ANALOG DEVICES LTC 3402 EMS Datasheet

FEATURES

■

Synchronous Rectification: Up to 97% Efficiency

■

2A Switch Current Rating

■

Fixed Frequency Operation Up to 3MHz

■

Wide Input Range: 0.5V to 5V

■

Very Low Quiescent Current: 38μA (Burst Mode
Operation)

■

2.6V to 5.5V Adjustable Output Voltage

■

0.85V (Typ) Start-Up Voltage

■

No External Schottky Diode Required (V

■

Synchronizable Switching Frequency

■

Burst Mode Enable Control

■

Antiringing Control Reduces Switching Noise

■

PGOOD Output

■

OPTI-LOOP® Compensation

■

Very Low Shutdown Current: <1μA

■

Small 10-Pin MSOP Package

OUT

< 4.3V)

U

APPLICATIO S

■

Cellular Telephones

■

Handheld Computers

■

MP3 Players

■

2-Way Pagers

■

GPS Receivers

■

Battery Backup Supplies

■

CCFL Backlights

LTC3402

2A, 3MHz Micropower

Synchronous Boost Converter

U

DESCRIPTIO

The LTC®3402 is a high efficiency, fixed frequency, step­up DC/DC converter that operates from an input voltage
below 1V. The device includes a 0.16Ω N-channel MOSFET

®

switch and a 0.18Ω P-channel synchronous rectifier.
Switching frequencies up to 3MHz are programmed with
an external timing resistor and the oscillator can be
synchronized to an external clock. An external Schottky
diode is optional but will slightly improve efficiency.

Quiescent current is only 38μA in Burst Mode operation,
maximizing battery life in portable applications. Burst
Mode operation is user controlled and can be enabled by
driving the MODE/SYNC pin high. If the MODE/SYNC pin
has either a clock or is driven low, then fixed frequency
switching is enabled.

Other features include a 1μA shutdown, antiringing con-
trol, open-drain power good output, thermal shutdown
and current limit. The LTC3402 is available in the 10-lead
thermally enhanced MSOP package. Lower current appli­cations should use the 1A rated LTC3401 synchronous
boost converter. Applications that require V

OUT

< 2.6V

should use the LTC3424.

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.

TYPICAL APPLICATIO

All Ceramic Capacitor 2-Cell to 3.3V at 1A Step-Up Converter

L1

3

V

10

SHDN

2

MODE/SYNC

6

PGOOD

1

R

R

t

30.1k

2.2μH

LTC3402

IN

V

GND

t

C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
L1: COILCRAFT: D03316P-222

VIN = 1.8V to 3V

+

2
CELLS

C1

10μF

0 = FIXED FREQ

1 = Burst Mode OPERATION

SW

OUT

U

Efficiency

100

V

OUT

3.3V
1A

4

7

8

FB

9

V

C

C3

5

470pF

R5
82k

R2

909k

C4

4.7pF

R1
549k

C2
44μF
(2 × 22μF)

3402 TA01

Burst Mode

90

OPERATION

80

70

60

50

40

EFFICIENCY (%)

30

20

10

VIN = 2.4V WITH SCHOTTKY

0

0.1

1MHz
CONSTANT
FREQUENCY

110

I

(mA)

OUT

100

1000

3402 TA02

3402fb

1

LTC3402

PACKAGE/ORDER I FOR ATIO

UU

W

1
2
3
4
5

R

t

MODE

V

IN

SW

GND

10
9
8
7
6

SHDN
V

C

FB
V

OUT

PGOOD

TOP VIEW

MS PACKAGE

10-LEAD PLASTIC MSOP

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

VIN, V

SW Voltage ................................................. – 0.5V to 6V

, Rt Voltages ......................... – 0.5V to (V

V

C

PGOOD, SHDN, FB, MODE Voltages ........... –0.5V to 6V

Voltages ...................................... – 0.5V to 6V

OUT

OUT

ORDER PART

NUMBER

+ 0.3V)

LTC3402EMS

Operating Temperature Range (Note 2) .. –40°C to 85°C

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

Lead Temperature (Soldering, 10 sec)..................300°C

Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/

T

= 125°C

JMAX

= 130°C/ W 1 LAYER BOARD

θ

JA

= 100°C/ W 4 LAYER BOARD

θ

JA

Consult LTC Marketing for parts specified with wider operating temperature ranges.

MS PART MARKING

LTSK

ELECTRICAL CHARACTERISTICS

The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VIN = 1.2V, V

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Start-Up Voltage I

Minimum Operating Voltage (Note 4) ● 0.5 V

Output Voltage Adjust Range ● 2.6 5.5 V

Feedback Voltage ● 1.22 1.25 1.28 V

Feedback Input Current VFB = 1.25V 1 50 nA

Quiescent Current—Burst Mode Operation VC = 0V, MODE/SYNC = 3.3V (Note 3) 38 65 μA
Quiescent Current—SHDN SHDN = 0V, Not Including Switch Leakage 0.1 1 μA

Quiescent Current—Active VC = 0V, MODE/SYNC = 0V, Rt = 300k (Note 3) 440 800 μA
NMOS Switch Leakage 0.1 5 μA
PMOS Switch Leakage 0.1 10 μA
NMOS Switch On Resistance 0.16 Ω
PMOS Switch On Resistance 0.18 Ω

NMOS Current Limit ● 2 2.5 A

NMOS Burst Current Limit 0.66 A

Maximum Duty Cycle Rt = 15k ● 80 85 %

Minimum Duty Cycle ● 0%

Switching Frequency Rt = 15k ● 1.6 2 2.4 MHz

MODE/SYNC Input High 1.4 V

MODE/SYNC Input Low 0.4 V

MODE/SYNC Input Current V
Error Amp Transconductance ΔI = – 5μA to 5μA, VC = V

PGOOD Threshold Referenced to Feedback Voltage – 6 –9 – 12 %

= 3.3V unless otherwise noted.

OUT

= <1mA 0.85 1.0 V

LOAD

MODE/SYNC

= 5.5V 0.01 1 μA

FB

85 μmhos

2

3402fb

LTC3402

ELECTRICAL CHARACTERISTICS

The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
V

= 1.2V, V

IN

PARAMETER CONDITIONS MIN TYP MAX UNITS

PGOOD Low Voltage I

PGOOD Leakage V

SHDN Input High VIN = V

SHDN Input Low 0.4 V

SHDN Input Current V

= 3.3V unless otherwise noted.

OUT

= 1mA 0.1 0.2 V

PGOOD

= 1V, I

V

OUT

= 5.5V 0.01 1 μA

PGOOD

SHDN

= 5.5V 0.01 1 μA

SHDN

= 20μA 0.1 0.4 V

PGOOD

1V

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 LTC3402E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating

with statistical process controls.
Note 3: Current is measured into the V

bootstrapped to the output pin and in the application will reflect to the
input supply by (V

Note 4: Once the output is started, the IC is not dependent upon the V
supply.

temperature range are assured by design, characterization and correlation

UW

TYPICAL PERFOR A CE CHARACTERISTICS

SW Pin and Inductor Current (IC)
in Discontinuous Mode. Ringing
Control Circuitry Eliminates High

Switching Waveform on SW Pin

SW

1V/DIV

50ns/DIV

50mA/DIV

3402 G01

Frequency Ringing Transient Response 5mA to 50mA

I

L

0A

SW

1V/DIV

0V

200ns/DIV

pin since the supply current is

OUT

) • I/Efficiency. The outputs are not switching.

OUT/VIN

(TA = 25°C unless otherwise noted)

V

OUT

100mV/DIV

50mA

I

OUT

5mA

3402 G02

C

= 22μF 200μs/DIV 3402 G03

OUT

L = 3.3μH

= 1MHz

f

OSC

IN

V

OUT

200mV/DIV

550mA

50mA

Transient Response 50mA to 500mA Burst Mode Operation

V

OUT

AC

100mV/DIV

SW

1V/DIV

= 22μF 200μs/DIV 3402 G04

C

OUT

L = 3.3μH
f

= 1MHz

OSC

V

= 1.2V 5ms/DIV 3402 G05

IN

V

= 3.3V

OUT

C

= 100μF

OUT

= 250μA

I

OUT

MODE/SYNC PIN = HIGH

V

OUT

100mV/DIV

SW

1V/DIV

Burst Mode Operation

AC

V

= 1.2V 200μs/DIV 3402 G06

IN

V

= 3.3V

OUT

C

= 100μF

OUT

= 20mA

I

OUT

MODE/SYNC PIN = HIGH

3402fb

3

LTC3402

UW

TYPICAL PERFOR A CE CHARACTERISTICS

(TA = 25°C unless otherwise noted)

Converter Efficiency 1.2V to 3.3V

100

90

Burst Mode

80

OPERATION

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 10 100 1000

300kHz

3MHz

1MHz

1
OUTPUT CURRENT (mA)

Start-Up Voltage
vs I

OUT

500

TA = 25°C

400

300

3402 G07

Converter Efficiency 2.4V to 3.3V

100

Burst Mode

90

OPERATION

80

70

300kHz

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 10 100 1000

1
OUTPUT CURRENT (mA)

3MHz

1MHz

Efficiency Loss Without Schottky
vs Frequency

14

TA = 25°C

12

10

8

3402 G08

Converter Efficiency 3.6V to 5V

100

Burst Mode OPERATION

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

VIN = 3.6V

0

0.1

1MHz
FIXED
FREQUENCY

110

LOAD CURRENT (mA)

Current Limit

3.4

3.2

3.0

2.8

100

1000

3402 G10

200

OUTPUT CURRENT (mA)

100

0

0.8

0.9

EA FB Voltage

1.28

1.27

1.26

1.25

VOLTAGE (V)

1.24

1.23

1.22
–15 25 105

–55

TEMPERATURE (°C)

1

1.1 1.2

VIN (V)

6

4

EFFICIENCY LOSS (%)

2

1.3

1.4

3402 G09

0

0.2

0.6 1.0

1.8 2.6 3.0

1.4 2.2

FREQUENCY (MHz)

3402 G11

Oscillator Frequency Accuracy

2.10
= 15k

R

t

2.05

2.00

FREQUENCY (MHz)

1.95

65

125

3402 G13

1.90

–15 25 105

–55

TEMPERATURE (°C)

65

125

3402 G14

2.6

CURRENT (A)

2.4

2.2

2.0
–55

NMOS R

0.30
V

OUT

0.25

0.20

0.15

RESISTANCE (Ω)

0.10

0.05
–55

–15 25 105

TEMPERATURE (°C)

65

DS(ON)

= 3.3V

–15 25 105

TEMPERATURE (°C)

65

125

3402 G12

125

3402 G22

4

3402fb

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LTC3402

(TA = 25°C unless otherwise noted)

PMOS R

0.30
V

= 3.3V

OUT

0.25

0.20

0.15

RESISTANCE (Ω)

0.10

0.05
–55

PGOOD Threshold

–7.0

–7.5

–8.0

–8.5

(%)

FB

–9.0

–9.5

–10.0

–10.5

PERCENT FROM V

–11.0

–11.5

–12.0

–55

DS(ON)

–15 25 105

TEMPERATURE (°C)

–15 25 105

TEMPERATURE (°C)

65

65

3402 G16

3402 G19

125

125

Start-Up Voltage

1.1

1.0

0.9

0.8

VOLTAGE (V)

0.7

0.6
–15 25 105

–55

TEMPERATURE (°C)

Burst Mode Operation Current

44

42

40

38

36

CURRENT (μA)

34

32

30

–15 25 105

–55

TEMPERATURE (°C)

Shutdown Threshold

1.10

1.05

1.00

0.95

0.90

0.85

0.80

VOLTAGE (V)

0.75

0.70

0.65

65

65

125

3402 G17

125

3402 G20

0.60

2.50

2.45

2.40

2.35

2.30

2.25

2.20

VOLTAGE (V)

2.15

2.10

2.05

2.00

–15 25 105

–55

TEMPERATURE (°C)

V

Turn-Off Voltage

OUT

–15 25 105

–55

TEMPERATURE (°C)

65

65

125

3402 G18

125

3402 G21

3402fb

5

LTC3402

U

UU

PI FU CTIO S

Rt (Pin 1): Timing Resistor to Program the Oscillator
Frequency.

10

•

OSC

310

=

Hz

R

t

f

MODE/SYNC (Pin 2): Burst Mode Select and Oscillator
Synchronization.

MODE/SYNC = High. Enable Burst Mode operation. The
inductor peak inductor current will be 1/3 the current
limit value and return to zero current on each cycle.
During Burst Mode operation the operation is variable
frequency, providing a significant efficiency improve­ment at light loads. It is recommended the Burst Mode
operation only be entered once the part has started up.

MODE/SYNC = Low. Disable Burst Mode operation and
maintain low noise, constant frequency operation.

MODE/SYNC = External CLK. Synchronization of the
internal oscillator and Burst Mode operation disable. A
clock pulse width of 100ns to 2μs is required to
synchronize.

VIN (Pin 3): Input Supply Pin.

SW (Pin 4): Switch Pin. Connect inductor and Schottky

diode here. For applications with output voltages over

4.3V, a Schottky diode is required to ensure that the SW
pin voltage does not exceed its absolute maximum
rating. Minimize trace length to keep EMI and high
ringing down. For discontinuous inductor current, a
controlled impedance is placed from SW to VIN from the

IC to eliminate high frequency ringing due to the resonant
tank of the inductor and SW node capacitance, therefore
reducing EMI radiation.

GND (Pin 5): Signal and Power Ground for the IC.

PGOOD (Pin 6): Power Good Comparator Output. This

open-drain output is low when VFB < –9% from its
regulation voltage.

V

(Pin 7): Output of the Synchronous Rectifier and

OUT

Bootstrapped Power Source for the IC. A ceramic capaci­tor of at least 1μF is required and should be located as
close to the V

FB (Pin 8): Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 2.6V to 5V.
The feedback reference voltage is typically 1.25V.

VC (Pin 9): Error Amp Output. A frequency compensation
network is connected to this pin to compensate the loop.
See the section “Compensating the Feedback Loop” for
guidelines.

SHDN (Pin 10): Shutdown. Grounding this pin shuts down
the IC. Tie to >1V to enable (VIN or digital gate output). To
operate with input voltages below 1V once the converter
has started, a 1M resistor from SHDN to VIN and a 5M
resistor from SHDN to V
esis. During shutdown, the output voltage will hold up to
VIN minus a diode drop due to the body diode of the PMOS
synchronous switch. If the application requires a com­plete disconnect during shutdown, refer to the section
“Output Disconnect Circuits.”

and GND pins as possible (Pins 7 and 5).

OUT

will provide sufficient hyster-

OUT

6

3402fb

BLOCK DIAGRA

W

LTC3402

+

1V TO

+ 0.3V

V

OUT

V

IN

3

SHDN SHUTDOWN

10

GND

5

ANTIRING

ANTICROSS

COND

CURRENT

LIMIT

PWM

LOGIC

SLEEP

SW

4

N

+

–

CURRENT

COMP

+

I

SENSE

AMP

–

2.8A TYP

–

+

+–

Σ

10mV

P

V

OUT

7

V

OUT

2.6V TO 5.5V

+

+

–

I

ZERO

AMP

+

1.25V

ERROR

AMP

–

FB

8

V

9

R1

C

POK

Burst Mode

CONTROL

R

t

1

6

N

OSC

SLOPE COMP

–

+

1.25V – 9%

MODE/SYNC

2

3402 BD

R2

3402fb

7

LTC3402

WUUU

APPLICATIO S I FOR ATIO

DETAILED DESCRIPTION

The LTC3402 provides high efficiency, low noise power
for applications such as portable instrumentation. The
current mode architecture with adaptive slope compensa­tion provides ease of loop compensation with excellent
transient load response. The low R
synchronous switches provide the pulse width modula­tion control at high efficiency.

The Schottky diode across the synchronous PMOS switch
provides a lower drop during the break-before-make time
(typically 20ns) of the NMOS to PMOS transition. The
addition of the Schottky diode will improve efficiency (see
graph “Efficiency Loss Without Schottky vs Frequency”).
While the IC’s quiescent current is a low 38μA, high
efficiency is achieved at light loads when Burst Mode
operation is entered.

Low Voltage Start-Up

The LTC3402 is designed to start up at input voltages of
typically 0.85V. The device can start up under some load,
(see graph Start-Up vs Input Voltage). Once the output
voltage exceeds a threshold of 2.3V, then the IC powers
itself from V
circuitry has no dependency on the input voltage, eliminat­ing the requirement for a large input capacitor. The input
voltage can drop below 0.5V without affecting the opera­tion, but the limiting factor for the application becomes the
availability of the power source to supply sufficient energy
to the output at the low voltages.

Low Noise Fixed Frequency Operation

Oscillator. The frequency of operation is set through a

resistor from the Rt pin to ground where f = 3 • 1010/Rt. An
internally trimmed timing capacitor resides inside the IC.
The oscillator can be synchronized with an external clock
inserted on the MODE/SYNC pin. When synchronizing the
oscillator, the free running frequency must be set to
approximately 30% lower than the desired synchronized
frequency. Keeping the sync pulse width below 2μs will
ensure that Burst Mode operation is disabled.

Current Sensing. Lossless current sensing converts the
peak current signal to a voltage to sum in with the internal
slope compensation. This summed signal is compared to

instead of VIN. At this point, the internal

OUT

, low gate charge

DS(ON)

the error amplifier output to provide a peak current control
command for the PWM. The slope compensation in the IC
is adaptive to the input and output voltage. Therefore, the
converter provides the proper amount of slope compensa­tion to ensure stability and not an excess causing a loss of
phase margin in the converter.

Error Amp. The error amplifier is a transconductance
amplifier with gm = 0.1ms. A simple compensation net­work is placed from the V

Current Limit. The current limit amplifier will shut the
NMOS switch off once the current exceeds its threshold.
The current amplifier delay to output is typically 50ns.

Zero Current Amp. The zero current amplifier monitors the
inductor current to the output and shuts off the synchro­nous rectifier once the current is below 50mA, preventing
negative inductor current.

Antiringing Control. The anitringing control will place an
impedance across the inductor to damp the ringing on the
SW pin during discontinuous mode operation. The LC
ringing (L = inductor, CSW = capacitance on the switch pin)
is low energy, but can cause EMI radiation.

Burst Mode Operation

Burst Mode operation is when the IC delivers energy to the
output until it is regulated and then goes into a sleep mode
where the outputs are off and the IC is consuming only
38μA. In this mode, the output ripple has a variable
frequency component with load current and the steady
state ripple will be typically below 3%.

During the period where the device is delivering energy to
the output, the peak current will be equal to 1/6 the current
limit value and the inductor current will terminate at zero
current for each cycle. In this mode the maximum output
current is given by:

I

OUT MAXBURST

()

Burst Mode operation is user controlled by driving the
MODE/SYNC pin high to enable and low to disable. It is
recommended that Burst Mode operation be entered after
the part has started up.

pin to ground.

C

V

IN

Amps

V

•≈6

OUT

SW

3402fb

8

WUUU

APPLICATIO S I FOR ATIO

LTC3402

COMPONENT SELECTION

Inductor Selection

The high frequency operation of the LTC3402 allows the
use of small surface mount inductors. The minimum
inductance value is proportional to the operating fre­quency and is limited by the following constraints:

3

L

H and L

>μ >

f

VV V

IN MIN OUT MAX IN MIN

•–

() ( ) ()

f Ripple V

••

OUT MAX

()

H

where

f = Operating Frequency (Hz)
Ripple = Allowable Inductor Current Ripple (A)
V
V

= Minimum Input Voltage (V)

IN(MIN)

OUT(MAX)

= Maximum Output Voltage (V)

The inductor current ripple is typically set to 20% to 40%
of the maximum inductor current.

R

SHDN

t

MODE
V
SW
GND

V

C

FB

IN

V

OUT

POK

Table 1. Inductor Vendor Information

SUPPLIER PHONE FAX WEBSITE

Coilcraft [phone] [phone] www.coilcraft.com

Coiltronics [phone] [phone] www.coiltronics.com

Murata [phone] [phone] www.murata.com

[phone]

Sumida

USA: [phone] [phone] www.japanlink.com

Japan: 81-3-3607-5111 81-3-3607-5144 sumida

Output Capacitor Selection

The output voltage ripple has several components. The
bulk value of the capacitor is set to reduce the ripple due
to charge into the capacitor each cycle. The max ripple due
to charge is given by:

IV

•

VR

BULK

=

PIN

CVf

••

OUT OUT

V

where

IP = Peak Inductor Current

The ESR can be a significant factor for ripple in most
power converters. The ripple due to capacitor ESR is
simply given by:

V

OUT

3402 F01

Figure 1. Recommended Component Placement. Traces
Carrying High Current Are Direct. Trace Area FB and VC Pins
Are Kept Low. Lead Length to Battery Should be Kept Short

For high efficiency, choose an inductor with a high fre­quency core material, such as ferrite, to reduce core
losses. The inductor should have low ESR (equivalent
series resistance) to reduce the I2R losses and must be
able to handle the peak inductor current without saturat­ing. Molded chokes or chip inductors usually do not have
enough core to support the peak inductor currents in the
1A to 2A region. To minimize radiated noise, use a toroid,
pot core or shielded bobbin inductor. See Table 1 for
suggested components and Table 1 for a list of component
suppliers.

VR

CESR

= IP • R

ESR

V

where

R

= Capacitor Series Resistance

ESR

Low ESR capacitors should be used to minimize output
voltage ripple. For surface mount applications, AVX TPS
series tantalum capacitors and Sanyo POSCAP or Taiyo­Yuden ceramic X5R or X7R type capacitors are recom­mended. For through-hole applications Sanyo OS-CON
capacitors offer low ESR in a small package size. See Table
2 for a list of component suppliers. In some layouts it may
be required to place a 1μF low ESR capacitor as close to the
V

and GND pins as possible.

OUT

Table 2. Capacitor Vendor Information

SUPPLIER PHONE FAX WEBSITE

AVX [phone] [phone] www.avxcorp.com

Sanyo [phone] [phone] www.sanyovideo.com

Taiyo Yuden [phone] [phone] www.t-yuden.com

3402fb

9

LTC3402

WUUU

APPLICATIO S I FOR ATIO

Input Capacitor Selection

The input filter capacitor reduces peak currents drawn from
the input source and reduces input switching noise. Since
the IC can operate at voltages below 0.5V once the output
is regulated, then demand on the input capacitor is much
less and in most applications a 4.7μF is recommended.

Output Diode

For applications with output voltages over 4.3V, a Schottky
diode is required to ensure that the SW pin voltage does
not exceed its absolute maximum rating. The Schottky
diode across the synchronous PMOS switch provides a
lower drop during the break-before-make time (typically
20ns) of the NMOS to PMOS transition. The Schottky
diode improves peak efficiency (see graph “Efficiency
Loss Without Schottky vs Frequency). Use of a Schottky
diode such as a MBR0520L, 1N5817 or equivalent. Since
slow recovery times will compromise efficiency, do not
use ordinary rectifier diodes.

Operating Frequency Selection

applications where physical size is the main criterion then
running the converter in this mode is acceptable. In
applications where it is preferred not to enter this mode,
then the maximum operating frequency is given by:

–

VV

OUT IN

f

MAX NOSKIP

where t

ON(MIN)

EFFICIENCY (%)

=

•

Vt

OUT ON MIN_()

Hz

= minimum on time = 120ns.

100

Burst Mode

90

OPERATION

80

70

300kHz

60

50

40

30

20

10

0

0.1 10 100 1000

1
OUTPUT CURRENT (mA)

3MHz

1MHz

3402 G08

There are several considerations in selecting the operating
frequency of the converter. The first is determining the
sensitive frequency bands that cannot tolerate any spec­tral noise. For example, in products incorporating RF
communications, the 455kHz IF frequency is sensitive to
any noise, therefore switching above 600kHz is desired.
Some communications have sensitivity to 1.1MHz. In this
case, a 2MHz converter frequency may be employed.

The second consideration is the physical size of the
converter. As the operating frequency goes up, the induc­tor and filter caps go down in value and size. The trade off
is in efficiency since the switching losses due to gate
charge are going up proportional with frequency. For
example in Figure 2, for a 2.4V to 3.3V converter, the
efficiency at 100mA is 5% less at 2MHz compared to
300kHz.

Another operating frequency consideration is whether the
application can allow “pulse skipping.” In this mode, the
minimum on time of the converter cannot support the duty
cycle, so the converter ripple will go up and there will be
a low frequency component of the output ripple. In many

Figure 2. Converter Efficiency 2.4V to 3.3V

Reducing Output Capacitance with a Load Feed
Forward Signal

In many applications the output filter capacitance can be
reduced for the desired transient response by having the
device commanding the change in load current, (i.e.
system microcontroller), inform the power converter of
the changes as they occur. Specifically, a “load feed
forward” signal coupled into the VC pin gives the inner
current loop a head start in providing the change in output
current. The transconductance of the LTC3402 converter
at the VC pin with respect to the inductor current is typically
170mA/100mV, so the amount of signal injected is pro­portional to the anticipated change of inductor current
with load. The outer voltage loop performs the remainder
of the correction, but because of the load feed forward
signal, the range over which it must slew is greatly
reduced. This results in an improved transient response.
A logic level feed forward signal, VFF, is coupled through
components C5 and R6. The amount of feed forward

10

3402fb

WUUU

APPLICATIO S I FOR ATIO

LTC3402

signal is attenuated with resistor R6 and is given by the
following relationship:

R

6

where ΔI

V

IN

⎛

VRV

515

•• •.

FF IN

⎜
⎝

VI

•–Δ

OUT OUT

= load current change.

OUT

LTC3402

3

V

IN

10

SHDN

2

MODE/SYNC

6

PGOOD

1

R

LOAD FEED

FORWARD

SIGNAL

t

V

GND

SW

OUT

V

V

FB

C

FF

⎞
⎟

⎠

4

7

8

9

5

3.3nF

R6

Figure 3

R

5≈

V

OUT

C3

R5

C5

3402 F03

Closing the Feedback Loop

The LTC3402 used current mode control with internal
adaptive slope compensation. Current mode control elimi­nates the 2nd order filter due to the inductor and output
capacitor exhibited in voltage mode controllers, and sim­plifies it to a single-pole filter response. The product of the
modulator control to output DC gain plus the error amp
open-loop gain equals the DC gain of the system.

GDC = G

G

CONTROL

CONTROLOUTPUT

2•

=

I

OUT

• G

V

IN

, GEA ≈ 2000

EA

The output filter pole is given by:

I

f

FILTERPOLE

=

OUT

VC

π ••

OUT OUT

Hz

The output filter zero is given by:

f

FILTERZERO

where R

=

2• • •π

is the capacitor equivalent series resistance.

ESR

1

RC

ESR OUT

Hz

A troublesome feature of the boost regulator topology is
the right half plane zero (RHP) and is given by:

2

VR

=

IN O

2π

LV

Hz

2

O

f

RHPZ

At heavy loads this gain increase with phase lag can occur
at a relatively low frequency. The loop gain is typically
rolled off before the RHP zero frequency.

The typical error amp compensation is shown in Figure 4.
The equations for the loop dynamics are as follows:

f

POLE

≈

1

22010

•• • •

1

π

6

Hz

C

C

1

whichis extremely closeto DC

f

ZERO

f

POLE

=

1

2

≈

2

2

1

RC

•• •

π

ZC

1

RC

•• •

π

ZC

Hz

1

Hz

2

Refer to AN76 for more closed-loop examples.

V

OUT

R1

R2

C

C2

3402 F04

ERROR

AMP

+

–

1.25V

FB

8

V

C

9

Figure 4

C

C1

R

Z

where C

is the output filter capacitor.

OUT

3402fb

11

LTC3402

UU

OUTPUT DISCO ECT CIRCUITS

Single Cell Output Disconnect

VIN = 0.9V TO 1.5V

3

V

IN

10

SHDN

2

MODE/SYNC

6

PGOOD

1

R

t

*SET RB TO FORCE BETA OF ≤100; RB =

0 = FIXED FREQUENCY

1 = Burst Mode OPERATION

Dual Cell Output Disconnect Allowing Full Load Start-Up

LTC3402

V

GND

SW

OUT

V

ZETEX

FMMT717

4

7

8

FB

9

C

5

– V

(V

OUT

– 0.7V) • 100

INMIN

I

OUTMAX

RB*

3402 TA03

V

C5
1μF

OUT

VIN = 1.8V TO 3V

R7

1M

0 = FIXED FREQUENCY

1 = Burst Mode OPERATION

3

V

IN

10

SHDN

2

MODE/SYNC

6

PGOOD

1

R

t

LTC3402

SW

V

OUT

GND

IRLML6401

4

7

8

FB

9

V

C

5

RG
1M

2N2222

3402 TA04

V

C5
1μF

OUT

3402fb

12

TYPICAL APPLICATIO S

LTC3402

U

Single Cell to 3V at 500mA, All Ceramic Capacitor, 3MHz Step-Up Converter

R4

L1

5.1M

VIN = 0.9V TO 1.5V

R3

1M

+

1
CELL

C1

3.3μF

0 = FIXED FREQUENCY

1 = Burst Mode OPERATION

3

V

IN

10

SHDN

2

MODE/SYNC

6

PGOOD

1

R

t

R

t

10k

2.2μH

LTC3402

SW

V

OUT

GND

C1: TAIYO YUDEN JMK212BJ335MG
C2: TAIYO YUDEN JMK325BJ106MM
D1: ON SEMICONDUCTOR MBRM120T3
L1: COILCRAFT DO1608-222

D1

4

7

8

FB

9

V

C

C3
470pF

5

R5
39k

866k

C4
20pF

R2

R1
619k

V

OUT

3V
500mA

C2
10μF

3404 TA05a

Efficiency

90

Burst Mode

80

OPERATION

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 10 100 1000

1

OUTPUT CURRENT (mA)

3MHz FIXED
FREQUENCY

3402 TA05b

Li-Ion to 5V at 300mA, 1MHz Step-Up Converter

VIN = 2.5V TO 4.2V

R3

3

1M

10

Li-Ion

C1

4.7μF

0 = FIXED FREQUENCY

1 = Burst Mode OPERATION

2

6

1

R

t

30.1k

L1

10μH

LTC3402

V

IN

SHDN

MODE/SYNC

PGOOD

R

t

SW

V

OUT

GND

*LOCATE COMPONENTS AS CLOSE TO
IC AS POSSIBLE
C1: TAIYO YUDEN JMK212BJ475MG
C2: TAIYO YUDEN JMK325BJ226MM
D1: ON SEMICONDUCTOR MBRM120T3
L1: SUMIDA CDH53-100

D1*

4

7

8

FB

9

V

C

C3
470pF

5

R5
82k

1.65M

C4

4.7pF

Efficiency

100

V

OUT

5V
600mA

R2

C2*

R1
549k

22μF

3402 TA07a

EFFICIENCY (%)

Burst Mode OPERATION

90

80

70

60

50

40

30

20

10

VIN = 3.6V

0

0.1

1MHz
FIXED
FREQUENCY

110

LOAD CURRENT (mA)

100

1000

3402 G10

3402fb

13

LTC3402

TYPICAL APPLICATIO S

High Efficiency, Compact CCFL Supply with Remote Dimming

U

C3

27pF

1kV

5

6

T1

= 2.5V TO 4.2V

V

IN

R5

Li-Ion

1M

C1

10μF

C1: TAIYO YUDEN JMK212BJ106MG
C2: PANASONIC ECH-U
D1: ZETEX ZHCS-1000
D2 TO D4: 1N4148

10 2 3

1

R1

300Ω

D1

LTC3402

3

V

IN

10

SHDN

2

MODE/SYNC

6

PGOOD

1

R

t

R

t

150k

L1: SUMIDA CD-54-330MC
Q1, Q2: ZETEX FMMT-617
T1: SUMIDA C1Q122

V

GND

SW

OUT

FB

V

C

4

CCFL

C2

Q1

4

7

8

9

5

Q2

0.22μF

L1
33μF

C5

1μF

C4

0.1μF

R4

D4

20k

D2 D3

R2

10k

CCFL BACKLIGHT APPLICATION CIRCUITS
CONTAINED IN THIS DATA SHEET ARE
COVERED BY U.S. PATENT NUMBER 5408162
AND OTHER PATENTS PENDING

R3
1k

DIMMING
INPUT
0V TO 2.5V

3402 TA06

14

3402fb

PACKAGE DESCRIPTION

U

MS Package

10-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1661)

0.889 ± 0.127
(.035 ± .005)

LTC3402

5.23

(.206)

MIN

0.305 ± 0.038

(.0120 ± .0015)

TYP

RECOMMENDED SOLDER PAD LAYOUT

0.254

(.010)

GAUGE PLANE

0.18

(.007)

NOTE:

1. DIMENSIONS IN MILLIMETER/(INCH)

2. DRAWING NOT TO SCALE

3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

3.20 – 3.45

(.126 – .136)

DETAIL “A”

DETAIL “A”

0.50

(.0197)

BSC

° – 6° TYP

0

0.53 ± 0.152

(.021 ± .006)

SEATING

PLANE

3.00 ± 0.102
(.118 ± .004)

(NOTE 3)

4.90 ± 0.152

(.193 ± .006)

0.17 – 0.27

(.007 – .011)

TYP

1.10

(.043)

MAX

12

0.50

(.0197)

BSC

0.497 ± 0.076

7

6

45

(.0196 ± .003)

REF

3.00 ± 0.102

(.118 ± .004)

(NOTE 4)

0.86

(.034)

REF

0.127 ± 0.076
(.005 ± .003)

MSOP (MS) 0603

8910

3

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.

3402fb

15

LTC3402

TYPICAL APPLICATIO

U

Triple Output Converter

D2 D3

0.1μF

3

V

10

SHDN

2

MODE/SYNC

6

PGOOD

1

R

R

t

30.1k

L1 2.2μH

LTC3402

IN

t

V

OUT

GND

SW

FB

V

0.1μF

VIN =1.8V TO 3V

R3

1M

+

2
CELLS

C1

4.7μF

0 = FIXED FREQ

1 = Burst Mode OPERATION

C1: TAIYO YUDEN JMK212BJ475MG
C2: TAIYO YUDEN JMK325BJ226MM
D1: ON SEMICONDUCTOR MBRM120T3
D2 TO D7: ZETEX FMND7000 DUAL DIODE
L1: SUMIDA CD43-2R2M

D4 D5

0.1μF 0.1μF 4.7μF

D1

4

7

8

9

C

5

C3
470pF

R5
82k

R2

909k

R1

549k
C4

4.7pF

D6

D7

4.7μF

–2.5V
1mA

8V
2mA

V

3.3V
500mA

C2
22μF

3402 TA08

OUT

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LT®1306 Sync, Fixed Frequency, Step-Up DC/DC Converter Internal 2A Switches; VIN As Low As 1.8V

LT1308A/LT1308B High Current, Micropower, Single Cell 600kHz DC/DC Converter 5V at 1A with Single Li-Ion Cell, V

LT1613 1.4MHz, Single Cell DC/DC Converter in SOT-23 VIN As Low As 1.1V, 3V at 30mA from Single Cell

LT1615 Micropower Step-Up DC/DC Converter in SOT-23 IQ = 20μA, 1μA Shutdown Current, VIN As Low As 1V

LT1619 High Efficiency Boost DC/DC Controller 1A Gate Drive, 1.1V to 20V Input, Separate VCC for Gate Drive

LTC1872 SOT-23 Boost DC/DC Controller 550kHz, 2.5V to 9.8V Input

LT1930/LT1930A 1.2MHz/2.2MHz DC/DC Converters in SOT-23 VIN = 2.6V to 16V, 5V at 450mA from 3.3V Input
LT1949 600kHz, 1A Switch PWM DC/DC Converter 1A, 0.5Ω, 30V Internal Switch, VIN As Low As 1.5V,

Low-Battery Detect Active in Shutdown

LTC3400 Single Cell, High Current (600mA), Micropower, VIN = 0.85V to 5.5V, Up to 92% Efficiency Synchronizable

Synchronous 1.2MHz Step-Up DC/DC Converter Oscillator from 100kHz to 1.2MHz, ThinSOT Package

LTC3401 Single Cell, High Current (1A), Micropower, VIN = 0.5V to 5V, Up to 97% Efficiency Synchronizable

Synchronous 3MHz Step-Up DC/DC Converter Oscillator from 100kHz to 3MHz, 10-Lead MSOP Package

LTC3424 Single Cell, High Current (2A), Micropower, V

= 1.5V, Up to 97% Efficiency Synchronizable

OUT

Synchronous 3MHz Step-Up DC/DC Converter Oscillator from 100kHz to 3MHz, 10-Lead MSOP Package

Linear Technology Corporation

16

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear.com

© LINEAR TECHNOLOGY CORPORATION 2000

to 34V

OUT

3402fb

LT 0607 REV B • PRINTED IN USA