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LTC3528/LTC3528B 1A, 1MHz Synchronous Step-Up DC/DC Converters in 3mm x 2mm DFN FEATURES

DESCRIPTION
The LTC(R)3528/LTC3528B are synchronous, fixed frequency step-up DC/DC converters with output disconnect. High efficiency synchronous rectification, in addition to a 700mV start-up voltage and operation down to 500mV once started, provides longer run-time for single or multiple cell battery-powered products. A switching frequency of 1MHz 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 enters Burst Mode operation at light loads, while the LTC3528B features continuous switching 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. The LTC3528/LTC3528B are offered in an 8-lead 3mm x 2mm x 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.

Delivers 3.3V at 200mA from a Single Alkaline/ NiMH Cell or 3.3V at 400mA from Two Cells VIN Start-Up Voltage: 700mV 1.6V 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(R) Operation with 12A Quiescent Current (LTC3528) Low Noise PWM Operation (LTC3528B) Internal Synchronous Rectifier Logic Controlled Shutdown: <1A Anti-Ringing Control Low Profile (3mm x 2mm x 0.75mm) DFN Package
APPLICATIONS

Medical Instruments Flash-Based MP3 Players Noise Canceling Headphones Wireless Mice Bluetooth Headsets
TYPICAL APPLICATION
100 4.7H 90 SW VIN 1.8V TO 3.2V 4.7F VIN VOUT 499k FB 287k
3528 TA01a
Efficiency and Power Loss
VOUT = 3.3V VIN = 2.4V 1000
100 EFFICIENCY (%) VOUT 3.3V 400mA 10F 80 EFFICIENCY 70 60 POWER LOSS 50 0.1 40 30 0.01 0.01 1000
3528 TA01b
POWER LOSS (mW)
10
LTC3528 PGOOD
33pF
1
OFF ON
SHDN GND
0.1
1
10
100
LOAD CURRENT (mA)
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LTC3528/LTC3528B ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW SHDN 1 FB 2 PGOOD 3 VOUT 4 9 8 VIN 7 SGND 6 PGND 5 SW
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) .............................................. -40C to 85C Storage Temperature Range................... -65C to 125C
DDB PACKAGE 8-LEAD (3mm x 2mm) PLASTIC DFN TJMAX = 125C, JA = 76C/W (NOTE 6) EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC3528EDDB#PBF LTC3528BEDDB#PBF TAPE AND REEL LTC3528EDDB#TRPBF LTC3528BEDDB#TRPBF PART MARKING LCYD LDDG PACKAGE DESCRIPTION 8-Lead (3mm x 2mm) Plastic DFN 8-Lead (3mm x 2mm) Plastic DFN TEMPERATURE RANGE -40C to 85C -40C to 85C
Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
PARAMETER Minimum Start-Up Voltage Output Voltage Adjust Range TA = 0C to 85C Feedback Voltage Feedback Input Current Quiescent Current--Shutdown Quiescent Current--Active Quiescent Current--Burst 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 Time to Output Maximum Duty Cycle Minimum Duty Cycle Frequency (Note 3) VFB = 1.15V VFB = 1.3V (Note 7) VFB = 1.3V CONDITIONS ILOAD = 1mA
The denotes the specifications which apply over the specified operating temperature range of -40C to 85C, otherwise specifications are at TA = 25C. VIN = 1.2V, VOUT = 3.3V, unless otherwise noted.
MIN

TYP 0.70
MAX 0.88 5.25 5.25
UNITS V V V V nA A A A A A A ns %
1.7 1.6 1.170 1.200 1 0.01 300 12 0.1 0.1 0.175 0.250
1.230 50 1 500 20 10 10
VSHDN = 0V, Not Including Switch Leakage, VOUT = 0V Measured on VOUT, Nonswitching (Note 4) Measured on VOUT, FB > 1.230V VSW = 5V, VOUT = 0V
N-Channel MOSFET Switch Leakage Current VSW = 5V
1.0 88 0.7
1.5 60 93 0 1.0 1.3

% MHz
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LTC3528/LTC3528B ELECTRICAL CHARACTERISTICS
PARAMETER SHDN Input High Voltage SHDN Input Low Voltage SHDN Input Current PGOOD Threshold Percentage PGOOD Low Voltage PGOOD Leakage Current VSHDN = 1.2V Referenced to Feedback Voltage Falling IPGOOD = 1mA VOUT = 1.6V, IPGOOD = 1mA VPGOOD = 5.5V -7 0.3 -10 0.05 0.05 0.01 CONDITIONS
The denotes the specifications which apply over the specified operating temperature range of -40C to 85C, otherwise specifications are at TA = 25C. VIN = 1.2V, VOUT = 3.3V, unless otherwise noted.
MIN 0.88 0.25 1 -13 0.1 0.2 1 TYP MAX UNITS V V A % V V A
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 is guaranteed to meet performance specifications from 0C to 85C. Specifications over -40C to 85C 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.
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 125C 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 76C/W. Note 7: The IC is tested in a feedback loop to make the measurement.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current and VIN for VOUT = 1.8V (LTC3528)
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 VIN = 1V VIN = 1.2V VIN = 1.5V 10 100 1 LOAD CURRENT (mA) 0.1 POWER LOSS 1 10 EFFICIENCY 100 POWER LOSS (mW) EFFICIENCY (%) 1000 100 90 80 70 60 50 40 30 20 10 0 0.01
(TA = 25C unless otherwise noted)
Efficiency vs Load Current and VIN for VOUT = 3V (LTC3528)
EFFICIENCY 1000
100 POWER LOSS (mW)
10 POWER LOSS 1
0.01 1000
VIN = 1V VIN = 1.5V VIN = 2.4V 0.1 10 100 1 LOAD CURRENT (mA)
0.1
0.01 1000
3528 G01
3528 G26
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LTC3528/LTC3528B TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current and VIN for VOUT = 3.3V (LTC3528)
100 EFFICIENCY 90 100 80 EFFICIENCY (%) 70 60 50 40 30 0.01 VIN = 1.2V VIN = 1.8V VIN = 2.4V VIN = 3V 0.1 1 10 100 LOAD CURRENT (mA)
3528 G02
(TA = 25C unless otherwise noted) No-Load Input Current vs VIN (LTC3528)
1000 130 110 100 POWER LOSS (mW) 90 IIN (A) 70 50 30 10 1 2 3 VIN (V) 4 5
3528 G04
Efficiency vs Load Current and VIN for VOUT = 5V (LTC3528)
1000 100 EFFICIENCY 90 80 EFFICIENCY (%) 70 10 60 50 40 30 0.01 VIN = 1.2V VIN = 2.4V VIN = 3.6V VIN = 4.2V 0.1 1 10 100 LOAD CURRENT (mA)
3528 G03
POWER LOSS (mW)
10 POWER LOSS
1
POWER LOSS 1
0.1
VOUT = 1.8V VOUT = 3V VOUT = 3.3V VOUT = 5V
0.01 1000
0.1 1000
Maximum Output Current vs VIN
800 700 600 10000
Minimum Load Resistance During Start-Up vs VIN
130 120 110 1000 DELAY (s) RLOAD () 100 90 80 70
Start-Up Delay Time vs VIN
IOUT (mA)
500 400 300 200 100 0 1 1.5 2 3 2.5 VIN (V) VOUT = 1.8V VOUT = 3.3V VOUT = 5V 3.5 4 4.5
3528 G05
100
60 10 0.7 0.8 VIN (V)
3528 G06
50 0.9 1 1 1.5 2 3 2.5 VIN (V) 3.5 4 4.5
3528 G07
Burst Mode Threshold Current vs VIN
40 VOUT = 1.8V 50
Burst Mode Threshold Current vs VIN
VOUT = 3V 60
Burst Mode Threshold Current vs VIN
VOUT = 3.3V RISING
30 RISING IOUT (mA) IOUT (mA)
40 RISING FALLING 20 IOUT (mA) 30 40
20 FALLING 10
FALLING 20
10
0
1
1.1
1.3 1.2 VIN (V)
1.4
1.5
3528 G08
0
1
1.5 VIN (V)
2
2.5
3528 G09
0 1 1.5 2 VIN (V) 2.5 3
3528 G10
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LTC3528/LTC3528B TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Threshold Current vs VIN
60 VOUT = 5V FREQUENCY CHANGE (%) 0.50 0.25 0 -0.25 RDS(ON) (m) -0.50 -0.75 -1.00 -1.25 -1.50 -1.75 -2.00 0 1 2 VIN (V)
3528 G11
(TA = 25C unless otherwise noted)
Oscillator Frequency Change vs VOUT
450 NORMALIZED TO VOUT = 3V 400 350 300 250 200
RDS(ON) vs VOUT
40 IOUT (mA) RISING FALLING 20
PMOS
NMOS 150 100 1.5
-2.25 3 4 1.5 2 2.5 3.5 3 VOUT (V) 4 4.5 5
2
2.5
3.5 3 VOUT (V)
4
4.5
5
3528 G12
3528 G13
Oscillator Frequency Change vs Temperature
5 4 FREQUENCY CHANGE (%) 3 2 CHANGE (%) NORMALIZED TO 25C 30
RDS(ON) Change vs Temperature
1.200
VFB vs Temperature
20
1.195
0 -1 -2 -3 -4 -5 -50 -30 30 -10 10 50 TEMPERATURE (C) 70 90
0 1.185 -10
-20 -50
VFB (V)
1
10
1.190
-30
30 -10 10 50 TEMPERATURE (C)
70
90
1.180 -50
-30
50 -10 10 30 TEMPERATURE (C)
70
90
3528 G14
3528 G15
3528 G16
Start-Up Voltage vs Temperature
850 13.5
Burst Mode Quiescent Current vs VOUT (LTC3528)
VIN = 1.2V
Fixed Frequency VOUT Ripple and Inductor Current Waveforms
START-UP VOLTAGE (mV)
800 CURRENT (A) 12.5
VOUT 20mV/DIV IL 200mA/DIV
750
700
11.5
650
VIN = 1.2V VOUT = 3.3V COUT = 22F CFF = 33pF IOUT = 100mA 1 2 3 VOUT (V) 4 5
3528 G18
2s/DIV
3528 G19
600 -50
-30
30 -10 10 50 TEMPERATURE (C)
70
90
10.5
3528 G17
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LTC3528/LTC3528B TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Waveforms
VOUT 1V/DIV IIN 200mA/DIV SHDN PIN VIN = 1.2V VOUT = 3.3V COUT = 10F L = 4.7H 200s/DIV
3528 G21
(TA = 25C unless otherwise noted) Load Step Response (Fixed Frequency, 3.6V to 5V)
VOUT and IIN During Soft-Start
VOUT 20mV/DIV INDUCTOR CURRENT 100mA/DIV VIN = 3.6V VOUT = 5V COUT = 22F CFF = 33pF ILOAD = 30mA 5s/DIV
3528 G20
VOUT 100mV/DIV LOAD CURRENT 200mA/DIV VIN = 3.6V VOUT = 5V COUT = 10F L = 4.7H 20s/DIV
3528 G22
Load Step Response (Burst Mode Operation, 3.6V to 5V, LTC3528)
VOUT 100mV/DIV LOAD CURRENT 200mA/DIV VIN = 3.6V VOUT = 5V COUT = 10F L = 4.7H 50s/DIV
3528 G23
Load Step Response (Fixed Frequency, 1.2V to 3.3V)
Load Step Response (Burst Mode Operation, 1.2V to 3.3V, LTC3528)
VOUT 100mV/DIV LOAD CURRENT 100mA/DIV VIN = 1.2V VOUT = 3.3V COUT = 10F L = 4.7H 50s/DIV
3528 G24
VOUT 100mV/DIV LOAD CURRENT 100mA/DIV VIN = 1.2V VOUT = 3.3V COUT = 10F L = 4.7H 50s/DIV
3528 G25
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 < 1A 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: VOUT = 1.20V * 1+ R2 R1 VOUT (Pin 4): Output Voltage Sense and Drain Connection of the Internal Synchronous Rectifier. PCB trace length from VOUT to the output filter capacitor (4.7F 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.
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PGOOD (Pin 3): Power Good Comparator Output. This open-drain output is low when VFB < 10% from its regulation voltage.
6
LTC3528/LTC3528B PIN FUNCTIONS
VIN (Pin 8): Battery Input Voltage. Connect a minimum of 1F 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.
BLOCK DIAGRAM
VIN 0.7V TO 5V L1 4.7H CIN 4.7F
8 VIN ANTI-RING VOUT VSEL VBEST VB
5 SW
WELL SWITCH VOUT 4 VOUT 1.6V TO 5.25V R2
1
SHDN 4M
SHUTDOWN
SHUTDOWN
GATE DRIVERS AND ANTI-CROSS CONDUCTION
-+
PK COMP SLOPE COMP
FB IZERO COMP
2 R1
COUT 10F
UVLO
UVLO
PK IZERO
START-UP LOGIC 1MHz OSC 3 PGOOD CLK MODE CONTROL (LTC3528) BURST CLAMP
+ -
VREF - 10% FB THERMAL SHUTDOWN TSD WAKE EXPOSED PAD 9
3528 BD
PGND 6
SGND 7
+ -
VREF
VREF
ERROR AMP SLEEP COMP
+ -
VREF FB
SOFT-START
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LTC3528/LTC3528B OPERATION
(Refer to Block Diagram)
The LTC3528/LTC3528B are 1MHz synchronous boost converters housed in an 8-lead 3mm x 2mm DFN package. With the ability to start-up and operate from inputs less than 0.88V, the devices feature 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. With its low RDS(ON) and low gate charge internal N-channel MOSFET switch and P-channel MOSFET synchronous rectifier, the LTC3528 achieves high efficiency over a wide range of load current. Burst Mode operation maintains high efficiency at very light loads, reducing the quiescent current to 12A. Operation can be best understood by referring to the Block Diagram. LOW VOLTAGE START-UP The LTC3528/LTC3528B 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 93% 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/LTC3528B contains internal circuitry to provide soft-start operation. The internal soft-start circuitry
slowly 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. Oscillator An internal oscillator sets the frequency of operation to 1MHz. Shutdown 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. VOUT = 1.20V * 1+ 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.
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R2 R1
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LTC3528/LTC3528B 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/LTC3528B 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 turn-on, 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 a battery on VIN. Thermal Shutdown If the die temperature exceeds 160C, the LTC3528/ LTC3528B will enter 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 15C.
Burst Mode OPERATION The LTC3528 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 continues switching at a fixed frequency of 1MHz, 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 transitions to sleep mode where the outputs are off and the LTC3528 consumes only 12A 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 (10F or greater). As the load current increases, the LTC3528 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 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. The LTC3528B features continuous PWM operation at 1MHz. At very light loads, the LTC3528B will exhibit pulse-skip operation.
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LTC3528/LTC3528B APPLICATIONS INFORMATION
VIN > VOUT OPERATION The LTC3528/LTC3528B 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 LTC3528/LTC3528B output disconnect feature allows an 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 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. PCB LAYOUT GUIDELINES The high speed operation of the LTC3528/LTC3528B demands careful attention to board layout. A careless layout will not produce the advertised performance. Figure 1 shows the recommended component placement. A large ground copper area with the package backside metal pad
+
VIN CIN
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 Inductor Selection The LTC3528/LTC3528B can utilize small surface mount chip inductors due to their fast 1MHz switching frequency. Inductor values between 2.2H and 4.7H 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 10H will increase size while providing little improvement in output current capability. The minimum inductance value is given by: L> where: Ripple = Allowable inductor current ripple (amps peakpeak) VIN(MIN) = Minimum input voltage VOUT(MAX) = Maximum output voltage VIN(MIN) * VOUT(MAX) - VIN(MIN) 1.2 * Ripple * VOUT(MAX)
(
) H
SHDN 1
8 VIN
FB 2 LTC3528 PGOOD 3
7 SGND
6 PGND
VOUT 4 COUT
5 SW
3528 F01
MULTIPLE VIAS TO GROUND PLANE
Figure 1. Recommended Component Placement for Single Layer Board
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LTC3528/LTC3528B APPLICATIONS INFORMATION
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/LTC3528B. To minimize radiated noise, use a shielded inductor. See Table 1 for suggested components and suppliers.
Table 1. Recommended Inductors
VENDOR Coilcraft (847) 639-6400 www.coilcraft.com Coiltronics Sumida (847) 956-0666 www.sumida.com TDK Toko (408) 432-8282 www.tokoam.com Wurth (201) 785-8800 www.we-online.com PART/STYLE LPO2506, MSS5131 MSS6122, MOS6020 ME3220, DO1608C 1812PS SD14, SD18, SD20 SD25, SD52 CD43 CDC5D23B CDRH5D18 CR43 VLP VLF , VLCF SLF , D53, D63 D73, D75 WE-TPC type M, MH
extremely low ESR and are available in small footprints. A 10F to 22F output capacitor is sufficient for most applications. Values larger than 22F 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/LTC3528B is designed to be stable with output capacitor values of 10F 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 33pF 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 10F 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 AVX Murata Taiyo-Yuden TDK PHONE (803) 448-9411 (714) 852-2001 (408) 573-4150 (847) 803-6100 WEBSITE www.avxcorp.com www.murata.com www.t-yuden.com www.component.tdk.com
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
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LTC3528/LTC3528B TYPICAL APPLICATIONS
1 Cell to 1.8V
100 4.7H 90 SW VIN 0.88V TO 1.6V 4.7F VIN VOUT 499k FB 1M
3528 TA02a
Efficiency
EFFICIENCY (%)
LTC3528 PGOOD
33pF
VOUT 1.8V 250mA 10F
80 70 60 50 40 30 0.01 VIN = 0.9V VIN = 1.2V VIN = 1.5V 0.1 1 10 100 1000
3528 TA02b
OFF ON
SHDN GND
LOAD CURRENT (mA)
Dual 1 Cell to 1.8V, 3V Sequenced Supply
4.7H
SW VIN 0.88V TO 1.6V 4.7F 475k VIN VOUT 499k FB 1M 33pF
VOUT1 1.8V 250mA 10F
LTC3528 PGOOD
Output Voltage Sequencing
VOUT2
OFF ON
SHDN GND
4.7H
0.5V/DIV
VOUT1 VIN PGOOD1
SW VIN 4.7F VOUT 499k FB 324k 33pF
VOUT2 3V 200mA 200s/DIV 10F
3528 TA03b
LTC3528 PGOOD SHDN GND
3528 TA03a
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LTC3528/LTC3528B TYPICAL APPLICATIONS
1 Cell to 3.3V
100 4.7H 90 SW VIN 0.88V TO 1.6V 4.7F VIN VOUT 499k FB 287k
3528 TA04a
Efficiency
EFFICIENCY (%)
LTC3528 PGOOD
33pF
VOUT 3.3V 200mA 10F
80 70 60 50 40 30 0.01 VIN = 0.9V VIN = 1.2V VIN = 1.5V 0.1 1 10 100 1000
3528 TA04b
OFF ON
SHDN GND
LOAD CURRENT (mA)
2 Cell to 3.3V
100 4.7H 90 SW VIN 1.8V TO 3.2V 4.7F VIN VOUT 499k FB 287k
3528 TA05a
Efficiency
EFFICIENCY (%)
LTC3528 PGOOD
33pF
VOUT 3.3V 400mA 10F
80 70 60 50 40 30 0.01 VIN = 1.8V VIN = 2.4V VIN = 3V 0.1 1 10 100 1000
3528 TA05b
OFF ON
SHDN GND
LOAD CURRENT (mA)
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13
LTC3528/LTC3528B TYPICAL APPLICATIONS
2 Cell to 5V
100 4.7H 90 SW VIN 1.8V TO 3.2V 4.7F VIN VOUT 1M FB 316k
3528 TA06a
Efficiency
EFFICIENCY (%)
VOUT 5V 300mA 22F
80 70 60 50 40 30 0.01 VIN = 1.8V VIN = 2.4V VIN = 3V 0.1 1 10 100 1000
3528 TA06b
LTC3528 PGOOD
OFF ON
SHDN GND
LOAD CURRENT (mA)
Li-Ion to 5V
100 4.7H 90 SW VIN 2.7V TO 4.2V 4.7F VIN VOUT 1M FB 316k
3528 TA07a
Efficiency
EFFICIENCY (%)
VOUT 5V 400mA 22F
80 70 60 50 40 30 0.01 VIN = 2.8V VIN = 3.6V VIN = 4.2V 0.1 1 10 100 1000
3528 TA07b
LTC3528 PGOOD
OFF ON
SHDN GND
LOAD CURRENT (mA)
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14
LTC3528/LTC3528B PACKAGE DESCRIPTION
DDB Package 8-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 0.05 (2 SIDES) 0.70 0.05 2.55 0.05 1.15 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.20 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 5
3.00 0.10 (2 SIDES)
R = 0.05 TYP
0.40 0.10 8
PIN 1 BAR TOP MARK (SEE NOTE 6)
2.00 0.10 (2 SIDES) 0.56 0.05 (2 SIDES) 0.75 0.05
0.200 REF
4 0.25 0.05 2.15 0.05 (2 SIDES)
1 0.50 BSC
PIN 1 R = 0.20 OR 0.25 x 45 CHAMFER
(DDB8) DFN 0905 REV B
0 - 0.05
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
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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/LTC3528B RELATED PARTS
PART NUMBER LTC3400/LTC3400B LTC3401 LTC3402 LTC3421 LTC3422 LTC3423/LTC3424 LTC3426 LTC3428 LTC3429 LTC3458 DESCRIPTION 600mA ISW, 1.2MHz, Synchronous Step-Up DC/DC Converters 1A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 2A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 3A ISW, 3MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 1.5A ISW, 3MHz Synchronous Step-Up DC/DC Converter with Output Disconnect 1A/2A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 2A ISW, 1.2MHz, Step-Up DC/DC Converter 500mA ISW, 1.25MHz/2.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 600mA ISW, 500kHz/2.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect and Soft-Start 1.4A ISW, 1.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect and Burst Mode Operation 1.7A ISW, 1.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect and Automatic Burst Mode Operation 70mA ISW, 10V Micropower Synchronous Boost Converter with Output Disconnect and Burst Mode Operation 400mA Micropower Synchronous Step-Up DC/DC Converter with Output Disconnect 400mA Micropower Synchronous Step-Up DC/DC Converter with Output Disconnect 500mA, 1MHz/2MHz Synchronous Boost Converters 550mA, 1MHz Synchronous Boost Converter COMMENTS 92% Efficiency VIN: 0.85V to 5V, VOUT(MAX) = 5V, IQ = 19A/300A, ISD < 1A, ThinSOTTM Package 97% Efficiency VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38A, ISD < 1A, 10-Lead MS Package 97% Efficiency VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38A, ISD < 1A, 10-Lead MS Package 95% Efficiency VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12A, ISD < 1A, QFN24 Package 95% Efficiency VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 25A, ISD < 1A, 3mm x 3mm DFN Package 95% Efficiency VIN: 0.5V to 5.5V, VOUT(MAX) = 5.5V, IQ = 38A, ISD < 1A, 10-Lead MS Package 92% Efficiency VIN: 1.6V to 4.3V, VOUT(MAX) = 5V, ISD < 1A, SOT-23 Package 92% Efficiency VIN: 1.8V to 5V, VOUT(MAX) = 5.25V, ISD < 1A, 2mm x 2mm DFN Package 96% Efficiency VIN: 0.5V to 4.4V, VOUT(MAX) = 5V, IQ = 20A/300A, ISD < 1A, ThinSOT Package 93% Efficiency VIN: 1.5V to 6V, VOUT(MAX) = 7.5V, IQ = 15A, ISD < 1A, DFN12 Package 94% Efficiency VOUT(MAX) = 6V, IQ = 12A, DFN Package
LTC3458L
LTC3459
VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10A, ISD < 1A, ThinSOT Package 95% Efficiency VIN: 1V to 4.5V, VOUT(MAX) = 3V, 3.3V or 5V, IQ = 7A, ISD < 1A, SC-70 Package 95% Efficiency VIN: 0.7V to 5V, VOUT(MAX) = 3V, 3.3V or 5V, IQ = 7A, ISD < 1A, SC-70 Package 94% Efficiency, VIN: 0.85V to 5V, VOUT(MAX) = 5.25V, IQ = 9A/ 250A, ISD < 1A, 2mm x 2mm DFN Package 95% Efficiency, VIN: 0.7V to 5.5V, VOUT(MAX) = 5.25V, IQ = 9A, ISD < 1A, 2mm x 2mm DFN Package
LTC3525-3/LTC3525-3.3 LTC3525-5 LTC3525L-3 LTC3526/LTC3526B LTC3526-2/LTC3526-2B LTC3526L
ThinSOT is a trademark of Linear Technology Corporation.
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 1007 REV A * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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