LTC3528BEDDB#TRPBF - ANALOG DEVICES

LTC3528/LTC3528B

3528fd

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

1A, 1MHz Synchronous

Step-Up DC/DC Converters

in 3mm × 2mm DFN

The LTC

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 induc-

tors 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,

short-circuit protection and thermal overload protection.

The LTC3528/LTC3528B are offered in an 8-lead 3mm ×

2mm × 0.75mm DFN package.

■ 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

Operation with 12µA Quiescent Current

(LTC3528)

■ Low Noise PWM Operation (LTC3528B)

■ Internal Synchronous Rectiﬁer

■ Logic Controlled Shutdown: <1µA

■ Anti-Ringing Control

■ Low Proﬁle (3mm × 2mm × 0.75mm) DFN Package

■ Medical Instruments

■ Flash-Based MP3 Players

■ Noise Canceling Headphones

■ Wireless Mice

■ Bluetooth Headsets

VIN

499k

4.7µH

287k

4.7µF

10µF

33pF

3528 TA01a

LTC3528

SHDN

PGOOD

VOUT

VIN

1.8V TO 3.2V

VOUT

3.3V

400mA

OFF ON

GND

LOAD CURRENT (mA)

0.01

100

3528 TA01b

0.1 1 10 1000

100

1000

0.1

0.01

EFFICIENCY (%)

POWER LOSS (mW)

EFFICIENCY

POWER LOSS

VOUT = 3.3V

VIN = 2.4V

Efﬁciency and Power Loss

L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered

trademarks and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks

are the property of their respective owners.

LTC3528/LTC3528B

3528fd

ELECTRICAL CHARACTERISTICS

ABSOLUTE MAXIMUM RATINGS

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 Junction Temperature Range

(Notes 2, 5) ............................................ –40°C to 125°C

Storage Temperature Range ................... –65°C to 125°C

(Note 1)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Start-Up Voltage ILOAD = 1mA l0.70 0.88 V

Output Voltage Adjust Range

TA = 0°C to 85°C

l1.7

1.6

5.25

Feedback Voltage (Note 7) l1.170 1.200 1.230 V

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

N-Channel MOSFET Switch Leakage Current VSW = 5V 0.1 10 µA

P-Channel MOSFET Switch Leakage Current VSW = 5V, VOUT = 0V 0.1 10 µA

N-Channel MOSFET Switch On-Resistance 0.175 Ω

P-Channel MOSFET Switch On-Resistance 0.250 Ω

N-Channel MOSFET Current Limit l1.0 1.5 A

Current Limit Delay Time to Output (Note 3) 60 ns

Maximum Duty Cycle VFB = 1.15V l88 93 %

Minimum Duty Cycle VFB = 1.3V l0 %

Frequency l0.7 1.0 1.3 MHz

The l denotes the speciﬁcations which apply over the speciﬁed operating

temperature range, otherwise speciﬁcations are at TA = 25°C (Note 2). VIN = 1.2V, VOUT = 3.3V, unless otherwise noted.

TOP VIEW

DDB PACKAGE

8-LEAD (3mm × 2mm) PLASTIC DFN

1SHDN

PGOOD

VOUT

VIN

SGND

PGND

TJMAX = 125°C, θJA = 76°C/W (NOTE 6)

EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB

LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC3528EDDB#PBF

LTC3528BEDDB#PBF

LTC3528EDDB#TRPBF

LTC3528BEDDB#TRPBF

LCYD

LDDG

8-Lead (3mm × 2mm) Plastic DFN

–40°C to 125°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/

PIN CONFIGURATION

ORDER INFORMATION

LTC3528/LTC3528B

3528fd

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 LTC3528/LTC3528B are tested under pulsed load conditions

such that TJ ≈ TA. The LTC3528E/LTC3528BE are guaranteed to meet

speciﬁcations from 0°C to 85°C junction temperature. Speciﬁcations

over –40°C to 125°C operating junction temperature range are assured

by design, characterization and correlation with statistical process

controls. Note that the maximum ambient temperature consistent with

these speciﬁcations is determined by speciﬁc operating conditions in

conjunction with board layout, the rated package thermal impedance

and other environmental factors. The junction temperature (TJ, in °C) is

calculated from the ambient temperature (TA, in °C) and power dissipation

(PD, in Watts) according to the formula:

TJ = TA + (PD • θJA)

where θJA = 76°C/W is the package thermal impedance.

PARAMETER CONDITIONS MIN TYP MAX UNITS

SHDN Input High Voltage 0.88 V

SHDN Input Low Voltage 0.25 V

SHDN Input Current VSHDN = 1.2V 0.3 1 µA

PGOOD Threshold Percentage Referenced to Feedback Voltage Falling –7 –10 –13 %

PGOOD Low Voltage IPGOOD = 1mA

VOUT = 1.6V, IPGOOD = 1mA

0.05

0.1

0.2

PGOOD Leakage Current VPGOOD = 5.5V 0.01 1 µA

ELECTRICAL CHARACTERISTICS

The l denotes the speciﬁcations which apply over the speciﬁed operating

temperature range, otherwise speciﬁcations are at TA = 25°C (Note 2). VIN = 1.2V, VOUT = 3.3V, unless otherwise noted.

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 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.

TYPICAL PERFORMANCE CHARACTERISTICS

Efﬁciency vs Load Current and VIN

for VOUT = 1.8V (LTC3528)

Efﬁciency vs Load Current and VIN

for VOUT = 3V (LTC3528)

(TA = 25°C unless otherwise noted)

LOAD CURRENT (mA)

0.01

EFFICIENCY (%)

POWER LOSS (mW)

100

3528 G01

100

1000

0.1

0.01

0.1 110 1000

VIN = 1V

VIN = 1.2V

VIN = 1.5V

EFFICIENCY

POWER

LOSS

LOAD CURRENT (mA)

0.01

EFFICIENCY (%)

POWER LOSS (mW)

100

3528 G26

100

1000

0.1

0.01

0.1 110 1000

VIN = 1V

VIN = 1.5V

VIN = 2.4V

EFFICIENCY

POWER

LOSS

LTC3528/LTC3528B

3528fd

LOAD CURRENT (mA)

0.01

100

3528 G03

0.1 1 10 1000

100

1000

0.1

EFFICIENCY (%)

POWER LOSS (mW)

VIN = 1.2V

VIN = 2.4V

VIN = 3.6V

VIN = 4.2V

EFFICIENCY

POWER

LOSS

No-Load Input Current vs VIN

(LTC3528)

Maximum Output Current vs VIN

Minimum Load Resistance During

Start-Up vs VIN Start-Up Delay Time vs VIN

Burst Mode Threshold Current

vs VIN

Efﬁciency vs Load Current and VIN

for VOUT = 5V (LTC3528)

Efﬁciency vs Load Current and VIN

for VOUT = 3.3V (LTC3528)

LOAD CURRENT (mA)

0.01

100

3528 G02

0.1 1 10 1000

100

1000

0.1

0.01

EFFICIENCY (%)

POWER LOSS (mW)

VIN = 1.2V

VIN = 1.8V

VIN = 2.4V

VIN = 3V

EFFICIENCY

POWER

LOSS

VIN (V)

IIN (µA)

110

130

2 3 4 5

3528 G04

VOUT = 1.8V

VOUT = 3V

VOUT = 3.3V

VOUT = 5V

VIN (V)

IOUT (mA)

700

2.5

3528 G05

400

200

1.5 2 3

100

800

600

500

300

3.5 4 4.5

VOUT = 1.8V

VOUT = 3.3V

VOUT = 5V

VIN (V)

0.7

RLOAD (Ω)

1000

100

10000

0.8 0.9 1

3528 G06

VIN (V)

DELAY (µs)

120

2.5

3528 G07

1.5 2 3

130

110

100

3.5 4 4.5

VIN (V)

IOUT (mA)

1.4

3528 G08

01.1 1.2 1.3 1.5

40 VOUT = 1.8V

ENTER BURST

EXIT BURST

VIN (V)

IOUT (mA)

3528 G09

01.5

VOUT = 3V

22.5

ENTER BURST

EXIT BURST

VIN (V)

IOUT (mA)

1.5 2

3528 G10

2.5 3

VOUT = 3.3V

ENTER BURST

EXIT BURST

TYPICAL PERFORMANCE CHARACTERISTICS

(TA = 25°C unless otherwise noted)

Burst Mode Threshold Current

vs VIN

Burst Mode Threshold Current

vs VIN

LTC3528/LTC3528B

3528fd

TEMPERATURE (°C)

–50 –25

600

START-UP VOLTAGE (mV)

700

850

050 75

3528 G17

650

800

750

25 100 125

VOUT (V)

10.5

CURRENT (µA)

11.5

12.5

13.5

2 3

3528 G18

4 5

VIN = 1.2V

Oscillator Frequency Change

vs VOUT RDS(ON) vs VOUT

Oscillator Frequency Change

vs Temperature RDS(ON) Change vs Temperature VFB vs Temperature

Start-Up Voltage vs Temperature

Fixed Frequency VOUT Ripple and

Inductor Current Waveforms

Burst Mode Quiescent Current vs

VOUT (LTC3528)

VIN (V)

IOUT (mA)

2 3

3528 G11

VOUT = 5V

ENTER BURST

EXIT BURST

VOUT (V)

1.5

FREQUENCY CHANGE (%)

–1.50

0.25

0.50

2.5 3.5 4

3528 G12

–2.00

–0.50

–1.00

–1.75

–0.25

–2.25

–0.75

–1.25

234.5 5

NORMALIZED TO VOUT = 3V

VOUT (V)

1.5

300

350

450

3 4

3528 G13

250

200

2 2.5 3.5 4.5 5

150

100

400

RDS(ON) (mΩ)

PMOS

NMOS

TEMPERATURE (˚C)

–50

FREQUENCY CHANGE (%)

25 75

3528 G14

–1

–2

–25 0 50 100 125

–3

–4

TEMPERATURE (˚C)

–50

CHANGE (%)

25 75

3528 G15

–25 0 50 100 125

–10

–20

TEMPERATURE (°C)

–50

1.196

VFB (V)

1.197

1.198

1.199

1.200

–25 0 25 50

3528 G16

75 100 125

VOUT

20mV/DIV

2µs/DIV 3528 G19

VIN = 1.2V

VOUT = 3.3V

COUT = 22µF

CFF = 33pF

IOUT = 100mA

200mA/DIV

TYPICAL PERFORMANCE CHARACTERISTICS

(TA = 25°C unless otherwise noted)

Burst Mode Threshold Current

vs VIN

LTC3528/LTC3528B

3528fd

PIN FUNCTIONS

Load Step Response (Fixed

Frequency, 1.2V to 3.3V)

Load Step Response (Burst Mode

Operation, 1.2V to 3.3V, LTC3528)

SHDN (Pin 1): Logic Controlled Shutdown Input. There is

an internal 4MΩ 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:

VOUT =1.20V •1+R2











PGOOD (Pin 3): Power Good Comparator Output. This

open-drain output is low when VFB < 10% from its regu-

lation 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.

Load Step Response (Fixed

Frequency, 3.6V to 5V)

Load Step Response (Burst Mode

Operation, 3.6V to 5V, LTC3528)

VOUT and IIN During Soft-Start

Burst Mode Waveforms

5µs/DIV 3528 G20

VIN = 3.6V

VOUT = 5V

COUT = 22µF

CFF = 33pF

ILOAD = 30mA

VOUT

20mV/DIV

INDUCTOR

CURRENT

100mA/DIV

VOUT

1V/DIV

SHDN PIN

200µs/DIV 3528 G21

VIN = 1.2V

VOUT = 3.3V

COUT = 10µF

L = 4.7µH

IIN

200mA/DIV

VOUT

100mV/DIV

20µs/DIV 3528 G22

VIN = 3.6V

VOUT = 5V

COUT = 10µF

L = 4.7µH

LOAD

CURRENT

200mA/DIV

VOUT

100mV/DIV

50µs/DIV 3528 G23

VIN = 3.6V

VOUT = 5V

COUT = 10µF

L = 4.7µH

LOAD

CURRENT

200mA/DIV

VOUT

100mV/DIV

50µs/DIV 3528 G24

VIN = 1.2V

VOUT = 3.3V

COUT = 10µF

L = 4.7µH

LOAD

CURRENT

100mA/DIV

VOUT

100mV/DIV

50µs/DIV 3528 G25

VIN = 1.2V

VOUT = 3.3V

COUT = 10µF

L = 4.7µH

LOAD

CURRENT

100mA/DIV

TYPICAL PERFORMANCE CHARACTERISTICS

(TA = 25°C unless otherwise noted)

LTC3528/LTC3528B

3528fd

BLOCK DIAGRAM

–

GATE DRIVERS

AND

ANTI-CROSS

CONDUCTION

LOGIC

CLK

UVLO PK

COMP

SLOPE

COMP

IZERO

COMP

ERROR AMP

SLEEP COMP

IZERO

WAKE

EXPOSED

PAD

–

WELL

SWITCH

MODE

CONTROL

(LTC3528)

UVLO

VREF VREF

SHDN

VBEST

START-UP

1MHz

OSC

TSD

THERMAL

SHUTDOWN

ANTI-RING

VSEL

VIN

VOUT

4.7µH

SHUTDOWN

CLAMP

BURST

SOFT-START

VREF

–

VREF – 10%

VOUT

SGND

3528 BD

PGND

COUT

10µF

VOUT

1.6V

TO 5.25V

PGOOD

CIN

4.7µF

VIN

0.7V

TO 5V

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.

GND (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.

PIN FUNCTIONS

LTC3528/LTC3528B

3528fd

OPERATION

The LTC3528/LTC3528B are 1MHz synchronous boost

converters housed in an 8-lead 3mm × 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 regula-

tion. 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 12µA. 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 pro-

vide 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. Although

SHDN can be driven above VIN or VOUT (up to the absolute

maximum rating) without damage, the LTC3528/LTC3528B

have a proprietary test mode that may be engaged if

SHDN is held in the range of 0.5V to 1V higher than the

greater of VIN or VOUT. If the test mode is engaged, normal

PWM switching action is interrupted, which can cause

undesirable operation in some applications. Therefore,

in applications where SHDN may be driven above VIN,

a resistor divider or other means must be employed to

keep the SHDN voltage below (VIN + 0.4V) to prevent the

possibility of the test mode being engaged. Please refer

to Figure 1 for two possible implementations

(Refer to Block Diagram)

±30% SHDN

LTC3528/LTC3528B

VCNTRL

±30% SHDN

LTC3528/LTC3528B

ZETEX ZC2811E

R > (VCNTRL/(VIN + 0.4) – 1) MΩ

VIN

3528 F01

Figure 1. Recommended Shutdown Circuits

when Driving SHDN Above VIN

LTC3528/LTC3528B

3528fd

Error Ampliﬁer

The error ampliﬁer is a transconductance type. The nonin-

verting 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+R2











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 cur-

rent 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.

Zero Current Comparator

The zero current comparator monitors the inductor cur-

rent 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 160°C, 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 15°C.

OPERATION

(Refer to Block Diagram)

LTC3528/LTC3528B

3528fd

OPERATION

(Refer to Block Diagram)

Burst Mode OPERATION

The LTC3528 will automatically enter Burst Mode opera-

tion 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 switch-

ing 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 opera-

tion, 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 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 automatically

leaves Burst Mode operation. Note that larger output ca-

pacitor 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.

LTC3528/LTC3528B

3528fd

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 de-

mands careful attention to board layout. A careless layout

will not produce the advertised performance. Figure 2

shows 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

Inductor Selection

The LTC3528/LTC3528B can utilize small surface mount

chip inductors due to their fast 1MHz switching frequency.

Inductor values between 2.2µH and 4.7µH 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 cur-

rent. 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)

( )

1.2 •Ripple •VOUT(MAX)

µH

where:

Ripple = Allowable inductor current ripple (amps peak-

to-peak)

VIN(MIN) = Minimum input voltage

VOUT(MAX) = Maximum output voltage

Figure 2. Recommended Component Placement for Single Layer Board

SHDN

PGOOD

LTC3528

VOUT

3528 F01

COUT

VIN

VIN CIN

SGND

PGND

MULTIPLE VIAS

TO GROUND PLANE

LTC3528/LTC3528B

3528fd

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 depen-

dent 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 induc-

tor 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 PART/STYLE

Coilcraft

(847) 639-6400

www.coilcraft.com

LPO2506, MSS5131

MSS6122, MOS6020

ME3220, DO1608C

1812PS

Coiltronics SD14, SD18, SD20

SD25, SD52

Sumida

(847) 956-0666

www.sumida.com

CD43

CDC5D23B

CDRH5D18

CR43

TDK VLP, VLF

VLCF, SLF

Toko

(408) 432-8282

www.tokoam.com

D53, 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 ap-

plications. 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/LTC3528B

is designed to be stable with output capacitor values of

10µF or greater. Although ceramic capacitors are recom-

mended, 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 capaci-

tor 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 10µF input capacitor is sufﬁcient

for most applications. Larger values may be used without

limitations. Table 2 shows a list of several ceramic capaci-

tor 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

LTC3528/LTC3528B

3528fd

TYPICAL APPLICATIONS

1 Cell to 1.8V

VIN

499k

4.7µH

4.7µF

10µF

33pF

3528 TA02a

LTC3528

SHDN

PGOOD

VOUT

VIN

0.88V TO 1.6V

VOUT

1.8V

250mA

OFF ON

GND

Dual 1 Cell to 1.8V, 3V Sequenced Supply

VIN

499k

475k

4.7µH

4.7µF

10µF

LTC3528

SHDN

PGOOD

VOUT

VIN

0.88V TO 1.6V

VOUT1

1.8V

250mA

OFF ON

GND

VIN

499k

4.7µH

324k

4.7µF

10µF

33pF

3528 TA03a

LTC3528

SHDN

PGOOD

VOUT

VOUT2

200mA

GND

33pF

Efﬁciency

Output Voltage Sequencing

VOUT2

VOUT1

VIN

PGOOD1

200µs/DIV

0.5V/DIV

3528 TA03b

LOAD CURRENT (mA)

0.01

100

3528 TA02b

0.1 1 10 1000

EFFICIENCY (%)

VIN = 0.9V

VIN = 1.2V

VIN = 1.5V

LTC3528/LTC3528B

3528fd

TYPICAL APPLICATIONS

1 Cell to 3.3V Efﬁciency

Efﬁciency2 Cell to 3.3V

VIN

499k

4.7µH

287k

4.7µF

10µF

33pF

3528 TA04a

LTC3528

SHDN

PGOOD

VOUT

VIN

0.88V TO 1.6V

VOUT

3.3V

200mA

OFF ON

GND

VIN

499k

4.7µH

287k

4.7µF

10µF

33pF

3528 TA05a

LTC3528

SHDN

PGOOD

VOUT

VIN

1.8V TO 3.2V

VOUT

3.3V

400mA

OFF ON

GND

LOAD CURRENT (mA)

0.01

100

3528 TA04b

0.1 1 10 1000

EFFICIENCY (%)

VIN = 0.9V

VIN = 1.2V

VIN = 1.5V

LOAD CURRENT (mA)

0.01

100

3528 TA05b

0.1 1 10 1000

EFFICIENCY (%)

VIN = 1.8V

VIN = 2.4V

VIN = 3V

LTC3528/LTC3528B

3528fd

TYPICAL APPLICATIONS

2 Cell to 5V Efﬁciency

EfﬁciencyLi-Ion to 5V

VIN

1M 68pF

4.7µH

316k

4.7µF

22µF

3528 TA06a

LTC3528

SHDN

PGOOD

VOUT

VIN

1.8V TO 3.2V

VOUT

300mA

OFF ON

GND

VIN

4.7µH

316k

4.7µF

22µF

3528 TA07a

LTC3528

SHDN

PGOOD

VOUT

VIN

2.7V TO 4.2V

VOUT

400mA

OFF ON

GND

68pF

LOAD CURRENT (mA)

0.01

100

3528 TA06b

0.1 1 10 1000

EFFICIENCY (%)

VIN = 1.8V

VIN = 2.4V

VIN = 3V

LOAD CURRENT (mA)

0.01

100

3528 TA07b

0.1 1 10 1000

EFFICIENCY (%)

VIN = 2.8V

VIN = 3.6V

VIN = 4.2V

LTC3528/LTC3528B

3528fd

PACKAGE DESCRIPTION

DDB Package

8-Lead Plastic DFN (3mm × 2mm)

(Reference LTC DWG # 05-08-1702 Rev B)

2.00 ±0.10

(2 SIDES)

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

0.40 ± 0.10

BOTTOM VIEW—EXPOSED PAD

0.56 ± 0.05

(2 SIDES)

0.75 ±0.05

R = 0.115

TYP

R = 0.05

TYP

2.15 ±0.05

(2 SIDES)

3.00 ±0.10

(2 SIDES)

PIN 1 BAR

TOP MARK

(SEE NOTE 6)

0.200 REF

0 – 0.05

(DDB8) DFN 0905 REV B

0.25 ± 0.05

0.50 BSC

PIN 1

R = 0.20 OR

0.25 × 45°

CHAMFER

0.25 ± 0.05

2.20 ±0.05

(2 SIDES)

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

0.61 ±0.05

(2 SIDES)

1.15 ±0.05

0.70 ±0.05

2.55 ±0.05

PACKAGE

OUTLINE

0.50 BSC

LTC3528/LTC3528B

3528fd

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER

D 01/11 Change to Operating Temperature Range

Revised Note 2

Replaced graphs G14, G15, G16, G17

Operations Shutdown section revised text; added Figure 1

(Revision history begins at Rev D)

LTC3528/LTC3528B

3528fd

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 l FAX: (408) 434-0507 l www.linear.com

 LINEAR TECHNOLOGY CORPORATION 2007

LT 0111 REV D • PRINTED IN USA

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