LINER LTC3528-2

LTC3528-2
1A, 2MHz Synchronous
Step-Up DC/DC Converter
in 2mm × 3mm DFN
FEATURES
DESCRIPTION
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The LTC®3528-2 is a synchronous, fixed frequency step-up
DC/DC converter with output disconnect. High efficiency
synchronous rectification, in addition to a 700mV startup voltage and operation down to 500mV once started,
provides longer run-time for single or multiple cell battery-powered products.
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Delivers 3.3V at 200mA from a Single Alkaline/
NiMH Cell or 3.3V at 400mA from Two Cells
VIN Start-Up Voltage: 700mV
0.50V to 5.5V Input Range
1.6V to 5.25V VOUT Range
Up to 94% Efficiency
Output Disconnect
2MHz Fixed Frequency Operation
VIN > VOUT Operation
Integrated Soft-Start
Current Mode Control with Internal Compensation
Burst Mode® Operation with 12μA Quiescent Current
Internal Synchronous Rectifier
Logic Controlled Shutdown: <1μA
Anti-Ringing Control
Low Profile (2mm × 3mm × 0.75mm) DFN Package
A switching frequency of 2MHz minimizes solution
footprint by allowing the use of tiny, low profile inductors and ceramic capacitors. The current mode PWM is
internally compensated, simplifying the design process.
The LTC3528-2 enters Burst Mode operation at light loads.
Anti-ringing circuitry reduces EMI by damping the inductor
in discontinuous mode. Additional features include a low
shutdown current, open-drain power good output, shortcircuit protection and thermal overload protection.
APPLICATIONS
The LTC3528-2 is offered in an 8-lead 2mm × 3mm ×
0.75mm DFN package.
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L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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Medical Instruments
Noise Canceling Headphones
Wireless Mice
Bluetooth Headsets
TYPICAL APPLICATION
Efficiency and Power Loss
100
90
2.2μH
4.7μF
VOUT
LTC3528-2
PGOOD
OFF ON
SHDN
GND
499k
68pF
VOUT
3.3V
400mA
10μF
FB
100
EFFICIENCY
70
10
60
50
40
1
POWER LOSS
30
287k
0.1
20
35282 TA01a
POWER LOSS (mW)
SW
VIN
EFFICIENCY (%)
80
VIN
1.8V TO 3.2V
1000
VOUT = 3.3V
VIN = 2.4V
10
0
0.01
0.1
1
10
100
0.01
1000
LOAD CURRENT (mA)
35282 TA01b
35282f
1
LTC3528-2
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
VIN Voltage ................................................... –0.3V to 6V
SW Voltage
DC............................................................ –0.3V to 6V
Pulsed < 100ns ........................................ –0.3V to 7V
SHDN, FB Voltage ........................................ –0.3V to 6V
VOUT ............................................................. –0.3V to 6V
PGOOD......................................................... –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 125°C
TOP VIEW
SHDN 1
FB 2
PGOOD 3
8 VIN
9
VOUT 4
7 SGND
6 PGND
5 SW
DDB PACKAGE
8-LEAD (3mm s 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 76°C/W (NOTE 6)
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3528EDDB-2#PBF
LTC3528EDDB-2#TRPBF
LDNZ
8-Lead (3mm × 2mm) 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
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
VIN Range
Operating, Excluding Start-Up
l
Minimum Start-Up Voltage
ILOAD = 1mA
l
Output Voltage Adjust Range
MIN
Feedback Voltage
(Note 7)
0.5
1.7
1.6
l
1.170
MAX
UNITS
5.5
V
0.88
V
5.25
5.25
V
V
1.200
1.230
V
0.70
l
TA = 0°C to 85°C
TYP
Feedback Input Current
VFB = 1.3V
1
50
nA
Quiescent Current—Shutdown
VSHDN = 0V, Not Including Switch Leakage, VOUT = 0V
0.01
1
μA
Quiescent Current—Active
Measured on VOUT, Nonswitching (Note 4)
300
500
μA
Quiescent Current—Burst
Measured on VOUT , FB > 1.230V
12
20
μA
0.1
10
μA
0.1
10
μA
N-Channel MOSFET Switch Leakage Current VSW = 5V
P-Channel MOSFET Switch Leakage Current
VSW = 5V, VOUT = 0V
N-Channel MOSFET Switch On Resistance
0.175
Ω
P-Channel MOSFET Switch On Resistance
0.250
Ω
1.5
A
60
ns
92
%
l
N-Channel MOSFET Current Limit
Current Limit Delay Time to Output
(Note 3)
Maximum Duty Cycle
VFB = 1.15V
l
1.0
87
35282f
2
LTC3528-2
ELECTRICAL CHARACTERISTICS
The 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
l
l
Frequency
SHDN Input High Voltage
0
1.8
2.0
2.4
0.88
SHDN Input Current
VSHDN = 1.2V
Referenced to Feedback Voltage Falling
PGOOD Low Voltage
PGOOD Leakage Current
1
μA
%
IPGOOD = 1mA
VOUT = 1.6V, IPGOOD = 1mA
0.05
0.05
0.1
0.2
V
V
VPGOOD = 5.5V
0.01
1
μA
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
76°C/W.
Note 7: The IC is tested in a feedback loop to make the measurement.
90
80
10
POWER
LOSS
40
1
30
VIN = 1V
VIN = 1.2V
VIN = 1.5V
0.1
10
100
1
LOAD CURRENT (mA)
0.1
0.01
1000
35282 G01
EFFICIENCY (%)
60
100
70
60
10
POWER
LOSS
50
40
1
30
20
VIN = 1V
VIN = 1.5V
VIN = 2.4V
10
0
0.01
0.1
10
100
1
LOAD CURRENT (mA)
POWER LOSS (mW)
70
1000
EFFICIENCY
80
100
POWER LOSS (mW)
EFFICIENCY (%)
100
1000
EFFICIENCY
0
0.01
(TA = 25°C unless otherwise noted)
Efficiency vs Load Current
and VIN for VOUT = 3V
100
10
V
–13
Efficiency vs Load Current
and VIN for VOUT = 1.8V
20
0.25
0.3
–7
TYPICAL PERFORMANCE CHARACTERISTICS
50
MHz
–10
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 LTC3528E-2 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over –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.
90
%
V
SHDN Input Low Voltage
PGOOD Threshold Percentage
UNITS
0.1
0.01
1000
35282 G26
35282f
3
LTC3528-2
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current
and VIN for VOUT = 3.3V
(TA = 25°C unless otherwise noted)
Efficiency vs Load Current
and VIN for VOUT = 5V
100
1000
No-Load Input Current vs VIN
100
EFFICIENCY
EFFICIENCY
90
90
110
100
50
VIN = 1.2V
VIN = 1.8V
VIN = 2.4V
VIN = 3V
40
30
0.01
0.1
1
10
10
POWER
LOSS
60
50
40
30
0.01
0.1
LOAD CURRENT (mA)
1
10
90
30
10
4
5
35282 G04
Minimum Load Resistance During
Start-Up vs VIN
800
Start-Up Delay Time vs VIN
130
10000
120
700
110
600
500
DELAY (μs)
1000
RLOAD (Ω)
IOUT (mA)
3
VIN (V)
35282 G03
Maximum Output Current vs VIN
400
300
100
100
90
80
70
200
VOUT = 1.8V
VOUT = 3.3V
VOUT = 5V
100
0
1
1.5
2
3
2.5
VIN (V)
3.5
4
60
50
10
4.5
0.7
0.8
0.9
IOUT (mA)
IOUT (mA)
40
EXIT BURST
40
ENTER BURST
20
20
1.3
1.2
VIN (V)
1.4
1.5
0
0
1
1.5
2
2.5
1
1.5
2
2.5
3
VIN (V)
VIN (V)
35282 G08
4.5
60
ENTER BURST
20
4
VOUT = 3.3V
VOUT = 3V
EXIT BURST
ENTER BURST
3.5
Burst Mode Threshold Current
vs VIN
60
EXIT BURST
40
3
2.5
VIN (V)
80
80
60
1.1
2
35282 G07
Burst Mode Threshold Current
vs VIN
VOUT = 1.8V
1
1.5
35282 G06
Burst Mode Threshold Current
vs VIN
80
1
1
VIN (V)
35282 G05
IOUT (mA)
2
1
LOAD CURRENT (mA)
35282 G02
0
VOUT = 1.8V
VOUT = 3V
VOUT = 3.3V
VOUT = 5V
50
0.1
1000
100
70
1
VIN = 1.2V
VIN = 2.4V
VIN = 3.6V
VIN = 4.2V
0.1
0.01
1000
100
70
IIN (μA)
1
80
EFFICIENCY (%)
POWER
LOSS
60
100
POWER LOSS (mW)
10
70
POWER LOSS (mW)
80
EFFICIENCY (%)
130
1000
35282 G09
35282 G10
35282f
4
LTC3528-2
TYPICAL PERFORMANCE CHARACTERISTICS
Oscillator Frequency Change
vs VOUT
Burst Mode Threshold Current
vs VIN
80
(TA = 25°C unless otherwise noted)
RDS(ON) vs VOUT
0.50
VOUT = 5V
450
0.25
400
IOUT (mA)
EXIT BURST
40
ENTER BURST
20
–0.25
350
–0.50
RDS(ON) (mΩ)
FREQUENCY CHANGE (%)
0
60
–0.75
–1.00
–1.25
NMOS
150
–2.00
–2.25
1
1.5
2
2.5
VIN (V)
3
3.5
4
1.5
2.5
2
3.5
3
VOUT (V)
4
35242 G11
2
2.5
3.5
3
VOUT (V)
4
3
4.5
5
35282 G13
VFB vs Temperature
RDS(ON) Change vs Temperature
1.200
20
1.195
2
1
0
–1
10
VFB (V)
CHANGE (%)
FREQUENCY CHANGE (%)
100
1.5
5
30
NORMALIZED TO 25°C
4
4.5
35282 G12
Oscillator Frequency Change
vs Temperature
5
PMOS
250
200
–1.50
–1.75
0
300
1.190
0
–2
1.185
–3
–10
–4
–5
–50
–30
30
–10 10
50
TEMPERATURE (°C)
70
–20
–50
90
30
–10 10
50
TEMPERATURE (°C)
–30
35282 G14
0.05
0
–0.05
–0.10
–0.15
200
400
600
LOAD CURRENT (mA)
70
90
Start-Up Voltage vs Temperature
VIN = 1.2V
0.15
0.10
0.05
0
–0.05
–0.10
800
750
700
650
–0.15
–0.20
0
50
100
150
200
LOAD CURRENT (mA)
3528-2 G27
50
–10 10
30
TEMPERATURE (°C)
35282 G16
START-UP VOLTAGE (mV)
CHANGE IN OUTPUT VOLTAGE (%)
CHANGE IN OUTPUT VOLTAGE (%)
0.10
–30
850
0.20
VIN = 3.6V
0
1.180
–50
Output Voltage vs Load Current
for VOUT = 3.3V
0.15
–0.20
90
35282 G15
Output Voltage vs Load Current
for VOUT = 5V
0.20
70
35282 G28
600
–50
–30
30
–10 10
50
TEMPERATURE (°C)
70
90
35282 G17
35282f
5
LTC3528-2
TYPICAL PERFORMANCE CHARACTERISTICS
Fixed Frequency VOUT Ripple and
Inductor Current Waveforms
(TA = 25°C unless otherwise noted)
Burst Mode Waveforms
VOUT and IIN During Soft-Start
VOUT
50mV/DIV
VOUT
20mV/DIV
VOUT
1V/DIV
IIN
200mA/DIV
INDUCTOR
CURRENT
100mA/DIV
IL
200mA/DIV
VIN = 1.2V
VOUT = 3.3V
COUT = 10μF
CFF = 33pF
IOUT = 100mA
L = 2.2μH
500ns/DIV
35282 G19
SHDN PIN
VIN = 3.6V
VOUT = 5V
COUT = 10μF
CFF = 33pF
ILOAD = 30mA
35282 G20
5μs/DIV
Load Step Response (Fixed
Frequency, 3.6V to 5V)
VIN = 1.2V
VOUT = 3.3V
COUT = 10μF
L = 2.2μH
200μs/DIV
35282 G21
Load Step Response (Burst Mode
Operation, 3.6V to 5V)
VOUT
100mV/DIV
VOUT
100mV/DIV
LOAD
CURRENT
200mA/DIV
LOAD
CURRENT
200mA/DIV
VIN = 3.6V
20μs/DIV
VOUT = 5V
COUT = 10μF
L = 2.2μH
LOAD CURRENT = 100mA TO 550mA
35282 G22
VIN = 3.6V
20μs/DIV
VOUT = 5V
COUT = 10μF
L = 2.2μH
LOAD CURRENT = 20mA TO 550mA
Load Step Response (Fixed
Frequency, 1.2V to 3.3V)
Load Step Response (Burst Mode
Operation, 1.2V to 3.3V)
VOUT
100mV/DIV
VOUT
100mV/DIV
LOAD
CURRENT
100mA/DIV
LOAD
CURRENT
100mA/DIV
20μs/DIV
VIN = 1.2V
VOUT = 3.3V
COUT = 10μF
L = 2.2μH
LOAD CURRENT = 20mA TO 170mA
35282 G23
35282 G24
VIN = 1.2V
20μs/DIV
VOUT = 3.3V
COUT = 10μF
L = 2.2μH
LOAD CURRENT = 10mA TO 160mA
35282 G25
35282f
6
LTC3528-2
PIN FUNCTIONS
SHDN (Pin 1): Logic Controlled Shutdown Input. There is
an internal 4M pull-down resistor on this pin.
• SHDN = High: Normal operation
• SHDN = Low: Shutdown, quiescent current < 1μA
FB (Pin 2): Feedback Input. Connect resistor divider tap
to this pin. The output voltage can be adjusted from 1.6V
to 5.25V by:
⎛ R2⎞
VOUT = 1.20V • ⎜1+ ⎟
⎝ R1⎠
PGOOD (Pin 3): Power Good Comparator Output. This
open-drain output is low when VFB < 10% from its regulation voltage.
VOUT (Pin 4): Output Voltage Sense and Drain Connection
of the Internal Synchronous Rectifier. PCB trace length
from VOUT to the output filter capacitor (4.7μF minimum)
should be as short and wide as possible.
SW (Pin 5): Switch Pin. Connect inductor between SW
and VIN. Keep PCB trace lengths as short and wide as
possible to reduce EMI. If the inductor current falls to
zero, or SHDN is low, an internal anti-ringing switch is
connected from SW to VIN to minimize EMI.
PGND (Pin 6): Power Ground. Provide a short direct PCB
path between PGND and the (–) side of the input and
output capacitors.
SGND (Pin 7): Signal Ground. Provide a short direct PCB
path between SGND and the (–) side of the input and
output capacitors.
VIN (Pin 8): Battery Input Voltage. Connect a minimum
of 1μF ceramic decoupling capacitor from this pin to
ground.
Exposed Pad (Pin 9): 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.
35282f
7
LTC3528-2
BLOCK DIAGRAM
VIN
0.7V
TO 5V
L1
2.2μH
CIN
4.7μF
8
5
VIN
SW
ANTI-RING
VOUT
VSEL
VBEST
1
SHDN
SHUTDOWN
SHUTDOWN
WELL
SWITCH
VB
VOUT
GATE DRIVERS
AND
ANTI-CROSS
CONDUCTION
R2
– +
4M
3
PK
COMP
VREF
PK
UVLO
UVLO
FB
IZERO
COMP
START-UP
2MHz
OSC
3
BURST
PGOOD
+
–
+
–
MODE
CONTROL
CLK
R1
ERROR AMP
SLEEP COMP
IZERO
LOGIC
COUT
10μF
2
SLOPE
COMP
+
–
VREF
VOUT
1.6V
TO 5.25V
4
VREF
FB
CLAMP
VREF – 10%
FB
THERMAL
SHUTDOWN
SOFT-START
TSD
WAKE
PGND
SGND
EXPOSED
PAD
6
7
9
35282 BD
35282f
8
LTC3528-2
OPERATION
(Refer to Block Diagram)
The LTC3528-2 is a 2MHz synchronous boost converter
housed in an 8-lead 3mm × 2mm DFN package. With the
ability to start up and operate from inputs less than 0.88V,
the device 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 and requires
minimal output filtering. Internal soft-start and internal
loop compensation simplifies the design process while
minimizing the number of external components.
ramps the peak inductor current from zero to its peak
value of 1.5A (typical), allowing start-up into heavy loads.
The soft-start time is approximately 0.5ms. The soft-start
circuitry is reset in the event of a commanded shutdown
or a thermal shutdown.
With its low RDS(ON) and low gate charge internal N-channel MOSFET switch and P-channel MOSFET synchronous
rectifier, the LTC3528-2 achieves high efficiency over a wide
range of load current. The LTC3528-2 features continuous
2MHz PWM operation over a wide range of load current.
At very light loads, the LTC3528-2 will enter Burst Mode
operation to maintain high efficiency. Operation can be
best understood by referring to the Block Diagram.
Shutdown
LOW VOLTAGE START-UP
The LTC3528-2 includes an independent start-up oscillator
designed to operate at an input voltage of 0.70V (typical).
Soft-start and inrush current limiting are provided during
start-up, as well as normal operating mode.
When either VIN or VOUT exceeds 1.6V typical, the IC enters
normal operating mode. Once the output voltage exceeds
the input by 0.24V, the IC 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
power to the output at the low voltages, and the maximum
duty cycle, which is clamped at 92% 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.
LOW NOISE FIXED FREQUENCY OPERATION
Soft-Start
The LTC3528-2 contains internal circuitry to provide softstart operation. The internal soft-start circuitry slowly
Oscillator
An internal oscillator sets the frequency of operation to
2MHz.
The converter is shut down by pulling the SHDN pin below
0.25V, and activated by pulling SHDN above 0.88V. 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 error amplifier is a transconductance type. The noninverting input is internally connected to the 1.20V reference
and the inverting 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. A voltage
divider from VOUT to ground programs the output voltage
via FB from 1.6V to 5.25V.
⎛ R2⎞
VOUT = 1.20V • ⎜1+ ⎟
⎝ R1⎠
Current Sensing
Lossless current sensing converts the peak current signal
of the N-channel MOSFET switch into a voltage which
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.
Current Limit
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 1.5A, independent of input or output voltage, unless VOUT falls below
0.7V, in which case the current limit is cut in half.
35282f
9
LTC3528-2
OPERATION
(Refer to Block Diagram)
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 20mA. 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-ringing control connects a resistor across the
inductor to prevent high frequency ringing on the SW pin
during discontinuous current mode operation. The ringing
of the resonant circuit formed by L and CSW (capacitance
on SW pin) is low energy, but can cause EMI radiation.
Output Disconnect
The LTC3528-2 is designed to allow true output disconnect by eliminating body diode conduction of the internal
P-channel MOSFET rectifier. This allows for VOUT to go to
zero volts during shutdown, drawing no current from the
input source. It also enables inrush current limiting at turnon, minimizing surge currents seen by the input supply.
Note that to obtain the advantages of output disconnect,
a Schottky diode cannot be connected between SW and
VOUT. The output disconnect feature also allows VOUT to be
forced above the programmed regulation voltage, without
any reverse current into the input power source.
Thermal Shutdown
If the die temperature exceeds 160°C, the LTC3528-2
enters thermal shutdown. All switches will be turned off
and the soft-start capacitor will be discharged. The device
will be enabled again when the die temperature drops by
approximately 15°C.
Burst Mode OPERATION
The LTC3528-2 will automatically 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 vs VIN. The load 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 LTC3528-2 continues switching at a fixed frequency of 2MHz, using the same error
amplifier and loop compensation for peak current mode
control. This control method minimizes output transients
when switching between modes. In Burst Mode operation, energy is delivered to the output until it reaches the
nominal regulated value, then the LTC3528-2 transitions to
sleep mode where the outputs are off and the LTC3528-2
consumes only 12μA of quiescent current from VOUT. Once
the output voltage has drooped slightly, switching resumes
again. This maximizes efficiency at very light loads by
minimizing switching and quiescent current losses. Burst
Mode output ripple, which is typically 1% peak-to-peak,
can be reduced by using more output capacitance (10μF
or greater).
As the load current increases, the LTC3528-2 automatically
leaves Burst Mode operation. Note that larger output capacitor values may cause this transition to occur at lighter
loads. The regulator will also leave Burst Mode operation if
a load transient occurs which causes the inductor current
to repeatedly reach current limit. Once the LTC3528-2 has
left Burst Mode operation and returned to normal operation, it will remain there until the output load is reduced
below the Burst threshold.
Burst Mode operation is inhibited during start-up and
until soft-start is done and VOUT is at least 0.24V greater
than VIN.
Single Cell to 5V Step-Up Applications
Due to the high inductor current slew rate in applications
boosting to 5V from a single cell (alkaline, NiCd or NiMH),
the LTC3528-2 may not enter Burst Mode operation at input voltages below 1.5V. For single cell to 5V applications
requiring Burst Mode operation, the 1MHz LTC3528 is
recommended. Refer to the Typical Performance Characteristics for the Burst Mode thresholds for different input
and output voltages.
35282f
10
LTC3528-2
APPLICATIONS INFORMATION
VIN > VOUT OPERATION
The LTC3528-2 maintains 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 recommended component placement. A large ground
copper area with the package backside metal pad properly
soldered will help to lower the chip temperature. A multilayer board with a separate ground plane is ideal, but not
absolutely necessary.
COMPONENT SELECTION
SHORT-CIRCUIT PROTECTION
Inductor Selection
The LTC3528-2 output disconnect feature allows an 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 750mA (typical).
SCHOTTKY DIODE
Although not required, 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 LTC3528-2 can utilize small surface mount chip inductors due to its fast 2MHz switching frequency. Inductor
values between 1.5μH and 3.3μH are suitable for most
applications. Larger values of inductance will allow slightly
greater output current capability by reducing the inductor
ripple current. Increasing the inductance above 10μH will
increase size while providing little improvement in output
current capability.
The minimum inductance value is given by:
L>
(
VIN(MIN) • VOUT(MAX) – VIN(MIN)
2 • Ripple • VOUT(MAX)
) µH
PCB LAYOUT GUIDELINES
The high speed operation of the LTC3528-2 demands
careful attention to board layout. A careless layout will
not produce the advertised performance. Figure 1 shows
SHDN 1
VOUT(MAX) = Maximum output voltage
CIN
8 VIN
FB 2
7 SGND
LTC3528-2
PGOOD 3
VOUT 4
COUT
Ripple = Allowable inductor current ripple (amps peakpeak)
VIN(MIN) = Minimum input voltage
+
VIN
where:
6 PGND
5 SW
35282 F01
MULTIPLE VIAS
TO GROUND PLANE
Figure 1. Recommended Component Placement
for Single Layer Board
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 handle the peak inductor current without saturating. Molded chokes and some chip
inductors usually do not have enough core area to support
the peak inductor currents of 1.5A seen on the LTC3528-2.
To minimize radiated noise, use a shielded inductor. See
Table 1 for suggested components and suppliers.
35282f
11
LTC3528-2
APPLICATIONS INFORMATION
Table 1. Recommended Inductors
VENDOR
PART/STYLE
Coilcraft
(847) 639-6400
www.coilcraft.com
DO1606T, MSS5131, MSS5121
MSS6122, MOS6020
ME3220, DO1608C
1812PS
Coiltronics
SD12, SD14, SD20
SD25, SD52
Sumida
(847) 956-0666
www.sumida.com
CD43
CDC5D23B
CDRH5D18
TDK
VLP, VLF
VLCF, SLF, VLS
Toko
(408) 432-8282
www.tokoam.com
D53, D62, D63
D73, D75
Wurth
(201) 785-8800
www.we-online.com
WE-TPC type M, MH
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 10μF to 22μF output capacitor is sufficient for most applications. Values larger than 22μF 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 LTC3528-2 is designed to be stable with output capacitor values of 10μF
or greater. 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 which
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 68pF 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 10μF input capacitor is sufficient
for most applications. 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 parts.
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
TYPICAL APPLICATIONS
Efficiency
1 Cell to 1.8V
100
2.2μH
90
VIN
4.7μF
VOUT
LTC3528-2
PGOOD
OFF ON
SHDN
GND
499k
68pF
VOUT
1.8V
250mA
10μF
FB
80
EFFICIENCY (%)
SW
VIN
0.88V TO 1.6V
70
60
50
1M
VIN = 0.9V
VIN = 1.2V
VIN = 1.5V
40
35282 TA02a
30
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
35282 TA02b
35282f
12
LTC3528-2
TYPICAL APPLICATIONS
Dual 1 Cell to 1.8V, 3V Sequenced Supply
2.2μH
SW
VIN
0.88V TO 1.6V
VIN
4.7μF
475k
VOUT
LTC3528-2
SHDN
Output Voltage Sequencing
10μF
FB
PGOOD
OFF ON
68pF
499k
VOUT1
1.8V
250mA
1M
GND
VOUT2
SW
VIN
4.7μF
VOUT1
VIN
PGOOD1
0.5V/DIV
2.2μH
VOUT
LTC3528-2
PGOOD
SHDN
GND
68pF
499k
VOUT2
3V
200mA
35282 TA03b
200μs/DIV
10μF
FB
324k
3528 TA03a
Efficiency
1 Cell to 3.3V
100
2.2μH
90
VIN
4.7μF
VOUT
LTC3528-2
PGOOD
OFF ON
SHDN
GND
499k
68pF
VOUT
3.3V
200mA
10μF
FB
80
EFFICIENCY (%)
SW
VIN
0.88V TO 1.6V
70
60
50
287k
35282 TA04a
VIN = 0.9V
VIN = 1.2V
VIN = 1.5V
40
30
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
35282 TA04b
35282f
13
LTC3528-2
TYPICAL APPLICATIONS
Efficiency
2 Cell to 3.3V
100
90
2.2μH
SW
VIN
1.8V TO 3.2V
VIN
4.7μF
VOUT
68pF
10μF
FB
PGOOD
OFF ON
499k
LTC3528-2
SHDN
VOUT
3.3V
400mA
EFFICIENCY (%)
80
60
50
287k
GND
70
VIN = 1.8V
VIN = 2.4V
VIN = 3V
40
35282 TA05a
30
0.01
0.1
1
10
1000
100
LOAD CURRENT (mA)
35282 TA05b
2 Cell to 5V
Efficiency
100
2.2μH
90
VIN
4.7μF
LTC3528-2
1M
68pF
22μF
FB
PGOOD
OFF ON
VOUT
5V
300mA
VOUT
SHDN
80
EFFICIENCY (%)
SW
VIN
1.8V TO 3.2V
60
50
316k
GND
70
VIN = 1.8V
VIN = 2.4V
VIN = 3V
40
35282 TA06a
30
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
35282 TA06b
Li-Ion to 5V
Efficiency
100
2.2μH
90
VIN
4.7μF
VOUT
LTC3528-2
PGOOD
OFF ON
SHDN
GND
1M
68pF
VOUT
5V
400mA
FB
80
EFFICIENCY (%)
SW
VIN
2.7V TO 4.2V
70
60
50
316k
35282 TA07a
VIN = 2.8V
VIN = 3.6V
VIN = 4.2V
40
30
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
35282 TA07b
35282f
14
LTC3528-2
PACKAGE DESCRIPTION
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 p0.05
(2 SIDES)
0.70 p0.05
2.55 p0.05
1.15 p0.05
PACKAGE
OUTLINE
0.25 p 0.05
0.50 BSC
2.20 p0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 p0.10
(2 SIDES)
R = 0.115
TYP
5
R = 0.05
TYP
0.40 p 0.10
8
2.00 p0.10
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.56 p 0.05
(2 SIDES)
0.200 REF
0.75 p0.05
0 – 0.05
4
0.25 p 0.05
1
PIN 1
R = 0.20 OR
0.25 s 45o
CHAMFER
(DDB8) DFN 0905 REV B
0.50 BSC
2.15 p0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
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 SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
35282f
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
LTC3528-2
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC3528/LTC3528
1A (ISW), 1MHz Synchronous Step-Up DC/DC Converters 94% Efficiency, VIN: 0.7V to 5.5V, VOUT(MAX) = 5.25V, IQ = 12μA,
ISD < 1μA, 3mm × 2mm DFN8 Package
with Output Disconnect
LTC3528B-2
1A (ISW), 2MHz Synchronous Step-Up DC/DC Converter
with Output Disconnect
94% Efficiency, VIN: 0.7V to 5.5V, VOUT(MAX) = 5.25V, IQ = 12μA,
ISD < 1μA, 3mm × 2mm DFN8 Package
LTC3400/LTC3400B
600mA (ISW), 1.2MHz, Synchronous Step-Up
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ISD < 1μA, ThinSOTTM Package
LTC3421
3A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter
with Output Disconnect
94% Efficiency VIN: 0.85V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12μA,
ISD < 1μA, 4mm × 4mm QFN24 Package
LTC3422
1.5A (ISW), 3MHz Synchronous Step-Up DC/DC
Converter with Output Disconnect
94% Efficiency VIN: 0.85V to 4.5V, VOUT(MAX) = 5.25V, IQ = 25µA,
ISD < 1µA, 3mm × 3mm DFN10 Package
LTC3426
2A (ISW), 1.5MHz, Step-Up DC/DC Converter
92% Efficiency VIN: 1.6V to 5.5V, VOUT(MAX) = 5V, IQ = 600µA,
ISD < 1μA, ThinSOT Package
LTC3427
500mA (ISW), 1.25MHz, Synchronous Step-Up DC/DC
Converter with Output Disconnect
94% Efficiency VIN: 1.8V to 5V, VOUT(MAX) = 5.25V, IQ = 350µA
ISD < 1µA, 2mm × 2mm DFN6 Package
LTC3429/LTC3429B
600mA (ISW), 550kHz, Synchronous Step-Up DC/DC
Converter with Output Disconnect and Soft-Start
96% Efficiency VIN: 0.85V to 4.3V, VOUT(MAX) = 5V, IQ = 20μA,
ISD < 1μA, ThinSOT Package
LTC3458/LTC3458L
1.4A/1.7A (ISW), 1.5MHz, Synchronous Step-Up DC/DC
Converter
94% Efficiency VIN: 0.85V to 6V, VOUT(MAX) = 7.5V/6V, IQ = 15μA,
ISD < 1μA, 3mm × 4mm DFN12 Package
LTC3459
80mA (ISW), Synchronous Step-Up DC/DC Converter
92% Efficiency VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10μA,
ISD < 1μA, ThinSOT Package
LT®3494/LT3494A
180mA/350mA (ISW), High Efficiency Step-Up DC/DC
Converter with Output Disconnect
85% Efficiency VIN: 2.3V to 16V, VOUT(MAX) = 38V, IQ = 65μA,
ISD < 1μA, 2mm × 3mm DFN6, ThinSOT Packages
LTC3523/LTC3523-2
600mA (ISW), Step-Up and 400mA Synchronous
Step-Down 1.2MHz/2.4MHz DC/DC Converters with
Output Disconnect
94% Efficiency VIN: 1.8V to 5.5V, VOUT(MAX) = 5.25V, IQ = 45μA,
ISD < 1μA, 3mm × 3mm QFN16
LTC3526/LTC3526L
LTC3526B
500mA (ISW), 1MHz 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 DFN6 Package
LTC3527/LTC3527-1
Dual 800mA/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 QFN16 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 QFN16 Package
ThinSOT is a trademark of Linear Technology Corporation.
35282f
16 Linear Technology Corporation
LT 0409 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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