LINER LTC3535EDD-PBF Dual channel 550ma 1mhz synchronous step-up dc/dc converter Datasheet

LTC3535
Dual Channel 550mA 1MHz
Synchronous Step-Up
DC/DC Converter
DESCRIPTION
FEATURES
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
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
VIN Start-Up Voltage: 680mV
1.5V to 5.25V VOUT Range
Up to 94% Efficiency
Output Disconnect
1MHz Fixed Frequency Operation
VIN > VOUT Operation
Integrated Soft-Start
Current Mode Control with Internal Compensation
Burst Mode® Operation with 9μA IQ Each Channel
Internal Synchronous Rectifier
Logic Controlled Shutdown (IQ < 1μA)
Anti-Ring Control
Low Profile (3mm × 3mm × 0.75mm)
12-Lead DFN Package
The LTC®3535 is a dual channel, synchronous, fixed frequency 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 footprint 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.
APPLICATIONS
n
n
n
n
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
Medical Instruments
Noise Canceling Headphones
Wireless Mice
Bluetooth Headsets
TYPICAL APPLICATION
Efficiency vs Load Current
4.7μH
SHDN1
VOUT2
OFF ON
VOUT2
3.3V
50mA
10μF
LTC3535
2.2μF
10μF
VIN2
FB1
SHDN2
FB2
90
1.78M
1M
GND SW2 GND
VOUT = 1.8V
80
511k
EFFICIENCY (%)
OFF ON
VIN
0.8V
TO 1.5V
VOUT1
100
VOUT1
1.8V
100mA
SW1
VIN1
70
VOUT = 3.3V
60
50
40
30
1M
20
4.7μH
3535 TA01
10
VIN = 1.2V
0
0.01
0.1
10
100
1
LOAD CURRENT (mA)
1000
3535 TA01b
3535f
1
LTC3535
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
VIN1,2 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
VOUT1,2 ......................................................... –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
12 FB1
VOUT1
1
SW1
2
GND
3
VOUT2
4
9 FB2
SW2
5
8 SHDN2
GND
6
7 VIN2
11 SHDN1
13
10 VIN1
DD PACKAGE
12-LEAD (3mm s 3mm) PLASTIC DFN
θJA = 45°C/W, θJC(PAD) = 10°C/W,
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3535EDD#PBF
LTC3535EDD#TRPBF
LDWV
12-Lead (3mm × 3mm) Plastic DFN
–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 TA = 25°C. VIN = 1.2V, VOUT = 3.3V unless otherwise noted.
PARAMETER
CONDITIONS
Minimum Start-Up Input Voltage
ILOAD = 1mA
Input Voltage Range
After Start-Up. (Minimum Voltage is Load Dependent)
Output Voltage Adjust Range
Feedback Pin Voltage
Feedback Pin Input Current
VFB = 1.30V
Quiescent Current—Shutdown
VSHDN= 0V, Not Including Switch Leakage, VOUT = 0V
Quiescent Current—Active
Measured on VOUT, Non-Switching
Quiescent Current—Burst
Measured on VOUT, FB > 1.230V
N-Channel MOSFET Switch Leakage Current
VSW = 5V
MIN
TYP
MAX
0.68
0.8
UNITS
V
l
0.5
5
V
l
1.5
5.25
V
l
1.165
1.195
1.225
V
1
50
nA
0.01
1
μA
250
500
μA
9
18
μA
0.1
5
μA
10
μA
P-Channel MOSFET Switch Leakage Current
VSW = 5V, VOUT = 0V
0.1
N-Channel MOSFET Switch On Resistance
VOUT = 3.3V
0.4
Ω
P-Channel MOSFET Switch On Resistance
VOUT = 3.3V
0.6
Ω
750
mA
60
ns
90
%
l
N-Channel MOSFET Current Limit
Current Limit Delay to Output
(Note 3)
Maximum Duty Cycle
VFB = 1.15V
l
550
87
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
Minimum Duty Cycle
VFB = 1.3V
MIN
TYP
MAX
0.75
1
1.25
l
0
l
Switching Frequency
UNITS
SHDN Pin Input High Voltage
%
MHz
0.8
V
SHDN Pin Input Low Voltage
0.3
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.
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) 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
100
EFFICIENCY
EFFICIENCY (%)
50
POWER LOSS
1
30
VIN = 1.0V
VIN = 1.2V
VIN = 1.5V
10
0.1
100
80
1
10
100
LOAD CURRENT (mA)
0.1
0.01
1000
3535 G01
90
80
70
10
60
50
POWER LOSS
1
40
30
VIN = 1.2V
VIN = 1.8V
VIN = 2.4V
VIN = 3.0V
20
10
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
POWER LOSS (mW)
10
60
POWER LOSS (mW)
70
20
EFFICIENCY
100
0.1
0.01
1000
VOUT = 5V
VOUT = 3.3V
70
IIN (μA)
100
40
No-Load Input Current vs VIN
1000
90
80
0
0.01
100
EFFICIENCY (%)
90
1000
VOUT = 2.5V
60
50
VOUT = 1.8V
40
30
20
10
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
VIN (V)
3535 G02
3535 G04
3535f
3
LTC3535
TYPICAL PERFORMANCE CHARACTERISTICS (Each Channel) TA = 25°C, unless otherwise noted.
Efficiency vs Load Current
and VIN for VOUT = 5V
100
50
POWER LOSS
40
30
1
VIN = 1.2V
VIN = 2.4V
VIN = 3.6V
VIN = 4.2V
20
10
0
0.01
0.1
VOUT = 1.8V
250
200
VOUT = 5V
150
100
100
0.1
50
0
0.5
0.01
1000
1
10
100
LOAD CURRENT (mA)
L = 4.7μH
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.75
0.85
0.95
1.05
1.15
VIN (V)
3526 G06
3535 G05
Burst Mode Threshold Current
vs VIN
Burst Mode Threshold Current
vs VIN
Start-Up Delay Time vs VIN
100
30
25
LOAD CURRENT (mA)
80
70
60
50
40
30
40
LEAVE BURST
20
ENTER BURST
15
VOUT = 2.5V
L = 4.7μH
35
LOAD CURRENT (mA)
VOUT = 1.8V
L = 4.7μH
90
DELAY (μs)
10
0.65
4.5
VIN (V)
3535 G03
10
LEAVE BURST
30
25
ENTER BURST
20
15
10
20
5
5
10
0
1.0
1.5
2.0
2.5 3.0
VIN (V)
3.5
4.0
0
4.5
1
1.25
VIN (V)
3
LOAD CURRENT (mA)
ENTER BURST
15
10
30
ENTER BURST
20
10
1.0
1.5
2.0
VIN (V)
2.5
3.0
3535 G08c
0
1.0
1
0
–1
–2
5
0
NORMALIZED TO VOUT = 3.3V
2
LEAVE BURST
FREQUENCY CHANGE (%)
LEAVE BURST
40
20
2
Oscillator Frequency Change
vs VOUT
VOUT = 5V
L = 4.7μH
25
1.75
3535 G08b
50
30
1.5
VIN (V)
Burst Mode Threshold Current
vs VIN
40
VOUT = 3.3V
L = 4.7μH
1.25
1
3535 G08a
Burst Mode Threshold Current
vs VIN
35
0
1.5
3535 G07
LOAD CURRENT (mA)
VOUT = 3.3V
VOUT = 2.5V
1000
IOUT (mA)
10
60
300
POWER LOSS (mW)
70
10000
VOUT = 3.3V
350
80
EFFICIENCY (%)
400
1000
EFFICIENCY
LOAD (Ω)
100
90
Minimum Load Resistance
During Start-Up vs VIN
Maximum Output Current vs VIN
1.5
2.0
2.5 3.0
VIN (V)
3.5
4.0
4.5
3535 G08d
–3
1.5
2.0
2.5
3.0 3.5
VOUT (V)
4.0
4.5
5.0
3535 G09
3535f
4
LTC3535
TYPICAL PERFORMANCE CHARACTERISTICS (Each Channel) TA = 25°C, unless otherwise noted.
Oscillator Frequency Change
vs Temperature
RDS(ON) vs VOUT
0.90
10
0.85
8
0.80
0.65
PMOS
0.60
0.55
0.50
0.45
4
2
0
–2
–4
NMOS
0.40
–6
1.1
1.0
0.9
0.8
–8
0.35
0.30
1.5
2.0
2.5
3.0 3.5
VOUT (V)
4.0
5.0
4.5
–10
–50
–30
–10 10
30
50
TEMPERATURE (°C)
0.7
–50
90
–30
–10 10
30
50
TEMPERATURE (°C)
70
90
3535 G12
Burst Mode Quiescent Current
vs VOUT
Start-Up Voltage vs Temperature
VFB vs Temperature
0.50
70
3535 G11
3535 G10
0.80
10.0
NORMALIZED TO 25°C
MEASURED ON VOUT
0.75
0.25
9.5
1mA LOAD
9.0
–0.25
0.65
IQ (μA)
0.70
0
VIN (V)
CHANGE IN VFB (%)
NORMALIZED TO 25°C
1.2
NORMALIZED RDS(ON)
RDS(ON) (Ω)
0.70
NORMALIZED TO 25°C
6
FREQUECNY CHANGE (%)
0.75
RDS(ON) Change vs Temperature
1.3
NO LOAD
8.5
–0.50
0.60
8.0
–0.75
0.55
7.5
–1.00
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
80
100
0.50
–50
25
0
25
50
TEMPERATURE (°C)
75
100
Fixed Frequency Switching
Waveform and VOUT Ripple
3535 G16
3.0 3.5
VOUT (V)
4.0
5.0
4.5
VOUT and IIN During Soft-Start
VOUT
1V/DIV
SW PIN
2V/DIV
VOUT
20mV/DIV
AC COUPLED
INDUCTOR
CURRENT
0.2A/DIV
VOUT
10mV/DIV
AC COUPLED
2.5
3535 G15
Burst Mode Waveforms
SW PIN
2V/DIV
2.0
3526 G14
3535 G13
VIN = 1.2V
500ns/DIV
VOUT = 3.3V AT 100mA
COUT = 10μF
7.0
1.5
INPUT
CURRENT
0.2A/DIV
SHDN PIN
1V/DIV
VIN = 1.2V
VOUT = 3.3V
COUT = 10μF
10μs/DIV
3535 G17
VOUT = 3.3V
COUT = 10μF
200μs/DIV
3535 G18
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)
VOUT
100mV/DIV
AC COUPLED
VOUT
100mV/DIV
AC COUPLED
LOAD
CURRENT
50mA/DIV
LOAD
CURRENT
50mA/DIV
VIN = 3.6V
100μs/DIV
VOUT = 5V
20mA TO 170mA STEP
COUT = 10μF
3535 G19
VIN = 3.6V
100μs/DIV
VOUT = 5V
50mA TO 150mA STEP
COUT = 10μF
Load Step Response
(Fixed Frequency)
3535 G20
Load Step Response
(from Burst Mode Operation)
VOUT
100mV/DIV
AC COUPLED
VOUT
100mV/DIV
AC COUPLED
LOAD
CURRENT
50mA/DIV
LOAD
CURRENT
50mA/DIV
VIN = 1.2V
100μs/DIV
VOUT = 3.3V
50mA TO 100mA STEP
COUT = 10μF
3535 G21
VIN = 1.2V
50μs/DIV
VOUT = 3.3V
5mA TO 100mA STEP
COUT = 10μF
3535 G22
3535f
6
LTC3535
PIN FUNCTIONS
VOUT1 (Pin 1): Output Voltage Sense and Drain of the
Internal Synchronous Rectifier for Channel 1. PCB trace
length from VOUT1 to the output filter capacitor (4.7μF
minimum) should be as short and wide as possible.
SHDN2 (Pin 8): Logic Controlled Shutdown Input for Channel 2. There is an internal 4MegΩ pull-down on this pin.
SHDN = High: Normal operation.
SHDN = Low: Shutdown, quiescent current < 1μA.
SW1 (Pin 2): Switch Pin for Channel 1. Connect inductor
between SW1 and VIN1. Keep PCB trace lengths as short
and wide as possible to reduce EMI. If the inductor current
falls to zero, or SHDN1 is low, an internal anti-ringing switch
is connected from SW1 to VIN1 to minimize EMI.
FB2 (Pin 9): Feedback Input to the gm Error Amplifier of
Channel 2. Connect resistor divider tap to this pin. The
output voltage can be adjusted from 1.5V to 5.25V by:
VOUT = 1.195V × [1 + (R4/R3)]
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.
VIN1 (Pin 10): Battery Input Voltage for Channel 1. Connect
a minimum of 1μF ceramic decoupling capacitor from this
pin to ground.
VOUT2 (Pin 4): Output Voltage Sense and Drain of the
Internal Synchronous Rectifier for Channel 2. PCB trace
length from VOUT2 to the output filter capacitor (4.7μF
minimum) should be as short and wide as possible.
SHDN1 (Pin 11): Logic Controlled Shutdown Input for Channel 1. There is an internal 4MegΩ pull-down on this pin.
SHDN = High: Normal operation.
SHDN = Low: Shutdown, quiescent current < 1μA.
SW2 (Pin 5): Switch Pin for Channel 2. Connect inductor
between SW2 and VIN2. Keep PCB trace lengths as short
and wide as possible to reduce EMI. If the inductor current
falls to zero, or SHDN2 is low, an internal anti-ringing switch
is connected from SW2 to VIN2 to minimize EMI.
FB1 (Pin 12): Feedback Input to the gm Error Amplifier
of Channel 1. Connect resistor divider tap to this pin. The
output voltage can be adjusted from 1.5V to 5.25V by:
VOUT = 1.195V × [1 + (R2/R1)]
VIN2 (Pin 7): Battery Input Voltage for Channel 2. Connect
a minimum of 1μF ceramic decoupling capacitor from this
pin to ground.
Exposed Pad (Pin 13): The Exposed Pad must be soldered
to the PCB ground plane. It serves as another ground
connection and as a means of conducting heat away
from the die.
3535f
7
LTC3535
BLOCK DIAGRAM
VIN1
0.8V
TO 5V
L1
4.7μH
CIN
2.2μF
10
2
VIN1
SW1
VOUT
VSEL
VBEST
WELL
SWITCH
VB
VOUT1
VOUT1
1.5V
TO 5.25V
1
ANTI-RING
11
SHDN1
SHUTDOWN
SHUTDOWN
GATE DRIVERS
AND
ANTI-CROSS
CONDUCTION
R2
FB1
– +
4M
3
IPK
COMP
VREF1
IPK
UVLO
IZERO
COMP
ERROR AMP
SLEEP COMP
IZERO
START-UP
LOGIC
+
–
MODE
CONTROL
CLK1
1MHz
OSC
R1
SLOPE
COMP
+
–
VREF
COUT1
10μF
12
VREF
CLAMP
5
VIN2
0.8V
TO 5V
TSD
THERMAL
SHUTDOWN
L2
4.7μH
7
WAKE
CSS
SW2
VIN2
VIN2
CIN2
2.2μF
VOUT2
VSEL
VBEST
WELL
SWITCH
VB
VOUT2
VOUT2
1.5V
TO 5.25V
4
ANTI-RING
8
SHDN2
SHUTDOWN
SHUTDOWN
GATE DRIVERS
AND
ANTI-CROSS
CONDUCTION
R4
FB2
– +
4M
3
IPK
COMP
VREF2
IPK
UVLO
START-UP
1MHz
OSC
+
–
MODE
CONTROL
CLK2
R3
ERROR AMP
SLEEP COMP
IZERO
LOGIC
IZERO
COMP
SLOPE
COMP
+
–
VREF
COUT2
10μF
9
VREF
CLAMP
THERMAL
SHUTDOWN
TSD
WAKE
CSS
GND
EXPOSED
PAD
GND
3
13
6
3535 BD
3535f
8
LTC3535
OPERATION
(Refer to Block Diagram)
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
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 VIN or VOUT for a given channel exceeds 1.3V
typical, the channel enters normal operating mode. When
the output voltage exceeds the input by 0.24V, the channel
powers itself from VOUT instead of VIN. At this point the
internal circuitry has no dependency on the VIN input voltage, eliminating the requirement for a large input capacitor.
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
low voltages, and maximum duty cycle, which is clamped at
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.
The following description of operation applies to each
channel. Note that references to VIN or VOUT apply to the
corresponding channel.
With a guaranteed ability to start up and operate from
inputs less than 0.8V, each channel features fixed frequency, 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.
With its low RDS(ON) and low gate charge internal N-channel
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.
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.
LOW NOISE FIXED FREQUENCY OPERATION
Soft-Start
The LTC3535 contains internal circuitry to provide softstart operation. The soft-start circuitry slowly ramps the
peak inductor current from zero to its peak value of 750mA
(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.
3535f
9
LTC3535
OPERATION
(Refer to Block Diagram)
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 current limit comparator delay to output is typically 60ns.
Peak switch current is limited to approximately 750mA,
independent of input or output voltage, unless VOUT falls
below 0.7V, in which case the current limit is cut in half.
Shutdown
Shutdown is accomplished by pulling the SHDN pin below
0.3V and enabled by pulling the SHDN pin above 0.8V. Note
that SHDN can be driven above VIN or VOUT, as long as it
is limited to less than the absolute maximum rating.
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 minimum and maximum error amp output voltage for improved
large-signal transient response. Power converter control
loop compensation is provided internally. An external
resistive voltage divider from VOUT to ground programs
the output voltage via FB from 1.5V to 5.25V.
⎛ R2 ⎞
VOUT = 1.195V • ⎜ 1+ ⎟
⎝ R1⎠
Current Sensing
Lossless current sensing converts the peak current signal of
the N-channel MOSFET switch into a voltage that is summed
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.
Zero Current Comparator
The zero current comparator monitors the inductor current 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.
Synchronous Rectifier
To control inrush current and to prevent the inductor
current from running away when VOUT is close to VIN, the
P-channel MOSFET synchronous rectifier is only enabled
when VOUT > (VIN + 0.24V).
Anti-Ringing Control
The anti-ring circuit connects a resistor across the inductor to prevent high frequency ringing on the SW pin
during discontinuous current mode operation. Although
the ringing of the resonant circuit formed by L and CSW
(capacitance on SW pin) is low energy, it can cause EMI
radiation.
3535f
10
LTC3535
OPERATION
(Refer to Block Diagram)
Output Disconnect
The LTC3535 is designed to allow true output disconnect
by eliminating body diode conduction of the internal Pchannel MOSFET rectifier. This allows for VOUT to go to zero
volts during shutdown, drawing no current from the input
source. It also allows for inrush current limiting at turnon, 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
between SW and VOUT. The output disconnect feature also
allows VOUT to be pulled high, without any reverse current
into a battery connected to VIN.
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.
Burst Mode OPERATION
Each channel of the LTC3535 will enter Burst Mode
operation at light load current and return to fixed frequency
PWM mode when the load increases. Refer to the Typical
Performance Characteristics to see the output load Burst
Mode threshold current vs VIN. The load current at which
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.
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
consumes only 9μA of quiescent current from VOUT for
each channel. When the output voltage droops slightly,
switching resumes. This maximizes efficiency at very light
loads by minimizing switching and quiescent losses. Burst
Mode output voltage ripple, which is typically 1% peak-topeak, can be reduced by using more output capacitance
(10μF or greater), or with a small capacitor (10pF to 50pF)
connected between VOUT and FB.
As the load current increases, the LTC3535 will automatically 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 operation and returned to normal operation, it will remain
there until the output load is reduced below the burst
threshold current.
Burst Mode operation is inhibited during start-up and
soft-start and until VOUT is at least 0.24V greater than VIN.
Note that each channel can enter or leave Burst Mode
operation independent of the other channel.
3535f
11
LTC3535
APPLICATIONS INFORMATION
VIN > VOUT OPERATION
COMPONENT SELECTION
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.
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 shortcircuit conditions, the peak switch current limit is reduced
to 400mA (typical per channel).
The LTC3535 can utilize small surface mount chip inductors due to their fast 1MHz switching frequency. Inductor
values between 3.3μH and 6.8μH are suitable for most
applications. Larger values of inductance will allow slightly
greater output current capability (and lower the Burst
Mode threshold) by reducing the inductor ripple current.
Increasing the inductance above 10μH will increase component size while providing little improvement in output
current capability.
The minimum inductance value is given by:
L>
SCHOTTKY DIODE
Although not recommended, adding a Schottky diode from
SW to VOUT will improve efficiency by about 2%. Note
that this defeats the output disconnect and short-circuit
protection features.
The high speed operation of the LTC3535 demands careful
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.
SHDN
VOUT1
VIN1
GND
GND
SHDN
(
VIN(MIN) • VOUT(MAX ) – VIN(MIN)
)
Ripple • VOUT(MAX)
where:
Ripple = Allowable inductor current ripple (amps peakpeak)
VIN(MIN) = Minimum input voltage
PCB LAYOUT GUIDELINES
VOUT2
Inductor Selection
VOUT(MAX) = Maximum output voltage
The inductor current ripple is typically set for 20% to
40% of the maximum inductor current. High frequency
ferrite core inductor materials reduce frequency dependent
power losses compared to cheaper powdered iron types,
improving efficiency. The inductor should have low ESR
(series resistance of the windings) to reduce the I2R power
losses, and must be able to support the peak inductor
current without saturating. Molded chokes and some chip
inductors usually do not have enough core area to support
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.
VIN2
Figure 1. Recommended Component Placement
3535f
12
LTC3535
APPLICATIONS INFORMATION
Table 1. Recommended Inductors
VENDOR
PART/STYLE
Coilcraft
(847) 639-6400
www.coilcraft.com
LPO4815
LPS4012, LPS4018
MSS5131
MSS4020
MOS6020
ME3220
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
(714) 852-2001
www.murata.com
LQH43C
LQH32C (-53 series)
301015
Sumida
(847) 956-0666
www.sumida.com
CDRH5D18
CDRH2D14
CDRH3D16
CDRH3D11
CR43
CMD4D06-4R7MC
CMD4D06-3R3MC
Taiyo-Yuden
www.t-yuden.com
NP03SB
NR3015T
NR3012T
TDK
(847) 803-6100
www.component.tdk.com
VLP
VLF, VLCF
Toko
(408) 432-8282
www.tokoam.com
D412C
D518LC
D52LC
D62LCB
Wurth
(201) 785-8800
www.we-online.com
WE-TPC type S, M
Output and Input Capacitor Selection
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
4.7μF to 10μF output capacitor is sufficient for most applications. 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.
The internal loop compensation of the LTC3535 is designed
to be stable with output capacitor values of 4.7μF or greater
(without the need for any external series resistor). Although
ceramic capacitors are recommended, low ESR tantalum
capacitors may be used as well.
A small ceramic capacitor in parallel with a larger tantalum
capacitor may be used in demanding applications that have
large load transients. Another method of improving the
transient response is to add a small feed-forward capacitor
across the top resistor of the feedback divider (from VOUT
to FB). A typical value of 22pF will generally suffice.
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
ceramic capacitor manufacturers. Consult the manufacturers directly for detailed information on their selection of
ceramic capacitors.
Table 2. Capacitor Vendor Information
SUPPLIER
PHONE
WEBSITE
AVX
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
Taiyo-Yuden
(408) 573-4150
www.t-yuden.com
TDK
(847) 803-6100
www.component.tdk.com
Samsung
(408) 544-5200
www.sem.samsung.com
3535f
13
LTC3535
TYPICAL APPLICATION
Single Cell to 3.3V Converter with 20 Seconds of Holdup with 30mA Load
VOUT
3.3V
30mA
4.7μH
499k
SW
VIN
0.8V
TO 1.5V
2.2μF
VIN1
VOUT1
SHDN1
VOUT2
4.25V
1M
1.78M
VIN2
FB1
SHDN2
FB2
GND SW2 GND
1.5M
VHOLDUP
CHOLD*
0.47μF
10μF
LTC3535
2.2μF
+
392k
1M
4.7μH
3535 TA02
*POWERSTOR PA-5R0H474-R
VIN
1V/DIV
VHOLDUP
2V/DIV
VOUT
2V/DIV
5s/DIV
3535 TA02b
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
3.50 p 0.05
2.10 p 0.05
2.38 p 0.05
1.65 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
3.00 p 0.10
(4 SIDES)
R = 0.115
TYP
7
0.40 p 0.10
12
2.38 p 0.10
1.65 p 0.10
PIN 1 NOTCH
R = 0.20 OR
0.25 s 45o
CHAMFER
PIN 1
TOP MARK
(SEE NOTE 6)
6
0.200 REF
1
0.23 p 0.05
0.45 BSC
0.75 p 0.05
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC3535
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC3400/LTC3400B
600mA ISW, 1.2MHz, Synchronous Step-Up
DC/DC Converters
92% Efficiency VIN: 1V to 5V, VOUT(MAX) = 5V, IQ = 19μA/300μA,
ISD < 1μA, ThinSOT Package
LTC3421
3A ISW, 3MHz, Synchronous Step-Up DC/DC Converter
with Output Disconnect
95% Efficiency VIN: 1V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12μA,
ISD < 1μA, QFN24 Package
LTC3422
1.5A ISW, 3MHz Synchronous Step-Up DC/DC
Converter with Output Disconnect
95% Efficiency VIN: 1V to 4.5V, VOUT(MAX) = 5.25V, IQ = 25μA,
ISD < 1μA, 3mm × 3mm DFN Package
LTC3426
2A ISW, 1.2MHz, Step-Up DC/DC Converter
92% Efficiency VIN: 1.6V to 4.3V, VOUT(MAX) = 5V, ISD < 1μA,
SOT-23 Package
LTC3427
500mA ISW, 1.2MHZ, Synchronous Step-Up DC/DC
Converter with Output Disconnect
93% Efficiency VIN: 1.8V to 4.5V, VOUT(MAX) = 5V,
2mm × 2mm DFN Package
LTC3428
500mA ISW, 1.25MHz/2.5MHz, Synchronous Step-Up
DC/DC Converters with Output Disconnect
92% Efficiency VIN: 1.8V to 5V, VOUT(MAX) = 5.25V, ISD < 1μA,
2mm × 2mm DFN Package
LTC3429
600mA ISW, 500kHz, Synchronous Step-Up DC/DC
Converter with Output Disconnect and Soft-Start
96% Efficiency VIN: 1V to 4.4V, VOUT(MAX) = 5V, IQ = 20μA/300μA,
ISD < 1μA, ThinSOT Package
LTC3458/LTC3458L
1.4A ISW, 1.5MHz, Synchronous Step-Up DC/DC
Converter/Output Disconnect/Burst Mode Operation
93% Efficiency VIN: 1.5V to 6V, VOUT(MAX) = 7.5V, IQ = 15μA,
ISD < 1μA, DFN12 Package
LTC3459
70mA ISW, 10V Micropower Synchronous Boost
Converter/Output Disconnect/Burst Mode Operation
VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10μA, ISD < 1μA,
ThinSOT Package
LTC3499
750mA (ISW), 1.2MHz, Step-Up DC/DC Converter with
Reverse Battery Protection and Output Disconnect
92% Efficiency VIN: 1.8V to 5.5V, VOUT(MAX) = 6V, IQ = 20μA,
ISD < 1μA, 3mm × 3mm DFN-8 Package, MSOP-8 Package
LTC3525-3
LTC3525-3.3
LTC3525-5
400mA Micropower Synchronous Step-Up DC/DC
Converter with Output Disconnect
95% Efficiency VIN: 1V to 4.5V, VOUT(MAX) = 3.3V or 5V, IQ = 7μA,
ISD < 1μA, SC-70 Package
LTC3525L-3
400mA Micropower Synchronous Step-Up DC/DC
Converter with Output Disconnect
93% Efficiency VIN: 0.88V to 4.5V, VOUT = 3V, IQ = 7μA,
ISD < 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 VIN: 0.85V to 5V, VOUT(MAX) = 5.25V, IQ = 9μA,
ISD < 1μA, 2mm × 2mm DFN-6 Package
LTC3526L
LTC3526LB
550mA, 1MHz, Synchronous Step-Up DC/DC
Converters with Output Disconnect
94% Efficiency VIN: 0.7V to 5V, VOUT(MAX) = 5.25V, IQ = 9μA,
ISD < 1μA, 2mm × 2mm DFN-6 Package
LTC3526/LTC3526B
500mA (ISW), 1MHz Synchronous Step-Up DC/DC
Converter with Output Disconnect
94% Efficiency VIN: 0.8V to 5V, VOUT(MAX) = 5.25V, IQ = 9μA,
ISD < 1μA, 2mm × 2mm DFN-6 Package
LTC3527/LTC3527-1
Dual 800mA and 400mA (ISW), 2.2MHz, Synchronous
Step-Up DC/DC Converter with Output Disconnect
94% Efficiency VIN: 0.7V to 5V, VOUT(MAX) = 5.25V, IQ = 12μA,
ISD < 1μA, 3mm × 3mm QFN-16 Package
LTC3528
LTC3528-2
1A (ISW), 1MHz Synchronous Step-Up DC/DC with
Output DisconnectConverter
94% Efficiency VIN: 0.7V to 5V, VOUT(MAX) = 5.25V, IQ = 12μA,
ISD < 1μA, 2mm × 3mm DFN-8 Package
LTC3537
600mA , 2.2MHz, Synchronous Step-Up DC/DC
Converter with Output Disconnect and 100mA LDO
94% Efficiency VIN: 0.7V to 5V, VOUT(MAX) = 5.25V, IQ = 30μA,
ISD < 1μA, 3mm × 3mm QFN-16 Package
LTC3539
LTC3539-2
2A (ISW), 1/2MHz, Synchronous Step-Up DC/DC
Converter with Output Disconnect
94% Efficiency VIN: 0.7V to 5V, VOUT(MAX) = 5.25V, IQ = 10μA,
ISD < 1μA, 2mm × 3mm DFN-8 Package
ThinSOT is a trademark of Linear Technology Corporation.
3535f
16 Linear Technology Corporation
LT 0109 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2009
Similar pages