–2
–4
–6
–8
–10
–50 –30 –10 10
30
50
70
90
1.5
2.5 3.0 3.5
4.0 4.5 5.0
2.0
–50 –30 –10 10
30
50
70
90
V
TEMPERATURE (°C)
TEMPERATURE (°C)
OUT
3535 G11
3535 G10
3535 G12
Burst Mode Quiescent Current
vs VOUT
Start-Up Voltage vs Temperature
VFB vs Temperature
0.80
0.75
0.70
0.65
0.60
0.55
0.50
10.0
9.5
9.0
8.5
8.0
7.5
7.0
0.50
0.25
NORMALIZED TO 25°C
MEASURED ON V
OUT
1mA LOAD
0
–0.25
–0.50
–0.75
–1.00
NO LOAD
40 60
TEMPERATURE (°C)
–50
25
0
25
50
75
100
1.5
3.0 3.5 4.0 4.5 5.0
(V)
–60 –40 –20
0
20
80 100
2.0 2.5
TEMPERATURE (°C)
V
OUT
3526 G14
3535 G13
3535 G15
Fixed Frequency Switching
Waveform and VOUT Ripple
VOUT and IIN During Soft-Start
Burst Mode Waveforms
V
SW PIN
2V/DIV
OUT
SW PIN
2V/DIV
1V/DIV
V
OUT
INPUT
CURRENT
0.2A/DIV
SHDN PIN
1V/DIV
20mV/DIV
V
OUT
AC COUPLED
10mV/DIV
INDUCTOR
CURRENT
0.2A/DIV
AC COUPLED
3535 G18
3535 G16
3535 G17
V
OUT
C
OUT
= 3.3V
= 10μF
200μs/DIV
V
V
C
= 1.2V
500ns/DIV
V
V
C
= 1.2V
10μs/DIV
IN
IN
= 3.3V AT 100mA
= 3.3V
= 10μF
OUT
OUT
OUT
OUT
= 10μF
3535f
5
LTC3535
TYPICAL PERFORMANCE CHARACTERISTICS (Each Channel) TA = 25°C, unless otherwise noted.
Load Step Response
(from Burst Mode Operation)
Load Step Response
(Fixed Frequency)
V
V
OUT
OUT
100mV/DIV
100mV/DIV
AC COUPLED
AC COUPLED
LOAD
CURRENT
50mA/DIV
LOAD
CURRENT
50mA/DIV
3535 G19
3535 G20
V
V
= 3.6V
= 5V
100μs/DIV
V
V
= 3.6V
= 5V
100μs/DIV
IN
OUT
IN
OUT
20mA TO 170mA STEP
= 10μF
50mA TO 150mA STEP
C
C
= 10μF
OUT
OUT
Load Step Response
(Fixed Frequency)
Load Step Response
(from Burst Mode Operation)
V
OUT
V
OUT
100mV/DIV
100mV/DIV
AC COUPLED
AC COUPLED
LOAD
CURRENT
50mA/DIV
LOAD
CURRENT
50mA/DIV
3535 G22
3535 G21
V
V
= 1.2V
50μs/DIV
V
V
= 1.2V
100μs/DIV
IN
OUT
IN
OUT
= 3.3V
= 3.3V
5mA TO 100mA STEP
= 10μF
50mA TO 100mA STEP
= 10μF
C
C
OUT
OUT
3535f
6
LTC3535
PIN FUNCTIONS
V
(Pin 1): Output Voltage Sense and Drain of the
SHDN2(Pin8):LogicControlledShutdownInputforChan-
OUT1
Internal Synchronous Rectifier for Channel 1. PCB trace
nel 2. There is an internal 4MegΩ pull-down on this pin.
length from V
minimum) should be as short and wide as possible.
to the output filter capacitor (4.7μF
OUT1
SHDN = High: Normal operation.
SHDN = Low: Shutdown, quiescent current < 1μA.
SW1 (Pin 2): Switch Pin for Channel 1. Connect inductor
FB2 (Pin 9): Feedback Input to the g Error Amplifier of
between SW1 and V . Keep PCB trace lengths as short
m
IN1
Channel 2. Connect resistor divider tap to this pin. The
and wide as possible to reduce EMI. If the inductor current
output voltage can be adjusted from 1.5V to 5.25V by:
fallstozero,orSHDN1islow,aninternalanti-ringingswitch
V
OUT
= 1.195V × [1 + (R4/R3)]
is connected from SW1 to V to minimize EMI.
IN1
V
(Pin10):BatteryInputVoltageforChannel1.Connect
GND (Pins 3, 6): Signal and Power Ground. Provide a
short direct PCB path between GND and the (-) side of
the input and output capacitors.
IN1
a minimum of 1μF ceramic decoupling capacitor from this
pin to ground.
SHDN1(Pin11):LogicControlledShutdownInputforChan-
V
(Pin 4): Output Voltage Sense and Drain of the
OUT2
nel 1. There is an internal 4MegΩ pull-down on this pin.
Internal Synchronous Rectifier for Channel 2. PCB trace
length from V
minimum) should be as short and wide as possible.
to the output filter capacitor (4.7μF
OUT2
SHDN = High: Normal operation.
SHDN = Low: Shutdown, quiescent current < 1μA.
SW2 (Pin 5): Switch Pin for Channel 2. Connect inductor
FB1 (Pin 12): Feedback Input to the g Error Amplifier
m
between SW2 and V . Keep PCB trace lengths as short
IN2
of Channel 1. Connect resistor divider tap to this pin. The
and wide as possible to reduce EMI. If the inductor current
output voltage can be adjusted from 1.5V to 5.25V by:
fallstozero,orSHDN2islow,aninternalanti-ringingswitch
V
OUT
= 1.195V × [1 + (R2/R1)]
is connected from SW2 to V to minimize EMI.
IN2
ExposedPad(Pin13):TheExposedPadmustbesoldered
to the PCB ground plane. It serves as another ground
connection and as a means of conducting heat away
from the die.
V
(Pin 7): Battery Input Voltage for Channel 2. Connect
IN2
a minimum of 1μF ceramic decoupling capacitor from this
pin to ground.
3535f
7
LTC3535
BLOCK DIAGRAM
L1
4.7μH
V
IN1
0.8V
TO 5V
C
IN
10
2
2.2μF
V
SW1
IN1
V
OUT
V
SEL
WELL
SWITCH
V
BEST
V
B
V
OUT1
V
OUT1
1.5V
1
TO 5.25V
ANTI-RING
GATE DRIVERS
AND
ANTI-CROSS
CONDUCTION
R2
R1
FB1
C
OUT1
10μF
12
SHDN1
4M
SHUTDOWN
11
SHUTDOWN
+
–
I
ZERO
COMP
3
SLOPE
COMP
I
PK
COMP
V
REF
V
REF1
–
+
I
PK
UVLO
ERROR AMP
SLEEP COMP
I
ZERO
START-UP
V
+
–
REF
LOGIC
MODE
CLK1
TSD
CONTROL
1MHz
OSC
CLAMP
WAKE
THERMAL
SHUTDOWN
L2
C
SS
4.7μH
SW2
5
7
V
IN2
V
IN2
0.8V
TO 5V
V
IN2
C
IN2
2.2μF
V
OUT2
V
SEL
WELL
SWITCH
V
BEST
V
B
V
OUT2
V
OUT2
1.5V
4
9
TO 5.25V
ANTI-RING
GATE DRIVERS
AND
R4
R3
FB2
C
OUT2
10μF
ANTI-CROSS
CONDUCTION
SHDN2
4M
SHUTDOWN
8
SHUTDOWN
+
–
I
ZERO
COMP
3
SLOPE
COMP
I
PK
COMP
V
REF
V
REF2
–
+
I
PK
UVLO
ERROR AMP
SLEEP COMP
I
ZERO
START-UP
V
+
–
REF
LOGIC
MODE
CLK2
TSD
CONTROL
1MHz
OSC
CLAMP
WAKE
THERMAL
SHUTDOWN
C
SS
EXPOSED
PAD
GND
3
GND
6
13
3535 BD
3535f
8
LTC3535
(Refer to Block Diagram)
OPERATION
The LTC3535 is a dual channel 1MHz synchronous boost
converter housed in a 12-lead 3mm × 3mm DFN package.
Each channel is identical and fully independent. They can
operate from the same source, or from different voltage
sources.
LOW VOLTAGE START-UP
The LTC3535 includes an independent start-up oscillator
designed to start up at an input voltage of 0.68V (typical).
Soft-start and inrush current limiting are provided during
start-up, as well as normal mode.
In addition, their output voltages can be tied together
to allow operation of a single output from two different
input sources. However, note that the two channels are
not designed to current share, so if both input voltages
are present either one may be supplying the load.
When either V or V
for a given channel exceeds 1.3V
OUT
IN
typical, the channel enters normal operating mode. When
the output voltage exceeds the input by 0.24V, the channel
powers itself from V
instead of V . At this point the
IN
OUT
internal circuitry has no dependency on the V input volt-
IN
The following description of operation applies to each
age,eliminatingtherequirementforalargeinputcapacitor.
The input voltage can drop as low as 0.5V. The limiting
factor for the application becomes the availability of the
power source to supply sufficient energy to the output at
lowvoltages,andmaximumdutycycle,whichisclampedat
90% typical. Note that at low input voltages, small voltage
drops due to series resistance become critical, and greatly
limit the power delivery capability of the converter.
channel. Note that references to V or V
apply to the
IN
OUT
corresponding channel.
With a guaranteed ability to start up and operate from
inputs less than 0.8V, each channel features fixed fre-
quency, current mode PWM control for exceptional line
and load regulation. The current mode architecture with
adaptive slope compensation provides excellent transient
load response, requiring minimal output filtering. Internal
soft-start and internal loop compensation simplifies the
design process while minimizing the number of external
components.
LOW NOISE FIXED FREQUENCY OPERATION
Soft-Start
The LTC3535 contains internal circuitry to provide soft-
start operation. The soft-start circuitry slowly ramps the
peakinductorcurrentfromzerotoitspeakvalueof750mA
(typical) in approximately 0.5ms, allowing start-up into
heavy loads. The soft-start circuitry is reset in the event
of a shutdown command or a thermal shutdown.
WithitslowR
andlowgatechargeinternalN-channel
DS(ON)
MOSFET switch and P-channel MOSFET synchronous
rectifier, the LTC3535 achieves high efficiency over a wide
range of load currents. Burst Mode operation maintains
high efficiency at very light loads, reducing the quiescent
current to just 9μA per channel. Operation can be best
understood by referring to the Block Diagram.
3535f
9
LTC3535
(Refer to Block Diagram)
OPERATION
Oscillator
Current Limit
An internal oscillator (independent for each channel) sets
the switching frequency to 1MHz.
The current limit comparator shuts off the N-channel
MOSFET switch once its threshold is reached. The cur-
rent limit comparator delay to output is typically 60ns.
Peak switch current is limited to approximately 750mA,
Shutdown
independent of input or output voltage, unless V
falls
OUT
Shutdown is accomplished by pulling the SHDN pin below
0.3VandenabledbypullingtheSHDNpinabove0.8V.Note
below 0.7V, in which case the current limit is cut in half.
that SHDN can be driven above V or V , as long as it
IN
OUT
Zero Current Comparator
is limited to less than the absolute maximum rating.
The zero current comparator monitors the inductor cur-
rent to the output and shuts off the synchronous rectifier
when this current reduces to approximately 30mA. This
prevents the inductor current from reversing in polarity,
improving efficiency at light loads.
Error Amplifier
The positive input of the transconductance error amplifier
is internally connected to the 1.195V reference and the
negative input is connected to FB. Clamps limit the mini-
mumandmaximumerrorampoutputvoltageforimproved
large-signal transient response. Power converter control
loop compensation is provided internally. An external
Synchronous Rectifier
To control inrush current and to prevent the inductor
resistive voltage divider from V
the output voltage via FB from 1.5V to 5.25V.
to ground programs
current from running away when V is close to V , the
OUT IN
OUT
P-channel MOSFET synchronous rectifier is only enabled
when V > (V + 0.24V).
OUT
IN
R2
R1
⎛
⎝
⎞
VOUT =1.195V • 1+
⎜
⎟
⎠
Anti-Ringing Control
The anti-ring circuit connects a resistor across the in-
ductor to prevent high frequency ringing on the SW pin
during discontinuous current mode operation. Although
Current Sensing
Losslesscurrentsensingconvertsthepeakcurrentsignalof
theN-channelMOSFETswitchintoavoltagethatissummed
with the internal slope compensation. The summed signal
is compared to the error amplifier output to provide a peak
current control command for the PWM.
the ringing of the resonant circuit formed by L and C
SW
(capacitance on SW pin) is low energy, it can cause EMI
radiation.
3535f
10
LTC3535
(Refer to Block Diagram)
OPERATION
Output Disconnect
In Burst Mode operation, the LTC3535 still switches at a
fixed frequency of 1MHz, using the same error amplifier
and loop compensation for peak current mode control.
This control method eliminates any output transient when
switching between modes. In Burst Mode operation,
energy is delivered to the output until it reaches the
nominal regulation value, then the LTC3535 transitions
to sleep mode where the outputs are off and the LTC3535
The LTC3535 is designed to allow true output disconnect
by eliminating body diode conduction of the internal P-
channelMOSFETrectifier.ThisallowsforV togotozero
OUT
volts during shutdown, drawing no current from the input
source. It also allows for inrush current limiting at turn-
on, minimizing surge currents seen by the input supply.
Note that to obtain the advantages of output disconnect,
there must not be an external Schottky diode connected
consumes only 9μA of quiescent current from V
for
OUT
each channel. When the output voltage droops slightly,
switchingresumes. Thismaximizesefficiencyatverylight
loadsbyminimizingswitchingandquiescentlosses.Burst
Modeoutputvoltageripple, whichistypically1%peak-to-
peak, can be reduced by using more output capacitance
(10μF or greater), or with a small capacitor (10pF to 50pF)
between SW and V . The output disconnect feature also
OUT
allows V
to be pulled high, without any reverse current
into a battery connected to V .
OUT
IN
Thermal Shutdown
If the die temperature exceeds 160°C, the LTC3535 will
go into thermal shutdown. All switches will be off and
the soft-start capacitor will be discharged. The device
will be enabled again when the die temperature drops by
about 15°C.
connected between V
and FB.
OUT
As the load current increases, the LTC3535 will automati-
cally leave Burst Mode operation. Note that larger output
capacitor values may cause this transition to occur at
lighter loads. Once the LTC3535 has left Burst Mode op-
eration and returned to normal operation, it will remain
there until the output load is reduced below the burst
threshold current.
Burst Mode OPERATION
Each channel of the LTC3535 will enter Burst Mode
operationatlightloadcurrentandreturntofixedfrequency
PWM mode when the load increases. Refer to the Typical
Performance Characteristics to see the output load Burst
Burst Mode operation is inhibited during start-up and
soft-start and until V
is at least 0.24V greater than V .
OUT
IN
Note that each channel can enter or leave Burst Mode
operation independent of the other channel.
Mode threshold current vs V . The load current at which
IN
Burst Mode operation is entered can be changed by
adjusting the inductor value. Raising the inductor value
will lower the load current at which Burst Mode operation
is entered.
3535f
11
LTC3535
APPLICATIONS INFORMATION
V > V
OPERATION
COMPONENT SELECTION
Inductor Selection
IN
OUT
The LTC3535 will maintain voltage regulation even when
the input voltage is above the desired output voltage. Note
that the efficiency is much lower in this mode, and the
maximum output current capability will be less. Refer to
the Typical Performance Characteristics.
The LTC3535 can utilize small surface mount chip induc-
tors due to their fast 1MHz switching frequency. Inductor
values between 3.3μH and 6.8μH are suitable for most
applications.Largervaluesofinductancewillallowslightly
greater output current capability (and lower the Burst
Mode threshold) by reducing the inductor ripple current.
Increasing the inductance above 10μH will increase com-
ponent size while providing little improvement in output
current capability.
SHORT-CIRCUIT PROTECTION
The LTC3535 output disconnect feature allows output
short circuit while maintaining a maximum internally set
current limit. To reduce power dissipation under short-
circuit conditions, the peak switch current limit is reduced
to 400mA (typical per channel).
The minimum inductance value is given by:
V
• VOUT(MAX) – V
(
)
IN(MIN)
IN(MIN)
L >
SCHOTTKY DIODE
Ripple• VOUT(MAX)
Althoughnotrecommended,addingaSchottkydiodefrom
where:
SW to V
will improve efficiency by about 2%. Note
OUT
that this defeats the output disconnect and short-circuit
Ripple = Allowable inductor current ripple (amps peak-
peak)
protection features.
V
V
= Minimum input voltage
IN(MIN)
PCB LAYOUT GUIDELINES
= Maximum output voltage
OUT(MAX)
ThehighspeedoperationoftheLTC3535demandscareful
attention to board layout. A careless layout will result in
reduced performance. Figure 1 shows the recommended
component placement. A large ground pin copper area
will help to lower the die temperature. A multilayer board
with a separate ground plane is ideal, but not absolutely
necessary.
The inductor current ripple is typically set for 20% to
40% of the maximum inductor current. High frequency
ferritecoreinductormaterialsreducefrequencydependent
power losses compared to cheaper powdered iron types,
improving efficiency. The inductor should have low ESR
(seriesresistanceofthewindings)toreducetheI2Rpower
losses, and must be able to support the peak inductor
currentwithoutsaturating.Moldedchokesandsomechip
inductorsusuallydonothaveenoughcoreareatosupport
the peak inductor current of 750mA seen on the LTC3535.
To minimize radiated noise, use a shielded inductor. See
Table 1 for suggested components and suppliers.
SHDN
V
OUT1
V
IN1
GND
GND
V
OUT2
V
IN2
SHDN
Figure 1. Recommended Component Placement
3535f
12
LTC3535
APPLICATIONS INFORMATION
Table 1. Recommended Inductors
4.7μF to 10μF output capacitor is sufficient for most ap-
plications. Larger values may be used to obtain extremely
low output voltage ripple and improve transient response.
X5R and X7R dielectric materials are preferred for their
ability to maintain capacitance over wide voltage and
temperature ranges. Y5V types should not be used.
VENDOR
PART/STYLE
Coilcraft
(847) 639-6400
www.coilcraft.com
LPO4815
LPS4012, LPS4018
MSS5131
MSS4020
MOS6020
ME3220
TheinternalloopcompensationoftheLTC3535isdesigned
tobestablewithoutputcapacitorvaluesof4.7μForgreater
(withouttheneedforanyexternalseriesresistor).Although
ceramic capacitors are recommended, low ESR tantalum
capacitors may be used as well.
DS1605, DO1608
Coiltronics
www.cooperet.com
SD10, SD12, SD14, SD18, SD20,
SD52, SD3114, SD3118
FDK
(408) 432-8331
www.fdk.com
MIP3226D4R7M, MIP3226D3R3M
MIPF2520D4R7
MIPWT3226D3R0
Murata
LQH43C
Asmallceramiccapacitorinparallelwithalargertantalum
capacitormaybeusedindemandingapplicationsthathave
large load transients. Another method of improving the
transientresponseistoaddasmallfeed-forwardcapacitor
(714) 852-2001
www.murata.com
LQH32C (-53 series)
301015
Sumida
(847) 956-0666
www.sumida.com
CDRH5D18
CDRH2D14
CDRH3D16
across the top resistor of the feedback divider (from V
to FB). A typical value of 22pF will generally suffice.
OUT
CDRH3D11
CR43
CMD4D06-4R7MC
CMD4D06-3R3MC
Low ESR input capacitors reduce input switching noise
and reduce the peak current drawn from the battery. It
follows that ceramic capacitors are also a good choice
for input decoupling and should be located as close as
possible to the device. A 2.2μF input capacitor is sufficient
for most applications, although larger values may be
used without limitations. Table 2 shows a list of several
ceramiccapacitormanufacturers.Consultthemanufactur-
ers directly for detailed information on their selection of
ceramic capacitors.
Taiyo-Yuden
www.t-yuden.com
NP03SB
NR3015T
NR3012T
TDK
VLP
VLF, VLCF
(847) 803-6100
www.component.tdk.com
Toko
(408) 432-8282
www.tokoam.com
D412C
D518LC
D52LC
D62LCB
Wurth
(201) 785-8800
www.we-online.com
WE-TPC type S, M
Table 2. Capacitor Vendor Information
SUPPLIER
AVX
PHONE
WEBSITE
(803) 448-9411
(714) 852-2001
(408) 573-4150
(847) 803-6100
(408) 544-5200
www.avxcorp.com
www.murata.com
www.t-yuden.com
www.component.tdk.com
www.sem.samsung.com
Output and Input Capacitor Selection
Murata
Low ESR (equivalent series resistance) capacitors should
be used to minimize the output voltage ripple. Multilayer
ceramic capacitors are an excellent choice as they have
extremely low ESR and are available in small footprints. A
Taiyo-Yuden
TDK
Samsung
3535f
13
LTC3535
TYPICAL APPLICATION
Single Cell to 3.3V Converter with 20 Seconds of Holdup with 30mA Load
V
OUT
4.7μH
3.3V
499k
30mA
V
SW
IN
V
HOLDUP
4.25V
1M
V
V
V
0.8V
IN1
OUT1
OUT2
+
TO 1.5V
C
HOLD
*
SHDN1
2.2μF
0.47μF
10μF
LTC3535
1.78M
V
FB1
FB2
IN2
SHDN2
392k
2.2μF
GND SW2 GND
1M
1.5M
4.7μH
3535 TA02
*POWERSTOR PA-5R0H474-R
V
IN
1V/DIV
V
HOLDUP
2V/DIV
V
OUT
2V/DIV
3535 TA02b
5s/DIV
3535f
14
LTC3535
PACKAGE DESCRIPTION
DC Package
12-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1725 Rev A)
0.70 p 0.05
2.38 p 0.05
1.65 p 0.05
3.50 p 0.05
2.10 p 0.05
PACKAGE
OUTLINE
0.25 p 0.05
0.45 BSC
2.25 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
R = 0.115
0.40 p 0.10
TYP
7
12
2.38 p 0.10
3.00 p 0.10
(4 SIDES)
1.65 p 0.10
PIN 1 NOTCH
PIN 1
TOP MARK
R = 0.20 OR
0.25 s 45o
CHAMFER
(SEE NOTE 6)
6
1
0.23 p 0.05
0.45 BSC
0.75 p 0.05
0.200 REF
2.25 REF
(DD12) DFN 0106 REV A
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
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 AND TIE BARS SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
3535f
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.
15
LTC3535
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
92% Efficiency V : 1V to 5V, V
LTC3400/LTC3400B
600mA I , 1.2MHz, Synchronous Step-Up
= 5V, I = 19μA/300μA,
OUT(MAX) Q
SW
IN
DC/DC Converters
I
< 1μA, ThinSOT Package
SD
LTC3421
3A I , 3MHz, Synchronous Step-Up DC/DC Converter 95% Efficiency V : 1V to 4.5V, V
= 5.25V, I = 12μA,
Q
SW
IN
OUT(MAX)
OUT(MAX)
with Output Disconnect
I
< 1μA, QFN24 Package
SD
LTC3422
1.5A I , 3MHz Synchronous Step-Up DC/DC
95% Efficiency V : 1V to 4.5V, V
SD
= 5.25V, I = 25μA,
Q
SW
IN
Converter with Output Disconnect
I
< 1μA, 3mm × 3mm DFN Package
LTC3426
2A I , 1.2MHz, Step-Up DC/DC Converter
92% Efficiency V : 1.6V to 4.3V, V
= 5V, I < 1μA,
SW
IN
OUT(MAX)
OUT(MAX)
SD
SOT-23 Package
LTC3427
500mA I , 1.2MHZ, Synchronous Step-Up DC/DC
93% Efficiency V : 1.8V to 4.5V, V
= 5V,
SW
IN
Converter with Output Disconnect
2mm × 2mm DFN Package
LTC3428
500mA I , 1.25MHz/2.5MHz, Synchronous Step-Up
92% Efficiency V : 1.8V to 5V, V
= 5.25V, I < 1μA,
SD
SW
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
DC/DC Converters with Output Disconnect
2mm × 2mm DFN Package
LTC3429
600mA I , 500kHz, Synchronous Step-Up DC/DC
96% Efficiency V : 1V to 4.4V, V
= 5V, I = 20μA/300μA,
Q
SW
IN
Converter with Output Disconnect and Soft-Start
I
< 1μA, ThinSOT Package
SD
LTC3458/LTC3458L
LTC3459
1.4A I , 1.5MHz, Synchronous Step-Up DC/DC
93% Efficiency V : 1.5V to 6V, V
= 7.5V, I = 15μA,
Q
SW
IN
Converter/Output Disconnect/Burst Mode Operation
I
< 1μA, DFN12 Package
SD
70mA I , 10V Micropower Synchronous Boost
V : 1.5V to 5.5V, V
= 10V, I = 10μA, I < 1μA,
SW
IN
OUT(MAX)
Q
SD
Converter/Output Disconnect/Burst Mode Operation
ThinSOT Package
LTC3499
750mA (I ), 1.2MHz, Step-Up DC/DC Converter with 92% Efficiency V : 1.8V to 5.5V, V
= 6V, I = 20μA,
OUT(MAX) Q
SW
IN
Reverse Battery Protection and Output Disconnect
I
< 1μA, 3mm × 3mm DFN-8 Package, MSOP-8 Package
SD
LTC3525-3
LTC3525-3.3
LTC3525-5
400mA Micropower Synchronous Step-Up DC/DC
Converter with Output Disconnect
95% Efficiency V : 1V to 4.5V, V
SD
= 3.3V or 5V, I = 7μA,
OUT(MAX) Q
IN
I
< 1μA, SC-70 Package
LTC3525L-3
400mA Micropower Synchronous Step-Up DC/DC
Converter with Output Disconnect
93% Efficiency V : 0.88V to 4.5V, V
SD
= 3V, I = 7μA,
OUT Q
IN
I
< 1μA, SC-70 Package
LTC3526/LTC3526B
LTC3526-2
LTC3526B-2
500mA, 1MHz/2.2MHz, Synchronous Step-Up DC/DC
Converters with Output Disconnect
94% Efficiency V : 0.85V to 5V, V
SD
= 5.25V, I = 9μA,
OUT(MAX) Q
IN
I
< 1μA, 2mm × 2mm DFN-6 Package
LTC3526L
550mA, 1MHz, Synchronous Step-Up DC/DC
Converters with Output Disconnect
94% Efficiency V : 0.7V to 5V, V
SD
= 5.25V, I = 9μA,
Q
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
LTC3526LB
I
< 1μA, 2mm × 2mm DFN-6 Package
LTC3526/LTC3526B
500mA (I ), 1MHz Synchronous Step-Up DC/DC
94% Efficiency V : 0.8V to 5V, V
= 5.25V, I = 9μA,
Q
SW
IN
Converter with Output Disconnect
I
< 1μA, 2mm × 2mm DFN-6 Package
SD
LTC3527/LTC3527-1
Dual 800mA and 400mA (ISW), 2.2MHz, Synchronous 94% Efficiency V : 0.7V to 5V, V
Step-Up DC/DC Converter with Output Disconnect
= 5.25V, I = 12μA,
Q
IN
I
< 1μA, 3mm × 3mm QFN-16 Package
SD
LTC3528
1A (I ), 1MHz Synchronous Step-Up DC/DC with
94% Efficiency V : 0.7V to 5V, V
SD
= 5.25V, I = 12μA,
Q
SW
IN
OUT(MAX)
OUT(MAX)
LTC3528-2
Output DisconnectConverter
I
< 1μA, 2mm × 3mm DFN-8 Package
LTC3537
600mA , 2.2MHz, Synchronous Step-Up DC/DC
Converter with Output Disconnect and 100mA LDO
94% Efficiency V : 0.7V to 5V, V
= 5.25V, I = 30μA,
Q
IN
I
< 1μA, 3mm × 3mm QFN-16 Package
SD
LTC3539
LTC3539-2
2A (I ), 1/2MHz, Synchronous Step-Up DC/DC
94% Efficiency V : 0.7V to 5V, V
= 5.25V, I = 10μA,
OUT(MAX) Q
SW
IN
Converter with Output Disconnect
I
< 1μA, 2mm × 3mm DFN-8 Package
SD
ThinSOT is a trademark of Linear Technology Corporation.
3535f
LT 0109 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
© LINEAR TECHNOLOGY CORPORATION 2009
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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